Purpose. To examine the temporal dynamics of light adaptation, we varied the duration of flicker before and after the probe in a probe-sinewave task.
Methods. A trial in the task proceeded as follows: the background flickered at either 1 or 8 Hz for x seconds, followed by one cycle of flicker during which a 13-msec probe was superimposed on the background, followed by y seconds of flicker. The durations of x and y were varied. The temporal position of the probe within the cycle of background flicker was randomly chosen to be at one of 8 phases (see panel A). The probe was a 1.5-degree circle centered on a 10-degree background (both had blurred edges). The subject pressed a key to indicate that s/he had or had not seen the probe. The intensity of the probe was adjusted using a QUEST routine. Intensities were in the photopic range.
Results. (i) With continuous flickering of the background (x and y effectively inf.), typical results look like the data in panels B & C. (ii) If y is set to 0 (and x effectively inf.), the results do not change. (iii) If x is set to 0 (and y effectively inf.) the results change: in the case of an 8 Hz background, probe threshold in the first (and sometimes second) phase is substantially less elevated (than in case (i)); in the case of a 1 Hz background, thresholds are nearly identical to those in case (i). (iv) If x and y are set to 0, the results are the same as in case (iii).
Conclusions. Adaptation to a flickering background is very fast. We computed predictions using Wilson's model of light adaptation [Wilson (1997) Vis Neurosci, 15, 403-423; Hood & Graham (1998) Vis Neurosci, 15, 957-967]. These predictions capture the fast adaptation, although other features of the data remain to be explained.
None. Supported by NIH grant EY08459.