PURPOSE: Tilt aftereffect (TAE) is the phenomenon that the perceived orientation of a test stimulus is altered after prolonged exposure to an oriented adaptor. This phenomenon has been widely considered to result from adaptation of orientation-selective neurons in the early visual cortex. In this study, we investigated whether the TAE could be induced from a perceived illusory orientation of adapting stimulus dissociated from its physical orientation, by taking advantage of a new illusion— the flash grab effect.
METHODS: Subjects viewed a physically vertical line that was repeatedly and briefly flashed on top of a patterned disk that oscillated clockwise and counterclockwise, with the flashed line presented at the moment of the rotation reversals. Importantly the adapting line was perceived as tilted away from vertical. Following adaptation to 11 cycles of the flashed line, a test line was briefly presented near vertical orientation at the corresponding location without the background disk.
RESULTS: Results showed that a significant TAE was induced by the perceived orientation. In contrast, when the physical orientation of the titled adapting line was adjust by each individual subject so that the adapting line was perceived to be vertical, no TAE was observed. Thus when perceived and physical orientations of the adapting lines are pitted against each other, the TAE is dependent on the perceived rather than the physical orientation. In separate experiments using multimodal neuroimaging methods, we have shown that the perceived tilt from flash grab effect is primarily due to feedback processing in the brain.
CONCLUSIONS: Our results suggest that higher-level processes and feedback signals play an important role in the TAE.