Orientation-selective adaptation improves perceptual grouping

The role of visual pattern adaptation, and learning, in spatial integration was investigated. Observers performed a perpetual grouping task in which they reported whether a grid of identical tilted bars (45{degrees} counterclockwise from the vertical) is perceived as rows or columns. Performance was measured multiple times during a testing session to determine the effects of repeated exposure to the stimuli. To test for possible effects of learning on the within-session dynamics, observers repeated the experiment on five different days. We found that repeated performance produced rapid within-day improvements, which were largely transient, and were not retained when tested on subsequent days. In addition, exposure to stimuli with equal orientation contributed to the within-session improvement, whereas stimuli having an orientation differing by 45{degrees} from the orientation used in the grouping task diminished the improvement previously obtained in the same session. Practice with the task, over days, resulted in faster improvements. The transient nature of these exposure-driven improvements and their susceptibility to interference by stimuli designed to reduce adaptation suggests that adaptation was the main cause for the observed improvements. Finally, to investigate the effects of adaptation on internal noise and on spatial integration, we employed an external noise paradigm, showing that internal noise reduction resulted from adaptation. Internal noise was reduced only when spatial integration was effective, suggesting that adaptation improved perception of global stimulus properties. Overall, our results suggest that the grouping task benefits from an adaptation process that rapidly adjusts the visual system to the statistics of the visual stimuli. We suggest that this effect is achieved through spatial decorrelation of neural responses. With practice, the visual system is able to adjust faster to changes in the statistics of the environment.