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Abstract

Action recognition is critical for successful human interaction. Previous research highlighted the importance of the motor system to visual action recognition. Little is known about the visual tuning properties of processes involved in action recognition. Here we examined the visual tuning properties of processes involved in action recognition by means of a behavioral adaptation paradigm. Participants looked at an adaptor image (showing a person hitting or waving) for 4s and subsequently categorized a briefly presented test image as either hitting or waving. The test images were sampled from a video sequence showing a person moving from a hitting to a waving pose. We found the perception of the ambiguous test image to be significantly biased away from the adapted action (action adaptation aftereffect (AAA)). In subsequent experiments we investigated the origin of the AAA. The contrast inversion and mirror flipping of the adaptor image relative to the test images did not abolish the AAA suggesting that local contrastive sensitive units are not solely responsible for the AAA. Similarly the AAA was present when we chose adaptor images that were equated in terms of their emotional content indicating that the AAA is not merely mediated by units sensitive to the emotional content of an action. Moreover presenting words (e.g. "hitting" or "waving") instead of images as adaptors led to the disappearance of the AAA providing evidence that abstract high level linguistic cues about actions alone did not induce the AAA. Finally we changed the action interpretation of the adaptors leaving their physical properties unchanged by means of priming. We found that the priming of the action interpretation of the adaptors modulated the size of the AAA. Im summary these results suggest that mechanisms underlying action recognition are particularly sensitive to the high-level interpretation of an action.