Effect of practice on visual backward masking.

Abstract

Five experiments studied practice effects for 4, 7, 11 subjects on visual backward masking using a signal-detection procedure under various conditions. Exp. I determined the minimum perceptible critical stimulus duration (CSD) for criterion identification of a target stimulus, the letter T or A. In Exp. II, the stimulus was presented at the critical stimulus duration (CSD) followed by a pattern mask at intervals of 20 to 120 msec. for 15 separate sessions. In Exp. III (N = 4) the mask followed the CSD in intervals of 2-msec. increments until subjects reached criterion accuracy. Exps. IV and V (Ns = 4, 7) provided partial replications of Exps. II and III. Naive subjects were used, and the stimulus duration was constant for all subjects. When masking functions were obtained at a threshold, considerable variability was found and subjects improve slowly or not at all over sessions. With a fixed supra-threshold stimulus, all subjects improve with practice. The inportance of these findings is discussed as they relate to common (and largely untested) assumptions made in the backward masking and perception literature.