Effects of flicker modulation depth on the detection of changes in target location.

Response times to a change in location of a small, low contrast target in a uniform flickering field were investigated under a range of flicker modulation depths. Increasing depth of modulation gave an increased response time for modulation depths from 0% (no flicker, to approx. 35%. Further increases in modulation depth had only a marginal effect on response time. It is shown that this effect is not due to flicker adaptation. The functional form of the modulation dependence is qualitatively similar to that reported by Badcock and Smith (1989, Vision Research, 29, 803-808), but shows a large difference in the modulation at which a levelling of performance occurred. It is shown that this difference is consistent with the presence of a third temporal filter, as proposed by Mandler and Makous (1984, Vision Research, 24, 1881-1887).

Detecting target shifts under uniform field flicker.

An experiment was performed in which a small target, viewed foveally, underwent 1 degree lateral shifts at quasi-random intervals. Subjects' response latency to the shift was investigated under various square-wave flicker conditions and compared to non-flickering conditions. Flicker was found to raise latencies, the effect peaking between 8 and 14 Hz. Under constant luminance difference between target and background the high target contrast phase was found to dominate the response cueing. The results are discussed in terms of a simple model of cumulative signal strength and adaptation processes.