ABSTRACT
Over the last 10 years or so, a good deal of evidence has accumulated that perception and action can dissociate from one another (for reviews, see Milner & Goodale, 1995; Rossetti & Pisella, 2002). For example, damage to different brain regions can selectively disrupt either perception but not action to visual stimuli (e.g. after damage to ventral areas mediating visual processing), or action but not the perception of stimuli (e.g. after damage to more dorsal
areas of cortex). Similarly, the effects of some visual illusions can be larger on perceptual judgements than on actions (Aglioti, DeSouza, & Goodale, 1995; Bridgeman, 2002; Haffenden & Goodale, 1998; for alternative views, see Franz et al., 2000; Pavani et al., 1999), while effects of temporal delay can be larger on action than on perceptual judgement tasks (Milner & Goodale, 1995). This contrast between perception and action may extend also to the processes involved in selecting between multiple stimuli for perception and in selecting the appropriate actions to a stimulus (selection for perception and selection for action). Neuroanatomical research indicates that selection for perception and selection for action to visual stimuli depend, respectively, on networks within anterior (frontal) and more posterior (parieto-occipital) regions (e.g. Posner & Petersen, 1990). Neuropsychological research indicates that patients with parietal damage can be impaired in the perceptual selection of stimuli on one side of space, rather than in acting to the affected side. For example, when required to cancel lines seen through a mirror, patients can have problems in orienting visual attention towards stimuli on the perceived contralesional side of space, even when an action to that stimulus would be made on the ipsilesional side. In contrast, they may orient appropriately to stimuli on the perceived ipsilesional side even when their actions are then made on the contralesional side (e.g. Ackroyd et al., 2002; Na, Adair, Williamson, Schwartz, Haws, & Heilman, 1998). This suggests a problem in perceptual selection rather than in acting towards the affected side. In contrast, patients with damage to, or disconnection of, more frontal brain regions can be impaired in selecting a task-appropriate action to a stimulus even though they select the appropriate stimulus to make an action to (e.g. Riddoch, Humphreys, & Edwards, 2000a, 2000b). In this case, action selection seems to be impaired while perceptual selection continues to operate. On this view, there are separate systems not only for object identification and the parameretization of actions to objects (e.g. Milner & Goodale, 1995), but also for selecting the objects to identify and the actions to make in the first place.
