Abstract

Vernier acuity for abutting stimuli is almost independent of exposure duration providing the target remains equally visible i.e. if the effect of time on detection is accounted for (Hadani et al., 1984; Waugh and Levi, ARVO 1990). Recently Watt¹ reported that for a variety of spatial discrimination tasks using line stimuli, thresholds continue to improve with time at least until 1000 msec. However, in Watt's experimental paradigm, a random noise mask immediately followed presentation of the discrimination target. We measured foveal line detection and abutting line vernier thresholds with and without a random noise mask immediately following the stimulus. Stimuli were presented on a uniform background of 132 cd/m². A self-paced rating-scale method of constant stimuli with feedback was used. The mask produced a significant increase in vernier thresholds for durations less than about 200 msec. However, it also increased detection thresholds over this range of durations. For masked vernier stimuli equated for visibility, no systematic effect of time on vernier acuity was found. These results suggest that for equally visible stimuli, no additional time is required to scan through a range of spatial filters in order to obtain the finest vernier thresholds.

© 1990 Optical Society of America