Grasping objects by their handles: A necessary interaction between cognition and action.

Abstract

Research has illustrated dissociations between "cognitive" and "action" systems, suggesting that different representations may underlie phenomenal experience and visuomotor behavior.However, these systems also interact.The present studies show a necessary interaction when semantic processing of an object is required for an appropriate action.Experiment 1 demonstrated that a semantic task interfered with grasping objects appropriately by their handles, but a visuospatial task did not.Experiment 2 assessed performance on a visuomotor task that had no semantic component and showed a reversal of the effects of the concurrent tasks.In Experiment 3, variations on concurrent word tasks suggested that retrieval of semantic information was necessary for appropriate grasping.In all, without semantic processing, the visuomotor system can direct the effective grasp of an object, but not in a manner that is appropriate for its use.Dissociations between cognition and action have been proposed in several domains, including perception (Gibson, 1979), attention (Mack & Rock, 1998), and the neural substrate of the visual system (Jeannerod, 1997;Milner & Goodale, 1995).It has been repeatedly demonstrated that phenomenal experience and visuomotor behavior reflect differences that are suggestive of a separation in the representations underlying each.Neuropsychological studies indicate dissociations between object discrimination and visually guided action.For example, one patient may fail to discriminate between two different-sized objects, but her grasp of the object conforms to its size (Goodale, Milner, Jakobson, & Carey, 1991).In contrast, another patient may discriminate objects accurately but is impaired in regard to reaching and grasping (Jakobson, Archibald, Carey, & Goodale, 1991).Similarly, behavioral studies indicate that normal people may perceive a hill to be steeper than it actually is, but a motoric response directed at the hill is made accurately (Proffitt, Bhalla, Gossweiler, & Midgett, 1995).Although clear evidence for functional dissociations exists, it is also the case that cognition can influence action.Studies have shown that both where and when an action occurs influence whether the motoric response remains independent from cognition.A visual agnosic patient must direct her actions toward the object for accurate performance.Although the patient's grasp is effective when directed at an object, manual estimations to the side of the