Perception, action & interaction: brain-damaged and normal evidence
The anatomical split between the ventral and dorsal streams of human vision is often identified with a functional distinction between vision-for-perception and vision-for-action. Whilst this dichotomy undoubtedly captures a broad organising principle, the emphasis on dissociations has tended to overshadow the role of inter-stream interactions in the production of coordinated behaviour. The importance of such interactions will be illustrated in two main ways. First, I shall re-visit neuropsychological evidence for the perception/action model, drawn from the visual form agnosic patient DF. Although DF’s action abilities are impressive by contrast with her perceptual abilities, a finer-grained analysis reveals limitations that imply multiple necessary roles for the ventral stream in the normal guidance of action. Second, I shall report recent tests of the idea that goal-directed actions are independent of perceptual processing within the ventral pathway. These studies show that actions are influenced by a range of pictorial cues to distance, including familiar size, which depends critically upon object recognition. The implications of these findings for dichotomous models of human vision will be considered.