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Yoshiharu Soeta

Publications and source records attributed to Yoshiharu Soeta.

15 recordsLinked to original sources
PubMed2006

Complex tone processing and critical band in the human auditory cortex.

Psychophysical experiments in humans have indicated that the auditory system has a well-defined bandwidth for resolution of complex stimuli. This bandwidth is known as the critical bandwidth (CBW). Physiological correlates of the CBW were examined in the human auditory cortex. Two- and three-tone complexes were used as the sound stimuli with all signals presented at 55 dB sound pressure level (SPL). The duration of stimulation was 500 ms, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory-evoked fields were recorded using a 122-channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths, and coordinates of the N1m waves, which were found above the left and right temporal lobes approximately 100 ms after the onset of stimulation, were analyzed. The results indicated that N1m amplitudes were approximately constant when the frequency separation of a two-tone complex or the total bandwidth of a three-tone complex was less than the CBW; however, the N1m amplitudes increased with increasing frequency separation or total bandwidth when these were greater than the CBW. These findings indicate critical band-like behavior in the human auditory cortex. The N1m amplitudes in the right hemisphere were significantly greater than those in the left hemisphere, which may reflect a right-hemispheric dominance in the processing of tonal stimuli.

Acoustic Stimulation↗
PubMed2006

Auditory evoked magnetic fields in relation to interaural time delay and interaural correlation.

The detection of interaural time differences (ITD) for sound localization depends on the similarity between the left and right ear signals, namely interaural correlation (IAC). Human localization performance deteriorates with decreasing IACs. In order to examine activity related to localization performance in the human cortex, auditory evoked magnetic fields to the ITD of bandpass noises with different IACs were analyzed. When the IAC was 0.95, the N1m amplitudes, i.e., the estimated equivalent current dipole moments, increased with increasing ITD. However the effect of ITD on the N1m amplitudes was not significant when the IAC was 0.5. When the ITD was 0.7 ms, the N1m amplitudes decreased with decreasing IACs. There were no systematic changes in the source location of N1m in the auditory cortex related to changes in ITD or IAC. The results suggest that localization performance is reflected in N1m amplitudes.

Acoustic Stimulation↗
PubMed2006

The effect of center frequency and bandwidth on the auditory evoked magnetic field.

Auditory evoked magnetic fields in relation to the center frequency of sound with a certain bandwidth were examined by magnetoencephalography (MEG). Octave band, 1/3 octave band, and 130 Hz bandwidth noises were used as the sound stimuli. All signals were presented at 60 dB SPL. The stimulus duration was 500 ms, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The latencies, source strengths and coordinates of the N1m wave, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, were analyzed. The results demonstrated that the middle frequency range had shorter N1m latencies and larger N1m amplitudes, and that the lower and higher frequency stimuli had relatively delayed N1m latencies and decreased N1m amplitudes. The N1m amplitudes correlated well to the loudness values in the frequency ranges between 250 and 2000 Hz. The source locations of N1m did not reveal any systematic changes related to the center frequency and bandwidth.

Acoustic Stimulation↗
PubMed2006

Effects of the frequency of interaural time difference in the human brain.

The two cues to the horizontal location sound sources are interaural time differences and interaural level differences. For low-frequency tones, interaural time differences provide effective and unambiguous information. For higher frequency sounds, however, interaural time differences provide ambiguous cues. In order to evaluate the effect of frequency of interaural time differences in the human auditory cortex, the auditory evoked fields to different interaural time differences of pure tone were examined. The results showed that the N1m magnitudes varied with the interaural time differences when the frequency of the pure tone was 800 Hz. The N1m magnitudes, however, did not vary with the interaural time differences when the frequency of the pure tone was 1600 Hz. These results indicate that localization performance might be reflected in N1m magnitudes.

Acoustic Stimulation↗
PubMed2005

Effects of the critical band on auditory-evoked magnetic fields.

Changes in the bandwidth affect the perceived loudness of a stimulus even when the level of the stimulus remains fixed. If the bandwidth of a sound is varied while maintaining the overall intensity, the loudness remains constant as long as the bandwidth is less than the critical bandwidth. If the bandwidth is increased beyond the critical bandwidth, the loudness increases with increasing bandwidth. Human cortical responses as a function of stimulus bandwidth were examined by recording auditory-evoked magnetic fields. The results showed that the N1m magnitudes, that is, the estimated equivalent current dipole moments, increased with increasing bandwidth when the bandwidth was increased beyond the critical bandwidth.

Acoustic Stimulation↗
PubMed2005

Auditory evoked fields to variations of interaural time delay.

Auditory motion can be simulated by presenting binaural sounds with time-varying interaural time delays. Human cortical responses to the rate of auditory motion were studied by recording auditory evoked magnetic fields with a 122-channel whole-head magnetometer. Auditory motion from central to right and then to central was produced by varying interaural time differences between ears. The results showed that the N1m latencies and amplitudes were not affected by the fluctuation of interaural time delay; however, the peak amplitude of P2m significantly increased as a function of fluctuation of the interaural time delay.

Acoustic Stimulation↗
PubMed2005

Auditory evoked magnetic fields in relation to bandwidth variations of bandpass noise.

Auditory evoked magnetic fields in relation to the bandwidth of bandpass noise were examined by magnetoencephalography (MEG). Pure tone and bandpass noises with center frequencies of 500, 1000 or 2000 Hz were used as the auditory signals. All source signals had the sound pressure level set at 74 dB. The stimulus duration was 0.5 s, with rise and fall ramps of 10 ms. Eight volunteers with normal hearing took part in the study. Auditory evoked fields were recorded using a neuromagnetometer in a magnetically-shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, decreased with increasing bandwidth of the bandpass noise. The latency and estimated equivalent current dipole (ECD) locations of N1m did not show any systematic variation as a function of the bandwidth for any of the center frequencies.

Acoustic Stimulation↗
PubMed2005

Auditory evoked magnetic fields in relation to iterated rippled noise.

Auditory evoked magnetic fields in relation to iterated rippled noise (IRN) were examined by magnetoencephalography (MEG). IRN was used as the sound stimulus to control the peak amplitude of the autocorrelation function of the sound. The IRN was produced by a delay-and-add algorithm applied to bandpass noise that was filtered using fourth-order Butterworth filters between 400-2200 Hz. All sound signals had the same sound pressure level. The stimulus duration was 0.5 s, with rise and fall ramps of 10 ms. Ten normal-hearing subjects took part in the study. Auditory evoked fields were recorded using a 122 channel whole-head magnetometer in a magnetically shielded room. The results showed that the peak amplitude of N1m, which was found above the left and right temporal lobes around 100 ms after the stimulus onset, increased with increase in the number of iterations of the IRN. The latency and estimated equivalent current dipole (ECD) locations of N1m did not show any systematic variation as a function of the number of iterations.

Acoustic Stimulation↗
PubMed2005

Effects of the degree of fluctuation on subjective preference for a 1 Hz flickering light.

Humans are believed to have a preferred amount of stimulus variation in their perceptual environment. Here, paired comparison tests were conducted to examine whether the fluctuation of a flickering light improves subjective preference. Sine-wave and bandpass noise acted as the light source. We have previously shown that the preferred temporal frequency of a flickering light without any fluctuation is approximately 1 Hz (Soeta et al 2002 Journal of the Optical Society of America A 19 289 - 294). This was used as the center frequency of the light source. The bandwidth was set at 1, 2, 4, 8, and 16 Hz, to control the amplitude of the first peak of the autocorrelation function, phi1. Results show that the preferred phi1 of a flickering light is 0.46.

Adult↗
PubMed2005

The optimal method for recording prosthetic heart valve sounds in clinical situations.

BACKGROUND: Valve sounds are thought to be useful in evaluating the functioning of prosthetic heart valves. In previous reports, two recording instruments have mainly been used, a condenser microphone (instrument A) and an accelerometer (instrument B), respectively. This study aimed to investigate the applicability of these conventional devices in recording mechanical heart valve sounds in daily clinical situations. In addition, two other instruments, namely, a stethoscope including a small microphone in its tube (instrument C) and an electrostethoscope (instrument D), were proposed and examined. METHODS: Mechanical valve sounds were recorded from postoperative patients using each-device and the signal to noise ratio (SNR) of each was calculated. Frequency characteristics of the two newly proposed instruments were also investigated by recording a sweep signal in an anechoic chamber. RESULTS: The SNR values of the new instruments were significantly superior to those of conventional ones (A, sound signals were not defined from noises; B, 0.97 +/- 0.59 dB; C, 11.5 +/- 4.7 dB; and D, 9.4 +/- 3.5 dB, respectively p<0.05). The frequency characteristics of the two newly proposed instruments were also shown to be acceptable (under 10 kHz), though resonance frequency peaks were observed. CONCLUSIONS: Two newly proposed instruments can record mechanical heart valve sounds more noiselessly and with more ease than previous ones, and their frequency characteristics are acceptable.

Acoustics↗
PubMed2004

Auditory evoked magnetic fields in relation to interaural cross-correlation of band-pass noise.

Auditory evoked magnetic fields of the human brain were analyzed in relation to the magnitude of the inter-aural cross-correlation (IACC). IACC of the stimuli was controlled by mixing diotic bandpass and dichotic independent bandpass noise in appropriate ratios. The auditory stimuli were binaurally delivered through plastic tubes and earpieces inserted into ear canals of the nine volunteers with normal hearing who took part in this study. All source signals had the same sound pressure level. Auditory evoked fields (AEFs) were recorded using a neuromagnetometer in a magnetically shielded room. Combinations of a reference stimulus (IACC=1.0) and test stimuli (IACC=0.2, 0.6, 0.85) were presented alternately at a constant interstimulus interval of 0.5 s and MEGs recorded. The results showed that the N1m latencies were not affected by IACC; however, the peak amplitude of N1m significantly decreased with increasing IACC.

Acoustic Stimulation↗
PubMed2002

Autocorrelation analyses of magnetoencephalographic alpha waves in relation to subjective preference for a flickering light.

Human cortical responses corresponding to the subjective preference for a flickering light of varying period were investigated. Paired-comparison tests were performed to examine the subjective preference for a flickering light, and MEG was recorded during presentations of the most preferred and less preferred flickering lights alternately. Results showed that the effective duration of the autocorrelation function, tau(e), which represents a repetitive feature of the MEG alpha waves, becomes longer during the preferred condition. This reveals that the brain repeats a similar rhythm under preferred conditions.

Adult↗
PubMed2002

Propagation of repetitive alpha waves over the scalp in relation to subjective preferences for a flickering light.

Paired-comparison tests were performed to examine subjective preferences for a flickering light. Electroencephalograms were then recorded from seven electrodes (10-20 system) during presentations of the most and least preferred flickering-light conditions. As a way of investigating the flow of alpha waves on the scalp over both the left and right hemispheres in relation to subjective preference, the alpha waves were analyzed by means of the cross-correlation function (CCF). The maximum value of the CCF, /phi(tau)/(max), between the alpha waves measured at different electrodes and its delay time, tau(m), were analyzed. Results show that the most preferred flickering light has a significant larger /phi(tau)/(max) than the least preferred flickering light, and that /phi(tau)/(max) decreases with increasing distance between comparison (O(1) or O(2)) and test electrodes. On the other hand, the delay time of the maximum value of the CCF, tau(m), increases with the distance between comparison and test electrodes.

Adult↗
PubMed2002

Relationship between subjective preference and alpha-wave activity in relation to temporal frequency and mean luminance of a flickering light.

Human cortical responses corresponding to the subjective preference for a flickering light under varying temporal frequency and mean luminance were investigated. Paired-comparison tests were performed to examine the subjective preference for a flickering light, and electroencephalograms (EEGs) were recorded from six electrodes (10-20 International Electrode Placement System) during presentations of the most-preferred and least-preferred flickering lights. The results showed a positive correlation between subjective preference and the effective duration of the autocorrelation function of the alpha waves measured at the visual cortex (O1 and O2 electrodes).

Adult↗