Criterion-free pattern and flicker thresholds.

Previous measurements of pattern and flicker thresholds in man have used the psychophysical method of adjustment and have required that the subject change criteria. Our new approach measures pattern and flicker thresholds by a criterion-free procedure that requires that the subject distinguish a test stimulus from control stimuli that differ from the test in only one dimension, the spatial dimension in the pattern experiments and the temporal dimension in the flicker experiments. By using this technique, we find that the subject's pattern sensitivity is equal to or greater than his flicker sensitivity for all flickering gratings except those that have extremely low spatial and moderate or high temporal frequencies (depending on the subjects). Furthermore, spatiotemporal interaction is evident in both the pattern and the flicker data. These results differ substantially from those obtained by the method of adjustment.