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Shaw, Billie Jo.
Intelligibility of clear speech at normal rates for older adults with hearing loss
h [electronic resource] /
by Billie Jo Shaw.
[Tampa, Fla] :
b University of South Florida,
ABSTRACT: Clear speech refers to a speaking style that is more intelligible than typical, conversational speaking styles. It is usually produced at a slower rate compared to conversational speech. Clear speech has been shown to be more intelligible than conversational speech for a large variety of populations, including both hearing impaired (Schum, 1996; Picheny, Durlach, & Braida, 1985; and Payton, Uchanski, & Braida, 1994) and normal hearing individuals (e.g. Uchanski, Choi, Braida, Reed, & Durlach, 1996) under a variety of conditions, including those in which presentation level, speaker, and environment are varied. Although clear speech is typically slower than normally produced conversational speech, recent studies have shown that it can be produced at normal rates with training (Krause & Braida, 2002).^ ^If clear speech at normal rates is shown to be as effective for individuals with hearing loss as clear speech at slow rates, it would have both clinical and research implications. The purpose of this study was to determine the effectiveness of clear speech at normal rates for older individuals with hearing loss. It examined the way in which intelligibility, measured as percent correct keyword scores on nonsense sentences, varied as a result of speaking mode (clear versus conversational speech) and speaking rate (slow versus normal) in six adults aged 55-75 years old with moderate, sloping, hearing loss. Each listener was presented with nonsense sentences in four speech conditions: clear speech at slow rates (clear/slow), clear speech at normal rates (clear/normal), conversational speech at slow rates (conv/slow), and conversational speech at normal rates (conv/normal) read by four different talkers. Sentences were presented monaurally in quiet to the listeners via headphones.^ Results indicated that clear/slow speech was the most intelligible condition overall. Neither conv/slow nor clear/normal provided an intelligibility benefit relative to conv/normal speech on average, suggesting that for older adults with moderate, sloping hearing loss, the combination of using clear speech and a slower speaking rate is more beneficial to intelligibility than the additive effects of altering either speaking rate or speaking mode alone. It has been suggested previously (Krause, 2001) that audiological characteristics may contribute to the lack of clear/normal benefit for certain listeners with hearing loss. Although clear/normal speech was not beneficial on average to listeners in this study, there were cases in which the clear/normal speech of a particular talker provided a benefit to a particular listener.^ Thus, severity and configuration of hearing loss alone cannot fully explain the degree to which listeners from hearing loss do (or do not) benefit from clear/normal speech. More studies are needed to investigate the benefits of clear/normal speech for different audiological configurations, including individuals with flat losses. In addition, the listening tasks should include more difficult conditions in order to compensate for potential ceiling effects.
Thesis (M.S.)--University of South Florida, 2006.
Includes bibliographical references.
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Adviser: Jean Krause, Ph.D.
x Speech-Language Pathology
t USF Electronic Theses and Dissertations.
Intelligibility of Clear Speech at Normal Rates For Older Adults with Hearing Loss by Billie Jo Shaw A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Communicati on Sciences and Disorders College of Arts and Sciences University of South Florida Major Professor: Jean Krause, Ph.D. Theresa Hnath-Chisolm, Ph.D. Catherine Rogers, Ph.D. Robert Zelski, Au.D. Date of Approval: November 13, 2006 Keywords: speech intelligibility, speaki ng rates, aging, communication breakdown, speech processing, hearing aids Copyright 2006 Billie Jo Shaw
Acknowledgements I wish to acknowledge and thank my th esis committee, Dr. Jean Krause, Dr. Theresa Chisolm, Dr. Catherine Rogers, and Dr. Robert Zelski for their guidance and support. I would especially like to thank my thesis advisor, Dr. Krause, for her continued dedication, direction, and patie nce throughout the project. I would also like to thank the listeners w ho gave their time in order to participate in this study. In addition, I am grateful to the staff of the USF Hearing & Balance Center; Dr. Sims and Dr. Clark from Physic ian's Choice Hearing & Dizziness Center; Dr. Tucker and Dr. Myers from the James A. Haley VeteranÂ’s Association Hospital; and the Hearing Loss Association of America, Tampa and Sarasota chapters for their assistance in recruiting participants for this project. Finally, I would I would like to than k my family and closest friend, Julie Jungerman, for her constant support and encouragement throughout this endeavor.
i Table of Contents List of Tables iii List of Figures iv Abstract v Chapter 1 Introduction 1 Chapter 2 Literature Review 3 Intelligibility of Clear Speech 3 Acoustical Factors 4 Rate 6 Clear Speech at Slow Rates 9 Clear Speech at Normal Rates 12 Additional Factors 14 Clear Speech and Hearing Loss 18 Hypothesis 19 Chapter 3 Methods 21 Participants 21 Materials 23 Procedures 24 Data Analysis 26 Chapter 4 Results 28
ii Main Effects 30 Interactions with Speaking Mode 31 Mode x Rate Interaction 31 Other Interactions with Speaking Mode 33 Interactions with Rate 35 Listener and Talker Interactions 37 Listener and Talker Interactions with Condition (Mode x Rate) 37 Other Li stener and Talker Interactions 38 Chapter 5 Discussion 43 Difficulty of Tasks 47 Future Work 49 Clinical Implications 51 List of References 53 Appendices 56 Appendix A: Listener Demographics 57 Appendix B: Norms for the Mini-Mental State Examination by Age and Education 59 Appendix C: Percentages of Keywords Correct 60 Appendix D: Within-s ubjects Effects and Interactions 64
iii List of Tables Table 1 ListenersÂ’ Audiol ogical Configurations 22 Table 2 Sentence Lists by Speaker and Condition 24 Table 3 Presentation Order of Stimuli 25 Table 4 Average Intelligibility 29 Table 5 Significant Effects and In teractions at the 0.01 level 30 Table 6 Pairwise Comparisons 33 Table 7 Average Listener Performance Across Studies 44 Table 8 Audiometric Characteristics of Hearing-Impaired Listeners from KrauseÂ’s (2001) Study 46 Table A1 Listener age, gender, and years of education 57 Table A2 ListenersÂ’ MMSE scores 57 Table A3 ListenersÂ’ Bilateral Audiological Thresholds 58 Table A4 Stimuli Presentation Levels 58 Table C1 Percentages for T1 60 Table C2 Percentages for T3 61 Table C3 Percentages for T4 62 Table C4 Percentages for T5 63
iv List of Figures Figure 1 Average intelligibility, in percent keywords correct, for each test condition (rate x mode). 32 Figure 2 Average performance, in percent keywords correct, for each listener in each speaking mode. 34 Figure 3 Average intelligibility, in percent keywords correct, for each talker in each mode. 35 Figure 4 Average performance, in percent keywords correct, for each listener at each rate. 36 Figure 5 Average intelligibility, in percent keywords correct, for each talker at each rate. 37 Figure 6 Average intelligibility, in percent keywords correct, for each talker at each rate and mode. 38 Figure 7 Average performances, in percent keywords correct, of every listener for each talker. 39 Figure 8 Average performance, in percent keywords correct, of every listener for each talker in each condition. 40
v Intelligibility of Clear Speech at Normal Rates for Older Adults with Hearing Loss Billie Jo Shaw ABSTRACT Clear speech refers to a speaking style th at is more intelligible than typical, conversational speaking styles. It is usually produced at a slower rate compared to conversational speech. Clear speech has been shown to be more intelligible than conversational speech for a large variety of populations, including both hearing impaired (Schum, 1996; Picheny, Durl ach, & Braida, 1985; and Pa yton, Uchanski, & Braida, 1994) and normal hearing individuals (e.g. Uchanski, Choi, Braida, Reed, & Durlach, 1996) under a variety of conditions including those in which pres entation level, speaker, and environment are varied. Although clear sp eech is typically slower than normally produced conversational speech, recent studies have shown that it can be produced at normal rates with training (Krause & Braida, 2002). If clear speech at normal rates is shown to be as effective for individuals with hearing loss as clear speech at slow rates, it would have both clinical and research implications. The purpose of this study was to determ ine the effectiveness of clear speech at normal rates for older individuals with hear ing loss. It examined the way in which intelligibility, measured as percent correct ke yword scores on nonsense sentences, varied as a result of speaking mode (clear versus conversational speech) a nd speaking rate (slow versus normal) in six adults aged 55-75 years old with m oderate, sloping, hearing loss. Each listener was presented with nonsense se ntences in four speech conditions: clear
vi speech at slow rates (clear/slow), clear speech at normal rates (clear/normal), conversational speech at sl ow rates (conv/slow), and c onversational speech at normal rates (conv/normal) read by four different talkers. Sentences were presented monaurally in quiet to the listene rs via headphones. Results indicated that clear/slow spe ech was the most intelligible condition overall. Neither conv/slow nor clear/normal provi ded an intelligibility benefit relative to conv/normal speech on average, suggesting that for older adults with moderate, sloping hearing loss, the combination of using clear speech and a slower speaking rate is more beneficial to intelligibility than the additive effects of altering either speaking rate or speaking mode alone. It has been suggested previously (Krause, 2001) that audiological characteristics may contribute to the lack of clear/normal benefit for certain listeners with hearing loss. Although clear/normal speech was not beneficial on average to listeners in this study, there were cases in which the cl ear/normal speech of a particular talker provided a benefit to a particular listener. Thus, severity and conf iguration of hearing loss alone cannot fully explain the degree to which listeners from hearing loss do (or do not) benefit from clear/normal speech. More studies are needed to investigate the benefits of clear/normal speech for different audiological configura tions, including individuals with flat losses. In addition, the listening tasks should include more di fficult conditions in order to compensate for potential ceiling effects.
1 Chapter 1 Introduction The purpose of this study was to determ ine the effectiveness of clear speech at normal rates for older individuals with hear ing loss. It examined the way in which intelligibility, measured as percent correct keyword scores on nonsense sentences presented in quiet, varies as a result of speaking mode (c lear versus conversational speech) and speaking rate (slow versus norma l) in adults aged 55-75 with moderate, sloping, hearing loss. Clear speech refers to a speaking style th at is more intelligible than typical, conversational speaking styles. The term can also be used to describe the speaking style utilized by talkers when attempting to sp eak more clearly. Clear speech, which is typically produced at a slower rate of speech, has been shown to be more intelligible for a large variety of populations, including both hearing impair ed (Schum, 1996; Picheny, Durlach, & Braida, 1985; and Payton, Ucha nski, & Braida, 1994) and normal hearing individuals (e.g. Uchanski, C hoi, Braida, Reed, & Durlach, 1996; Krause & Braida, 2002; Gagne, Rochette, & Charest, 2002). The results of these studies indicate that clear speech is effective for increasing overall intelligibility under a variety of conditions, including those in which presentation level, sp eaker, and environment are varied. Although clear speech is typi cally slower than normally produced conversational speech, recent studies have shown that it can be produced at normal rates with training
2 (Krause & Braida, 2002). Since clear speech at normal rates is a relatively new breakthrough, it is necessary to test its eff ectiveness in various environments and with various populations. Because rate is a factor in intelligibil ity, one cannot assume that all of the previously established benefits of clear speech at slow rates will also extend to clear speech at normal rates. There is particular interest in the intellig ibility benefit of cl ear speech at normal rates for individuals with hearing loss. If cl ear speech at normal rates is shown to be as effective with this population as clear speech at slow rates, it would have both clinical and research implications. It is possible th at caregivers and family members would be able to utilize clear speech at normal rates effectively when addre ssing individuals with hearing loss, enhancing communi cation efficiency and thereby increasing quality of life. In addition, future studies in to the acoustic differences be tween clear and conversational speech at normal rates may result in a be tter understanding of acoustic-phonetic factors contributing to intelligibility. Such an unde rstanding may also be applied to improving hearing aid technology. Furthermore, th ese studies may also identify common characteristics of individuals who benefit from the use of clear speech, as well as characteristics of those who do not benefit from its use.
3 Chapter 2 Literature Review Intelligibility of Clear Speech Picheny et al. (1985) were the first to re port that overall inte lligibility increased significantly when speakers were instructed to speak clearly. In that study, three male speakers were recorded utilizing both cl ear and conversational speech while reading nonsense sentences. Five listeners with mode rate to severe sens orineural hearing loss (pure tone averages ranged from 45-74 dB SPL) were presented with sentences in quiet at three different levels: most comfortable loudness level (MCL), maximum listening level (MAX), and MCL-10 dB. In addition, two types of frequency-gain characteristics were utilized: ORTH (orthotelephonic: stimuli presented w ith a relatively fl at frequency-gain characteristic), and OMCL (octaves most co mfortable level: stimuli were filtered into four octave bands, with each band adjusted to MCL). This resulted in a total of 36 experimental conditions (3 ta lkers x 2 modes x 3 listening levels x 2 frequency-gain characteristics). Each listener was presented with 50 sentences for each experimental condition. Use of clear speech resulted in incr eased intelligibility of all phoneme classes studied for these listeners with sensorin eural hearing loss. The phoneme categories included: fricatives, plosives, semivowels, na sals, and vowels. In addition, the overall intelligibility of clear speech, averaged acro ss speakers, was 17 percentage points higher than that of conversational speech.
4 Subsequent studies have shown that the intelligibility benefit obtained from clear speech is a very robust phenomenon. For example, Schum (1996) determined that unpracticed talkers were able to produce more intelligible speech when asked to speak clearly. This was true regardless of the speakerÂ’s age. Ten y oung speakers (aged 22-39 years old) and ten elderly speakers (aged 62-70 years old) participated in the study. All talkers produced clear speech which led to intelligibility scores greater than those obtained for conversational speech by listene rs aged 60-77 years ol d with sensorineural hearing loss. Each listener had auditory thresholds (averaged over 500, 1000, 2000, and 4000 Hz) that fell between 20 and 70 dB HL in at least one ear. Percent-correct scores were converted to rationalized arcsine transform units (RAUs). This conversion equalizes the variance across performance leve ls, while producing num erical values in RAUs that are similar to the original per cent-correct scores (St udebaker, 1985). The average increase in intelligibility for young talkers was 22 RAU, and 17 RAU for older talkers. These findings were consistent with earlier studies conducte d by Picheny et al. (1985). Even though the speakers in Schu mÂ’s (1996) study were not given specific instructions on how to produce clear speech, all were able to produce speech with improved intelligibility and all listeners be nefited, indicating a very strong effect. Acoustical Factors Once large and consistent intelligibilit y benefits of clear speech had been established, researchers also began to focu s on the acoustical differences between clear and conversational speech to determine whic h acoustic properties might be responsible for the improvement. In 1986, Picheny, Durl ach, and Braida analyzed differences between clear and conversationa l speech. Their results can be classified into global,
5 phonological, and phonetic differences. Si gnificant global differences included differences in average speaking rates and paus e distributions. The average speaking rate for clear speech was 90-100 words per minut e (wpm), compared to 160-200 wpm for conversational speech. In addition, the numbe r and duration of paus es increased during clear speech. Phonological differences between clear and conversational speech included frequency of occurrence for vowel reducti on (vowels that became schwa-like), burst elimination (stop consonants that were produ ced without the burst), and sound insertions (schwa vowels that were inserted after voi ced consonants). Vowel reduction decreased by approximately 50% in clear speech as co mpared to conversational speech. Burst elimination occurred in approximately 60% of opportunities in conve rsational speech, but only in approximately 15% of opportunities for clear speech (Picheny et al., 1986). Other phonological differences, including degeminati on (identical phonemes merging into one sound across word barriers), alveolar flap, a nd miscellaneous sound deletions were not as pervasive overall, and did not differ subs tantially between clea r and conversational speech. Phonetic changes included differences in short-term RMS spectra, and segmental phone durations. Clear speech produced minimal changes to formant frequencies. Clear speech samples indicated increased segmental phone duration for tense vowels, and increased VOT for unvoiced plosives. Ch anges in vowel space were noted more frequently in lax vowels under clear sp eech conditions (Picheny et al., 1986). In the studies conducted by Picheny et al ., some speakers were naturally more clear than others regardless of speaking mode. Other studies aimed at identifying acoustic characteristics of highly intelligible speech therefore focused on determining why some speakers were more intelligible th an others, even when all speakers were
6 utilizing clear speech. Gagne, et al., (2002) noted significant intraspeaker differences in intelligibility for the same stimuli, produced in the same speaking style (57 occurrences of statistically significant differences out of 216 paired comparisons). In addition, not all speakers in this study produced consistent sign ificant clear speech benefits. Bradlow, Torretta, and Pisoni (1995) also examined the acoustic characteristics that make some talkers more intelligible than others. Re sults from the study indicated that overall intelligibility was not correlated with mean fundamental frequency. However, clear speech tended toward a wider fundamental frequency range. In addition, there was a significant positive correlation between F1 range and intelligibility. There was no significant correlation between intel ligibility and the range for F2. Rate After the initial findings of acoustic differences betw een clear and conversational speech, one hypothesis was that rate, and the number and duration of pauses, were the primary factors affecting intelligibility of speech. This hypothesis stemmed from the recognition of rate as the most obvious a nd consistent difference between clear and conversational speech. Therefore, early rese arch focused on the role of rate in clear speech. For example, a study was conducted in which clear speech sentences were sped up using a uniform time-scaling process in whic h the duration of all elements of the clear speech sample were altered by the same amount This procedure allowed researchers to alter the durations of sentences and produce sped clear speech sentences with the same overall duration as conversational speech (Picheny, Durlach, & Braida, 1989). In addition, conversational speech sentences were submitted to similar time-scale modifications to slow the speech, resulting in conversational speech sentences with the
7 same overall duration as clear speech. The stim uli were presented to five listeners with sensorineural hearing loss. Both processed speech conditions (alt ered clear, altered conversational) resulted in redu ced intelligibility scores. Th e average decrease in scores for processed conversational (i.e. slowed) speech was 15 percentage points. The average decrease for processed clear (i.e. sped) speech was 29.8 percentage points. In order to rule out the effect of processi ng as a factor, the stimuli were processed again in order to restore their original rates. This restored sp eech also resulted in scores lower than those of unprocessed speech for both clear and c onversational stimuli. However, the differences were within an average of eight percentage points of the original speech. This indicates that signal processing had so me adverse effect on intelligibility, but not enough to account for the sizeable decreases in intelligibility scores obtained for processed speech in both conversational and cl ear modes. Therefore, uniform changes in speaking rate alone are not responsible for differences in intelligibility. Another study of the role of rate in clear speech was conducted using nonuniform time scaled speech (Uchanski, Choi, Braida Reed, & Durlach, 1996). This study used the same speakers and nonsense sentences as the study conducted by Picheny et al. (1989) but differed from the earlier research in that nonuniform processing altered the rate phoneme by phoneme (Uchanski et al., 1996) rather than uniformly expanding or contracting the entire sent ence (Picheny et al., 1989). Non-uniform processing was achieved by measuring the durations of matc hing segments in clear and conversational speech and inserting or deleting amplitude spect ra within the spectrogram to achieve the desired change in duration. As in the previous time-scali ng study (Picheny et al., 1989), the sentences were processed to achieve sl owed conversational a nd accelerated clear
8 speech, and reprocessed in order to return th em to their original rates and control for processing of the stimuli as a potential intellig ibility factor. The subjects consisted of four individuals with hearing loss, and two individuals with normal hearing. The results of this study were compared to those of Pi cheny et al. (1989). Overall, nonuniform time scaling had a less deleterious effect on intelligibility than uniform time scaling, but no benefit was found for slowing conversational speech in this manner. On average, processed (i.e. slowed) convers ational speech resulted in a 5 percentage point decrease when nonuniform time scaling was utilized, as compared to the 15 percentage point decrease obtained for uniform time scaling. Similarly, the intelligib ility of processed (i.e. accelerated) clear speech decreased by an average of six percentage points when nonuniform time scaling was employed, compared to 29.8 percentage points for uniform time scaling. Speeding up clear speech had a negative effect on intelligibility, while slowing down conversational speec h also resulted in decreased intelligibility. Therefore, it can be concluded that clear speech intellig ibility involves factors other than a simple decrease in speaking rate. These findings are supported by those of Bradlow et al. (1995), which showed no correlation between speaking rate and speech intelligibility. After these failed attempts to produce cl ear speech at normal rates through signal processing, Krause and Braida (2002) conducted a study to determine whether clear speech at normal rates could be obtained na turally. Researchers were able to train speakers to produce clear speech at normal rates. A metronome was utilized during training to assist speakers in maintaining th eir individual normal rates. In addition, the speakers received continuous f eedback on the intelligibility of their productions. Eight listeners (four male, four female), who were native English speakers with normal hearing,
9 were presented with a variety of speech stimu li at a signal-to-noise ratio (SNR) of -2 dB. Intelligibility was measured in six differen t speech conditions: clear speech at slow (clear/slow), normal (clear/normal), and quick (clear/quick) rates; and conversational speech at slow (conv/slow), normal (conv/nor m), and quick (conv/quick) rates. The results of the study indicate that clear speech at slow rates was the most intelligible condition, averaging 63% keywords correct. This was followed clos ely by clear speech at normal rates (59%), conversational speech at slow rates (51%), and clear speech at quick rates (46%). Findings from this study sugg est that the intelligib ility benefit of clear speech is mostly independent of rate, talker, and listener for normal hearing listeners in noise. Although cross-talker differences were noted, all talkersÂ’ inte lligibility increased when utilizing clear speech as compared to conversational speech (Krause & Braida, 2002). Since normal hearing listeners obtained comparable benefits for clear/slow and clear/normal speech (compared to conv/normal) the question has been raised as to whether clear speech at normal rates has comp arable benefits for other populations and environments that show benefit from clear speech produced at slow rates. Clear Speech at Slow Rates Clear speech at slow rates has been show n to be beneficial in several different environments and to have positive effects for a variety of populations. For example, Gagne et al. (2002) examined the benefits of clear speech in audio, visual, and audiovisual environments. The study consisted of 6 female talkers, and 12 listeners (11 female and 1 male) with hearing and vision within normal ranges. The primary language for all participants was French. The s ubjects were divided into small groups and presented with each of auditory, visual, and audiovisual stimuli. Scores were based on
10 percent-correct syllable recognition tasks. Re sults indicated a positive clear speech effect for all three modalities. For the auditory-s peech condition, six of six talkers produced significant improvements in intelligibility (13% on average) of clear speech, and five of six talkers produced significant clear speech results for both the visual-speech (9.6% on average) and audiovisual-speec h (6.8% on average) conditions. A similar study examined the effects of visual-only cues and auditory-only conditions in clear speech (Helfer, 1997). Resu lts of that study indica ted that the benefits of clear speech for visual-only cues and aud itory-only conditions were additive for nine young, normal hearing individuals. Compari ng auditory-only scores, clear speech produced an approximately 10 percentage point advantage over conversational speech. When visual cues were included, auditory -visual clear speech stimuli produced perceptual scores approximately 15 percenta ge points higher than auditory-visual conversational stimuli. Additional research on listening environm ents has examined the intelligibility benefits for clear speech at slow rates presented in reverberation and background noise (Payton et al., 1994). Three individual e xperiments were conducted. Five normal hearing and two hearing impaired listene rs were exposed to simulated acoustic environments featuring three levels of reve rberation, three levels of noise, and three combinations of noise and reverberation. Th e results of the study indicate that clear speech was more intelligible in every environment for every listener, both normal hearing and hearing impaired. There was an overall difference of 21 percen tage points between clear and conversational speech when scores we re averaged across listeners, experiments and environments.
11 Krause and Braida (2003) examined the e ffectiveness of clear speech at slow rates in three types of signal degr adation conditions: reverberat ion, low pass, and high pass environments. Five native English speakers with normal hearing were presented aurally with nonsense sentences. A different group of listeners was employed for each condition tested. The results of this study indicated that clear speech was consistently more intelligible than conversational speech across all environments. In addition to these various environments clear speech at normal rates has been shown to help speech perception in diffe rent populations. For example, one study (Helfer, 1998), indicated that older listeners (aged 61-88 ye ars old) benefit from both visual cues and clear speech. Fifteen subjects within this ag e range were recruited for the study. There were no restrictions on hearing thresholds, thus ensuring a range of hearing loss among the subjects. According to Helf erÂ’s (1998) findings, hearing loss was not correlated with the size of clear speech benefit, indicating th at clear speech should present some benefit to olde r listeners, regardless of audiological thresholds. Working with a different population, Br adlow, Kraus, and Hayes, (2003) examined the perceptual effects of naturally produced clear speech at slow rates for 63 children diagnosed with learning disabilities. Results of that experiment indicated that the magnitude of the clear speech effect wa s 9.2 on the RAU scale fo r this population. In addition, pairwise comparisons of speech rece ption scores indicated that children with learning disabilities, when presented with cl ear speech stimuli, performed comparably to children without diagnosed lear ning disabilities who were pr esented with conversational speech stimuli. These results imply that cl ear speech has the potential to correct for decreased perceptual effects resulting from learning disabilities in children.
12 Bradlow and Bent (2002) examined the e ffects of naturally produced clear speech at slow rates on another popul ation, non-native listeners. The subjects for this study consisted of a group of normal-hearing nativ e English listeners, and a group of 32 normal-hearing non-native English listener s. Although two talkers produced stimuli sentences, each participant heard English se ntences read by only one talker. Conditions included clear and conversational sentence produ ctions at two differe nt signal-to-noise ratios, -4 dB and -8 dB. The non-native list eners showed a clear sp eech benefit of 5 RAU overall. However, this benefit was smaller than that for native listeners, which was 16 RAU. In a later study, Krause a nd Braida (2003) also examined the effects of clear speech on intelligibility for non-native listeners. In contrast to the results of Bradlow and Bent (2002), Krause and Braida found the cl ear speech benefit for non-native listeners (25.5 percentage points averaged across two talk ers) to be comparable to the benefit for native listeners (27 percentage points averaged across two talkers). The discrepancy in the results from these two studies may be re lated to differences in amount and length of listenersÂ’ exposure to English or the nature of the speech materials utilized in the experiments. Bradlow and Bent (2002) us ed meaningful sentences, while Krause and Braida used nonsense sentences for their study. Clear Speech at Normal rates The finding that speakers can be trained to produce clear speech at normal rates (Krause, 2002) has led to studies aimed at determining whether clear speech at normal rates has comparable benefits for the same sets of populations and environments as clear/slow speech. Because this is a relatively new developm ent, most of the work to
13 date which focuses on clear speech at normal rates to date has concentrated on listeners with normal hearing. For example, Krause a nd Braida (2002) first demonstrated that clear speech at normal rates had a 14 point be nefit in noise for ei ght individuals with normal hearing. In a subsequent study, this benefit was replicated with five normal hearing listeners. Results from this sec ond study indicated clear/ normal intelligibility averaging 51.3% across talkers, and conv/normal averaging 3 4.8%. This resulted in a 16.5 percentage point advantage for the cl ear/normal condition (Krause, 2001). Continuing their examination of the effectiv eness of clear speech at normal rates, Krause and Braida (2003) st udied the effects of listening environment and population on clear speech at normal rates. Normal hearing listeners were presented with stimuli from two speakers in three different conditions: low pass (1/3 octave bands with center frequencies ranging 80Hz-1000Hz), high pass (1/3 octave band with a center frequency of 3150Hz), reverberant (senten ces were convolved to produce effects similar to a room with 0.60 reverberation impulse response time). In addition, stimuli were presented to non-native listeners in speech shaped noise at a signal to noise ratio of 0 dB. Listeners in the non-native condition consisted of normal hearing listeners who learned English as a second language. For all conditions tested, results indicated a clear speech benefit for clear/slow speech. However, results for cl ear/normal speech varied with talker and condition (low pass, high pass, reverberation, non-native listener). One talker (T5) showed increased intelligibility for clear/nor mal speech in three out of four conditions, while the other talker (T4) showed increased intelligibility for clear/normal speech in only one out of four conditions.
14 With the completion of this preliminary work investigating the clear speech benefit at normal rates for listeners with normal hearing, a natural next question is whether or not clear speech produced at normal rates is beneficial to people with hearing loss. Krause (2001) conducted a preliminary study of intelligibility of speech presented in a variety of conditions for three listeners with stable sensorineural hearing losses. Three speaking modes were presented at a normal rate: clear, conversational, and processed conversational. In addition, two speaking modes were presented at a slow rate: conversational and processed conversational. The processed conditions were created by modifying formant frequencies, fundamental frequencies, and temporal envelopes in order to mimic the acoustic properties of clear speech. Results of this study indicated that clear/normal speech was the most intelligible condition at normal rates (69%), followed by conv/normal (62%). Processed conditions ranged from 61%-23% intelligibility. Although clear/normal speech produced an a dvantage of 7 percentage points over conv/normal, this benefit was not statistically significant. There ar e several factors that may be related to this lack of significance. These include the age of listeners, degree and audiological configuration of hearing loss, and the limited number of subjects in the study. More research is needed to ex amine these factors more thoroughly. Additional Factors While not specific to clear speech, much is known about the effects of age and audiological thresholds on speech per ception. Dubno, Dirks, and Morgan (1984) examined the effects of mild sensorineura l hearing loss and chr onological age on speech recognition in noise. Four groups of listene rs served as subjects for this study (young normal hearing, young hearing loss, older nor mal hearing, and older hearing loss).
15 Several measures were recorded for each list ener. These included pure-tone thresholds, babble thresholds, loudness discomfort levels for babble, speech recognition scores in quiet, and signal to noise ratios required for 50% accuracy at each of 56, 72, and 88 dB SPL. In addition, researchers recorded sp eech levels for 50% performance on both high and low predictability sentences in quiet. Results for these tasks in quiet showed significant differences between the normal hearing and hearing loss groups. No significant differences were found between the young and older groups. Although older listeners consistently performed worse in noise than did younger listen ers with equivalent audiological thresholds, these age effects were not observed in quiet. All subjects required more beneficial signal-to-noise ra tios as the stimulus tasks became more difficult. Differences between listener groups may be accounted for by factors in speech perception that can be associated with age or hearing loss. It ha s been suggested that elderly listenersÂ’ speech understanding abiliti es are influenced by memory factors and by the demands of the recognition task. Gor don-Salant and Fitzgibbons (1997) studied the effects of recall task, speech rate (manipulat ed through use of interword intervals), and contextual cues on speech recognition for young and elderly listeners. Four groups of subjects (young normal hearing, elderly normal hearing, young hearing impaired, and elderly hearing impaired) were presented with low and high context sentences. The sentences were presented in noise at five different speaking rates. Resu lts indicated that elderly listeners performed better on final word recall tasks than on sentence recall tasks. This supports the theory that the memory demands of the recall task affect the performance of elderly listeners.
16 In a later study, Gordon-Salant and Fitz gibbons (1999) examined the effects of age and hearing status on performance dur ing temporally based speech and nonspeech measures (temporal manipulation of acous tic signals and vari ation in stimulus complexity). The subject group configurations were similar to those of the 1997 study (young normal hearing, elderly normal hear ing, young hearing impaired, and elderly hearing impaired). The hearing loss groups we re matched on the basi s of listenersÂ’ pure tone thresholds, thus minimizing the possi bility of differences in audiological configurations as a between-groups factor The hearing loss groups consistently performed more poorly than the normal hearing groups. However, none of the interactions involving he aring status were found to be sta tistically significant. The results of this study indicate that central pro cessing factors may cause poorer psychoacoustic performance in older listeners. In addition, aging affects the ability to process rapid speech segments. This factor may have an adverse affect on intelligibility of clear speech when produced at normal rates. Peters, Moore, and Baer (1998) conducted experiments to investigate the effects of temporal and spectral dips, which refer to changes in amplit ude over time and in frequency, respectively, on speech intelligibility in background noise for individuals with normal hearing and those with hearing loss. Four groups of subjects (young normal hearing, elderly normal hearing, young heari ng loss, and elderly hearing loss) were presented with 10 varying conditions of bac kground noise. In one experiment, sentence lists were presented to all subjects wit hout frequency response shaping. Researchers measured the decrease in listenersÂ’ speech re ception thresholds (SRT) in noise as a result of spectral and temporal dips. Results of th is experiment indicated that listeners with
17 hearing loss received less bene fit from spectral and temporal dips than did listeners with normal hearing. The young normal hearing ( YNH) group received the most benefit, while the elderly hearing lo ss (EHL) group received the leas t benefit. The authors reported that the age difference in speech pe rception was most likely due to auditory factors, considering that the EHL group experi enced a greater degree of hearing loss than that of the YHL (young hearing loss) group ove rall. In a second experiment, the two hearing loss groups (YHL, EHL) were tested with frequency-gain characteristics corresponding to NAL (National Acoustic La boratory) procedures (Byrne & Dillon, 1986). NAL procedures provide the standard prescription for frequency shaping based on audiogram results. The results of this experiment indicated that the YHL group received greater benefit from spectral and te mporal dips than did the EHL group and age was moderately correlated with SRTs for these conditions. The combined results of these experiments indicated that the overall pe rformance of hearing loss groups was poorer than that of the normal hearing groups, even with amplification. One explanation for this difference in performance on speech percepti on tasks is related to the smaller dynamic range of people with hearing loss when co mpared to that of individuals with normal hearing. A limited dynamic range makes it di fficult to supply enough linear gain to make the speech spectrum audible, without allowi ng noise to become uncomfortably loud. The masking effect of background noise had a subs tantial negative effect on the performance of listeners with hearing loss. These result s imply that individuals with sensorineural hearing loss have less ability to utilize spectral and temporal dips in background noise than individuals with normal hearing. In addition, age was significantly correlated with
18 SRTs in background noise with spectral and/ or temporal dips when amplification was utilized. Clear Speech and Hearing Loss There is some research to suggest that cl ear speech is less beneficial for hearing impaired listeners, possibly because hearing lo ss affects the way listeners utilize acoustic cues (e.g. Ferguson & Kewley-Port, 2002). For example, Ferguson and Kewley-Port (2002) compared the properties of clear and conversational vowels. Four experiments were performed in order to determine whic h acoustical cues were most important for vowel identification in normal hearing and hear ing impaired listeners. The results of the first experiment indicated that clear sp eech vowels were more intelligible than conversational vowels by an average of 15 percentage points for young, normal hearing listeners. In contrast, speaking mode was not statistically significan t for elderly, hearing impaired listeners. These subjects demonstr ated the expected clear speech advantage for back vowels. However, the opposite effect o ccurred for front vowels, which resulted in an overall noneffect for clear vowels. Th e authors acknowledge that this may be attributed to the speaking style of the speaker, rather than being indicative of clear speech in general. However, the results suggest th at hearing loss changes the way listeners use acoustic information to identify vowels. In contrast to the results of Ferguson and Kewley-Port (2002), a number of other studies have shown that heari ng impaired individuals generally benefit from clear speech at slow rates (Schum, 1996; Picheny et al., 1985; Payton et al., 1994). Studies which have shown clear speech advantage for indivi duals with hearing loss typically involve stimuli consisting of sentences, rather than individual words. A lthough sentence stimuli
19 may be either nonsense or meaningful, additi onal acoustical context is provided that may be a factor in increased intelligibility scores for these materials. Additional research into clear speech at normal rates may lend insight into the role of other factors affecting speech intelligibility such as age and hearing loss. Hypothesis The body of previous research on clear spee ch intelligibility indicates that clear speech at slow rates is beneficial in a vari ety of environments and for many populations. The work of Krause and Braida (2002, 2003) al so indicates that it is possible to obtain naturally produced clear speech at normal rate s, while maintaining at least a portion of the intelligibili ty benefit, for some populations and environments. The task remains to test clear speech at normal rates with a va riety of subject populations in order to determine whether the benefit of clear speech persists at normal ra tes for all populations. The work of Gordon-Salant and Fitzgibbons (1999) indicates that aging negatively affects an individualÂ’s ability to process rapid speech segments. In addition, Peters et al. (1998) found that elderly listeners with hearing loss had higher speech reception thresholds in noise than did young listeners w ith hearing loss, and that listeners with hearing loss performed worse than those w ith normal hearing on speech reception tasks overall, even when supplied with amplificati on. This leads to th e question of whether clear speech will maintain its intelligibility be nefit for older adults (both normal hearing and those with hearing loss) when spoken at normal rates. Panagiotopoulos (2005) found that older adults with normal hearing received a 21 percentage point advantage (relative to conv/normal speech) when listening to clea r/slow speech, and a 14 percentage point advantage for clear/normal, indicating that cl ear/normal speech is advantageous for older
20 listeners with normal hearing. The purpose of the current study was to ascertain how intelligibility, measured as percent correct keyword scores on nonsense sentences presented in quiet, varies as a result of speaking mode (clear vs. conversational speech), talker, and speaking rate (slow vs. normal) in adults over age 55 w ith moderate sloping hearing loss. Comparison of these results with those of Panagiotopoulos (2005) was conducted to obtain information concerning the effect of hearing loss alone. In light of the information gathered at the beginning of the study on the effects of clear speech at both normal and slow rates, it is hypothesized that the intelligibility scores of clear speech at normal rates to exceed t hose of conversational speech at normal rates for older adults with hearing loss. In additi on, I expected clear speech at slow rates to be more intelligible for this population th an clear speech at normal rates.
21 Chapter 3 Methods Participants The participants in this study consisted of six listeners recruited from audiology clinics, hearing loss support groups, and retire ment communities in the Tampa, FL area. Demographic information (age, gender, and year s of education) for the six listeners is listed in Table A1 of Appendix A. In orde r to be included in the study, subjects were required to be native speakers of English be tween 55-75 years of age; pass a cognitive screening; and present with a moderate, bi laterally symmetric, sloping hearing loss. The Mini Mental State Exam (MMSE) (Folstein, Folstein, & McHugh, 1975) was utilized as a cognitive screeni ng tool. ListenerÂ’s scores on this task were compared to normative data (Crum, Anthony, Bassett, & Fo lstein, 1993) based on age and educational level (see Appendix B). Participants were requ ired to score within one standard deviation of the norm, or higher, to participate in the study. All potential listeners who were screened met this requirement. The MMSE sc ores for the six listeners who participated in the experiment are listed in Table A2 of Appendix A. To qualify as having a moderate loss appropriate for inclusion in the study, each listenerÂ’s pure tone average (average of thresholds at 500, 1000, and 2000 Hz) was required to fall between 35 and 60 dB. For th e loss to be considered sloping for the purposes of the study, thresholds were required to increase (i.e worsen) by at least 15 dB
22 between 500 Hz and 2000 Hz. Listeners with th resholds that increased (worsened) by as little as 10 dB were also accepted if the di fference between thresholds at 500 and 1000 Hz or between thresholds at 1000 and 2000 Hz met the 15 dB criteria. In addition, thresholds at 4000 Hz and 8000 Hz were required to be equal to or higher (i.e. poorer) than thresholds at 2000 Hz. Audiograms dated within the last year we re provided by subj ects prior to their beginning the study. This was to ensure that al l subjects met the inclus ion criteria. Table 1 illustrates the participantsÂ’ relevant audiolog ical information for the ear which received stimuli during the experiment. Bilateral audiolog ical thresholds are li sted in Table A3 of Appendix A. Table 1. ListenersÂ’ Audi ological Configurations Thresholds (dB) at Frequency (Hz) Listener Age Test Ear PTA (dB) Slope 500 10002000 4000 8000 L1 68 R 37 10 35 30 45 50 80 L2 72 R 48 25 35 50 60 65 70 L3 57 L 46 15 35 55 50 60 55 L4 74 L 37 35 25 25 60 65 80 L5 66 L 52 55 30 40 85 80 75 L6 74 L 40 15 30 45 45 75 90 The original intention was for 8-10 list eners to participate in this study. In addition, the criteria for audiol ogical configuration was initia lly more stringent, including pure tone averages between 40 and 60 dB, and a minimal 25 dB slope. Due to difficulty
23 in finding persons who met this criteria despite extensive recruitment efforts, the number of participants was reduced to six, and the inclusion crit eria was broadened. These changes were introduced in order to increase th e rate at which subjec ts were recruited so that the timeline of the experiment could be maintained. Materials Sentences were drawn from a database compiled for a previous study involving clear and conversational speech at both slow and normal rates (Krause & Braida, 2002). Nonsense sentences were used in order to control for contextual cues as an intelligibility factor. The sentences are s yntactically correct, but without semantic meaning, such as, Â“Our egg waits for his expor tÂ” (Krause & Braida, 2002). The stimuli consisted of eight unique lists of 50 nonsense sentences read by four different talkers (two lists per talker). Th ese four talkers were chosen from a group of five, due to their ability to produce a cl ear speech intelligibility benefit (for young, normal hearing listeners) without slowing thei r speech rates. Each talker produced two lists of sentences. One list was dedicated to no rmal rate conditions, th e other to slow rate conditions. Each list was read twice, once using clear speech, and once using conversational speech. Therefore, each talk er produced 50 utterances in each of the following conditions: clear speech at norma l rates (clear/normal) averaging 174 wpm; conversational speech at normal rates (conv/nor mal), averaging 178 wpm; clear speech at slow rates (clear/slow), av eraging 89 wpm; and conversat ional speech at slow rates (conv/slow), averaging 1 03 wpm (Krause, 1995).
24 Table 2. Sentence Lists by Speaker and Condition List Speaker Condition 1 conv/normal clear/normal 2 T1 conv/slow clear/slow 3 conv/normal clear/normal 4 T3 conv/slow clear/slow 5 conv/normal clear/normal 6 T4 conv/slow clear/slow 7 conv/normal clear/normal 8 T5 conv/slow clear/slow Instrumentation consisted of headphones c onnected to the output of a Lynx Audio sound card and a computer system utilizing Matlab software. Matlab is a signal processing software program that was used to control frequency-gain characteristics and presentation level of stimuli. All instrument ation was calibrated prio r to the start of the experiment in order to ensure that the e xperimental systemÂ’s output frequencies and levels were accurate. In addition to the speech stimuli, the Salthouse (1991) materials were utilized to assess participantsÂ’ cogniti ve processing speed. These materials consist of letter and pattern comparison tasks, in whic h participants determined whether pairs of stimuli were the same or different. Procedures Each listener attended te sting sessions roughly once a week for a minimum of four weeks. The sessions were 2-3 hours in duration. During each session, the listeners heard four lists, representing each of th e four test conditi ons (clear/normal, conversational/normal, clear/slow, and conve rsational/slow). Test condition order was counterbalanced across sessions to control for sequencing and learning effects. In
25 addition, a week long break at the midpoint of the study served to further reduce possible learning effects. Subjects in group 1 follo wed one schedule for weekly presentation of stimuli. Subjects in group 2 followed a di fferent schedule. After the week-long break, subjects in group 1 were presented with the s timuli previously given to group 2, and vice versa. Each sentence list was re peated once in varying conditions. Table 3. Presentation Order of Stimuli WEEK GROUP 1 GROUP 2 1 T1 List 1 conv/normal T1 List 2 clear/slow T3 List 5 clear/normal T3 List 6 conv/slow T1 List 1 clear/normal T1 List 2 conv/slow T3 List 5 conv/normal T3 List 6 clear/slow 2 T3 List 3 clear/normal T3 List 4 conv/slow T5 List 7 conv/normal T5 List 8 clear/slow T3 List 3 conv/normal T3 List 4 clear/slow T5 List 7 clear/normal T5 List 8 conv/slow 3 BREAK BREAK 4 T1 List 1 clear/normal T1 List 2 conv/slow T3 List 5 conv/normal T3 List 6 clear/slow T1 List 1 conv/normal T1 List 2 clear/slow T3 List 5 clear/normal T3 List 6 conv/slow 5 T3 List 3 conv/normal T3 List 4 clear/slow T5 List 7 clear/normal T5 List 8 conv/slow T3 List 3 clear/normal T3 List 4 conv/slow T5 List 7 conv/normal T5 List 8 clear/slow Stimuli were presented through headphones, without hearing ai ds. This allowed the examiner to better control the presentation level and frequency-gain characteristics of the stimuli. Each listener had their hearing corrected th rough the headphones. This
26 correction was based on their individual audiograms, utilizing the National Acoustic Laboratory-Revised (NAL-R) procedure (Byrne & Dillon, 1986) and the Matlab software. This method of frequency-shaping allowed the evaluator to compensate for any possible differences in heari ng aid types among the subjects. Stimuli were presented at the most comfortable loudness level (MCL) for each listener. The presentation levels that the listeners selected are listed in Table A4 of Appendix A. In addition, the Matlab program was equippe d with a user interface that allowed listeners to set their own pace for stimulus presentation. Listeners were asked to reproduce each sentence that wa s presented to them aurally. They were given a choice of writing or typing their responses. The same scoring system established by Pi cheny et al. (1985) was used for this experiment. Intelligibility scores were based on percentages of correct keywords. Keywords included nouns, verbs, adverbs, and adjectives. Inserting, omitting, or misidentifying phonemes counted as errors. In serting or omitting plurals or past tense suffixes did not count as errors. Data Analysis The data collected consisted of percenta ges of keywords correctly identified by listeners in each of the following conditions: clear/normal, clear/slow, conv/normal, and conv/slow. Data were recorded on an Excel spreadsheet and converted to graphs for visual analysis. A four-way analysis of variance (ANOVA) was applied to test significance of the results. In addition to analyzing intelligibility differences between conditions, data were examined for a rela tionship between cognitive processing ability
27 and speech perception ability. Cognitive proc essing scores consisted of the number of Salthouse (1991) tasks correctly co mpleted within 30 seconds.
28 Chapter 4 Results The purpose of this study was to investigate how speech intelligibility, measured by percent keywords correct, varied with speaking mode, speaking rate, talker and listener for older listeners with moderate, slopi ng hearing loss. In addition to determining the relative intelligibility of each condition, the data collected were examined for a relationship between cognitive processing ability and speech perception ability. Specifically, cognitive processing scores were examined in relation to both the overall performance of listeners and to the clear speech benefit obt ained. Visual inspection of the data suggested no relationship in either case. Nonparametric statistical analysis (SpearmanÂ’s rho) also show no statistically significant correlations, although the analysis was underpowered and more subjects would be needed to confirm this result. In order to assess intellig ibility differences between conditions, keyword scores for each condition were examined. Keyword scores for each listener are presented in Appendix C, and Table 4 shows the averag e intelligibility of each condition. In analyzing the intelligibility benefit of each condition, the conv/normal condition was considered the baseline because it best repr esents typical speech. Clear/slow was the most intelligible condition overall and provi ded a 7.7 percentage point intelligibility benefit relative to conv/normal on average. However, neither conv/slow nor clear/normal provided any intelligibility benefit, suggesti ng that for older adults with moderate,
29 sloping hearing loss, the combination of clear speech and slower rate on average is more beneficial than the additive effects of a ltering either speaking ra te or speaking mode alone. Table 4. Average Intelligibility Condition Average Keyword Score (% correct) clear/slow 84 clear/normal 74 conv/slow 77 conv/normal 77 A four-way repeated measures analys is of variance (ANOVA) was performed on keyword scores after an arcsine transformation ( Ij/100) was applied to equalize the variances. The analysis included three with in-subjects factors (ra te, speaking mode, and talker) and one between subjects factor (listener). Table 5 lists F-ratios and significance levels for those effects and in teractions that were statisti cally significant (p<0.01). Each of these will be discussed in de tail in the sections below. A complete listing of all effects and interactions, including t hose that were not found to be significant, can be found in Appendix D.
30 Table 5. Significant Effects a nd Interactions at the 0.01 level Effect F df SignificanceEta Squared listener 144.855 5 .000 0.443 talker 58.075 3 .000 0.107 rate 48.129 1 .000 0.029 mode 10.814 1 .001 0.007 listener x talker 2.238 15 .005 0.021 talker x rate 24.832 3 .000 0.046 talker x mode 6.540 3 .000 0.012 rate x mode 41.652 1 .000 0.025 talker x rate x mode 10.733 3 .000 0.020 listener x talker x rate x mode 2.957 15 .000 0.027 Main Effects As shown in Table 5, all main effects were statistically significant. Of the four factors in this study, the effects of speaki ng mode and speaking rate were of primary interest since they show the degree to which the listeners in this study benefited from clear speech and slow speech, respectively. Regarding speaking mode, average keyword scores were 79.3% for clear speech and 76.6% for conversational speech. Although significant, the small difference in overall intellig ibility (2.7 percenta ge points) between clear and conversational speaking modes indicat es that this was not a large effect ( 2 = 0.007). Rather, the interaction of mode and rate had a larger effect on intelligibility than the main effect of mode. This interacti on will be discussed in the next section. Regarding speaking rate, average keyword scor es were 80.4% for slow rate speech and 75.4% for normal rate speech. The average be nefit for slow speech was 5 percentage
31 points overall, a somewh at larger effect ( 2 = 0.029), indicating that listeners benefited noticeably from slow rates as compared to normal rates on average. The remaining factors, talker and listener, were both statistically significant in the ANOVA because some talkers were more inte lligible than others and some listeners performed better than others. For instance, T5 was the most intelligible talker, producing an average intelligibil ity of 85.6%. The least intelligible talker, T4, produced an average intelligibility score of 73.9%. Similarly, av erage listener scores ranged from 61.7%91.8%, indicating that the tasks were inherently more difficu lt for some listeners than others. Such intelligibility differences between talkers and performance differences between listeners were expected, and the more pertinent information to this study is the interaction between talker or listener and th e mode and rate factors (i.e. the extent to which the benefit provided by clear speech or sl ow speech varies for different talkers or different listeners). These interactions will be discussed in detail later in the chapter. Interactions with Speaking Mode Mode x Rate Interaction In order to examine the interaction of rate with speaking mode, Figure 1 shows the overall average across talker and listener fo r each condition tested. This figure allows for comparisons of the effect of rate within the two modes (c lear and conversational). As shown in Figure 1, the clear/slow condition s howed a 7.7 percentage point benefit over conv/normal overall. This supports the findi ngs of Picheny et al. (1985), who found a clear (clear/slow) speech a dvantage over conversational sp eech for listeners with moderate to severe hearing lo ss. In addition, clear/slow sp eech exhibited a comparable intelligibility benefit over both conv/slow speech (7.7 percentage points) and
32 clear/normal speech (10 percentage points). Conversational speech, regardless of rate, had similar intelligibility on average (77%). In other words, clear speech was beneficial to intelligibility at slow rates (clear/slow Â– conv/slow = +7 points) but not at normal rates (clear/normal Â– conv/normal = -3 points). Th ese data indicate that for listeners with moderate, sloping losses in quiet conditions, th e benefit of slow ra te is dependent on speaking mode, and the benefit of clear sp eech is dependent upon rate. The ANOVA confirmed that the rate x mode interacti on was significant and accounted for roughly the same amount of variance ( 2 = 0.025) as rate alone. 0 10 20 30 40 50 60 70 80 90 100 clr/slowclr/normconv/slowconv/norm ConditionAverage % Correct Figure 1. Average intelligibility, in percen t keywords correct, for each test condition (rate x mode). Error bars indicate +/1 standard error from the mean. Because the rate x mode interaction was shown to be significant in the ANOVA, post hoc t-tests were conducted to evaluate pairwise comparisons of the four conditions. These comparisons served to further evaluate differences that were observed between the
33 conditions. A Bonferroni adjustment for mu ltiple comparisons was implemented in the ttest results to compensate for the increased chance of Type I error associated with multiple comparisons. As shown in Table 6, results of the pairwise comparisons confirmed that clear/slow speech was significa ntly more intelligible than every other condition and that the other three conditions di d not differ significantly from each other. Table 6. Pairwise Comparisons 99% Confidence Interval for Difference (I) Condition (J) Condition Mean Difference (I-J) Std. Error Sig. Lower Bound Upper Bound conv/slow clear/slow conv/normal clear/normal -.098* .005 .037 .011 .015 .017 .000* 1.000 .214 -.137 -.049 -.022 -.060 .059 .095 clear/slow conv/slow conv/normal clear/normal .098* .103* .135* .011 .013 .013 .000* .000* .000* .060 .057 .088 .137 .149 .183 conv/norm conv/slow clear/slow clear/normal -.005 -.103* .032 .015 .013 .013 1.000 .000* .141 -.059 -.149 -.015 .049 -.057 .079 clear/norm conv/slow clear/slow conv/normal -.037 -.135* -.032 .017 .013 .013 .214 .000* .141 -.095 -.183 -.079 .022 -.088 .015 *Significant at the .01 level. Other Interactions with Speaking Mode Figure 2 shows the average intelligibility obtained by listeners in each speaking mode, which shows why the interaction of listener and mode was not statistically significant. Five out of six listeners showed increased scor es on clear speech tasks (see
34 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6 Listener% correct Av clear Av convFigure 2). The remaining listener, L2, performed equally well for conversational and clear speech modes, averaging 91.8% for each. This may indicate a ceiling effect, in which her baseline performance (conversat ional speech conditions) was so high that improvement could not be shown. Thus, with the exception of thos e effected by ceiling effects, listeners generally benefited from clear speech. Figure 2. Average performance, in percent ke ywords correct, for each listener in each speaking mode. Talkers, on the other hand, did not all ach ieve comparable benefits from speaking clearly when intelligibility was averaged acro ss listeners. As shown in Figure 3, three of the four talkers did demonstrate increased overall intelligibility in clear speech conditions, as compared to conversational speech for listeners with hearing loss in quiet. In other words, most talkers were more in telligible when utilizing clear speech. This indicates that clear speech is beneficial for most talkers. However, the size of the clear
35 0 10 20 30 40 50 60 70 80 90 100 T1T3T4T5 Talker% correct Av clear Av convspeech benefit varied from 2.3% (T1) to 8.5% (T4), and one talker (T3) was actually less intelligible on average when utilizing clear speech. As a result of these talker differences, the interaction of talker and mode was statistically significant. Figure 3. Average intelligibility, in percen t keywords correct, for each talker in each mode. Error bars indicate +/1 standard error from the mean. Interactions with Rate Figure 4 shows the average intelligibility obtained by listeners at each speaking rate, which shows why the interaction of liste ner and rate was not si gnificant. As shown in Figure 4, every listener performed better ac ross talkers when presented with the slow rate.
36 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6 Listener% Correct Av. Slow Av. Norm Figure 4. Average performance, in percent ke ywords correct, for each listener at each rate. Every talker, however, did not perform similarly when speaking slowly. As Figure 5 illustrates, tw o of the four talkers achieved similar intelligibility benefits for slow speech conditions, as compared to normal rates. One talker, T4, showed a benefit for the normal rate relative to the slow rate, and the last talker, T5, exhibited comparable intelligibility in both slow (85.4%) and norma l rate conditions (85.9%). These data indicate that it is not necessa ry for everyone to decrease speak ing rate in order to improve intelligibility, as two of the four talkers did no t exhibit a slow rate benefit. Because of these sizeable differences between talkers, the interaction of talker and rate was statistically significant, and the corresponding effect size was relatively large. In fact, this interaction accounted fo r more of the variance ( 2 = 0.046) in intel ligibility scores than mode or rate alone as well as the other interactions w ith mode and rate.
37 0 10 20 30 40 50 60 70 80 90 100 T1T3T4T5 Talker% correct Av. Slow Av. Norm Figure 5. Average intelligibility, in percent keyw ords correct, for each talker at each rate. Error bars indicate +/1 sta ndard error from the mean. Listener and Talker Interactions Listener and Talker Interacti ons with Condition (Mode x Rate) The three-way interaction of listener, mode, and rate was not significant in the ANOVA. This is because all listeners followe d the same general pattern when data were averaged across talkers. Speci fically, clear/slow was the mo st intelligible condition on average for all listeners. In addition, the clear/normal condition did not show improvement over conv/normal on av erage for any of the listeners. On the other hand, the relative intelligibil ity of the four condi tions did not follow the same pattern for all talkers, and the inte raction of talker, rate, and mode, shown in Figure 6, was statistically significant. Clear /slow was the most intelligible condition overall for three of the four talkers but for the remaining talker, T3, the conv/slow
38 condition was most intelligible. Thus, T3Â’s data alone would seem to indicate that a slower rate provides a benefit over speech at no rmal rates, regardless of speaking mode. However, as shown in Figure 6, only two of th e talkers exhibited intelligibility benefits for both slow conditions (conv/slow, clear/slow) compared to conv/normal. For the remaining two talkers (T4, T5), one slow condition was the most intelligible, and the other was least intelligible. In other word s, reduction of speaking rate alone was not sufficient to guarantee increased speech intell igibility for all talkers. However, when talkers spoke slowly and clearly, all achieved a benefit relative to conv/normal speech. 0 10 20 30 40 50 60 70 80 90 100 T1T3T4T5 Talker% correct clr/slow clr/norm conv/slow con/norm Figure 6. Average intelligibility, in percent ke ywords correct, for each talker at each rate and mode. Error bars indicate +/1 standard error from the mean. Other Listener and Talker Interactions Figure 7 shows the average intelligibility of each talker for the various listeners, which shows why the interaction of listener and talker was st atistically significant in the ANOVA. Although T5 was the most intelligible talker for each listener, there was no
39 discernible intelligibility pattern for the remaining talkers when compared across listeners. In other words, with the exception of T5, each listener found different talkers more intelligible. 0 10 20 30 40 50 60 70 80 90 100 L1 L2 L3 L4 L5L6 ListenerAverage % Correct T1 T3 T4 T5 Figure 7. Average performances, in percent ke ywords correct, of every listener for each talker. Each listener also showed different eff ects of condition, depending on the talker. Figure 8 shows the four-way interaction, talker x listener x mode x rate. All listeners benefited overall from the slow rate, and t hose listeners who showed any benefit from a speaking mode favored clear speech over convers ational. However, the rate and mode that was most intelligible varied across talker and listener, and the talker x listener x mode x rate interaction was statistically significant. The effect size was 2 = 0.027, which suggests that speaking mode and rate c onstituted a small but substantial impact on
40 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6Listener% Correct 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6Listener% Correct 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6Listener% Correct clr/slow clr/norm conv/slow conv/norm 0 10 20 30 40 50 60 70 80 90 100 L1L2L3L4L5L6Listener% Correct clr/slow clr/norm conv/slow conv/normintelligibility for talker x listener interactions (about the same amount as rate alone or the rate x mode interaction). a) T1 b) T3 c) T4 d) T5 Figure 8. Average performance, in percent keyw ords correct, of every listener for each talker in each condition. Panel a) shows data for T1, panel b) shows data for T3, panel c) shows data for T4, and panel d) shows data for T5. Consistent with previous studies (e.g. Picheny et. al., 1985), the benefits of clear/slow speech were robust. Not onl y was it the most intelligible condition on
41 average, but the clear/slow speech of T1, T3, and T4 produced an intelligibility benefit over conv/normal speech for every listener, and T5 produced a clear/slow benefit for three of six listeners (L1, L5, and L6). Of the remaining th ree listeners, one constituted a potential ceiling effect. In other words, the listener performed so well in the conv/normal condition that there may not have been room to show improvement in the clear/slow condition. This resulted in a clear/slow benefit for 21 out of 24 talker/listener combinations. In comparison of conv/slow and conv/normal conditions, 11 out of 24 talker/listener combinations showed a benef it for conv/slow over conv/normal. Of the 13 talker/listener interac tions that did not benefit from c onv/slow, two could have resulted from possible ceiling effects. Individual talker s differed considerably in this comparison. For example, T3 exhibited a conv/slow benef it for each listener, while T4 did not show a conv/slow benefit for any listeners. Although ceiling effects may account for some of the differences between the benefits of rate (conv/slow compared to conv/normal), and speech mode (clear/slow compared to conv/slow ) the combination of slow rate and clear mode was more beneficial overall. Finally, it should be noted that although clear/normal speech did not provide an intelligibility advantage over conv/normal speech on average, eight talker/listener combinations did exhibit a clear/normal be nefit over conv/normal. Moreover, of the 16 talker/listener combinations that did not produce a clear/normal benefit, six were potential ceiling effects. T5 produced possible ceiling effects for four of the six listeners, while T3 did not produce any possible ceiling eff ects. All of these differences seem to indicate that some talkers have greater potential for producing cl ear speech at normal
42 rates which provides an intelligibility advantag e to older listeners with moderate, sloping hearing loss.
43 Chapter 5 Discussion The results of this study i ndicate that older listeners with moderate, sloping losses benefit from clear/slow speech relative to conv/normal, which is similar to typical conversational speech. These findings support previous research (Picheny et al., 1985; Payton et al., 1994; Schum, 1996) on the benefi ts of clear speech at slow rates for listeners of various ages with various audiom etric characteristics. Of note, however, is that slowing rate alone may provi de a similar or greater benefit for some listeners in this population, while other listeners require both slow rate and clear mode to receive a benefit. Although clear speech at normal rates has been shown to provide a benefit for young normal hearing listeners in noise (SNR = 2 dB; Krause & Braida, 2002) and older normal hearing listeners in noise (SNR = 0 dB; Panagiotopoulos, 2005), this benefit was not widely seen in quiet for older listeners with sloping hearing loss. However, each listener did benefit from clear speech at norma l rates from specific talkers. There was no apparent pattern as to which listener/talker interaction produced cl ear/normal benefit, although T4 exhibited a clear/normal benefit over conv/slow for each listener. This seems to indicate that the degree of benefit, if any, of clear speech at normal rates is dependent on both talker and listener for liste ners with moderate, sloping losses in quiet. To analyze the effect of hearing loss on the clear speech benefit, the results of this study were compared to those of Panagiot opoulous (2005). Panagi otopolous evaluated
44 listeners with normal hearing, who were r oughly the same age as the listeners with hearing loss in this study. Table 7 shows the comparison of percent keywords correct between the present study and the previous study. Again, the average percentages for conv/normal should be viewed as a baseline for comparison to the other conditions. In parentheses is the increase in percenta ge points of each condition compared to conv/normal. Table 7. Average Listener Performance Across Studies Current study: older listeners hearing loss SNR = dB ( quiet) Panagiotopolous (2005): older listeners normal hearing SNR = 0 dB Conv/normal 77% 45% Conv/slow 77% ( +0 ) 66% ( +21 ) Clear/normal 74% ( -3 ) 59% ( +14 ) Clear/slow 84% ( +7 ) 68% ( +23 ) In PanagiotopolousÂ’ (2005) study, older listeners with normal hearing benefited from clear speech at normal rates (relative to conv/normal), but not at slow rates (relative to conv/slow). In the current study, older lis teners with moderate, sloping losses showed the opposite effect, benefiting from the clear/ slow condition (relative to conv/slow), but not clear/normal (relative to conv/normal). As shown in Table 7, the two slow conditions resulted in the highest average scores for PanagiotopolousÂ’ study, in which listeners were presented with stimuli in background noise. Because of the inherent difficulty of the
45 listening tasks, it is possible that a ceili ng effect limited the amount of clear/slow advantage obtainable during th e study. Similarly, the average clear/normal performance in the current study was within three percentage points of conv/normal, indicating a possible ceiling effect for speech at normal rates. Although the listeners with hearing loss in this st udy did not benefit from clear/normal speech, it cannot be concluded that no hearing-impaired listeners would benefit from clear/normal speech. Krau se (2001) conducted a study of speech intelligibility for three listeners with sens orineural hearing losses. Test conditions included clear and conversational speech in quiet at both slow a nd normal rates, and utilized the same talkers and sentence lists as in the curr ent study. Results of KrauseÂ’s experiment indicated that two of the listener s, GI and GT, received a consistent benefit from clear speech at normal rates in comparis on to conversational speech at normal rates. The audiometric characteristics of the three listeners in Kr auseÂ’s study are presented in Table 8. Visual inspection of the audiometri c characteristics of these three listeners indicates that those who benef ited from clear/normal speech pres ented with relatively flat hearing losses across threshol ds. The listener who did not exhibit a clear/normal benefit on average, RK, presented with a sloping loss comparable to the listeners in the current study (L1-L6). As with the listeners in this study, RK did obtain a benefit from clear/normal speech from particular talker s, but not on average across all talkers.
46 Table 8. Audiometric Characteristics of H earing-Impaired Listeners from KrauseÂ’s (2001) Study Thresholds (dB) at Frequency (Hz) Listener Sex Age Test ear PTA 50010002000 4000 8000 Slope GI M 65 L 50 60 45 45 55 85 No RK M 64 L 40 20 40 60 65 NR Yes GT M 40 R 56.7 55 55 60 90 85 No Given the small number of listeners in KrauseÂ’s (2001) study and lack of clear/normal benefit for RK the average benefit of clear/normal speech was not statistically significant. Krause suggested th ree possible explanations for this lack of expected clear/normal benefit. One possibili ty was that the clear/normal benefit did not extend to older listeners. This possibili ty is unlikely, based on the results of Panagiotopoulos (2005) who found a 14 percen tage point clear/normal advantage for older listeners with normal hearing. Another possibility was that hearing-impaired listeners did not benefit from clear/normal sp eech. This possibility is also unlikely, due to KrauseÂ’s (2001) results which indicated that two out of three hearing-impaired listeners exhibited an intelligibility benefit. KrauseÂ’s third possibl e explanation was that audiometric characteristics ma y be factors in the potential benefits of clear/normal speech. This is the most likely explanation for the lack of overall clear/normal benefit exhibited by RK. RKÂ’s sloping hearing lo ss was consistent with the audiological configuration exhibited by the listeners in the current study (L1-L6). Like RK, these listeners did not benefit from clear/normal speech on average. However, there were talker/listener combinations from both studi es in which listeners did benefit from clear/normal (T1 and L5; T3 and L4, L2; T4 and RK, L4; T5 and L3).
47 In a previous study of vowel intelligibility in clear speech, Ferguson and KewleyPort (2002) found no significant difference between clear and conversational speech for elderly hearing impaired listeners. Seven out of nine listeners in the Ferguson and Kewley-Port study met the criteria for sloping loss presented in the current study. This supports the hypothesis that audiometric char acteristics are factor s in potential clear speech benefit, particularly if Ferguson and Kewley-PortÂ’s talkers were using a form of clear/normal speech. Specifically, older adults with sloping heari ng loss may not receive the same clear/normal speech benefit as older adults with normal hearing or flat hearing losses. However, talkers in Ferguson a nd Kewley-PortÂ’s study most likely produced a form of clear/slow speech, because they were given no specific instructions or training to produce clear speech at normal rates. In su ch a case, audiometric characteristics could not fully explain the lack of clear speech benef it in that study, because all listeners in this study received a benefit from clear/slow speec h. It is possible, however, that listeners cannot fully benefit from clear/slow speech unless properly amplifie d, since listeners in this study were amplified and Ferguson a nd Kewley-PortÂ’s listeners were not. Difficulty of Tasks One difference that should be noted be tween the current study and KrauseÂ’s (2001) study is that digital hearing aids ar e now more commonly used by listeners with hearing loss. Because the NAL-R amplif ication provided via headphones in these experiments mimics a frequency-gain characte ristic more likely to be produced by analog hearing aids, it is possible that the listeners were not acclimated to this type of signal processing and therefore, not able to take a dvantage of all the acoustic cues available to them during the experiment. This possibili ty is not likely to explain the lack of
48 clear/normal benefit, because all conditions wo uld have been negativel y affected to some extent. However, if the differences in am plification strategy primarily affected the acoustic cues which provide the clear speech advantage at normal rates, then this explanation could account for the lack of clear/n ormal benefit. To eliminate this potential confounding factor, one solution would be to al low time for training listeners to use the NAL-R amplification presented via headphone s, providing them w ith extra practice sessions before recording data. However, this additional procedure would be cumbersome and not representative of real-wor ld listening situations Another solution would be to present the experimental stimu li in a sound field, allowing the listeners to utilize their own hearing aids. This adjustment to the pr ocedures would eliminate the need for additional training time and provide more realistic data for real-world listening conditions. Another issue that arose in the current study that was different from the Krause (2001) study is the presence of ceiling effects. As mentioned earlier, it is likely that L2Â’s data exhibited a ceiling effect due to her cons istently high scores on all listening tasks. T5Â’s data may have also exhibited a ceiling e ffect in that all listeners showed greatest intelligibility for this talker, regardle ss of condition. In addition, some other talker/listener combinations resulted in hi gh scores that may have reflected a ceiling effect (T1/L6, T1/L1, T4/L5). Ceiling e ffects may impact the data by limiting the amount of improvement that can be recorded between conditions. For example, if a listener scores high in the conv/normal condition, there is little room for an increased score in the clear speech conditions. To elim inate this problem in future experiments, one solution would be to increase the difficu lty of the task, thus reducing the likelihood
49 of high scores in the baseline condition. One wa y to increase task difficulty would be to recruit listeners with more severe pure-tone averages and/or more steeply sloping hearing losses. This would increase the difficulty of the task; however listeners may feel frustrated at their lack of su ccess and could become reluctant to complete the experiment. Another possibility would be to add background noise and manipulate the SNR so that the speech signal would be more ambiguous. Again, participant frustration levels would need to be monitored. In the current experiment, most of the lis teners expressed some frustration with the difficulty of the task, even those liste ners whose performance indicated relatively high levels of success. This frustration wa s not reported for the older listeners with normal hearing in PanagiotopolousÂ’s (2005) st udy, which utilized the same talkers and sentence lists, even though the listeners in PanagiotopolousÂ’s st udy performed worse on average across all conditions than the listeners in this study. It is possible that this difference in reactions to the same stimuli is related to the listeners Â’ hearing status, and that listeners with hearing loss are more suscep tible to frustration for this type of listening task. Only one listener, L2, expressed enjoym ent of the tasks in the current study. Her reaction to the listening tasks could have been influenced by two factors: 1) she was the only female participant, and 2) her performa nce scores were highest overall, indicating that she found the task easier th an the other participants. It is likely that increasing the difficulty of this task would have resulted in more negative reactions by all listeners. Future Work Future research in this area should in clude increased numbers of subjects and presentation of stimuli in a sound field, as opposed to headphones, to provide more real-
50 world data. Because audiological configurati on appears to be a factor in performance levels for listeners with hear ing loss, future studies shoul d focus on these differences. One possible research focus would be to c onfirm KrauseÂ’s (2001) findings of a clear speech benefit for listeners with flat hearing losses. Due to the nature of the tasks presen ted in the current study, spelling errors, typographical errors, and poor handwriting create d several situations in which judgment calls had to be made during the scoring proce ss. Because all responses were scored by the same person, scoring was consistent acr oss listeners, talkers, and conditions. However, if greater numbers of subjects in fu ture studies result in the need for multiple scorers, it will be important to check inter-rater reliability. An additional consideration for future research is increasing the difficulty of tasks to counteract the possibi lity of ceiling effects. Util izing background noise is likely the most effective way to do this. Curre nt research (Smart, 2006) is focusing on establishment of psychometric functions fo r clear/slow, clear/normal, conv/slow, and conv/normal speech for young normal hearing listene rs in noise. Psychometric functions, which show variation in performance levels as a function of variati ons in SNR, would not only characterize the degree to which the clear speech benefit varies with difficulty of task, but would also facilitate pinpointing th e most appropriate SNR to compensate for potential floor or ceiling effects in normal hear ing listeners. Therefore, the results of this research may also provide insight into es tablishing the most appropriate SNRs for listeners with hearing loss. It may be necessa ry to provide unique SNRs for each listener participating in the study due to differing au diological configurati ons. Because adding noise to the stimuli will increase task di fficulty, the following recommendations are
51 offered to minimize listener frustration: 1) shorter experiments, in which each listener hears stimuli from only one talker, thus reduc ing the number of sessi ons to be attended and the amount of stimuli presented to each listener; 2) shorter duration for individual sessions, reducing the amount of frustration in each session; 3) group sessions, in which listeners will have an opportunity to interact with other participan ts and understand that the tasks are challenging for everyone; and 4) different speech materials, such as single words or meaningful sentences that may redu ce the memory load inherent in the task, thereby allowing listeners to focus more cogni tive effort on listening and to experience a reduction in any errors due to misremembering stimuli. Clinical Implications Older listeners with sloping hearing lo ss exhibited a benefit from slow speech relative to typical conversational speech. Clear/slow speech was the most intelligible condition overall, indicating that while slowing ra te is effective, the use of clear speech is also valuable in increasing intelligibility. Because clear/normal speech was not benefi cial to this population on average, it would not be recommended for clinical use. Rather, clear/slow speech is likely the most effective mode of communication to be used in clinical settings with this population as it has been shown to be equally, if not more effective, for all liste ners in this group. However, some individuals did benefit from the clear/normal speech of certain talkers. Therefore, some clients may request that normal rates be utili zed during treatment sessions with certain clinicians or fam ily members, and these requests should be considered valid.
52 Even though clear/normal speech is not the most effective tool for initiating therapy, it does have potential applications to hearing aids Further research into the acoustic characteristics present in those ta lker/listener combinations which showed a clear/normal benefit may result in hearing aid technology that is able mimic this effect. Although some individuals may ultimately show preference for normal speaking rates, clear/slow speech should be considered the most effective communication mode in which to initiate ther apy. It would be helpful for clinicians to practice clear speech and use it during therapy, as it has been shown to be effective for various populations, including those w ith a sloping hearing loss.
53 List of References Bradlow, A. R., & Bent, T. (2002). The cl ear speech effect for non-native listeners. Journal of the Acoustical Society of America, 112, 272-284. Bradlow, A. R., Kraus, N., & Hayes, E. (2003). Speaking clearly for children with learning disabilities: Sent ence perception in noise. Journal of Speech, Language and Hearing Research, 46, 80-97. Bradlow, A. R., Torretta, G. M., & Pisoni, D. B. (1995). Intelligibility of normal speech I: Global and fine-grained acoustic-phonetic talker char acteristics (Progress Rep. No. 20). Blommington: Indiana Univ ersity, Speech Research Laboratory. Byrne, D. & Dillon, H. (1986). The nationa l acoustic laboratories new procedures for selecting the gain and frequenc y response of a hearing aid. Ear and Hearing, 7, 257-265. Crum, R. M., Anthony, J. C., Bassett, S. S., & Folstein, M. F. ( 1993). Population-based norms for the Mini-Mental State Examin ation by age and education level. Journal of the American Medical Association, 269 2386-2391. Dubno, J.R., Dirks, D.D., & Morgan, D. E. (1984). Effects of age and mild hearing loss on speech recognition in noise. Journal of the Acoustical Society of America, 76 87-96. Ferguson, S. H., & Kewley-Port, D. (2002) Vowel intelligibility in clear and conversational speech for normal-hearing and hearing-impaired listeners. Journal of the Acoustical Society of America 112 259-271. Folstein, M. F., Folstein, S. E., & McHugh, P. R. (1975). Mini-Mental State: A practical method for grading the state of patients for the clinician, Journal of Psychiatric Research, 12, 189-198. Gagne, J. P., Rochette, A. J., & Charest, M. (2002). Auditory, vi sual, and audiovisual clear speech. Speech Communication 37 213-230. Gordon-Salant, S., & Fitzgibbons, P. J. (1997) Selected cognitive factors and speech recognition performance among you ng and elderly listeners. Journal of SpeechLanguage-Hearing Research, 40 423-431.
54 Gordon-Salant, S., & Fitzgibbons, P. J. (1999). Profile of auditory temporal processing in older listeners. Journal of Speech-Language-Hearing Research, 42 300-311. Helfer, K. (1997). Auditory and auditory-v isual perception of cl ear and conversational speech. Journal of Speech, Language, and Hearing Research 40 432-443. Helfer, K. (1998). Auditory and auditory-v isual recognition of cl ear and conversational speech by older adults. Journal of the American Academy of Audiology, 9 234242. Krause, J. (1995). Effects of speaking rate and speaking mode on intelligibility Unpublished masterÂ’s thesis, Massachus etts Institute of Technology, Boston. Krause, J. (2001). Properties of naturally produced clear speech at normal rates and implications for inte lligibility enhancement Unpublished doctoral dissertation, Massachusetts Institute of Technology, Boston. Krause, J., & Braida, L. (2002). Investigati ng alternative forms of clear speech: The effects of speaking rate and sp eaking mode on intelligibility. Journal of the Acoustical Society of America 112 2165-2172. Krause, J., & Braida, L. (2003). Effects of listening environmen t on intelligibility of clear speech at normal speaking rates. Iranian Audiology 2 39-47. Panagiotopoulos, A. (2005). Benefits of clear speech at normal rates for older adults with normal hearing. Unpublished masterÂ’s thesis, University of South Florida. Payton, K., Uchanski, R., & Braida, L. (1994). Intelligibility of c onversational and clear speech in noise and reverberation for liste ners with normal and impaired hearing. The Journal of the Acoustical Society of America 95 1581-1592. Peters, R., Moore, B., & Baer, T. (1998). Sp eech reception thresholds in noise with and without spectral and temporal dips for hearing-impaired and normally hearing people. Journal of the Acoustical Society of America, 103 577-587. Picheny, M. A., Durlach, N. I., & Braida, L. D. (1985). Speaking clearly for the hard of hearing I: Intelligibility differences between clear and conversational speech. Journal of Speech and Hearing Research 28 96-103. Picheny, M. A., Durlach, N. I., & Braida, L. D. (1986). Speaking clearly for the hard of hearing II: Acoustic char acteristics of clear and conversational speech. Journal of Speech and Hearing Research 29 434-446.
55 Picheny, M. A., Durlach, N. I., & Braida, L. D. (1989). Speaking clearly for the hard of hearing III: An attempt to determin e the contribution of speaking rate to differences in intelligibility between clear and conversational speech. Journal of Speech and Hearing Research 32 600-603. Salthouse, T. A. (1991). Mediation of adult age differences in cognition by reductions in working memory and speed of processing. Psychological Science, 2, 179-183. Schum, D. J. (1996). Intelligibility of clear and conversational speech of young and elderly talkers. Journal of the American Academy of Audiology 7 212-218. Smart, J. B. (2006). Personal communication. Studebaker, G. A. (1985). A Â“ra tionalizedÂ” arcsine transform. Journal of Speech and Hearing Research 28(3), 455-462. Uchanski, R. M., Choi, S. S., Braida, L. D., Reed, C. M., & Durlach, N. I. (1996). Speaking clearly for the hard of hearing IV: Further studies of the role of speaking rate. Journal of Speech and Hearing Research 39(3), 494-509.
57 Appendix A: Listener Demographics Table A1. Listener age, ge nder, and years of education Listener Age Gender Education L1 68 M MBA L2 72 F College (3 yrs) L3 57 M High School L4 74 M College (2 yrs) L5 66 M B.A. L6 74 M Tech College Table A2. ListenersÂ’ MMSE scores Listener Score L1 28 L2 30 L3 28 L4 29 L5 30 L6 29
58 Appendix A (Continued) Table A3. ListenersÂ’ Bilate ral Audiological Thresholds Thresholds (dB) at Frequency (Hz) Listener Ear 250 500 10002000 4000 8000 R 40 35 30 45 50 80 L1 L 45 30 20 20 50 60 R 25 35 50 60 65 70 L2 L 30 35 40 50 70 80 R 30 40 55 50 55 60 L3 L 30 35 55 50 60 55 R 45 45 40 55 60 70 L4 L 25 25 25 60 65 80 R 25 30 45 85 75 70 L5 L 25 30 40 85 80 75 R 25 30 35 30 50 70 L6 L 15 30 45 45 75 90 Table A4. Stimulus Presentation Levels Presentation Level Listener Pure Tone RMS Peak L1 88.5 dB SPL 103.3 dB SPL L2 96.3 dB SPL 107.7 dB SPL L3 98.6 dB SPL 106.2 dB SPL L4 89.9 dB SPL 105.2 dB SPL L5 96.1 dB SPL 106.8 dB SPL L6 95.5 dB SPL 107.4 dB SPL
59 Appendix B: Norms for the Mini-Mental State Examination by Age and Education Age Range Education 50-54 55-59 60-64 65-69 70-74 75-79 Mean 23 22 23 22 22 21 0-4 years SD 2.6 2.7 1.9 1.7 2.0 2.2 Mean 27 26 26 26 26 25 5-8 years SD 2.4 2.9 2.3 1.7 1.8 2.1 Mean 28 28 28 28 27 27 9-12 years SD 2.2 2.2 1.7 1.4 1.6 1.5 Mean 29 29 29 29 28 28 13+ years SD 1.9 1.5 1.3 1.0 1.6 1.6 *Adapted from Crum et al. (1993).
60 Appendix C: Percentages of Keywords Correct Table C1. Percentages for T1 L1 L2 L3 L4 L5 L6 T1 conv/normal 65.7182.8657.1457.1457.14 74.29 76.4785.2952.9461.7667.65 79.41 77.7897.2261.1152.7863.89 75.00 83.33100.0058.3358.3352.78 80.56 86.4994.5972.9764.8678.38 94.59 Average 22.214.171.1249.064.0 80.9 T1 conv/slow 81.0891.8967.5748.6575.68 81.08 93.9490.9181.8251.5281.82 90.91 80.0080.0057.1440.0068.57 80.00 100.0097.0682.3570.5979.41 94.12 90.6390.6384.3853.1375.00 84.38 Average 88.990.174.352.676.0 86.0 T1 clear/normal 78.7981.8272.7345.4569.70 87.88 64.7191.1864.7167.6576.47 91.18 88.2491.1858.8244.1261.76 73.53 75.0077.7850.0055.5677.78 80.56 88.8980.5638.8944.4469.44 63.89 Average 79.284.456.651.471.1 79.2 T1 clear/slow 81.0894.5978.3851.3575.68 91.89 90.9196.9775.7672.7390.91 100.00 88.5791.4365.7165.7180.00 85.71 91.1885.2979.4179.4194.12 94.12 96.8896.8881.2587.5096.88 90.63 Average 89.593.076.070.887.1 92.4
61 Appendix C (Continued) Table C2. Percentages for T3 T3 conv/normal 82.3585.2947.0655.8852.94 85.29 68.5782.8674.2948.5774.29 74.29 65.7185.7165.7148.5765.71 74.29 77.1480.0062.8640.0080.00 68.57 94.1285.2970.5947.0685.29 70.59 Average 77.583.864.248.071.7 74.6 T3 conv/slow 78.13100.0068.7565.6384.38 93.75 97.2294.4477.7872.2277.78 86.11 91.6794.4480.5680.5677.78 91.67 100.0094.2960.0077.1494.29 97.14 88.5794.2960.0065.7177.14 82.86 Average 91.495.469.572.482.2 90.2 T3 clear/normal 64.7185.2958.8264.7173.53 73.53 77.1497.1445.7168.5771.43 85.71 62.8691.4348.5740.0062.86 68.57 62.8688.5751.4342.8660.00 62.86 79.4197.0661.7652.9458.82 67.65 Average 69.491.953.253.865.3 71.7 T3 clear/slow 81.25100.0087.5059.3887.50 90.63 80.5697.2277.7861.1191.67 83.33 75.0083.3369.4455.5686.11 80.56 94.2997.1482.8665.7182.86 94.29 91.4385.7180.0057.1488.57 82.86 Average 84.592.579.359.887.4 86.2
62 Appendix C (Continued) Table C3. Percentages for T4 T4 conv/normal 82.8697.1477.1471.4391.43 88.57 87.8890.9169.7057.5893.94 87.88 80.0094.2968.5740.0082.86 94.29 82.3585.2952.9452.9473.53 70.59 73.5391.1867.6564.7176.47 82.35 Average 81.391.867.357.383.6 84.8 T4 conv/slow 51.4382.8648.5754.2931.43 65.71 68.5791.4360.0057.1471.43 68.57 61.7682.3547.0658.8255.88 79.41 55.5686.1150.0052.7855.56 63.89 68.7587.5031.2556.2546.88 59.38 Average 61.086.047.755.852.3 67.4 T4 clear/normal 68.5791.4371.4371.4391.43 77.14 84.8590.9163.6469.7087.88 84.85 51.4388.5765.7165.7168.57 88.57 67.6582.3555.8850.0079.41 55.88 79.4188.2461.7655.8876.47 73.53 Average 70.288.363.762.680.7 76.0 T4 clear/slow 88.5797.1482.8677.1494.29 94.29 88.5797.1482.8662.8694.29 94.29 85.2991.1864.7167.6582.35 97.06 88.8986.1158.3363.8994.44 86.11 81.2593.7568.7559.3871.88 84.38 Average 86.693.071.566.387.8 91.3
63 Appendix C (Continued) Table C4. Percentages for T5 T5 conv/normal 100.00100.0084.2178.9592.11 94.74 88.24100.0058.8273.5388.24 91.18 87.1096.7783.8764.5293.55 90.32 94.29100.0065.7171.4394.29 94.29 86.1197.2261.1166.6794.44 91.67 Average 91.498.970.771.392.5 92.5 T5 conv/slow 83.7897.3070.2751.3586.49 83.78 93.94100.0078.7963.64100.00 96.97 91.1891.1888.2473.5385.29 91.18 79.41100.0061.7650.0079.41 88.24 91.8989.1970.2762.1694.59 94.59 Average 88.095.473.760.089.1 90.9 T5 clear/normal 89.47100.0078.9560.5397.37 100.00 91.1891.1879.4167.6591.18 94.12 93.5590.3290.3270.9793.55 93.55 91.4394.2980.0051.4388.57 88.57 88.8994.4472.2266.6786.11 91.67 Average 90.894.379.963.291.4 93.7 T5 clear/slow 91.8994.5959.4675.6881.08 97.30 96.97100.0066.6778.79100.00 100.00 94.1297.0682.3588.24100.00 82.35 85.2997.0664.7182.3591.18 94.12 94.5994.5964.8686.4997.30 100.00 Average 92.696.667.482.393.7 94.9
64 Appendix D: Within-subjects Effects and Interactions Dependent Variable: rau Source Type III Sum of Squares df Mean Square F Sig. Corrected Model 15.310(a)950.16113.186 0.000 Intercept 593.8741593.87448,591.382 0.000 listener 8.85251.770144.855 0.000 talker 2.12930.71058.075 0.000 rate 0.58810.58848.129 0.000 mode 0.13210.13210.814 0.001 listener talker 0.410150.0272.238 0.005 listener rate 0.03650.0070.582 0.714 talker rate 0.91030.30324.832 0.000 listener talker rate 0.186150.0121.014 0.440 listener mode 0.13750.0272.249 0.049 talker mode 0.24030.0806.540 0.000 listener talker mode 0.199150.0131.083 0.370 rate mode 0.50910.50941.652 0.000 listener rate mode 0.04550.0090.739 0.594 talker rate mode 0.39430.13110.733 0.000 listener talker rate mode 0.542150.0362.957 0.000 Error 4.6933840.012 Total 613.876480 Corrected Total 20.003479 a. R Squared = .765 (Adjusted R Squared = .707)