Subjects compared the pitches of two test-tones separated by a 2.5-second retention interval. A tone (A tone) of the same pitch as the first test-tone or a tone (B tone) of a little different pitch (+2% or 2%) from that test-tone was interpolated during the interval. B tone elicited N2b component of ERPs, a subcomponent of N200. Since N2b is considered to reflect the controlled processing (Näätänen and Picton, 1986), it is suggested that the storage process of pitch information is associated with the controlled processing. The recognition performance was more severely affected by B tone compared with A tone. B tone led exclusively the development of CNV on the left temporal area toward the second test-tone. Moreover, ERPs elicited by the test-tone were more negative after B tone than after A tone in a latency range from 300 to 500ms. This diffrences could be attributed to the search-related negativity. We could explain these results that pitch information was rehearsed in a short-term memory when the sensory storage was prevented.
The effects of lowered EEG vigilance under the continuous dark environment on the amount and the duration of slow wave sleep (Stage 3+4 : SWS) were examined on 7 male subjects (19-26y). Two of 7 subjects gave up the experiment, so that the data of those 2 subjects were omitted from present analysis. They lived alone for 72 h under the sound-proofed environment with no time cues and constant darkness, and their polygraphic recordings were monitored. Referential central (C3) and occipital (O1) EEGs were frequency-analyzed every 15 min for a duration of 61 s, when the C3 EEG was showing stage W (EEG waking). Peak analysis of power spectra in alpha band (8-13Hz) showed that the peak alpha frequency (frequency of the maximal peaks in alpha band) in the waking periods decreased from the first day of experiment to the end (mean 1.85Hz, SD 0.71Hz, range 1.0-3.0Hz). This decline of peak frequency was stepwise in each subject. The results of principal component analysis confirmed this tendency and the factor loading patterns well demonstrated the stepwise shift points of alpha peak. Then we divided the experiment periods in accordance with the peak shift points so as to equalize the level of EEG vigilance and gathered the sleep stage data in each of these periods. The results of this study showed that the level of EEG vigilance in the waking periods did not affect the amount of SWS, but the duration of SWS. The occurrence of fragmented SWS increased in parallel with the lowering EEG vigilance. We conclude that the appearance of SWS depends not simply on the quantity of waking period but the quality of the period.
This study examined the brain potentials associated with fixation pauses following saccadic eye movements during a target detection task. A random number (0-9) was presented at one of the three horizontal positions in random order on a CRT every 780 ms. Eight students were instructed to move their eyes to each stimulus and to detect a target number (10 %). EEGs and EOGs were recorded. EEGs time-locked to the onset of fixation pauses were averaged. The lambda potential with peak latency of about 100 ms appeared predominantly at the occiput, but it showed no definite difference between the target and non-target. In contrast, the parietal dominant positivity peaking at about 400 ms appeared to the fixations at the targets. The positive component was considered as P3 which had been reported in studies of ERPs. The results indicated that endogenous potentials were elicited by fixation pauses in the natural eye movement situation.