Biomedical subjects

C M Mikami

Publications and source records attributed to C M Mikami.

5 recordsLinked to original sources

PubMed1996

Phase effects on the middle and late auditory evoked potentials.

A masking level difference (MLD) paradigm was used to investigate the presence of an electrophysiologic correlate of the psychoacoustic MLD in the middle and late auditory evoked potentials. In experiment 1, middle latency potentials were recorded in six normal-hearing young adults using vertex and temporal electrode montages. Tone bursts of 500 Hz presented in SoNo and Spi No conditions produced no threshold differences that were consistent with an MLD. In experiment 2, late latency potential (P2) thresholds to 500-Hz tone bursts under various phase conditions in noise were measured and compared to behavioral thresholds from the same stimuli. Ten subjects provided behavioral and P2 thresholds to SoNo, S pi No, So N pi S pi N pi, SmNo, and SmNm conditions. The rank order of behavioral and P2 thresholds and MLDs was consistent with previous literature on the behavioral MLD. Cortical contributions were confirmed as necessary for the production of the electrophysiologic MLD and, by analogy, the psychoacoustic MLD.

Adult↗

PubMed1995

Binaural phase effects in the auditory brainstem response.

This study investigated the possibility of a correlate of the masking level difference (MLD) in the auditory brainstem response (ABR), given that behavioral data indicate the brainstem origination of the MLD. Previous studies have reported MLD characteristics in the late auditory evoked potentials. In the present study, stimuli were presented in S(o)N(o) and S pi N(o) to female adults with normal hearing. In experiment 1, a binaural phasic difference potential (BPD) was derived by subtracting the suprathreshold ABRs to S(o)N(o) from S pi N(o) for tone pips of 500 to 4000 Hz. The magnitude of the BPD was inversely related to frequency. In experiment 2, thresholds to 500-Hz tone pips in S(o)N(o) and S pi N(o) were equal. In a case study of a subject with no behavioral MLD, the 500-Hz BPD was abnormal on one side, suggesting unilateral interruption of phase synchrony in the brain stem. Thus, the results of this study, in conjunction with previous studies on late potential correlates of the MLD, suggest that the ability to maintain phase information through the brain stem is necessary but not sufficient to generate the MLD.

Adult↗

PubMed1992

The late auditory evoked potential masking-level difference as a function of noise level.

The purpose of this study was to determine whether the masking-level difference (MLD) obtained with the late (P2) auditory evoked potentials has characteristics similar to those reported for the behavioral MLD with respect to the effects of noise level. Psychoacoustic studies have shown that the magnitude of the MLD increases as a function of the noise level. In the present study, P2 thresholds were measured in SoNo (signals and noise in phase at the ears) and S pi No (signals out of phase and noise in phase at the ears) conditions for noise levels of 0-60 dB pressure spectrum level (Lps). Subjects were 5 normal-hearing young adults. The difference in SoNo and S pi No thresholds, or the MLD, increased linearly as the noise levels increased through 60 dB Lps, whereas the behavioral MLD magnitude is reported to saturate at high noise levels. These results suggest that the late-potential MLD reflects characteristics similar to, but not identical with, those of the behavioral MLD.

Adult↗

PubMed1992

Effects of cochlear hearing loss on the ABR latencies to clicks and 1000 Hz tone pips.

High-frequency hearing losses can substantially confound the interpretation of click-evoked auditory brainstem responses (ABRs). One method proposed to circumvent the problem is to use frequency-specific tone pips to stimulate equivalent areas on the basilar membrane in normal and pathologic groups, or in both ears of asymmetrically impaired patients. This retrospective study investigated the ABRs to clicks and 1000-Hz tone pips from 90 asymmetrically impaired subjects with cochlear pathology. The 4000 Hz threshold significantly affected the wave V latencies from both clicks and tone pips for the most severely impaired subjects. The wave V latencies were highly correlated between ears for both stimuli, but the correlation was higher with the 1000-Hz tone pips. It was concluded that the use of 1000-Hz tone pips can supplement the interpretation of click-evoked ABRs, particularly in patients whose 2000- and/or 4000-Hz thresholds are worse than 75 dB HL.

Acoustic Stimulation↗

PubMedDate not supplied

Effects of noise bandwidth on the late-potential masking level difference.

The masking level difference (MLD) is a psychoacoustic phenomenon derived from the subtraction of S pi No thresholds (signals pi radians out of phase and noise in phase at the two ears) from SoNo thresholds (signals and noise in phase at the two ears). The purpose of this study was to determine if the MLD derived from the late components (P1, N1, P2, N2) of the auditory evoked potentials was a physiological correlate of the behavioral MLD. Subjects were 15 young adults with normal hearing. Comparisons were made between behavioral and late potential thresholds to 500 Hz stimuli in So and S pi conditions in quiet, and to 500 Hz stimuli in SoNo and S pi No conditions in narrow band (50 Hz) and wide band (600 Hz) noise. No significant differences were seen for behavioral or late-potential thresholds to So and S pi conditions. The S pi No thresholds was significantly lower than the SoNo threshold, yielding an MLD for both the behavioral and physiological responses. The magnitudes of both the behavioral and late-potential MLD were larger with the narrow band noise than with the wide band noise. Evidence, therefore, is provided that the late-potential MLD reflects similar processes as are responsible for the behavioral MLD.

Acoustic Stimulation↗