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Auditory evoked potentials: the use of frequency selective masking techniques in cochlear research
S144 50 Hz BAEPs (p = 0.002). The latency-distribution of Ib seemed to be bimodal. A bifid wave I11 was found in 3.5% of 10 Hz and 7.4% of 50 Hz BAEPs. Latency distributions were found to be double- (or multi)-peaked for wave 1,11,111 (50Hz), IV and V (10Hz). Thus, several generators may contribute to single waves in the human BAEP. The subcomponents are more easily recognized at higher stimulation rates but differences were not found between C- and R-click groups. They must be recognized as a normal variation of the human BAEP.
P21.04 BRAIN-STEM AUDITORY EVOKED POTENTIALS IN NORMAL ADULTS AFTER RAREFACTION, CONDENSATION AND ALTERNATING ACOUSTIC STIMULI. N. Monastiriotis. E. Koutra, A. Siafakas, B. Mantouvalos and C. Papageorgiou
example, Rutten and Kuper, Hearing Research 1982. 8; 157). One conclusion was that AP tuning deteriorates with increasing hearing loss. This led us to explore a faster method for obtaining information about frequency selectivity i.e. by measuring so-called 'derived responses'. These derived responses, or narrow band masked APs (NAPs) are theoretically related to tuning curve quality, at least in a linear filter model. To test this relation both complete tuning curves and NAPs were determined in twenty cases. The results indicate that the theoretically supposed tinearity is too crude an assumption.
P21.06 ETHNIC VARIATIONS IN THE BRAIN-STEM AUDITORY EVOKED POTENTIAL (BAEP). C.T. Tan and N.M.F. Murray (London, UK)
(Athens, Greece An interesting factor influencing latency and amplitude of BAER's is the polarity of the sound wave i.e. stimulation with rarefaction (R) or condensation stimuli or alternation of these two. Fifty normal adults were examined with the 3 modes. The main finding was that R-pips produced, a higher percentage (more than 80%), of well-defined waves IV and V, whereas the other modes tended to elicit variable waves IV and V (in more than 40% of the cases). In a greater number of cases R-pips evoked better waves I-V, with shorter latencies than the other modes, but in some instances the alternating mode evoked better waves and this compromise was more advantageous with fewer stimulus-related artifacts and cochlear microphonics. Waves VI and VII were elicited, usually without any relationship with the mode used. The details of the trial are described and the possible reasons for the arising differences of the responses which arise are discussed.
P21.05 AUDITORY EVOKED POTENTIALS: T H E USE OF FREQUENCY SELECTIVE MASKING T E C H N I Q U E S IN COCHLEAR RESEARCH.
BAEPs were recorded in 10 male and 10 female ethnic Chinese (mean age 29.9 years for each sex) and 9 male and 9 female Caucasians (mean age 27.8 and 25.1 years respectively). BAEP components I to V were each of longer mean latency in Chinese subjects than in Caucasians: latency differences were small (1 0.02 msec, II 0.08 reset, 1II 0.08 reset, IV 0.18 msec and V 0.09 msec) and were statistically significant for waves II, llI, 1V and V (p < 0.05). There was no significant difference in the inter-potential intervals 1 V, I 11I and 1Ii V. Mean skull circumference was 1.9 cm greater in Caucasians. The BAEP differences between the 2 racial groups studied here are small, less than those between males and females of the same race, and the reason for this variation is uncertain: ethnic differences in skull shape (brachycephaly versus dolichocephaly) and myelin sheath thickness are possible contributory factors. When normative BAEP data are acquired the ethnic distribution of the population should be taken into account and the importance of using inter-potential intervals rather than absolute latencies is stressed.
14LL. C. Rutten
P21.07 POWER SPECTRAL ANALYSIS OF THE AVERAGED AUDITORY EVOKED POTENTIAL TO MONAURAL STIMULATION.
(Enschede, The Netherlands)
J. W. Jutai and J.H. Gruzelier
Cochlear hearing disability is characterized by two symptoms: internal attenuation of sound level ('hearing loss') and deterioration of frequency selectivity. The first aspect is expressed electrocochleographically (ECochG) by increased compound action potential (CAP) thresholds. The second aspect can be measured in ECochG by determining CAP tuning curves and CAP suppression areas. The following two questions 1) does AP tuning quality deteriorate with increasing hearing loss 2) is AP suppression correlated with hearing loss, were answered earlier (see for
(London, UK) In previous work we were able to demonstrate how power spectral analysis (PSA) of the visual evoked potential (VEP) might be useful in understanding the neurophysiology of the VEP, and in quantifying the VEP for various psychophysiological purposes (Jutai et al., Psychophysiol., 1984, 21: 665). Specifically, we suggested that certain frequency components of the VEP might be sensitive to phasic cortical desynchronization mediated by thalamic disinhibition. A preliminary study of
P21.04 BRAIN-STEM AUDITORY EVOKED POTENTIALS IN NORMAL ADULTS AFTER RAREFACTION, CONDENSATION AND ALTERNATING ACOUSTIC STIMULI. N. Monastiriotis. E. Koutra, A. Siafakas, B. Mantouvalos and C. Papageorgiou
example, Rutten and Kuper, Hearing Research 1982. 8; 157). One conclusion was that AP tuning deteriorates with increasing hearing loss. This led us to explore a faster method for obtaining information about frequency selectivity i.e. by measuring so-called 'derived responses'. These derived responses, or narrow band masked APs (NAPs) are theoretically related to tuning curve quality, at least in a linear filter model. To test this relation both complete tuning curves and NAPs were determined in twenty cases. The results indicate that the theoretically supposed tinearity is too crude an assumption.
P21.06 ETHNIC VARIATIONS IN THE BRAIN-STEM AUDITORY EVOKED POTENTIAL (BAEP). C.T. Tan and N.M.F. Murray (London, UK)
(Athens, Greece An interesting factor influencing latency and amplitude of BAER's is the polarity of the sound wave i.e. stimulation with rarefaction (R) or condensation stimuli or alternation of these two. Fifty normal adults were examined with the 3 modes. The main finding was that R-pips produced, a higher percentage (more than 80%), of well-defined waves IV and V, whereas the other modes tended to elicit variable waves IV and V (in more than 40% of the cases). In a greater number of cases R-pips evoked better waves I-V, with shorter latencies than the other modes, but in some instances the alternating mode evoked better waves and this compromise was more advantageous with fewer stimulus-related artifacts and cochlear microphonics. Waves VI and VII were elicited, usually without any relationship with the mode used. The details of the trial are described and the possible reasons for the arising differences of the responses which arise are discussed.
P21.05 AUDITORY EVOKED POTENTIALS: T H E USE OF FREQUENCY SELECTIVE MASKING T E C H N I Q U E S IN COCHLEAR RESEARCH.
BAEPs were recorded in 10 male and 10 female ethnic Chinese (mean age 29.9 years for each sex) and 9 male and 9 female Caucasians (mean age 27.8 and 25.1 years respectively). BAEP components I to V were each of longer mean latency in Chinese subjects than in Caucasians: latency differences were small (1 0.02 msec, II 0.08 reset, 1II 0.08 reset, IV 0.18 msec and V 0.09 msec) and were statistically significant for waves II, llI, 1V and V (p < 0.05). There was no significant difference in the inter-potential intervals 1 V, I 11I and 1Ii V. Mean skull circumference was 1.9 cm greater in Caucasians. The BAEP differences between the 2 racial groups studied here are small, less than those between males and females of the same race, and the reason for this variation is uncertain: ethnic differences in skull shape (brachycephaly versus dolichocephaly) and myelin sheath thickness are possible contributory factors. When normative BAEP data are acquired the ethnic distribution of the population should be taken into account and the importance of using inter-potential intervals rather than absolute latencies is stressed.
14LL. C. Rutten
P21.07 POWER SPECTRAL ANALYSIS OF THE AVERAGED AUDITORY EVOKED POTENTIAL TO MONAURAL STIMULATION.
(Enschede, The Netherlands)
J. W. Jutai and J.H. Gruzelier
Cochlear hearing disability is characterized by two symptoms: internal attenuation of sound level ('hearing loss') and deterioration of frequency selectivity. The first aspect is expressed electrocochleographically (ECochG) by increased compound action potential (CAP) thresholds. The second aspect can be measured in ECochG by determining CAP tuning curves and CAP suppression areas. The following two questions 1) does AP tuning quality deteriorate with increasing hearing loss 2) is AP suppression correlated with hearing loss, were answered earlier (see for
(London, UK) In previous work we were able to demonstrate how power spectral analysis (PSA) of the visual evoked potential (VEP) might be useful in understanding the neurophysiology of the VEP, and in quantifying the VEP for various psychophysiological purposes (Jutai et al., Psychophysiol., 1984, 21: 665). Specifically, we suggested that certain frequency components of the VEP might be sensitive to phasic cortical desynchronization mediated by thalamic disinhibition. A preliminary study of