Fig. 5. Effect of time of day under natural laboratory light on root-mean-square voltage (Vrms) values (mean ± S.D. of 200 ms following the due-time of the first missing flash) at different times of the day. Values are averages of 5 days of recordings and show the diurnal fluctuation. After basal (spontaneous) values of approximately 300 µV, there is a clear increase in Vrms during daylight hours (06:00–18:00 h) with a return to basal levels after 20:00 h. A comparison with the light intensity values (shown in lx) in the experimental room averaging the same 5 days of recording (thin line) shows the extreme non-correspondence between omitted stimulus potential (OSP) and prevailing light. The skewness of the room light is due to the sun shining through the window near sunset.
