中川 誠司

To investigate human brain responses that correspond to annoyance of bandpass noise, magnetoencephalographic (MEG) measurements and analyses by autocorrelation function (ACF) and cross-correlation function (CCF) were carried out. MEG is a noninvasive technique for investigating neuronal activity in the living human brain. The center frequency of the bandpass noise was 1000 Hz and the bandwidth was varied at five levels (0, 40, 80, 160, and 320 Hz). All stimuli were fixed at the same sound pressure level (74 dBA). The duration of the stimulus was 2.0 s. The scale values of annoyance of each subject were obtained by the paired-comparison tests. In MEG measurements, combinations of a reference stimulus (pure tone) and test stimuli (bandpass noise) were presented alternately 30 times at a constant 2 s interstimulus interval. The magnetic responses induced by the stimuli were recorded and analyzed by the ACF and the CCF. The results showed that the effective duration of the ACF, τ e , of 8-13 Hz range, representing repetitive features within the signal itself, becomes shorter and maximum value of the CCF, |φ(τ)| max , of 8-13 Hz range, representing the degree of similar repetitive features recorded at two different channels, becomes smaller during presentations of annoying stimulus. It is considered that the shorter τ e and smaller |φ(τ)| max indicate that the brain is unstable under annoying conditions.

Auditory sensation is affected by a forward masker, and this phenomenon has been demonstrated in a neural adaptation model and a temporal window (integration) model. To study forward masking in the central auditory system, the growth of the N1m amplitude was measured by varying the signal delay. In the adaptation model, the masking increases as the signal delay decreases. However, in our results, the minimum N1m amplitude was observed at a signal delay of 40 ms. As the signal delay decreased from 40 ms, the N1m amplitude increased although the masking increased. Our results suggest that the growth of the N1m amplitude largely depends on temporal integration at signal delays below 40 ms.

真空圧密工法は,バーチカルドレーンが打設された軟弱地盤を気密シートで覆い,真空圧を作用させて圧密促進を図る工法である。最近,全国的に軟弱地盤対策工として採用されるケースが増加しており,その有用性が数多く報告されている。しかし,そのメカニズムの解明と地盤の変形挙動の予測が課題として指摘されている。本報告は,軟弱粘土の弾粘塑性モデルを用いた土・水連成圧密解析法により真空圧密工法を採用した改良地盤の圧密解析を行い,真空載荷時の応力経路挙動について考察している。

Recent studies on noninvasive recordings from human brain have shown the existence of taste-elicited activation areas in the cerebral cortex. While functional MRI (f-MRI) and positron CT (PET) are often used for these studies, the magnetoencephalogram (MEG) is the most commonly used instrument for these noninvasive measurements. One advantage of the MEG measurements is the ability to measure rapid taste-elicited time-course data. In this current study, we used brain magnetic fields to quantitate the stimulus latencies evoked by different taste stimuli that use different peripheral transduction mechanisms. Recent work has shown that taste stimuli that presumably act through different transduction processes show different MEG-measured latencies. Here, we measured the latencies due to citric acid and sucrose and compared these with the latency due to the action of the taste-modifying substance contained in miracle fruit during stimulation by citric acid. Miracle fruit has the property of changing the sour taste of acids to sweet taste. The use of this taste-modifying substance allows us to compare the latency of two very different sweet-taste-evoking substances. © 2002 Elsevier Science B.V.

To investigate human cortical responses that correspond to subjective preference of sound fields, an attempt is made here to analyze the autocorrelation function (ACF) of magnetoencephalography (MEG) under the condition of varying delay time of single reflections. According to previous studies, it is assumed that a similar repetitive feature of the MEG alpha-waves range (8-13 Hz) is related to subjective preference in terms of the effective duration of the ACF. The source signal was the word "piano" which had a 0-35 s duration. The delay time, Δtl, was varied at five levels (0, 5, 20, 60, and 100ms). The scale values of the subjective preference of each subject were obtained by the paired-comparison tests. To compare the results of the MEG measurements with the scale values of the subjective preference, combinations of a reference stimulus (Δtl=0ms) and test stimuli (Δtl=0, 5, 20, 60, and 100ms) were presented alternately 50 times, and the MEGs were analyzed. It is found that subjective preference for each individual and the effective duration of the ACF of the MEG alpha waves are linearly related. © 2002 Elsevier Science Ltd. All rights reserved.