Learning motion discrimination with suppressed MT

We studied perceptual learning in motion discrimination when the brain's middle temporal area (MT/V5) was functionally suppressed. This was achieved by using the "paired-dots" motion stimulus where the two dots in a pair always move in counter-phase over a short distance [J. Neurosci. 14 (1994) 7357]. The motion directional signal of the stimulus is therefore always 0 on average. As a result, this stimulus activates MT in Rhesus monkeys no more than flicker noise does [J. Neurosci. 14 (1994) 7367]. We added a new manipulation to eliminate the Glass pattern in the original stimulus that would have otherwise provided a static orientation cue. Two such new motion stimuli were presented sequentially, in a 2AFC task. Subjects decided if the global motion-axis of the stimuli changed clockwise or counter-clockwise. When the task difficulty was set at 60% correct, none of the subjects could learn with feedback, even though their performance was well above chance. However, when the task difficulty was set instead at 70% correct, a new group of subjects was able to learn. Hence, learning motion discrimination was possible when MT was presumably eliminated.