Velocity-dependent improvements in single-dot direction discrimination.

Thirty-six Brown University students participated in three experiments designed to address perceptual learning. In each experiment, visual discrimination thresholds were tracked over 4,200 trials. Results from Experiment 1 suggest that the pattern of threshold reduction on a single-dot motion-direction discrimination task was stimulus direction specific and matched (in a velocity-dependent manner) the threshold reduction pattern previously reported for a line-orientation discrimination task. In Experiment 2, it was determined that the stationary-line-orientation-specific practice effects originally reported by Vogels and Orban (1985) could be replicated but were contingent on line length. Similarly, the results from Experiment 3 suggest that practice effects originally reported by Ball and Sekuler (1987) could be replicated but were contingent on stimulus velocity. Implications for the mechanisms underlying direction and orientation discrimination are considered.