Kiyoko Kobayashi

An Evaluation of 40-Hz Event-Related Potentials in Young Children

In order to investigate the clinical utility of the 40-Hz event-related potential (40-Hz ERP) for young children, the effects of stimulus rate on the amplitude of the auditory brain stem response-Na deflection were compared between adults and young children. A prominent increase in the amplitude was observed in the adult subjects with stimulus rates of 35 and 40/s. On the contrary, no amplitude increment was found in the responses from young children at these stimulus rates. The mean amplitude of the responses from young children tended to decrease at stimulus rates above 30/s. These results show that precautions must be taken in the clinical application of 40-Hz ERP to infants and young children.

Effects of stimulus repetition rate on slow and fast components of auditory brain-stem responses

Effects of stimulus repetition rate on the slow and fast components of the auditory brain-stem response (ABR) were investigated in 10 adult subjects with normal hearing. The ABRs were recorded with click stimuli at repetition rates of 8, 13.3, 23.8, 40 and 90.9/sec and at an intensity level of 55 dB nHL. Power spectral analysis of the averaged responses was performed. Then the responses were divided into a slow component (0-400 Hz) and a fast component (400-1500 Hz) by using digital filtering technique. The magnitude of the slow component was little affected with increasing stimulus rate from 8/sec to 90.9/sec, while successive waves of the fast component, including wave V, decreased in amplitude as stimulus rate was increased. The latency of the slow component and each wave of the fast component was prolonged with increasing click rates. The shift of latency became longer in the later waves than in the earlier waves.

Frequency Composition of Auditory Middle Responses

Power spectral analysis and digital filtration were performed on the auditory middle responses (AMR) to click stimuli in six subjects with normal hearing. The spectral analysis revealed that the main power of the AMR was located at frequencies between 30 and 50 Hz with a peak at 40 Hz. A small elevation of power observed in the spectrum between 90 and 180 Hz was considered to be due to the ABR and the earliest part of the AMR. Typical AMR components, namely Na, Pa, Nb and Pb, were constantly recognised with digital high-pass (HP) filtration at 30 Hz. With increasing cut-off frequencies up to 50 Hz, the peak latencies of Na and Pa remained unchanged, while their magnitudes markedly decreased. On the other hand, Pb completely disappeared with 40 Hz filtration, forming two distinct positive peaks at about 55 and 80 ms after the stimulus onset. In some cases, three small positive peaks were seen following Pa with HP filtration at 50 Hz. With 60 Hz HP filtration, main components of the AMR substantially disapp...

Auditory middle responses in young children.

In order to ascertain if any substantial difference exists in the auditory middle responses (AMR) between adults and young children, a digital high-pass (HP) filtering technique was applied to the responses in 26 young children aged 1-7 years and nine adults with normal hearing. Two significant differences were found between the HP-filtered responses in children and those in adults. Pa in the responses from adults was consistently recognized with HP filtering up to 50 Hz, while Pa in young children was effectively detected only with 20 Hz HP filtering. It was mostly eliminated when the HP filter was set at 30 or 40 Hz. Pb was identified in most of the adult responses, particularly with HP filtering at 30 Hz. On the other hand, it was not visually distinguished in the responses from young children with any HP filter setting.

Effect of Natural Sleep on Auditory Steady State Responses in Adult Subjects with Normal Hearing

Auditory 40-Hz steady state response (SSR), auditory brainstem response (ABR), and middle-latency response (MLR) were recorded in 12 healthy adult females with normal hearing while awake and asleep. The responses were recorded with 500-Hz tone pips at 55 dBnHL. Synthesized SSR were made by superimposing the recorded ABR and MLR waveforms (ABR-MLR), and their amplitudes were compared with those of the actually recorded SSR. In the waking state, the ratio of the mean amplitude of recorded SSR to that of synthesized SSR was 0.819, whereas in the sleeping state it decreased to 0.522, a statistically significant difference. The results indicate that the SSR can be predicted from the linear superimposition of ABR and MLR in the waking state, but not in the sleeping state.

Effects of Analog and Digital Filtering on Auditory Middle Latency Responses in Adults and Young Children

Effects of analog high pass (HP) filtering were compared with those of zero phase-shift digital filtering on the auditory middle latency responses (MLR) from nine adults and 16 young children with normal hearing. Analog HP filtering exerted several prominent effects on the MLR waveforms in both adults and young children, such as suppression of Po (ABR), enhancement of Nb, enhancement or emergence of Pb, and latency decrements for Pa and the later components. Analog HP filtering at 20 Hz produced more pronounced waveform distortions in the responses from young children than from adults. Much greater latency decrements for Pa and Nb were observed for young children than for adults in the analog HP-filtered responses at 20 Hz. A large positive peak (Pb) emerged at about 65 ms after the stimulus onset. From these results, the use of digital HP filtering at 20 Hz is strongly recommended for obtaining unbiased and stable MLR in young children.

Effect of tone-burst frequency on fast and slow components of auditory brain-stem response.

By means of digital filtering, averaged auditory brain-stem responses (ABR) were divided into slow and fast components with frequency compositions of 50-300 Hz and 400-1 500 Hz, respectively, and the relation of the two components to stimulus frequency was investigated. Tone bursts with a rise-decay time of two periods of the chosen frequency with no plateau (2-0-2) and with a 4 ms rise-decay time with no plateau (8 ms duration) were used as acoustic stimuli. Tone-burst frequencies were 0.5, 1, 2, 4 and 8 kHz at an intensity level of 40 dB nHL. The amplitude ratio of wave V of the fast component to the slow component decreased with decreasing stimulus frequency, and it remained almost unchanged at each stimulus frequency regardless of the rise-decay time of the stimuli. From these results, it became clear that the frequently-mentioned audiometric difficulties for lower frequency stimuli in ABR testing are related mainly to the low amplitude of the fast component for the frequency range below 1.0 kHz. The slow component, with relatively large amplitude for the low-frequency stimuli, is regarded as the most useful index in the ABR for threshold estimation of hearing.

Auditory brainstem response (ABR) to tone pips in hearing-impaired children.

The correspondence between ABR thresholds to tone pips and behavioral thresholds at 500, 1000 and 2000 Hz was studied in 13 normal and 55 hearing-impaired children, including 42 sensori-neural losses and 13 conductive losses. The childrens ages ranged from 1 year 3 months to 8 years. Tone pips were provided with 2-cycle rise-fall times and 2-cycle plateaus. The correlations between the two measures were highly significant at 3 frequencies both in sensori-neural losses and conductive losses. In the subjects with sensori-neural losses, the ABR thresholds tended to be lower than the behavioral thresholds. Mean threshold differences between the ABR and behavioral audiometry at each frequency in sensori-neural losses were 1.6, 0.26 and 5.8 dB, respectively. On the other hand, in the subjects with conductive losses, the ABR thresholds were higher than the behavioral ones by 9.6, 7.8 and 7.5 dB at respective frequencies. Therefore, the hearing acuity in young children with sensori-neural losses can be predicted with accuracy from the ABR thresholds to tone-pips at 500, 1000 and 2000 Hz.

Effect of Sleep on Binaural Interaction in Human Auditory Evoked Potentials

Binaural interaction (BI) in ABR, MLR and two kinds of 40-Hz steady-state responses (SSRs) were measured in the waking and sleeping states in normal adults. Eleven samples each were collected from 20 subjects. The ABR and MLR were elicited with 500-Hz tone pips. The SSRs were elicited with the same tone pips (pipSSR) or sinusoidally amplitude-modulated tones of the same frequency (samSSR). The amplitude differences between the summed monaural and binaural responses relative to the summed monaural responses were referred to as BI. ANOVA showed that the mean BI in the responses tested was significantly lower (p < 0.005) in the sleeping state than in the waking state. Ad hoc analysis revealed that the significant difference (p < 0.05) in BI between the waking and sleeping states occurred in the pipSSR and samSSR. The BI became larger in the order, ABR, samSSR, pipSSR, MLR, in both the waking and sleeping states. Significant differences (p < 0.05) were detected in the BI during sleep between the MLR and each of the other three responses, whereas in the waking state no significant difference was found between the MLR and tone-pip SSR.

The postauricular myogenic response in normal children and children with microtia

SummaryThe effect of the development of postauricular muscles on the postauricular myogenic response (PAR) was investigated in normal children and children with microtia. There were no differences between the PAR of normal children and that of the intact ear of children with microtia. The PAR obtained from the normal and microtic sides of children with unilateral microtia showed no significant differences as regards waveform, latency, threshold, or amplitude. Our findings suggest that the development of the postauricular muscle does not affect the PAR, and it seems difficult to explain the large individual variations in the PAR by intersubjective differences in muscle development.