Visual priming effects for prehension movements

Abstract

There are known to be two major visual processing pathways from the occipital lobe to the temporal and parietal lobes: the ventral visual processing system, which is involved in conscious object identification, and the dorsal visual processing system, which is involved in spatial, attentional, and behavioral processing, both conscious and unconscious. However, little is known about how these pathways are employed in reaching and grasping movements. In the present study, we attempted to tease apart contributions of the two pathways by manipulating two aspects of visual stimuli, i.e. object identity, which is expected to engage the ventral pathway, and object orientation, which is relevant for grasping actions and is thus expected to engage the dorsal pathway. In the experiment we conducted, healthy subjects performed reaching and grasping movements after being briefly exposed to a visual stimulus, and we measured the priming effects that the visual stimulus had for the reaching and grasping movements. In doing so, we distinguished four conditions, depending on (i) whether the preceding visual stimulus consisted of the same type of image as the image that the subject was subsequently shown and was to try to grasp and (ii) whether the orientation of the preceding visual stimulus was such that it was likely to elicit movement of the hand that the subject was to move in the grasping action subsequently. The results showed significant priming effects of both types with no interaction between them, suggesting that both visual pathways are independently involved in reaching and grasping movements.