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Panagos Panagiotopoulos, Athina.
The benefits of clear speech at normal rates for older adults with normal hearing
h [electronic resource] /
by Athina Panagos Panagiotopoulos.
[Tampa, Fla.] :
b University of South Florida,
Thesis (M.S.)--University of South Florida, 2005.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
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ABSTRACT: Clear speech is a type of speaking style that improves speech intelligibility for many individuals. For example, one study showed a 17 percentage point increase in intelligibility over conversational speech for individuals with sensorineural hearing loss (Picheny et al., 1985). The clear speech benefit also extends to children with learning disabilities (Bradlow et al., 2003), non-native listeners (Bradlow and Bent, 2002), and other populations. Although clear speech is typically slower than conversational speech, it can be produced, naturally, at normal rates with training. For young listeners with normal hearing, clear speech at normal rates (clear/normal) is more intelligible than conversational speech (conv/normal) and is almost as beneficial as clear speech at slow rates (clear/slow) (Krause and Braida, 2002).However, a preliminary study by Krause (2001), found that clear/normal speech may benefit some older listeners with hearing loss but not others, suggesting that age may be a factor in the clear speech benefit at normal rates. It is evident, though, that clear speech at slow rates benefits this population (Picheny et al., 1985; Payton et al., 1994; Schum, 1996; Helfer, 1998). Therefore, the purpose of the study was to examine older listeners with normal hearing to determine how speech intelligibility, measured by % correct keyword scores, varies with speaking mode, speaking rate, talker and listener. Results were then compared to previously collected data from younger listeners with normal hearing (Krause and Braida, 2002) in order to isolate the effect of age on the size of clear speech benefit at slow and normal speaking rates.Eight adults (ages 55-68) with normal hearing participated in speech intelligibility tests.
Adviser: Jean C. Krause, Ph.D.
x Speech-language Pathology
t USF Electronic Theses and Dissertations.
The Benefits of Clear Speech at Normal Rates for Older Listeners With Normal Hearing by Athina Panagos Panagiotopoulos A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Communicati on Sciences and Disorders University of South Florida Major Professor: Jean C. Krause, Ph.D. Theresa Hnath-Chisolm, Ph.D. Jennifer Lister, Ph.D. Date of Approval July 28, 2005 Keywords: speech intelligibility, speaking rate, hearing impaired, aging, acoustic properties, hearing aids communication breakdown Copyright 2005, Athina Panagos Panagiotopoulos
Acknowledgments I would like to thank my thesis committ ee, Dr. Jean Krause, Dr. Theresa HnathChisolm, and Dr. Jennifer Lister I would like to especially thank Dr. Jean Krause, my thesis advisor, for all the time and effort spent on this project. Her guidance and dedication to this project is most appreciated. I would also like to thank th e listeners who have made this study possible. I am grateful for the wonderful participants that put in many hours to help us conduct this research. Finally, I am so grateful for my husband, Te d, for his constant love and support. I thank my family, Mom, Dad, Patty, Dean, Rita, and George, for their love and encouragement through all of my endeavors.
i Table of Contents List of Tables................................................................................................................i ii List of Figures................................................................................................................ iv Abstract....................................................................................................................... ....v Chapter 1 Introduction...................................................................................................1 Chapter 2 Background...................................................................................................4 Role of Rate........................................................................................................4 Artificially Produced Clear Speech at Normal and Fast Rates...............4 Naturally Produced Clear Speech at Normal Rates................................6 Acoustic Properties of Clear Speech...................................................................7 Properties of Clear Speech at Slow Rates...............................................7 Properties of Clear Speech at Normal Rates...........................................8 Clear Speech and its Relevance..........................................................................9 Clear Speech and Environments...........................................................10 Populations and clear/slow Speech.......................................................11 Populations and clear/normal Speech...................................................12 Aging and Speech Intelligibility...........................................................12 Aging and Clear Speech....................................................................................14 Sentence Intelligibility in clear/slow Speech........................................14 Vowel Intelligibility in clear/slow Speech............................................15 Sentence Intelligibility in clear/normal Speech....................................15 Summary...........................................................................................................16 Chapter 3 Methods.......................................................................................................17 Participants........................................................................................................17 Materials ..........................................................................................................18 Procedures.........................................................................................................20 Chapter 4 Results.........................................................................................................24 Effect of Mode..................................................................................................27 Effect of Rate....................................................................................................30 Effect of Talker.................................................................................................31 Effect of Listener..............................................................................................33 The Role of Cognitive Processing Speech........................................................34 Chapter 5 Discussion and Future Research.................................................................39
ii Chapter 6 Clinical Implications ..................................................................................44 References..................................................................................................................... 48 Appendices....................................................................................................................5 2 Appendix A: Screening Results.......................................................................53 Table A1 Listener Dem ographics and MMSE Scores..........................53 Table A2 Results of Hearing Screening................................................53 Appendix B: Listener Data..............................................................................54 Appendix C: ANOVA Statistics......................................................................55 Table C1 Within-subjects Effects and Interactions..............................55 Table C2 Between-subjects Effects......................................................56
iii List of Tables Table 1 Description of Talkers...........................................................................19 Table 2 Sentence Lists per Talker and Condition..............................................20 Table 3 Presentation Order of Stimuli for Listeners..........................................22 Table 4 Average Speech Intelligibility per Talker in Each Condition ..............25 Table 5 Significant Effects and In teractions at the 0.01 level...........................26 Table 6 Pairwise Comparisons of Modes and Rates..........................................27 Table 7 Summary of Performance on Salt house Tasks, Overall Performance in the Study, and Clear Speech Benefit................................................35 Table 8 Spearmans Rho ( ) Correlation Coefficients......................................38 Table 9 Average Listener Pe rformance Across Studies.....................................40
iv List of Figures Figure 1 Average intelligibility, in percent key words correct, for each condition. Performance averaged across talker and listener (Grand Average). Error bars indicate +/1 standard error above and below the mean..............................................................................30 Figure 2 Average speech intelligibilit y, in percent key words correct for each talker in each condition. Perf ormance averaged per listener. Error bars indicate +/1 standard error above and below the mean.....32 Figure 3 Average performances, in percent key words correct, of every listener, for each talker in the four conditions......................................34 Figure 4 Data were graphed and regression lines were calculated. In each figure, y-axis represents 1) aver age % key words correct (averaged across talker and condition) fo r overall performance data and 2) difference in % correct scor es between clear/normal and conv/normal (averaged across talk er) for clear speech benefit data. Figure a) represents Letter comparison task. Figure b) represents Pattern comparison task. Significant correlation found between accuracy on Pattern task and overall performance in the study............................................................................................36
v The Benefits of Clear Speech for Ol der Adults with Normal Hearing Athina Panagiotopoulos ABSTRACT Clear speech is a type of speaking style that improves speech intelligibility for many individuals. For example, one study showed a 17 percentage point increase in intelligibility over conversational speech for individuals with sensorineural hearing loss (Picheny et al., 1985). The clear speech benefit also extends to children with learning disabilities (Bradlow et al ., 2003), non-native listeners (Bradlow & Bent, 2002), and other populations. Although clear speech is t ypically slower than conversational speech, it can be produced, naturally, at normal ra tes with training. For young listeners with normal hearing, clear speech at normal rates (cle ar/normal) is more intelligible than conversational speech (conv/normal) and is almo st as beneficial as clear speech at slow rates (clear/slow) (K rause & Braida, 2002). However, a preliminary study by Krause (2001), found that clear/normal speech may benef it some older listeners with hearing loss but not others, suggesting that age may be a factor in the clear speech benefit at normal rates. It is evident, though, that clear sp eech at slow rates benefits this population (Picheny et al., 1985; Payton et al., 1994; Schum, 1996; Helf er, 1998). Therefore, the purpose of the study was to examine older liste ners with normal hearing to determine how speech intelligibility, measured by % corr ect keyword scores, varies with speaking mode, speaking rate, talker a nd listener. Results were th en compared to previously collected data from younger listeners with normal heari ng (Krause & Braida, 2002) in
vi order to isolate the effect of age on the size of clear speech benefit at slow and normal speaking rates. Eight adults (ages 55-68) with normal heari ng participated in speech intelligibility tests. Each listener was presented with the speech of 4 talkers in 4 speaking styles: conv/normal, clear/normal, conv/slow and clear/s low, drawn from recordings made for an earlier study (Krause & Brai da, 2002). Stimuli were nons ense sentences presented monoaurally with speech-shaped noise in the background. Results showed that clear/slow and conv/ slow were the most intelligible speaking conditions. However, clear/normal was also more intelligible than conv/normal, demonstrating that a talker does not need to decrease rate to improve intelligibility for listeners with normal hearing, regardless of age. More studies are needed to investigate any similariti es between conv/slow and clear/slow, since performance by older listen ers was highest in th ese two conditions. Signal-to-noise ratio (SNR) also needs to be controlled in future studies to further characterize the effect of ag e on clear speech benefits at slow and normal speaking rates.
1 Chapter 1 Introduction Clear speech is a type of speaking style us ed to facilitate conversations in difficult communication settings. It is typically slower than conve rsational speech and more intelligible. Studies have show n that clear speech is more in telligible than conversational speech for different types of listeners in va rious listening conditions, such as noise and reverberation. Picheny, Durlac h, and Braida (1985) conducted one of the first studies to assess any benefits of clear speech for a gr oup of individuals with sensorineural hearing loss (SNHL). Clear speech had a 17 percentage point increase in intelligibility over conversational speech. Other populations th at benefited from clear speech included young listeners with normal hearing (Uchansk i, Choi, Braida, Reed, & Durlach, 1996), individuals who were older with hearing loss (Picheny et al., 1985), children with language learning disabilities (LLD) (Bradl ow, Kraus, & Hayes, 2003), and non-native listeners (Bradlow & Bent 2002). Although a number of studies have investigated benefits of clear speech use for older liste ners with hearing loss and younger listeners with normal hearing in difficult listening situ ations (e.g., Payton et al., 1994; Krause & Braida, 2002; Ferguson & Port 2002), few studies have in cluded older listeners with normal hearing (e.g., Helfer, 1998). In addi tion, very few studies have controlled speaking rate when examining the clear speech effect (e.g., Krause & Braida, 2002). Therefore, the purpose of this study was to de termine the benefits of clear speech at normal rates for older adults with normal heari ng. In particular, variables such as mode,
2 rate, listener and talker were examined to determine their effect, if any, on speech intelligibility for older adults with normal hearing. Although it is typically slow er, clear speech can be produced at normal rates with training (Krause & Braida, 2002). This form of clear speech is know n as clear/normal speech. The investigation of clear/normal sp eech is important for several reasons. As mentioned, clear/slow speech benefits many popul ations. Therefore, it is important to determine whether clear/normal speech can be as beneficial to these populations as clear/slow speech. In additi on, investigating the acoustic pr operties of clear speech continues to provide furthe r understanding of the scienc e behind the way speech is produced. For example, it has been show n in conversational speech many sounds are missing or dropped due to assimilation. The sounds in clear speech, on the other hand, are full, accurate and precise in production (Schum, 1996). Increased understanding of clear speec h, particularly clear/normal speech, may also help improve the function of hearing aids For instance, if c onversational speech can be processed by the aid and altered to clear speech, then this coul d help a person with hearing loss in communication settings. Howe ver, if this processing slowed down the speech, the person with hearing loss could fall behind in a conversati on. If clear speech could be produced at normal rates by a hear ing aid, this problem w ould be eliminated and the person with hearing loss would benefit. Furthermore, it is beneficial to use clear speech in a clinical setting with all clients. This will maximize understanding and eliminate unnecessary repetition. If clear speech is not used, some clients may feel aw kward in asking for repetition, resulting in poor communication. As mentioned, clear sp eech is naturally slower. When applying
3 clear speech to a clinical setting, slowing sp eech rate may also slow down the pace of the session. If clear speech can be produced at norm al rates and still be intelligible, then the sessions time would not be compromised a nd the client could benefit from additional time spent on therapy.
4 Chapter 2 Background Clear speech has many acoustic properties that differ from conversational speech. For example, Picheny, Durlach, and Braida ( 1986) noted changes in vowel formants and an increase in voice onset time of unvoiced pl osives when clear speech was produced. Although there are many acoustic differen ces between the two speaking styles, researchers focused more on speech rate, because it was the most observable acoustic difference between conversationa l and clear speech. When cl ear speech is produced, the talker naturally slows down hi s or her rate. The average sp eaking rate for conversational and clear speech at a normal rate is between 160-200 words per minute (wpm). For clear speech at slow rates, the speaking rate t ypically decreases by an average of 50-100 wpm (Picheny et al., 1986). Picheny et al. (1986) determined that th e rate of clear speech is reduced by inserting and lengthening pauses as well as increasing duration of speech sounds. Although clear speech is typically sl ower, talkers can produce clear speech at normal rates with training (Krause & Braida 2002). Whether or not clear speech at normal rates is as beneficial to different popul ations and environments as clear speech at slow rates should be investigated. Role of Rate Artificially Produced Clear Speech at Normal and Fast Rates Much early work in clear speech focu sed on whether a slower rate was the main acoustic factor responsible for increasing speech intelligibility. Attempts were made to
5 produce clear speech, artificia lly, without slowing down the rate. However, these attempts were unsuccessful. In one study, th e rate of clear speech was altered to a conversational (i.e. normal) rate and the rate of conversational sp eech was altered to a clear (i.e. slow) rate, and then back to their original ra tes (Picheny, Durlach, & Braida, 1989). After processing, intelligibility scores decreased in both cases. After restoring the processed material back to their original ra tes, the intelligibility scores were not brought back up to their unprocessed levels in either case, but were both within an average of 8 percentage points of the orig inal score. The authors concluded that intelligibility of conversational speech could not be increased simply by unifo rmly adjusting the duration of speech to achieve a slower speaking rate. Another study also experimented with sp eech rate. Speech rates were adjusted by non-uniform time scaling, pauses, and fast clear speech (Uchanski et al., 1996). Time scaling was achieved by measuring the durat ion of the same phonemes in clear and conversational production of a given sentence. For example, the duration of individual phonemes was measured in both speaking styles. The difference in measurement for each phoneme was then used to decrease the duration of that phoneme in clear speech, resulting in a normal rate production of that phoneme, or to increase the duration of that phoneme in conversational speec h, resulting in a slow rate production of that phoneme. Time scaling of all phonemes decreased speech intelligibility scores by 5 percentage points for conversational speech slowed to cl ear rates and decreased by 24 percentage points for clear speech sped to conversationa l rates. When keywords were excised from their sentences, scores were slightly lowe r than when in their sentence contexts (Uchanski et al., 1996). Uchanski et al. (1996) also studied th e role of pauses, which are
6 more and longer in clear speech. Pauses were defined as silent intervals longer than 10 ms between words, excluding periods of sile nce due to plosives (Picheny et al., 1986). Uchanski et al. (1996) found th at adding pauses to convers ational speech as well as deleting pauses from clear speech decreased sp eech intelligibility. Clear speech was also attempted naturally at different rates. Fo r example, a professional fast talker was instructed to produce clear speech at rates close to 170, 200 and 400 words per minute (wpm). The goal was to improve or maintain speech intelligibility without altering rate; however, intelligibility scores were negativel y correlated with speaking rate. In other words, the higher the speech rate, in clear or conversational m odes, the lower the intelligibility scores (Uchanski et al., 1996). Naturally produced clear speech at normal rates Because attempts to artificially speed cl ear speech had failed, Krause and Braida (2002) explored speaking mode s that talkers could produce naturally instead of using artificial enhancement. Listeners with normal hearing were used to determine if alternative forms of clear speech exist naturally at normal speaking rates. The talkers in the study underwent intensive training and th en were recorded in various modes and rates. Modes used were clear speech or conversational (conv) sp eech. Rates included slow and normal as well as other rates that will not be discussed here. The modes and rates tested were combined to make the fo llowing conditions: clear/slow, clear/normal, conv/slow and conv/normal. Results of the st udy indicated that af ter training, perception of clear speech at a normal rate was 14 pe rcentage points higher than perception of conversational speech at normal rate and just 4 percentage points lo wer than clear/slow speech. This signified that it is possible to produce clear speech without altering speech
7 rate. Krauses other work was also able to replicate (verify) the benefits of naturally produced clear speech at normal rates. For normal hearing listeners, there was a 16 percentage point increase in scores with clear/normal over conv/normal (Krause, 2001). Acoustic Properties of Clear Speech It is unclear which acoustic characteristics are respons ible for increased speech intelligibility in clear speech, indicating the need for further studies. Acoustic characteristics are not likely to contribute equa lly to the intelligibil ity advantage of clear speech (Krause & Braida, 2004). Krause and Brai da (2004) noted that it is possible that some characteristics do not contribute at al l to increased intelligibility while other important factors may not have been identifi ed based on type of measurements used in each study. Since clear speech is advantageous, it is important to determine what aspects of clear speech make it more intelligible th an conversational speech. To begin this process, the acoustic properties of clear and conversational speech must be compared (Picheny et al., 1986). Properties of clear speech at slow rates In an investigation of the acoustic differences between conv/normal and clear/slow speech, Picheny et al. (1986) found that clear sp eech had a greater number and longer duration of pauses, and le ngth of words. There were no differences in long term RMS spectra or formant frequencies. Vo wel modification, when vowels become more schwa-like, occurred more in conversational speech than clea r speech. Burst elimination, when the stop burst is deleted, occurred mos tly in conversational sp eech. Sound insertion occurred almost always in clear speech. In addition, talkers tended to increase level of consonants when speaking clearl y. Although consonant-vowel (C V) ratio, or the ratio of
8 energy in a consonant relative to the neighboring vowel, was not explicitly measured in this study, this change likely resulted in an increased CV ratio for clear speech. Another property of clear/slow speech re lates to the listeners perception that continuous speech is broken up into separate words. Therefore, word boundaries were examined in other investigations of the ac oustic characteristics of clear speech. These studies reported that speakers attempt to mark word boundaries in clear speech, but not in conversational speech (Cutler & Butterfield, 1990). For example, the speakers would stress words boundaries before weak syllables because they are hard to perceive in difficult listening conditions. In another st udy by these two researchers, it was shown that the duration, fundamental fr equency (F0) levels, and intens ity of weak syllables were lengthened as well (Cutler & Butterfield, 1991). Properties of clear speech at normal rates Further investigation to identify acoustic properties found in clear/normal speech was also made by Krause (2004) who found several differences between clear and conversational speech at normal rates. Firs t, there was an increase in the fundamental frequency (F0) average and range for clear/no rmal speech. This is relevant because females have higher F0 average and range than males and are generally more intelligible than males, therefore an increase in F0 av erage and range may play a role in speech intelligibility. Second, more intensity was noted in formant frequencies in clear speech at normal rates, not found in conversational speech. For example, in clear/normal speech there was an increase in leve l in the second and third forman ts of vowels. Krause also identified differences in temporal envel ope modulations between clear/normal and conv/normal speech that could have possible importance in cueing manner and voicing.
9 She used signal transformations that a ltered these three prop erties (fundamental frequency, formant intensity, and temporal e nvelope modulations) and created processing schemes in her study, to determine what prope rties enhance speech intelligibility. In Process A, vowel formant energy was increased by raising formant amplitudes; in Process B, the fundamental frequency (F0) was modified to increase the average and expand the range of F0 values; and in Pro cess C, low frequency modulations of the intensity envelopes were enhanced in severa l octave bands (Krause, 2001). None of these processing schemes resulted in intelligib ility improvements that could account for a substantial portion of the intelligibility benefit observed for clear/normal speech, suggesting that additional properties associat ed with the increased intelligibility of clear/normal speech have yet to be identified. Finally, Krause (2001) noted that talker s may have different strategies for producing clear/normal speech because each ta lker appeared to select only a few characteristics from the many that exist. This may occur because there are many characteristics used to produce clear/slow speech but the talker cannot retain all them at normal speaking rates when producing clear/ normal speech. Therefore, variation in speech intelligibility of talkers may be due to the many different char acteristics that were chosen. Clear Speech and its Relevance Clear speech is relevant for many p opulations and in various communication settings. When clear, accurate speech is produced, it can benefit a listener, especially with hearing loss, in different communi cation environments (Schum, 1997). In conversational speech, sounds are mixed toge ther or dropped from the words. These
10 traits of conversational speech may result in a communication breakdown, especially in a difficult environment. Clear speech and environments The benefits of clear speech extend to different types of environments. For example, when noise is added, clear speech is more intelligible than conversational speech (Payton, Uchanski, & Braida, 1994). Payton et al. (1994) conducted a study to determine if listeners with normal hearing a nd listeners with hear ing loss would benefit from clear speech in various acoustic environments. These acoustic environments had different levels of noise (signal-to-noi se ratios of 0.0 dB, 5.3 dB, and 9.5 dB) and reverberation. For example, the anechoic environment (ANEC) had no reverberation. Environments living room (LIVR), and conference room (CONF) had reverberation times of 0.18s and 0.60s, respectively. Results indicated that clear speech was more intelligible than conversational speech fo r younger listeners with normal hearing and older listeners with hearing loss in all degrad ed listening conditions (noise, reverberation and hearing loss). Clear/slow speech is beneficial in various environments; however, the benefit of clear/normal varies based on talker and type of environment (Krause & Braida, 2003). In Krause and Braidas study ( 2003), clear/slow was beneficial in all environments (hi/low pass filters, reverbera tion, and non-native listeners). The benefit of clear/normal varied across the five talkers, labeled T1-T5. Fo r example, T5s clear/normal speech improved speech intelligibility in three of the envi ronments, whereas T4s clear/normal speech improved speech intelligibility in only one envi ronment. The variation across talkers is
11 possibly due to the strategies each talker used to produce clear/normal speech and frequency ranges in the hi/low pass filters. Populations and clear/slow speech Those with hearing loss are just one gr oup of individuals that benefit from clear/slow speech. The advantage of clear sp eech applies to other populations as well. For example, clear speech benefits children with diagnosed learning disabilities (LD), such that performance, measured by key words correct, increases when clear speech is produced (Bradlow et al., 2003). The per cent correct scores were converted to rationalized arcsine transformation units (rau) to facilitate statistical analysis (Studebaker, 1985). For children with LD, the clear speech effect was great er when the signal-to-noise ratio (SNR) was lower (10.06 rau) and when a female talker presented the stimuli (11.99 rau). Non-native listeners also benefit fr om clear speech (Bradlow & Bent, 2002). The mean difference between clear and conversat ional speech for non-native listeners was 11.11 rau. Another population that benefits from clear/slow speech is young adults with normal hearing and vision. For example, young listeners with normal hearing benefited from clear speech in every mode in a study that measured speech intelligibility of syllables in auditory only (A), visual onl y (V), and audiovisual (AV) presentation conditions (Gagne, Rochette, & Charest, 2002). These modes were included in the study because according to Gagne et al. (2002), speech perception is a multimodal phenomenon. Furthermore, listeners with a wide range of hearing loss who have speechreading abilities also benefit from clear speech (Helfer, 1998) such that speech intelligibility scores increased when clear speech was produce d. It was also noted that
12 words presented with auditory-visual (AV) cues were easier to understand than those presented in the auditory (A) only mode, which was expected (Helfer, 1998). Finally, many studies show the benefits of clear speech for those with hearing loss. In an article summarizing such studi es, Schum (1997) states that clear speech benefits those with hearing loss, whether th ey are wearing heari ng aids or cochlear implants. Clear speech is a technique that Schum recommends for family and friends of those who can benefit from it. Populations and clear/normal speech As mentioned earlier, recent research has focused on whether clear/normal speech has similar benefits as clear/slow speech does for various populations. For example, Krause (2001) investigated if the intelligibility benefit of clear/normal speech reported for young listeners with normal hearing can be ex tended to populations with hearing loss. She found that young listeners with normal h earing benefited from clear/normal speech, but the older listeners with hearing loss di d not. For the young listeners with normal hearing (age range 16-43 years) there was a 16 percentage poi nt increase in scores for clear/normal over conv/normal. The older lis teners with hearing loss (age range 40-65 years) had a slight increase in scores but not enough to be st atistically significant. The outcome of this study prompted a question of wh ether age is a factor in the clear speech benefit. Aging and Speech Intelligibility When studies include participants who ar e both older and have hearing loss, the question arises of whether age alone is a fact or that affects speech intelligibility and the benefits of clear speech, part icularly since some aspect s of hearing are known to
13 deteriorate with age (Gordon-Salant & Fitz gibbons, 1999). For example, it has been suggested that cognitive factors affect older listeners speech intelligibility regardless of hearing status. When young and older listen ers with normal hearing and young and older listeners with hearing loss were compared on speech intelligibility, the results showed that although listeners with hearing loss pe rformed more poorly than listeners with normal hearing in most conditions (GordonSalant & Fitzgibbons, 1997), the listeners who were older, in general, performed poorer than the listeners who were younger, regardless of hearing status. For example, the listeners who were older did poorer on longer test items than shorter ones. This indi cates that cognitive factors, such as memory are significant, and may affect the perf ormance of listeners who are older. In another study, listeners who were olde r again performed mo re poorly than the listeners who were younger in all noise condi tions (Gordon-Salant & Fitzgibbons, 1999). Listeners with hearing loss performed more poor ly than those with normal hearing. Time compressed speech was difficult for older pe rsons to recognize, probably due to deterioration of central timing mechanisms which may be a possible reason for the decline in speech perception (Gordon-Salant & Fitzgibbons, 1999). Age and hearing status are significan t in word recogn ition (Dubno, Dirks, & Morgan, 1984). In this study, the speech leve l required for each lis tener to attain 50% word recognition in quiet and noisy environm ents was investigated. Sentences were taken from the Speech Perception in Noise (SPIN) test. Young listeners with normal hearing and hearing loss, and older listen ers with normal hearing and hearing loss participated in the study. Hearing leve l, but not age was si gnificant under quiet conditions. All listeners with hearing loss had higher thresholds (16 dB) than all the
14 listeners with normal hearing in order to a ttain 50% word recogn ition. An even higher threshold (22 dB) was needed for keywords in low predictability sentences. In noisy conditions, the main effect of age, as well as the effect of hearing level, was significant. That is, listeners who were older, regardless of hearing status, needed an increase in signal-to-babble ratio in dB (S/B) as the materials increased in difficulty. Spectral and temporal dips are also im portant in speech intelligibility when background sounds are present (Peters, Moor e, & Baer, 1998). In the background with both dips present, the older listeners, with normal heari ng and hearing loss, did worse than the younger listeners. The older listene rs with hearing loss needed the speech level 19 dB higher than the younger li steners with hearing loss, in dicating a strong correlation between speech recognition thresholds (S RTs) in background sound with spectral and temporal dips and age. Aging and Clear Speech Sentence intelligibility in clear/slow speech As mentioned earlier, it is ev ident that older listeners, particularly those with hearing impairment, do benefit from clear/sl ow speech. First, Picheny et al. (1985) found that the benefit of clear/slow speech for older listeners with hearing loss over conversational speech was 17 percentage point s. There was also a 26 percentage point increase over conversational speech for olde r listeners (ages 50-59 years) with hearing loss in Payton et al .s study (1994). Since aging affects speech intelligibility, researcher s have begun to study the benefits of clear speech and aging. In one study, young and elderly talkers were not much different in producing clear speech (Schum, 1996). Of 60 older listeners with
15 hearing loss in the study, three were randomly assigned to each one of the 20 talkers (10 young, 10 elderly). Both the young and the elderly talkers were intellig ible to the older listeners with hearing loss. On average, th e older listeners (ages 60-77 years) received a 16.9 rau benefit when the talkers used clea r/slow speech compared to conversational speech (Schum, 1996). Moreover, studies have shown that as a person ages, speech perception decreases, regardless of hearing status, but more so when hearing loss is present (Helfer, 1998; Dubno et al., 1984). Age is significantly and negatively correlated with the perception of conversational speech (Helfer, 1998). In ot her words, as age in creases, conversational speech perception in audio-visual (AV) mode decreases. Ye t Helfer also found that as age increases, so does the benefit of clear/slow speech, in the AV mode. Vowel intelligibility in clear/slow speech A further study involving age and clear/sl ow speech investigated differences in vowel intelligibility between young listeners with normal heari ng and older listeners with hearing loss (Ferguson & Port, 2002). The results indicated that the young, normal hearing listeners had a 15 per centage point increase in scor es with clear speech. There was no significant difference in scores betw een clear and conversational modes for the older listeners with hearing loss. Sentence intelligibility in clear/normal speech As stated previously, clear speech at norma l rates is beneficial for listeners with normal hearing (Krause & Braida, 2002). Howe ver, older listeners with hearing loss did not benefit significantly in noise when compared to the normal hearing listeners (Krause, 2001). The older listeners ages ranged from 43-65 years in Krauses study. Possible
16 reasons for the results could be age, configur ation of hearing loss, or the limited number of participants in the study. Summary In sum, it is evident that clear speech is beneficial fo r many populations in various environments. Clear speech can also be produced without slowing down speaking rate. However, older listeners with hearing loss ma y not benefit as much from clear/normal as clear/slow speech. The main question then, is whether hearing st atus affects speech intelligibility or does age also play a role. Therefore, the purpose of this study was to examine how speech intelligibility, measured by % correct keyword scores for eight listeners (55-68 years of age), varies with: a) speaking mode: clear or conversational b) speaking rate: slow or normal c) talker: four talkers that were pre-r ecorded to present to each listener d) listener: individual factors that may in fluence each older lis teners performance To examine the role of age, the results for ol der listeners in the present study were then compared to the results for younge r listeners in previous studie s. Specifically, the data obtained were compared to data obtained with the same stimuli and conditions from eight young listeners (18-29 years of age) by Krause and Braida (2002).
17 Chapter 3 Methods Participants For the purpose of this study, eight norm al hearing listeners, ages 55-75, were recruited from the Tampa, Florida area. Each listener was a native English speaker with a high school diploma or its equivalent. In orde r to be included in th is study, the subjects were required to pass audiological and cogni tive screenings. Fi rst, the audiological screening was administered. Hearing was c onsidered normal if thresholds were 25 dB HL or better at 250, 500, 1000, 2000 and 4000 Hz and 35 dB HL or better at 6000 and 8000 Hz. Normal hearing was required in at l east one ear. The mild hearing loss at the higher frequencies was considered acceptabl e since there is a change in hearing thresholds with age, and these thresholds are typical for persons in this age range (Brant & Fozard, 1990). Next, the Mini Mental St ate Exam (MMSE) (Folstein, Folstein, & McHugh, 1975) was administered to determin e cognitive abilities. A score of 22 or better out of 30 possible points was considered normal. Twenty interested individuals were screen ed before the eight participants were acquired. All potential participants passe d the MMSE. The most common reason for exclusion was high frequency hearing loss, wh ich is typical in this age group (Brant & Fozard, 1990). The first eight participants to complete and pass the screenings were included in the study. The eight participants included three males and five females and had an age range of 55-68. Detailed dem ographics and MMSE scores of individual
18 participants can be found in Table A1 in Appendix A. As shown in Table A2 in Appendix A, three of these participants pa ssed the audiological screening with normal hearing in both ears, while five of these pa rticipants passed the a udiological screening with normal hearing in only one ear. Sin ce stimuli were presented monaurally, normal hearing in one ear was sufficient for the study. Materials The Salthouse (1991) materials were used to assess cognitive processing speed of participants. The materials included a lett er comparison task and a pattern comparison task. The letter comparison task consisted of 21 pairs, and the pa ttern comparison task consisted of 30 pairs. In both processing tasks, the participan ts were to look at a set of patterns or letters and decide if they were the same or different. The participants were to complete as many pairs as possible in 30 s econds, but to also work as accurately as possible. They were scored based on how ma ny of the patterns completed were correct. The resulting scores were used to see if there was any correlat ion between cognitive processing scores and performance in the study. Stimuli for the speech intel ligibility experiment were drawn from a database collected for an earlier study on clear speech at normal rates (Krause & Braida, 2002). The sentences in the database were nonsense sentences. In other words, the sentences had no semantic meaning; however, they we re syntactically correct. An example sentence is The right cane could guard an e dge. Nonsense sentences were used in order to avoid any guessing by the listeners using se mantic context cues. The sentences in the database were produced by five different talkers (T1, T2, T3, T4 and T5). T1, T3, T4 and T5 were selected because they improved speech intelligibility with clear speech without
19 altering speech rate. T2 did not present similar results as the other talkers, and therefore was excluded. A description of the talkers, from Krause and Brai das study (2002) is summarized in Table 1. The talkers were from the Boston area and had experience in public speaking. Table 1 Description of Talkers Talker Sex Speaking Experience Years T1 Female College television, radio, public speaking 5 T3 Female Broadcasting student 2 T4 Female Debate team 6 T5 Male Debate team 7 As shown in Table 2, eight unique lists of 50 sentences were selected from the database. Each list was r ecorded twice by one of the ta lkers, once in conversational mode and once in clear mode at a particular rate. Specifically, each talker recorded one list in both conversational mode and clear mode at normal rates and one list in both conversational mode and clear mode at slow rates. Combining the two rates and two modes resulted in four conditions per talker : conv/normal, conv/slow, clear/normal, and clear/slow, as shown in Table 2. The listene rs were then tested on these lists of 50 nonsense sentences. In the end there were f our talkers, two list s per talker, and two conditions per list. Each list contained 50 sentences, resulti ng in 800 stimuli per listener.
20 Table 2 Sentence Lists per Talker and Condition Talker List Conditions List 1 Conv/normal Clear/normal T1 List 2 Conv /slow Clear/slow List 3 Conv /normal Clear/normal T3 List 4 Conv /slow Clear/slow List 5 Conv /normal Clear/normal T4 List 6 Conv /slow Clear/slow List 7 Conv /normal Clear/normal T5 List 8 Conv /slow Clear/slow Speech shaped noise (noise with same long-term frequency characteristics as typical speech) was added to the background. The signal-to-noise ra tio (SNR) was 0dB, meaning there was an equal balance in le vel between noise and signal output. Procedures First, cognitive processing speed of pa rticipants was assessed by administering the two Salthouse tasks, letter comparison a nd pattern comparison. Each participant was instructed to look at pa irs of letter strings or patterns and determine if the items in the pair were the same or different. Before each ta sk, the participant was given three trials as practice. After the practice tr ials, the participant was given 30 seconds to complete the given task. The participant was timed w ith a stopwatch and after 30 seconds the participant was inst ructed to stop. The part icipants were scored based on what percent of the pairs completed were correct. The results were used later in the study to examine the relationship between cognitive processi ng speed and performance on the speech intelligibility tasks.
21 Each listener then particip ated in the speech intelligibility experiment for a minimum of four sessions for 2-3 hours each se ssion. Listeners were tested individually and attended sessions no more than once a wee k. Some participants attended weekly sessions while other participants required longer breaks between se ssions due to vacation plans or other scheduled events. When half th e lists had been presented to a listener, he or she was given an additional weeklong brea k. The purpose of the break was to allow time to rest as well as avoid improved perfor mance due to sentence repetition. In other words, since each talker reco rded each list in two conditions the break would allow time to reduce the chances of the listener remembering words fr om the nonsense sentences. Table 3 shows how and when the stimuli were presented. For example, the conditions per list that listeners 1-4 h eard in weeks 1 and 2 were not heard by listeners 5-8 until weeks 4 and 5. The conditions per list that li steners 5-8 heard in weeks 1 and 2 were not heard by listeners 1-4 until weeks 4 and 5. The purpose of counterbalancing the stimuli in this manner was to average out variance in listener performance due to any potential learning effects that might have rema ined even after the weeklong break.
22 Table 3 Presentation Order of Stimuli for Listeners WEEK LISTENERS 1-4 LISTENERS 5-8 1 T1 List 1-conv/normal T1 List 2-clear/slow T4 List 5-clear/normal T4 List 6-conv/slow T1 List 1-clear/normal T1 List 2-conv/slow T4 List 5-conv/normal T4 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 T4 List 5-conv/normal T4 List 6-clear/slow T1 List 1-conv/normal T1 List 2-clear/slow T4 List 5-clear/normal T4 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 The sentences for the speech intelligibility experiment were presented monaurally over headphones connected to a computer and pl ayed from software called Matlab. The participants who passed the sc reening in only one ear were restricted to that ear throughout the experiment. The participants wi th bilateral normal hearing were permitted to alternate ears but only between sentence lists. Prior to the start of data collection, the listener was fam iliarized with the computer equipment that was used in the study. On th e first day, participants were given a practice list of 50 different sentences than those used for data collection to accommodate to the SNR. They were instructed to do as many practice sentences as necessary before beginning the real senten ce lists. On the participants first days, the range of practice
23 materials used was 10-30 sentences. For subsequent sessions, continuing with the remaining practice materials was an option. Tw o listeners, L6 and L8, did not utilize the practice sentence list again afte r the first session. The remai nder of the listeners practiced at least one more time in subsequent sessions For example, L1-L5 completed between 5 and 10 practice items in their second sessions and then did not reque st the practice list again. L7 used the practice list the most. She completed all 50 practice items in the first three sessions. The Matlab software provided the listene r with control over the presentation of the stimuli. For instance, when ready to hear a sentence, the listener clicked on the play button using the mouse. Sentences could not be repeated; however, the listener did not listen to the next sentence until ready. Listeners were encouraged to take breaks as often as needed. The listeners usually took short, stretching breaks between sentence lists and a longer break during the midpoint of the session. The stimuli were presented over headphones at a sound level of approximate ly 82 dB SPL. None of the participants complained of the sound level, indicating th at it was within a comfortable range. The listener listened to sentences played from the Matlab software and responded by writing the sentence that he or she perceived on the answer sheet provided. Responses were scored based on the percentage of ke y words correctly iden tified by each listener and followed the same scoring system as Pi cheny et al. (1985). Keywords correct included nouns, verbs and adjectives. E rrors such as inserting, omitting, or misidentifying a single phoneme in the word, were counted as incorrect. Errors such as inserting or omitting a plural or past tense suffix were counted correct.
24 Chapter 4 Results The purpose of this study was to investigate how speech intelligibility, measured by percent key words correct varied with speaking mode, speaking rate, talker and listener for older listeners with normal heari ng. This study is cons idered a parametric experiment consisting of ratio data. In a parametric experiment, independent variables (mode, rate, talker and listener) can be si multaneously examined for main effect and interactions with the dependent variable (% ke ywords correct). Results were analyzed in three ways. First, key word scores for each condition were tabulated in an Excel Spreadsheet. Second, data were graphed for vi sual analysis. Finall y, a four-way analysis of variance (ANOVA) was used to test significance of the results. Inferential statistics were used because conclusions were drawn from the results obtained. Key word scores for each listener are listed in Appendix B. These results are summarized in Table 4 which shows re sults for each talker, averaged across the listeners. For example, the average listener performance, in percent key words correct, for T1, in the conv/normal condition is 43%. The average listener performance for all talkers in the conv/normal condition is 45%. St andard deviations and standard errors for each condition are also included.
25 Table 4 Average Speech Intelligibility per Talker in Each Condition Talker conv/normalconv/slow clear/normalclear/slow T1 43% 72% 52% 71% T3 28% 66% 51% 45% T4 49% 58% 55% 74% T5 61% 69% 77% 84% AVG 45% 66% 59% 68% SD 13.5% 6.2% 12.5% 16.6% STD ERR 5% 2% 4% 6% In analyzing the results, conv/normal should be viewed as the baseline condition. When comparing the other three conditions to conv/normal, it can be seen that clear/slow and conv/slow provided the most intelligibi lity benefit overall. In the clear/slow condition, the average key words correct wa s 68%, a 23 percentage point increase over conv/normal. The conv/slow condition was al so more intelligible than conv/normal by 21 percentage points, with an average of 66% correct key words. Clear/normal speech also provided a benefit; the average percent key words correct across listeners and talkers was 59% for clear/normal, a 14 percentage point increase over conv/normal. These results suggest that the talker does not have to decrease rate in order to increase speech intelligibility. A four-way repeated measures analysis of variance (ANOVA), with three withinsubjects factors (rate, mode and talker) and one between-s ubjects factor (listener) was performed on key-word scores, af ter an arcsine transformation ( Ij/100) to equalize the
26 variances. F-ratios and significance levels for those effects and interactions that are significant (p<0.01) are listed in Table 5. A complete listing of th ese values for all effects and interactions, includ ing those that were not signif icant, can be found in Table C1 in Appendix C. As shown in Table 5, all main effects and several interactions were significant at p<0.01. Table 5 Significant Effects and Inte ractions at the 0.01 level Effect F Hypothesis df Error df Sig. EtaSquared mode 202.101 1 32 .000 5.11 rate 826.128 1 32 .000 17.78 talker 218.390 3 30 .000 24.36 listener 54.667 7 32 .000 13.29 rate x mode 61.931 1 32 .000 2.24 rate x talker 20.905 3 30 .000 2.32 mode x talker 57.464 3 30 .000 3.07 rate x mode x talker 64.698 3 30 .000 7.83 rate x mode x talker x listener 2.770 21 96 .000 2.49 In addition, post-hoc t-tests were performed to determine significant differences for all pairwise comparisons of conditions (m odes and rates). A Bonferroni adjustment for multiple comparisons was implemented in th e t-test results. Results are listed in
27 Table 6. Differences between each pair of c onditions were statistically significant except for the difference between conv/slow and clear/slow. Table 6 Pairwise Comparisons of Modes and Rates (I) cond (J) cond Mean Diff. (I-J) Std. Error Sig.a 99% Confidence Interval Lower Bound Difference 99% Confidence Interval Upper Bound Difference conv/slow clear/slow conv/normal clear/normal -.030 .225* .077* .010 .010 .009 .027 .000 .000 -.064 .190 .047 .004 .260 .107 clear/slow conv/slow conv/normal clear/normal .030 .255* .107* .010 .008 .009 .027 .000 .000 -.004 .227 .078 .064 .284 .137 conv/normal conv/slow clear/slow clear/normal -.225* -.255* -.148* .010 .008 .010 .000 .000 .000 -.260 -.284 -.181 -.190 -.227 -.115 clear/normal conv/slow clear/slow conv/normal -.077* -.107* .148* .009 .009 .010 .000 .000 .000 -.107 -.137 .115 -.047 -.078 .181 = significant at the 0.01 level Effect of Mode The ANOVA indicated that the main effect of mode was statistically significant. In other words, clear speech was more intellig ible overall than conve rsational speech. On average, key word scores for clear sp eech were 64% and key word scores for conversational speech were 56%.
28 To examine the effect of the mode x rate interaction, which wa s also statistically significant, the overall average across talker and listener for each condition is presented in Figure 1. This figure allows comparisons of the effect of mode within rates. At normal rates, conv/normal can be viewed as the baseline condition. The average percent key words correct across listeners and ta lkers was 45% for conv/normal. In the clear/normal condition, average percent key wo rds correct across lis teners and talkers was 59%, a 14 percentage point increase ove r conv/normal. The post-hoc pairwise comparison, listed in Table 6, verifies that the difference between these conditions was significant (p<0.01). In other words, clea r/normal speech provided a statistically significant benefit over conv/normal speech. This significance verifies that the talker does not have to decrease rate in order to increase speech intelligibility. As mentioned earlier, clear/slow and conv/slow were the most intelligible speaking conditions overall. To examine the ef fect of mode at slow rates, conv/slow can be viewed as the baseline condition. Averag e speech intelligibility, based on key words correct, for conv/slow was 66%. In the cl ear/slow condition, speech intelligibility increased by only 2 percentage points. Pa irwise comparison indicated no significant difference between these two conditions, as seen in Table 6. Taken together, the effect of mode at slow rates and norma l rates explains why the mode x rate interaction was found to be significant in the ANOVA. In other words, at normal rates, mode made a difference in speech intelligibility; however, at slow rates there was no significant difference, indicating that the size of cl ear speech benefit varies at different speaking rates. In the present study, the average performance in the conv/slow condition proved to be higher than expected for the older nor mal hearing listeners. Surprisingly, conv/slow
29 was just as intelligible as clear/slow, which is different than previous research findings for younger normal hearing listeners: Krause and Braida (2002) found a 12 percentage point benefit for clear/slow relative to conv/ slow for such listeners. Although this difference with previous studies for the conv/ slow condition is not yet fully understood, it should be noted that the average benefit of the clear/slow condition was consistent with Krause and Braida (2002) a nd other previous studies. The benefit of clear/slow compared to conv/normal in this study, which provided a 23 point statistically significant (p <0.01, see Table 6) improvement in intellig ibility, was similar to the benefit reported in previous studies where rate was not a c ontrolled factor (e.g., Pi cheny et al., 1985).
30 Figure 1 Average intelligibility, in percent key wo rds correct, for each condition. Performance averaged across talker and listener (Grand Aver age). Error bars indicate +/1 standard error above and below the mean. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% conv/normalconv/slowclear/normalclear/slow Condition% Key Words Correct Effect of Rate The ANOVA indicated that the main effect of rate was statistically significant. This means that speech produced at slow rate s was more intelligible overall than speech produced at normal rates. Clear/slow and c onv/slow speech was more intelligible than clear/normal and conv/normal speech, respectively. On average key word scores for speech produced at slow rates were 67% a nd key word scores for speech produced at normal rates were 52%.
31 To re-examine the statistically significan t mode x rate interaction, the effect of rate within mode can also be examined. Fr om Figure 1, it can be seen that conv/slow condition was more intelligible than conv/ normal by 21 percentage points, with an average of 66% correct key words. Similarl y, in the clear/slow condition, the average key words correct was 68%, a 9 percentage poin t increase over clear/normal. Again, both post-hoc pairwise comparisons, listed in Tabl e 6, verify that these differences were significant (p<0.01). To summarize, either speaking mode (conversational or clear) produced at a slow rate was more intelligib le than that speaking mode produced at a normal rate. However, the size of the benefit that results from a slower speaking rate is larger for conversational speech (21 points) th an for clear speech (9 points), which again explains why the mode x rate inte raction was statistically significant. Effect of Talker The main effect of talker was also statistically significant according to the ANOVA. In other words, some talkers were mo re intelligible than others. For example, T5 was the most intelligible and T3 was the least intelligible. Average percent key word scores in the four conditions ranged from 61-84% correct for T5 and 28-66% correct for T3. Of the interactions with talker, three were statistically significant according to the ANOVA: mode x talker, rate x talker, mode x rate x ta lker. To examine these interactions in more detail, average speech in telligibility for each talker is shown in Figure 2. Despite these interact ions and individual talker differences, Figure 2 shows that relative benefits of each condition are observe d across all talkers. For example, if conv/normal is again viewed as the baseli ne condition, the benefits of clear/normal
32 speech compared to conv/normal can be noted fo r all talkers, as seen in Figure 2. Speech intelligibility for T1 increased 9 percentage points. T3 and T5 had a 23 and 16 percentage point increase, resp ectively. T4 had the smallest benefit, a 6 percentage point increase in speech intelligibility. Figure 2 Average speech intelligibility, in percent key words correct for each talker in each condition. Performance averaged across listener. E rror bars indicate +/1 standard error above and below the mean. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%T1 T 3 T4 T5Talker% Key Words Correct conv/normal conv/slow clear/normal clear/slow
33 Effect of Listener Figures 3a through 3d display each listen ers performance fo r each talker and condition. From these figures, th e listener effect can be de rived. The main effect of listener was also statistically significant acco rding to the ANOVA. This means that some listeners performed better than others. For example, L6 tended to perform the poorest of all the listeners, with ke y word scores ranging from 17-72%, and L8 had the highest scores in all conditions, with key word scores ranging from 39-91%. L6 later disclosed that he suffered from two trau matic brain injuries (TBI) in his past; however, he scored within normal limits on the MMSE. Of the interactions with listener, onl y rate x mode x talker x listener was statistically significant. Despite this inte raction and individual listener differences, Figure 3 shows that relative benefits of each condition are observed across all listeners. For example, although L6 has a history of TB I and overall poor performance, it can be seen that he still follows the same general pa ttern seen from all listeners. Conv/slow and clear/slow are the most intelligible conditions Also, clear/normal is more intelligible than conv/normal.
34 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% normalslownormalslow conv conv clear clear Talker 1% Key Words Correct L1 L2 L3 L4 L5 L6 L7 L8 Talker 3 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% normalslownormalslow conv conv clear clear % Key Words Correct L1 L2 L3 L4 L5 L6 L7 L8 Talker 4 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% normalslownormalslow conv conv clear clear % Key Words Correct L1 L2 L3 L4 L5 L6 L7 L8 Talker 50% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% normalslownormalslow conv conv clear clear % Key Words Correct L1 L2 L3 L4 L5 L6 L7 L8Figure 3 Average performances, in percent key words corr ect, of every listener, for each talker in the four conditions. a) b) c) d) The Role of Cognitive Processing Speed Lastly, the results of the Salthouse tasks were used to assess cognitive processing speed and to explore whether a relationship might exist between such skills and either overall speech intelligibility or amount of benefit obtained from clear speech. There were two tasks administered, letter comparison and pattern comparison. The participants had
35 30 seconds to complete each of the tasks and were then scored on accuracy. Table 7 lists the scores of the processing tasks as well as overall intelligibility performance and clear speech benefit for each listener in the study. Overall intelligibil ity performance was defined as the average performance of each listener across all talk ers and conditions, and clear speech benefit was defined as the di fference between each listeners clear/normal and conv/normal scores, averag ed across listener. The data were then graphed as a scatter plot, and linear regressi on equations were calculated as can be seen in Figure 4. Table 7 Summary of Performance on Salthouse Task s, Overall Performance in the Study, and Clear Speech Benefit Listener Letter Comparison (%) Pattern Comparison (%) Overall Performance (%) Clear Speech Benefit (%) L1 100 83 58 16 L2 100 88 58 11 L3 100 100 63 17 L4 100 100 60 14 L5 100 100 62 15 L6 77 63 45 17 L7 100 100 62 10 L8 100 100 69 11
36 R2 = 0.7212 R2 = 0.1474 0% 10% 20% 30% 40% 50% 60% 70% 80% 50%60%70%80%90%100% % Correct of Letters Completed Overall Performance Clear Speech Benefit Linear (Overall Performance) Linear (Clear Speech Benefit)Figure 4 Data were graphed and regression lines were calculated. In e ach figure, y-axis represents 1) average % key words correct (averaged across talker and condition) for overall performance data and 2) difference in % correct scores betwee n clear/normal and conv/normal (averaged across talker) for clear sp eech benefit data. Figure a) represents Letter comparison task. Figure b) represen ts Pattern comparison task. Significant correlation found between accuracy on Pattern task and overall performance in the study. a)
37 R2 = 0.8231 R2 = 0.1398 0% 10% 20% 30% 40% 50% 60% 70% 80% 50%60%70%80%90%100% % Correct of Patterns Completed Overall Performance Clear Speech Benefit Linear (Overall Performance) Linear (Clear Speech Benefit)b) Spearmans rho ( ) correlation coefficients were used to assess the relationship between cognitive processing speed, as meas ured by accuracy on each of the Salthouse tasks, and overall performance on the intellig ibility tasks in the st udy. These results are summarized in Table 8. The moderate corr elation between letter comparison accuracy and overall performance, =.577, was not statistically signi ficant. However, a strong positive correlation, =.873, was found between pattern comparison accuracy and overall performance. This correlati on was statistically significant at p<0.01 and indicates that the more accurate the participant wa s in the pattern comparison tas k, the better he or she did on the speech intelligibility tasks.
38 Table 8 Spearmans Rho ( ) Correlation Coefficients Spearman Rho ( ) Letter Comparison and overall average performance .577 Letter Comparison and clear speech benefit -.412 Pattern Comparison and overall average performance .873* Pattern Comparison and clear speech benefit -.300 = significant at the 0.01 level As seen in Table 8, correlation was also examined between cognitive processing scores and average clear speech benefit per li stener. Weak negative correlations were found for letter and pattern comparison and clear speech benefit. However, these correlations were not statistically significant.
39 Chapter 5 Discussion and Future Research From this study it can be concluded that for older listeners with normal hearing, clear speech at normal rates is more intel ligible than conversational speech at normal rates. Although clear/normal is not as inte lligible as clear/slow and conv/slow for the older listeners with normal hearing, it still has a 14 percentage point increase over conv/normal, indicating that rate does not have to decrease to improve speech intelligibility. Also, the same size benefit from clear/normal speech was seen in the younger listeners with normal hearing in Krause and Braidas study (2002). To analyze the age factor, the results of this study were compared to Krause and Braidas study (2002), which included young listeners with normal hearing. It is important to note the differences in SNRs in the two studies. Krause and Braida (2002) used a SNR of -2 dB with the younger listener s. In both studies, the purpose of the SNR was to avoid ceiling or floor effects. In particular, 0 dB SNR was employed in the present study in order to avoi d floor effects. In other wo rds, since it is known that listeners who are older, in general, pe rform poorer than listeners who are younger (Gordon-Salant & Fitzgibbons, 1997), an easie r SNR was used to prevent the older listeners in this study from scoring too low. Table 9 shows the comparison of percent key words correct between the present study and the previous study. Again, the aver age percentages for conv/normal should be
40 viewed as a baseline for comparison to th e other conditions. In parentheses is the increase in percentage points of each condition compared to conv/normal. Table 9 Average Listener Performance Across Studies Current study: older listeners with normal hearing SNR = 0 dB Krause and Braidas study (2002): younger listeners with normal hearing SNR = -2 dB Conv/normal 45% 45% Conv/slow 66% ( +21 ) 51% (+6 ) Clear/normal 59% ( +14 ) 59% ( +14 ) Clear/slow 68% ( +23 ) 63% ( +18 ) For the normal rate conditions, the older listeners performed more poorly overall than the younger listeners. Despite the SNR difference, both populat ions had an average of 45% key words correct in conv/normal, and both populations had an average of 59% key words correct in clear/normal. Even t hough the scores for these conditions were the same for both groups, this level of performa nce for older listeners is actually worse because of the easier SNR presented to them compared to younger listeners. If the SNR for the younger listeners was 0 dB, they woul d have scored higher in conv/normal and clear/normal compared to the older listeners. In addition, it is importa nt to note that there is a 14 percentage point increase when clear speech at normal rate was obtained for both
41 populations regardless of SNR, indicating that age is not a factor in the clear speech benefit at normal rates. For the slow rate conditions, the older lis teners seem to have outperformed the younger listeners in reception of both convers ational and clear speech. The older listeners had average scores of 66% and 68% in conv/slow and clear/ slow, respectively. The younger listeners had average scores 51% and 63% in conv/sl ow and clear/slow, respectively. However, the difference in SNR could account for why it may seem that the older listeners outperformed the younger list eners in the clear/slow condition. If the SNR was the same in both studies, both populat ions may have performed similarly at the slow rates. In other words, if the younger listeners were presented the stimuli at 0 dB SNR, their scores would increa se, possibly to the levels obtai ned by the older listeners. However, it is unclear what the size of in crease in scores would be, and the size of increase in conv/slow would also not necessar ily be the same as the size of increase in clear/slow. Therefore, additional testing of both groups at each SNR is needed in order to determine the relative performance of the older and younger listeners for each of the conditions at slow rates. One unexpected finding at slow rates was th at clear speech (68%) did not provide a benefit over conv/slow (66%) for older listeners with norm al hearing. In Krause and Braidas previous study (2002) the younger listener s received a 12 point benefit from clear/slow relative to conv/sl ow speech whereas, the older lis teners in the present study performed about the same in both slow conditions. Since both groups experienced a benefit from clear speech at normal rates bu t only younger listeners experienced a benefit at slow rates, an age by rate interaction may be present. To investigate this possibility,
42 further testing of both groups and SNRs is wa rranted. Other possible explanations of the results are also discussed below. One possible explanation is the different SNRs. The results may have been different if the SNRs were the same. For exam ple, the size of the clear speech benefit is typically larger in more difficult listening environments (e.g., Payton et al., 1994; Helfer, 1998; Bradlow & Bent, 2002; Bradlow et al., 2003) Consequently, it is possible that if the older listeners were tested at SNR = -2 dB they might have experienced a larger clear speech benefit, perhaps more comparable to the younger listeners at slow rates. Another possible explanation is that thes e results may reflect a difference between the two groups in noise. Perhaps the lack of benefit of clear/slow relative to conv/slow for older listeners represents a ceiling effect for that group in noise. In other words, the older listeners at tained their highest possible perform ance levels in noise for conv/slow speech and could not achieve higher speech intelligibility for clear/slow speech. Finally, a third explanation could be that, for older adults with normal hearing, conv/slow functions as a type of clear speech for them. In such a case, it could then be expected that for older listeners, conv/slo w would provide a comparable intelligibility benefit (relative to conv/normal) as clear/slow at a variety of signal to noise ratios, even though no such benefit is apparent for younger li steners. Furthermore, such a finding would suggest that conv/slow speech has ac oustic properties different from conv/normal speech that benefit older listeners. If this is the case, then an acoustical analysis of the two speaking conditions would be needed. Fo r example, the acoustical research could then clarify why conv/slow a nd clear/slow are intelligible for older adults and only clear/slow is intelligible for younger adults. Also, the analysis could determine the
43 acoustical differences between conv/normal and conv/slow. In sum, further testing of both groups at the same SNR is needed. Futu re research should control for the SNR as well as age to answer these questions.
44 Chapter 6 Clinical Implications In summary, older listeners experience a large intelligibility benefit from clear/normal speech (14 point benefit rela tive to conversationa l speech). Although, clear/slow (23 point benefit) and conv/slow ( 21 point benefit) were the most intelligible conditions, the benefit of clear/normal is mo st notable because speaking rate does not have to decrease to improve speech intel ligibility for listeners who are older. Furthermore, the amount of benefit from clear speech at normal rate s is roughly the same (14 percentage points) for thes e listeners as for younger listen ers. Therefore, hearing aid technology, based on clear speech, should provide comparable benefit to listeners of any age. The hearing aid can process convers ational speech into clear speech without slowing down rate and as a result, the liste ner will not fall behind in the conversation. In addition, there is a be tter understanding of the re lative intellig ibility of conversational and clear speech at normal a nd slow rates. The present study provides more information regarding th e effect of mode and rate of speech production on speech intelligibility. The study also brings up ne w questions, such as why do older adults benefit from conv/slow as much as they do from clear/slow. Finally, knowing that rate does not have to decrease in order to improve speech intelligibility, productivity in therapy sessions may increase, regardless of the clients age. Using clear speech at a normal rate wi ll increase the efficiency of the session and reduce communication breakdowns.
45 Because of theses benefits, clinicians, es pecially those working with children and older adults, should be trained for clinical a pplication of clear speech. From the present and previous studies, it has been shown th at adults with normal hearing, young and old, benefit from clear/normal speech. Therefore, training should not onl y include clinicians working with hearing loss populations, or childr en with learning disabilities. The benefit of clear speech should be brought to the attention of all clin icians in fields such as audiology, speech-language pathology and education, just to name a few. Presently, few sources can be found for tr aining clear speech. Ti ps for producing clear speech can be found in Don Schums Otic on pamphlet (1996) or from Krause and Braidas study (2002) which de scribed formal training proc edures for eliciting clear speech. Krause and Braidas study (2002) trai ned professional speak ers to produce clear speech at a normal rate. In their study, th e talkers underwent roughl y six hours of intense training. Rate was regulated using metronom e clicks and speech intelligibility was achieved by using young listeners with normal hearing to recognize all key words. However, neither of these sources is ideal for training clinicia ns to produce clear speech at normal rates. Schums informati on (1996) does not regulate for rate. It is aimed at producing clear speech that is natu rally slower. Krause and Braidas study (2002) for clear speech at normal rates involve d intense training in a laboratory setting, which is not feasible for clinic ians and communication partners. Because the benefits of clear/normal speech are evident, it would be useful to develop more practical means of training. For example, training clear speech could be completed in workshop type settings as a weeken d course or part of a curriculum. This workshop may be ideal for the university setting where student s are educated. A
46 workshop for the public could also be offered for family, friends and other professionals to learn about clear/normal speech and its benefits. The workshops should be led by professionals or clinicians who have resear ched clear speech at different rates. It is important to note that it may not be possible for all talkers to achieve immediate results when learning to produce clear speech at normal rates. For example, Krause and Braida (2002) se lected talkers who showed potential for producing clear speech without altering rate, but T2 did not fully accomplish the goal in the time frame provided. This will not be uncommon because all talkers are different and will use different characteristics to achieve clear/nor mal speech. For example, some talkers may modify the production of vowels and others may make stops more evident by including the bursts. Because there are many characteri stics for clear/normal that can be used, not all talkers will use the same characteristics; hence, every talker will be different, and some will require more time than others to learn to produce clear speech at normal rates. In the meantime, tips and exercises for learning to produce clear speech at slow rates, such as those in Schums Oticon pack et (1996) are useful, because studies have shown that most talkers can learn to produce clear speech at slow rates within 15 minutes, which includes instruction and practice (e.g., Schum, 1997). The Oticon packet instructs talkers to use pauses, intonation, stress, and to produce accurately, fully formed sounds. Also, it is important to not forget othe r good communication habits such as reducing background noise, face to face communication and appropriate lighting (Schum, 1996). In conclusion, clear speech is a type of speaking style that benefits many populations, from children to adults, in difficu lt communication settings Better yet, clear speech does need a slower rate to be inte lligible. Clear/normal speech is fairly new
47 research and still needs to be investigated to further explore the relationship between rate, speaking style and speech intelligibility.
48 References Bradlow, A.R., & Bent, T. (2002). The clea r 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. Cutler, A., & Butterfield, S. (1990). Durationa l cues to word boundaries in clear speech. Speech Communication, 9 (5/6), 485-495. Cutler, A., & Butterfield, S. (1991). Word boundaries in clear speech: A supplementary report. Speech Communication, 10 335-353. 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, 6, 87-96. Ferguson, S.H. & Kewly-Port D. (2002). Vowel intelligibility in cl ear 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, visual and audiovisual clear speech. Speech Communication, 37 213-230.
49 Gordon-Salant, S. (1987). Effects of acousti c modification on consonant recognition by elderly hearing-impaired subjects. Journal of the American Academy of Audiology, 81 (4), 1199-1202. Gordon-Salant, S., & Fitzgibbons, P.J. (1997) Selected Cognitive Factors and speech recognition and speech recognition pe rformance among young and elderly listeners. American Speech-Language-Hea ring Association, 40, 423-431. Gordon-Salant, S. & Fitzgibbons, P.J. (1999). Pr ofile of auditory temporal processing in older listeners. Journal of Speech, Language, and Hearing Research, 42, 300-311. Helfer, K.S. (1998). Auditory and auditory-visual recognition of clear and conversational speech by older adults. Journal of the American Ac ademy of Audiology, 9, 234242. Krause, J.C. (2001). Properties of naturally produced clear speech at normal rates and implications for intel ligibility enhancement. Unpublished doctoral dissertation, Massachusetts Institute of Technology. Krause, J.C. & Braida, L.D. (2002). Investig ating alternative form s 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.C. & Braida, L.D. (2003). Effects of listening environment on intelligibility of clear speech at normal speaking rates. Iranian Audiology, 2 Krause, J.C. & Braida, L.D. (2004). Acoustic properties of naturally produced clear speech at normal speaking rates. Journal of the Acoustical Society of America, 115, 362-378.
50 Payton, K.L., Uchanski, R.M., & Braida, L.D. (1994). Intelligibility of conversational and clear speech in noise and reverberati on for listeners with normal and impaired hearing. Journal of the Acoustical Society of America, 95, 1581-1592. Peters, R.W. et al. (1997). Speech reception thre sholds in noise with and without spectral and temporal dips for hearing-impa ired 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 c onversational 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 a nd conversational speech. Journal of Speech and Hearing Research, 29, 434-446. Picheny, M.A., Durlach, N.I., & Braida, L.D. (1989). Speaking clearly for the hard of hearing III: An attempt to determine 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 ag e differences in cognition by reductions in working memory and speed of processing. Psychological Science, 2, 179-183. Schum, D.J. (1996). Intelligibility of cl ear and conversational speech of young and elderly talkers. Journal of the American Academy of Audiology, 7, 212-218. Schum, D.J. (1997). Beyond h earing aids: Clear speech training as an intervention strategy. Journal of the American Academy of Audiology, 50 (10), 36-40.
51 Studebaker, G.A. (1985). A ra tionalized arcsine transform. Journal of Speech and Hearing Research, 28, 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: Furthe r studies of the role of speaking rate. Journal of Speech and Hearing Research, 39, 494-509.
53 Appendix A: Screening Results Table A1 Listener Demographi cs and MMSE Scores Listener Age Sex MMSE Score L1 55 F 28 L2 58 F 30 L3 68 M 29 L4 67 F 30 L5 60 M 30 L6 62 M 29 L7 59 F 30 L8 61 F 30 Table A2 Results of Hearing Screening Ear Tested 250 kHz (in dB) 500 kHz (in dB) 1 kHz (in dB) 2 kHz (in dB) 4 kHz (in dB) 6 kHz (in dB) 8 kHz (in dB) L1 Right* 20 20 10 5 10 15 15 Left* 10 5 15 15 0 10 5 L2 Right* 25 20 0 5 5 10 15 Left 30 30 15 5 15 15 25 L3 Right 30 25 15 5 15 25 30 Left* 20 10 10 10 20 25 25 L4 Right* 10 5 10 5 20 30 30 Left* 10 5 0 20 15 35 25 L5 Right* 25 15 0 10 25 15 20 Left 25 20 10 10 35 20 20 L6 Right* 15 15 10 5 10 30 30 Left 10 20 20 35 55 65 65 L7 Right* 15 20 15 10 20 25 15 Left* 15 20 10 15 20 25 20 L8 Right* 25 10 20 10 20 35 30 Left 30 15 15 10 10 35 40 = ear used in study. If bot h ears are marked, participant allowed to alternate ears between lists, if desired. A ll other participants were restricted to the ear that passed.
54 Appendix B: Listener Data Talker Mode/Rate L1 L2 L3 L4 L5 L6 L7 L8 Avg T1 conv/normal 0.37 0.390.460.460.540.220.44 0.56 43.0% T1 conv/slow 0.70 0.710.770.780.700.600.70 0.80 72.0% T1 clear/normal 0.51 0.490.610.500.490.440.49 0.62 51.9% T1 clear/slow 0.68 0.690.730.710.800.480.75 0.80 70.5% T3 conv/normal 0.29 0.290.2188.8.131.52.34 0.39 27.9% T3 conv/slow 0.63 0.600.660.680.740.440.67 0.85 65.9% T3 clear/normal 0.50 0.420.530.580.520.280.55 0.68 50.8% T3 clear/slow 0.42 0.480.490.480.410.360.41 0.54 44.9% T4 conv/normal 0.50 0.460.530.540.410.310.53 0.61 48.6% T4 conv/slow 0.58 0.750.630.510.550.440.54 0.61 57.6% T4 clear/normal 0.54 0.520.590.530.630.390.56 0.65 55.1% T4 clear/slow 0.69 0.730.790.710.770.650.81 0.79 74.3% T5 conv/normal 0.52 0.580.560.570.710.430.73 0.74 60.5% T5 conv/slow 0.70 0.670.750.680.710.570.66 0.77 68.9% T5 clear/normal 0.77 0.710.800.750.840.680.84 0.79 77.3% T5 clear/slow 0.81 0.820.880.830.900.720.83 0.91 83.8%
55 Appendix C: ANOVA Statistics Table C1 Within-subjects Effects and Interactions Effect F Hypothesis df Error df Sig. EtaSquared *rate 826.128 1 32 .000 17.78 rate x listener 2.733 7 32 .024 0.41 *mode 202.101 1 32 .000 5.11 mode x listener 1.489 7 32 .206 0.26 *talker 218.390 3 30 .000 24.36 talker x listener 1.159 21 96 .305 1.18 *rate x mode 61.931 1 32 .000 2.24 rate x mode x listener .908 7 32 .513 0.23 *rate x talker 20.905 3 30 .000 2.32 rate x talker x listener 1.500 21 96 .096 1.00 *mode x talker 57.464 3 30 .000 3.07 mode x talker x listener .970 21 96 .506 0.64 *rate x mode x talker 64.698 3 30 .000 7.83 *rate x mode x talker x listener 2.770 21 96 .000 2.49 = significant at the 0.01 level
56 Appendix C: ANOVA Sta tistics (Continued) Table C2 Between-subjects Effects Effect Type III Sum of Squares Mean Square F Hypothesis df Error df Sig. EtaSquared *listener 3.306 .472 57.444 7 32 .000 13.29 = significant at the 0.01 level