Abstract: PURPOSE: Action and perception interact reciprocally to shape human behavior. Recent studies have revealed an action effect, in which a simple action (i.e., key-press) towards a prime stimulus biases attention in a subsequent visual search in favor of objects that match the prime. Here we investigated whether the action effect was a generalized phenomenon that could affect context-dependent visual size perception and whether it took place at the early or late stage of visual processing.
METHODS: Participants were required to make a key-press response to or passively view a circle prime whose color, size and location matched the central circle of the Ebbinghaus illusion presented subsequently. Immediately they performed a size matching task, during which a target circle surrounded by four large or small context circles and a comparison circle were simultaneously presented, and they were required to adjust the size of the comparison circle to match that of the target circle without time limit.
RESULTS: The results showed that a prior key-press response to the circle prime significantly reduced the Ebbinghaus illusion effect compared to the passive viewing condition. Notably, the action effect persisted even when the central target and surrounding inducers of the Ebbinghaus configuration were presented to different eyes.
CONCLUSIONS: These findings provide clear evidence that a prior action can exert a strong influence on context-dependent visual size perception, and it mainly affects the late visual processing stage.

Key words: Action, Ebbinghaus illusion, Size perception