In the present study the perceptual discrimination threshold (DT) was estimated using a VEP method. At first, to examine the relationship between perceptual judgment and VEPs, 8 subjects of 18 to 22 years old were presented with single and double flashes (the luminosity of a flash was 40 cd/m²). The double-flash interval was varied from DT-20 to DT+20 ms by 10ms steps based on each subject's DT. The VEPs of single-and double-flash were recorded from the occipital area (Oz), and analyzed with “EDAS-software program.” The component of the double-flash VEP to the second stimulus was estimated from the latency of P₂ component (about 100ms) or N₂ component (about 150ms) of the single flash VEP. It was observed that the latency of P₂ component or N₂ component of the double-flash VEP to the second stimulus nearly coincided with the P₂ or N₂ latency of the single flash VEP only when the interstimulus interval (ISI) was longer than the DT. Next, the waves created from summation of the single-flash VEP and the same VEP by DT-20 to DT+20ms delays correlated highly with those of the corresponding actual double-flash VEP. Because of this high degree of similarity in the waveform, double-flash model VEPs were made through summation of the single-flash VEP and the same VEP by 30 to 100ms delays in 10ms steps. It was found that the waves of the double-flash model VEPs to the second flash correlated highly with those of single-flash VEPs only when the ISI used for making the model VEPs was equal to or longer than the DT. These results suggest that the perceptual discrimina-tion threshold of double flashes is estimated by the double-flash VEP models created from the single-flash VEPs.

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Many profoundly retarded persons (PRs) show weak responsive behaviors to auditory and visual stimuli. The present study aimed to examine activating effects of vestibular-proprioceptive stimulus which influence responses of PRs to the calls of subject's name. Subjects were 19 PRs (CA, 2 : 9-22 : 11, DA, 0 : 2-1 : 5). As a vestibular-proprioceptive stimulus, the eccentric pendular rotating movement was used (Fig. 1). According to the appearance of eye movements during the rotation of the head, PRs were classified into 4 groups (Fig. 3); 5 PRs who showed compensatory eye movement (Group I), 2 PRs who showed transient eye movement (Group II), 7 PRs who did not show any relationship between eye movements and head positions (Group III), and 5 PRs with no eye movement (Group IV). In 5 out of 7 subjects of Groups I and II, behaviors of turning head as well as smiling toward the source of calling names were observed clearly after vestibular-proprioceptive stimulation (Fig. 5). It was pointed out that a vestibular-proprioceptive stimulus has some effect which activates orienting and exploring responses in PRs.

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In Japan, there is a set of experiences called kanashibari, which is symptomatically identical to sleep paralysis with or without hypnagogic hallucinations. In a former study (Fukuda et al., 1987a), the author and co-workers have investigated this phenomenon by a questionnaire method and have found that among the normal population the phenomenon is apparently more common than has been usually appreciated. The author conducted this study to confirm the coincidence between kanashibari and sleep paralysis polygraphically, and then to investigate the characteristics of sleep onset REM periods (SOREMPs) with the kanashibari phenomenon. The two subjects with frequent experiences of kanashibari and the other two subjects without the experience slept under an altered sleep schedule. The schedule, which consisted of reversal of usual sleep-wakefulness cycle and sleep interruption. One of the subjects reported that she had been about to have a kanashibari attack during the experiment. During the REM sleep, when the subject was probably about to experience kanashibari, abundant alpha EEG and an elevated heart rate were observed. The author suggests the relations between a higher consciousness level in kanashibari and the abundant alpha EEG, and between emotional components of the phenomenon and the increased heart rate.

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A microcomputer-based system for the recording and analysis of the auditory evoked potentials (AEPs) was developed. A software system consists of three parts. (1) Measurement of the AEPs : By the use of the A/D converter with DMA interface and the D/A converter with internal clock, the AEPs are recorded while acoustic stimuli are being presented. The AEPs are averaged in realtime and the waveform is displayed on the CRT with every presentation of acoustic stimuli. (2) Off-line data analysis : One can measure the values of response amplitude and latency at two vertical cursors on the averaged AEP waveform which is displayed on the CRT. A waveform difference between two averaged AEP waveforms is calculated and listed to a file. (3) Topographic disply : Interpolation is carried out by means of the two-variable sampling function. The interpolated values are quantized to 11 levels. The potential distributions are graphically displayed on the CRT. We have confirmed that the system is useful in the analysis of the AEPs of the Mynah bird.

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