Tokuro Suzuki

Auditory Brain Stem Responses to Pure Tone Stimuli

The vertex-positive brain stem responses (BSR) to tone pips were recorded on 20 adult subjects with normal hearing. The overall frequency response of the amplifier system was 0.5 to 3000 Hz. No high-pass filter was used in the recording system. Tone pips at 500, 1000, 2000 and 4000 Hz with 2-cycle rise-decay times and one-cycle peak were delivered to the subjects at intervals of 75 msec. The BSR was detected in 53 to 73% of the tests at 10 dB SL and 89 to 100% at 20 dB SL. No significant difference was found in the response detectability between four test tones of 500 to 4000 Hz. Mean latency of the response as an inverse function of test frequency was proved to be linear and could be resolved into regression equations: y=4.56x+8.16 (10 dB SL), y=3.77x+7.76 (20 dB SL), y=2.81x+7.63 (30 dB SL), where y and x indicated a mean latency and one cycle duration of a test frequency, respectively. This result suggested that the responses were elicited through the regions on the basilar membrane proper to each nomi...

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.

Rise Time of Pure-Tone Stimuli in Brain Stem Response Audiometry

In order to identify the area of a pure tone stimulus effective for evoking the auditory brain stem response (ABR), the amplitude, latency and detectability of the response were measured as a function of stimulus rise time with a fixed onset slope of a linear-shaped envelope. The test was performed on 8 normal adults with 2- and 0.5 -kHz tone pips at various intensity levels from 50 to 15 dB HL. The ABR was elicited by the very early part of the stimulus, and the succeeding part had little effect in eliciting the response, if the initial part was intense enough to evoke the response. At lower intensity levels, where the initial part did not reach an intensity level sufficient to evoke a full size response, a limited period of the succeeding part participated in evoking the response. The effective duration of the stimulus was estimated at 1.5 ms for 2 kHz and at 3 ms for 0.5 kHz. From these results, the authors propose that acceptable rise times of pure-tone stimuli for brain stem response audiometry are 3, 2, 1.5 and 1 ms for tone pips of 0.5, 1, 2 and 4 kHz, respectively.

Power Spectral Analysis of Auditory Brain Stem Responses to Pure Tone Stimuli

Power spectral analysis and digital filtration of the auditory brain stem responses to tone burst stimuli were carried out in three adult subjects with normal hearing. Three dominant peaks (peaks A. B, C), ranging in frequency 50-150, 500-600, and 1000-1100 Hz, were observed in the spectrograms of the responses to 4 kHz at 80 dB SL. Power of higher frequency components (peaks B and C) decreased markedly or disappeared completely with decreased intensity as well as decreased frequency of stimulus, while peak A around 100 Hz consistently appeared regardless of stimulus intensity or frequency. Main spectral components of the individual waves in the ABR were determined as follows: peak A for the slow positive deflection in the response, peak B for waves VI and VII, peak C for waves II and IV, and peaks B and C for waves I, III and V.

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...

Age-Related Morphological Changes in Auditory Middle-Latency Response

Age-related changes in the waveforms of the middle latency response (MLR) were investigated in 9 adults and 28 children aged between 4 and 14 years. The children were classified into three groups according to their age. For obtaining characteristic configurations in the responses for each group, composite group averaging was performed by summating the individual recordings in each group. With high-pass digital filtering at 20 Hz, composite MLR for adults showed a well-defined Na-Pa-Nb-Pb complex with peak latencies at about 17, 30, 45 and 63 ms, respectively. The composite response for children aged 4-7 years was characterized by a broad positive deflection (Pa) followed by a negative peak (Nb) at about 40 and 60 ms after stimulus onset, respectively. The peak latency of Pa was close to the adult value in the composite MLR for subjects aged 8-11 years, while the complete adult pattern in the later part of the response was not reached even in the composite response for subjects aged 12-14 years.

Effect of high-pass filter on auditory brain stem responses to tone pips.

The effect of high-pass filters on the vertex-positive brain stem response to tone pips at 500, 1000, 2000 and 4000 Hz was investigated in normal adults. The tape-recorded responses were averaged through high pass filters with 3 dB attenuation at 50, 100 and 200 Hz and with a slope of 6 dB/oct, and their amplitudes were compared with those of the averaged responses without filtering. These 3 filters reduced the amplitudes of the responses to 500-Hz tone pips by 3.3, 7.1 and 10.6 dB respectively. On the other hand, the mean attenuations caused by the same series of filters on the response amplitudes at 2000 Hz were only 0.2, 2.9 and 5.4 dB respectively. The responses at 4000 Hz were similar to those at 2000 Hz. This distinct difference in the effect of the high-pass filters suggests that the dominant frequency component of the brain stem response at 500 Hz is significantly lower than that at 2000 Hz and above. The results indicate that the use of a high-pass filter with cutoff frequency over 50 Hz is not recommended for recording the slow positive deflection of the brain stem response to low frequency tones.

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.