Visibility, timing and vernier acuity

To investigate the relationship between contrast detection and vernier acuity for abutting targets, the effects of varying target exposure duration (12-2000 msec) on vernier and contrast detection thresholds for long, thin lines and sinusoidal gratings (1 and 8 c/deg), were measured. Vernier thresholds decreased with both increasing exposure duration and increasing target contrast. Predictions made for equally visible targets show that the effect of exposure duration on vernier thresholds is almost completely accounted for by its effect on target visibility. Vernier thresholds and contrast detection thresholds for line targets were also measured in the presence of a spatiotemporal mask, for different exposure durations. Again, once the effect of this mask on target visibility was accounted for, there was virtually no remaining effect of exposure duration on vernier thresholds. The results of these experiments suggest that similar spatial mechanisms mediate both contrast detection thresholds and vernier thresholds for abutting targets; and that the processes involved in target detection and the extraction of relative position information are limited by the same factors.