Abstract
A rotational aftereffect can be induced in an ambiguously rotating kinetic dot object (KDO) following a period of viewing in which stereo or perspective cues have caused the object to appear to rotate unambiguously (Nawrot & Blake, 1989; Petersik, 1984). In addition an ambiguously rotating, transparent KDO appears to rotate unambiguously when immersed in a plane of dots translating parallel to the dots of the object (front surface against planar flow; Sereno & Sereno, 1999). For many observers it is sufficient to surround the KDO with an annulus of translating dots to induce a consistent percept of rotation against the direction of the annulus dots. We conducted two experiments in which observers viewed an ambiguous KDO in combination with either a whole field or annulus of translating dots. After 20 seconds of viewing, during which observers report seeing the KDO rotate opposite to the surrounding field, the observers viewed and reported the direction of rotation of the KDO in isolation. In control trials, the KDO appeared on a field of twinkling dots in the first part of the trial, or a translating field was present without the KDO in the first portion of the trial. These latter trials give rise to a brief conventional aftereffect in which the KDO appears to rotate with front surface motion opposite to the direction of field translation seen earlier. In the experimental conditions, we find there is a rotational aftereffect that is against the direction of rotation reported during the first part of the trial, and in the direction of the unambiguously translating field. In the case of the trials with an annulus, the object is not in the same retinal region as the neurons experiencing motion adaptation. Therefore, this is a rotational aftereffect that cannot be attributed to local motion detector adaptation.