Directional specificity in tilt aftereffect induced with moving contours: a reexamination.

In the tilt aftereffect a grating or bar is perceived as being slightly rotated from its veridical orientation if it is preceded by a similar adaptation stimulus with a slightly different orientation. It has been reported that the tilt aftereffect is not direction specific. That is, the magnitude of the misperception was not affected by whether the adaptation and test stimuli were moving in the same or the opposite directions. However, when we required subjects to fixate on a stationary spot during adaptation to a moving grating, the tilt aftereffect was strongest when both stimuli moved in the same direction. Moreover, the tilt aftereffect was not direction specific without such fixation. These results are consistent with the distribution shift model in which the perceived orientation reflects the distribution of orientation selective units, some of which are also direction selective.