Abstract
A visual object can appear tilted away from the orientation of surroundings. This orientation repulsion may involve a sluggishly evolving orientation representation. To track this temporal evolution, we quantified repulsion when a pair of inducers having complementary orientation distributions were alternated at various frequencies (50–2.5 Hz). If the frequency was higher than the temporal resolution of the induction process, the two inducers would effectively merge into an isotropic distribution and no orientation bias would be available for the process. In Experiment 1, an orthogonal pair of D2 patterns were used as inducers. Such pairs were randomly distributed on the entire display, alternating in synchronicity. A target, a near-vertical Gabor patch, was briefly flashed to the left or right of the fixation point during alternation. Observers indicated whether the target appeared tilted clockwise or counter-clockwise. In separate sessions, they indicated whether the inducers were clockwise or counter-clockwise at the target onset. The repulsion increased rapidly as the frequency of inducers decreased and reached the maximum at 17 Hz, while conscious accessibility to the orientation of the inducers was at chance. In Experiment 2, we aimed to maximize the repulsion by using another alternating pair of inducers. One was a bandpass texture having a narrow band of orientation distribution, and the other was a bandnotched texture having a complementary distribution in comparison to the former. They occupied the annulus region abutting a briefly flashed target, another bandpass texture. The repulsion increased gradually to the maximum at 2.5 Hz. Conscious accessibility to the orientation of the inducers also increased but leveled off at 6.3 Hz. We suggest that two distinct kinds of evolving processes are involved in the formation of orientation repulsion: one is proceeding outside conscious access and short-lived; the other is proceeding after the establishment of conscious access and long-lasting.