Comparison of thresholds for high-speed drifting vernier and a matched temporal phase-discrimination task.

Overview

For rapidly translating targets, vernier thresholds correspond to millisecond asynchronies between targets. The 'temporal hypothesis' is that these thresholds reflect the limiting sensitivity of asynchrony detectors. Previous studies showed that temporal thresholds are generally higher than vernier thresholds, but failed to reject the 'temporal hypothesis' because stimuli had differing spatiotemporal characteristics, and temporal thresholds depend strongly on stimulus and task. Here we use matched grating stimuli to test - and reject - the temporal hypothesis. Expressed as asynchrony, temporal phase discrimination was typically 10-fold poorer than vernier thresholds, and differed in dependence on spatial frequency, temporal frequency, contrast, and susceptibility to stroboscopic masks.