Rejection of trials and subjects.

For details, see Method. Subjects were rejected if more than half of trials were rejected. Note that controls were tested in one session while PD were tested two sessions, explaining a larger number, but comparable ratio, of rejected trials. “Effect of both” represents effect of both button press and eye movement. “Imbalance” represents imbalance of perceptual direction, meaning that less than 3 trials were classifiable as either dominantly- left or right responses.