Perceptual learning on orientation and direction discrimination.

Two experiments were conducted to determine the extent to which perceptual learning transfers between orientation and direction discrimination. Naive observers were trained to discriminate orientation differences between two single-line stimuli, and direction differences between two single-moving-dot stimuli. In the first experiment, observers practiced the orientation and direction tasks along orthogonal axes in the fronto-parallel plane. In the second experiment, a different group of observers practiced both tasks along a single axis. Perceptual learning was observed on both tasks in both experiments. Under the same-axis condition, the observers' orientation sensitivity was found to be significantly elevated after the direction training, indicating a transfer of learning from direction to orientation. There was no evidence of transfer in any other cases tested. In addition, the rate of learning on the orientation task was much higher than the rate on the direction task. The implications of these findings on the neural mechanisms subserving orientation and direction discrimination are discussed.