Processing of natural images is feedforward: a simple behavioral test.

Natural images can be classified so rapidly that it has been suggested that their analysis is based on a first single pass of processing activity through the visuomotor system. We tested this theory in a visuomotor priming task in which speeded pointing responses were performed toward one of two target images containing a prespecified stimulus (e.g., animal vs. non animal, ellipse vs. rectangle). Target pictures were preceded by prime pictures of the same or an opposite category, linked to either the same or an opposite pointing response. We found that pointing trajectories were initially controlled by the primes alone, but independently of information in the actual targets. Our data indicate that prime and target signals remained strictly sequential throughout all processing stages, meeting unprecedentedly stringent behavioral criteria for feedforward processing (rapid-chase criteria). Our findings suggest that visuomotor priming effects capture the output of the very first pass of information through the visuomotor system, before output is affected by recurrent information.