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Effect of intensity increment on P300 amplitude
h [electronic resource] /
by Tim Skinner.
[Tampa, Fla.] :
University of South Florida,
Professional research project (Au.D.)--University of South Florida, 2004.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
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ABSTRACT: The purpose of this study was to determine the effects of task difficulty on the amplitude and latency of the P300 by altering the intensity of the oddball stimulus. A P300 was obtained on 22 adult subjects ranging in age from 21 to 34 years of age (mean = 24 years) with normal hearing. The "frequent stimulus" was a 1000 Hz or 4000 Hz tone burst, gated with a rise and fall time of 10 msec and 20 msec plateau, presented at 75 dBn HL The "oddball stimulus" was a tone burst of the same frequency (1000 Hz or 4000 Hz)presented at 77, 79, or 81 dBn HL. A four-channel recording was made with linked reference electrodes and the following montages:Cz-A1+A2, Pz-A1+A2, and Fz-A1+A2. The fourth channel was used to monitor "eye blink" activity. The investigation tested the null hypothesis that changing the intensity of the oddball stimuli would not result in a significant change in either the amplitude or latency of the P300. Analyses of Variance (ANOVA) indicate that P300 latency and amplitude did not differ significantly by run, stimulus frequency, intensity of the oddball, or montage. Thus the null hypothesis was supported.
Adviser: Hurley, Raymond M.
t USF Electronic Theses and Dissertations.
THE UNIVERSITY OF SOUTH FLORIDA COLLEGE OF ARTS AND SCIENCES Effect of Intensity Increment on P300 Amplitude By Tim Skinner An Audiology Doctoral Project submitted to the Faculty of the Department of the Communication Sciences and Disorders University of South Florida In partial fulfillment of the requirements for the degree of Doctor of Audiology Raymond M. Hurley, Ph.D., Chair Jennifer J. Lister, Ph.D. Robert F. Zelski, Au.D. Date Tampa, Florida Version 6.0
2. Effect of Intensity Increment on P300 Amplitude Tim Skinner (Abstract) The purpose of this study was to determine th e effects of task difficulty on the amplitude and latency of the P300 by altering the intensity of the oddball stimulus. A P300 was obtained on 22 adult subjects ranging in age from 21 to 34 years of age (mean = 24 years) with normal hearing. The frequent stimulus was a 1000 Hz or 4000 Hz tone burst, gated with a rise and fall time of 10 msec and 20 msec plateau, presented at 75 dBn HL The oddball stimulus was a tone burst of the same frequency (1000 Hz or 4000 Hz)presented at 77, 79, or 81 dBn HL. A four-channel recording was made with li nked reference electrodes and the following montages:Cz-A1+A2, Pz-A1+A2, and Fz-A1+A2. Th e fourth channel was used to monitor "eye blink" activity. The investigati on tested the null hypot hesis that changing th e intensity of the oddball stimuli would not result in a significant change in either the amplitude or latency of the P300. Analyses of Variance (ANOVA) indicate that P300 latency and amplitude did not differ significantly by run, stimulus frequency, intensity of the oddball, or montage. Thus the null hypothesis was supported.
3. Introduction The P300 (P 3 ) is an auditory evoked potential (AEP) referred to as a cognitive or event-related response occurring in the 300 ms ec latency region with a large positive voltage peak, hence P, after an acoustic stimulus. Like most long latency poten tials (LLP), the P300 is an endogenous response, highly dependent upon subject attention to auditory stimuli. The P300 is typically recorded with the patient attendi ng or listening for a rare, oddball, or target stimulus that is presented along with frequent stimu li. The stimulus that occurs the majority of the time is the frequent stimulus and the infreq uent stimulus is known as the oddball. In the oddball test paradigm, two stimuli are presente d with one occurring between 80% and 85% of the time and the other occurring between 15% and 20% of the time. The participant is asked to respond, usually by counting out loud or by pr essing a button, when the oddball stimuli is perceived. The major peak is a large positive voltage (5 V) occurring approximately 300 msec after the rare or "oddball" response (Polich, 1996). The P300 response is believed to reflect processing at the medial temporal lobe (hippocampus); however, the exact neural generators are not clear at this time (Molnar, 1994). It is known that the P300 response changes throughout the lifespan Full maturity of the P300 does not occur until about 15 years of age. From bi rth through 15 years of age, latencies decrease, while amplitudes increase. The reverse is tr ue from about 40 years of age through death; latencies slowly increase and amplitudes decrease. The P300 is classified as an endogenous poten tial, meaning that it or iginates from within the subject and is dependent on the subject attending to or pro cessing the stimuli. (Halgren, Marinkovic, & Chauvel, 1998). Unlike the audito ry brainstem response (ABR), the P300 is not directly impacted by the stimulus characteristics. Attention and st ate of arousal are the two most important factors in eliciting a P300 response. In order to adequately assess the P300 response,
4. the subject must actively attend to the oddball stimulus and be able to discriminate it from the frequent stimulus. If the subject is unable to discriminate the oddball from the frequent stimulus, then the P300 will not be present (Hall, 1992). As the stimulus, both frequent and oddball, are reduced in intensity towards threshold, the amplit ude of the P300 decreases (Papanicolaou et al., 1985; Covington & Polich, 1996; Sugg & Polich, 1995) Therefore, most P300 protocols use a 75 to 80 dB nHL stimulus intensity to d ecrease amplitude variability (Polich, 1998). P300 amplitudes and latencies ar e used clinically to assess patients with Alzheimers Disease, Parkinsons Disease, and dementia. Patients with these neurodegenerative disorders tend to have prolonged P300 latencies, believed to be related to changes in neurotransmitters (Kugler, Taghavy, & Platt, 1993). The P300 can be extremely va luable tool when evaluating general cognitive function (Polich & Herbst, 2000). P300 latencies have been shown to increase, while amplitudes decrease, with decreases in cogn itive function (Polich, Howard, & Starr, 1983). It is important, from both clinical and resear ch perspectives, to design paradigms that will improve the utility of the P300. In 1995, Sugg and Polich found that the discrimination task needs to be difficult enough to el icit a P300 response. They found that if the discrimination task is too simple (> 7 dB or >50 Hz), the amplitude decreases while the latency increases. The P300 also becomes less reliable outside of those para meters. Since the characteristics of the P300 are affected by cognitive processing, th eoretically, the more difficult the oddball task, the greater the amplitude of the P300 response. The proposed study was designed to determine if a simple psychoacoustic ability can be measured electroph ysiologically. The psychoacoustic ability of interest for this study was in tensity discrimination. Intensity discrimination thresholds are depe ndent on the frequency and sensation levels of the stimuli (Turner, Zwislock i, & Filion, 1989). Intensity diffe rence limens decrease as the sensation levels are increased (Yost, 1994). The intensity discrimination for a normal hearing
5. adult for a stimulus with a sensation level above 60 dB HL is less than 1 dB (Gelfand, 1998). The purpose of this study is to determine th e effects of changing the difficulty of the discrimination task on the amplitude and latency of the P300 by altering the intensity of the oddball stimulus. Methods Participants Twenty-two participants (5 males and 17 fe males) between the ages of 21 and 34 years (mean = 24 years of age) participated in this stu dy. All participants in this study were required to have normal hearing and normal middle ear f unction with no known neurological or cognitive disorders. Normal hearing was defined as air conduction thresholds at or below 20 dB HL for the frequencies 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz in each ear (American National Standard Institute, 1996; American Speech-Langu age and Hearing Association, 1985). Normal middle ear function was defined as an ear can al volume between 0.5 ml and 2.0 ml, a peak pressure between daPa and +100 daPa, and a compliance value between 0.2 ml and 1.8 ml. Contralateral acoustic reflexes we re measured and were required to fall within normal limits determined by the published acoustic reflex threshold 90% cutoff values (Silman & Gelfand, 1981). These criteria for inclusion were used in order to make the group as homogenous as possible. The participants were not financially compensated. Instrumentation Air conduction thresholds were measured using an Interacoustics (Model AC40) audiometer and middle ear function was determined using a GSI Tympstar. For P300 measures, stimulus presentation and signal aver aging were controlled by a Nicolet Spirit evoked potential system. All equipment used was calibrated according to ANSI specifications.
6. Materials and Procedures The hearing test and middle ear measur es were conducted at the Communication Sciences and Disorders Audiology C linic at the University of South Florida. The P300 testing was conducted in a research laboratory in th e Department of Comm unication Sciences and Disorders using a Nicolet Spirit evoked potential system. The frequent stimulus used was a 1000 Hz or 4000 Hz tone burst, gated with a rise and fall time of 10 msec and a 20 msec plateau, presented at 75 dBn HL. The oddball stimulus was a tone burst of the same frequency (1000 or 4000 Hz) presented at 77, 79, or 81 dBn HL. Th e frequent tone bursts were presented in a stimulus train with a probability of 80% wh ile the oddball tone bur sts occurred with a probability of 20% within the stimulus train. Rarefaction was used as the polarity and the time window was 600 msec. The responses were band pass filtered between 1 and 30 Hz. Thirty responses for each oddball were averaged and constituted one run. The tone bursts were presented binaurally through ER-3 insert earphones at a rate of 0.77 per second. A four-channel recording was made with linked reference elec trodes and the following montage: Cz-A1+A2, PzA1+A2, and Fz-A1+A2. The fourth channel was us ed to monitor "eye blink" activity. If the amplitude of the fourth channel exceeded 5 V in the region of the P300, the run was discarded. The forehead (Fpz) was used as the ground. Im pedance was maintained below 2000 ohms. The P300 measures took place in a double walled IAC sound treated room. The starting oddball intensity was counterbalanced. Participants were instructed to respond to the oddball stimulus by pressing a button that they were given. The patient response button was unattached, but the participant did not have knowledge of this. P300 amplitude and latency for each oddball were recorded for each subject. All subjects were i nvolved in two runs for each stimulus frequency and intensity combination for a total of 12 runs. A ll of the runs and the in itial hearing test were completed in one session.
7. Results Figure 1 displays the mean audiometric thresholds for all participants. Figures 2a and 2b display the mean ( SE) amplitude for each intensity level by electrode montage. In order to determine 0510152025dB HTL100010000Frequency (Hz) Right Ear Left Ear Figure 1. Mean ( SD) hearing thresholds levels (HTLs) for all participants if these mean data were significantly different, the data were analyzed using a 4-way Analysis of Variance (ANOVA) with four within subjects variables (run, frequency, intensity of the oddball, and montage). For amplitude, only one interaction reached statistical significance, that between run and frequency [F (1,21)= 4.33, p = 0.05]. A Tukey post-hoc analysis of the significant interaction between run and frequency revealed that none of the possible combinations of run and frequency differed significantly from each other (p>0.05).
8. 0123456789Amplitude (V)Cz-A1+A2Fz-A1+A2Pz-A1+A2Montage 81 dB 1 kHz 79 dB 1 kHz 77 dB 1 kHz 0123456789Amplitude (V)Cz-A1+A2Fz-A1+A2Pz-A1+A2Montage 81 dB 1 kHz 79 dB 1 kHz 77 dB 1 kHz Figures 2a and 2b. Mean ( SE) P300 amplitude at the three electrode montages for the three intensity levels at 1000 and 4000 Hz.
9. Figures 3a and 3b illustrate the mean latency for each intensity level by electrode montage. In order to determine if these mean data were significantly different, the data were analyzed using a 4-way ANOVA with four within subjects variables (run, frequency, intensity of the oddball, and montage). None of the main effects (run, frequency, intensity of the oddball, and montage) or interactions were significant (p > 0.05). 050100150200250300350400Latency (msec)Cz-A1+A2Fz-A1+A2Pz-A1+A2Montage 81 dB 1kHz 79 dB 1 kHz 77 dB 1 kHz Figures 3a. Mean ( SE) P300 latency at the three electrode montages for the three intensity levels at 1000 Hz. The SE values are so small that the error bars are not visible on this figure.
10. 050100150200250300350400Latency (msec)Cz-A1+A2Fz-A1+A2Pz-A1+A2Montage 81 dB 4 kHz 79 dB 4 kHz 77 dB 4 kHz Figure 3b. Mean ( SE) P300 latency at the three electrode montages for the three intensity levels at 4000 Hz. The SE values are so small that the error bars are not visible on this figure. Figures 4 and 5 display the mean ( SE) test retest raw data for run 1 versus run 2 for amplitude and latency respectively. There were no significant differences between run 1 and run 2 for either amplitude or latency as analyzed using the two 4-way ANOVAs described above.
11. 02.557.510Amplitude (V)777981Intensity (dB) Re-Test 4 kHz Test 4 kHz Re-Test 1 kHz Test 1 kHz Figure 4. Mean ( SE) P300 test-retest amplitude for the three intensity levels at 1000 Hz and 4000 Hz. 050100150200250300350400P300 Latency (msec)777981Intensity (dB) Re-Test 4 kHz Test 4 kHz Re-Test 1 kHz Test 1 kHz Figure 5. Mean ( SE) P300 test-retest latency for the three intensity levels at 1000 Hz and 4000 Hz. The SE values are so small that the error bars are not visible on this figure.
12. There were no statistically si gnificant effects seen in any of the analyses of the data associated with this experiment. We originally hypothesized that changing the intensity of the oddball stimuli would not resu lt in a change in either the ampl itude of the latency of the P300. According to the data and analysis a bove, our hypothesis is supported. Discussion Though it has been proposed that the amplitude and latency of the P300 is affected by the difficulty of a discrimination task, this study ha s found that this is not the case (Sugg & Polich, 1995). Previous studies have de monstrated that the P300 is influenced by cognitive factors (Polich & Herbst, 2000; Kugler, Taghavy, & Platt, 1993), suggesting a potential clinical application. This study explored the clinical utility of the P300. This study investigated the e ffect of the magnitude of the intensity difference between the frequent and oddball stimulus on the amplitude and latency of the P300. The results indicated that the intensity difference betw een the frequent and oddball stimulus had no effect on either the latency or the amplitude of the P300. Further, the P300 did not vary as a function of the electrode montage. There several possible reasons that the manipulation of th e intensity difference between the frequent stimulus and the oddball stim ulus did not affect the amplitude or the latency of the P300. First, the P300 is believed to reflect processing that occurs primarily at the level of the medial temporal lobe (Molnar, 1994). The intensity di scrimination task used in this study may be processed at a lower le vel of the auditory pathway. If the stimulus is processed at a lower level, then the P300 may be unaffected. Second, the intensity discrimination task may not have been difficult enough to make it cognitiv ely challenging enough to affect the P300. Different psychoacoustic tasks should be used in future testing to assess the hypothesis of this study.
13. Summary The present study suggests th at the P300 is unaffected by changes in the intensity difference between the frequent and oddball stimulus More research is needed to completely understand the neural generators that are involved in the form ation of the P300. Different paradigms also need to be designed to help incr ease the clinical utility of the P300. Although the intensity discrimination task did not result in any changes to the P300, other tasks such as frequency discrimination or gap dete ction may prove to be useful.
14. References American National Standards Institute. (1996). American national standards specifications for audiometers (ANSI S3.6-1996). New York: Author. American Speech-Language-Hearing Associat ion. (1985). Guidelines for identification audiometry. ASHA 27(5), 49-52. Covington, J., & Polich, J. (1996). P300, stimulus intensity, and modality. Electroencephalography and Clinical Neurophysiology, 100, 579-584. Gelfand, S. (1998). Hearing: An introduction to psycholog ical and physiological acoustics. New York: Marcel Dekker. Halgren, E., Marinkovic, K., & Chauvel, P. (1998). Generators of the late cognitive potentials in auditory and visual oddball tasks. Electroencephalography and Clinical Neurophysiology, 106, 156-164. Hall, J. (1992). Handbook of auditory evoked responses Needham Heights, Massachusetts: Allyn and Bacon. Katzman, R. (1987). Aging and de mentia symposium abstract. Neuroscience, 22: S1. Kugler, C.F.A., Taghavy, A., Platt, D. (1993). The event-related P300 potential analysis of cognitive human brain aging: A review. Gerontology, 39, 280-303. Molnar, M. (1994). On the origin of the P3 event-related pote ntial component. International Journal of Psychophysiology, 17, 129-134. Papanicolaou, A., Loring, D.,Raz, N., & Eisenberg, H. (1985). Relationship between stimulus intensity and the P300. Psychophysiology, 27 326-329. Polich, J. (1996). Meta-analysis of P300 normative aging studies. Psychophysiology, 33 334353.
15. Polich, J. (1998). P300 clinical utility and control of variability. Journal of Clinical Neurophysiology, 15, 14-33. Polich, J., & Herbst, K. (2000). P300 as a clin ical assay: Rationale, evaluation, and findings. International Journal of Psychophysiology, 38 3-19. Polich, J., Howard, L., & Starr, A. (1983). P300 latency correlates with digit span. Psychophysiology, 20, 665-669. Silman, S., & Gelfand, S.A. (1981). The relations hip between magnitude of hearing loss and acoustic reflex threshold levels. Journal of Speech and Hearing Research, 46 312-316. Sugg, M., & Polich, J. (1995). P300 from auditory stimuli: Intensity and frequency effects. Biological Psychology, 41 255-269. Turner, C., Zwislocki, J., & Filion, P. (1989). Intensity discrimination determined with two paradigms in normal and hearing impaired subjects. Journal of the Acoustical Society of America, 86, 109-115. Yost, W. (1994). Fundamentals of hearing: An introduction. London, England: Academic Press.