The intention to act improves unilateral left neglect: two demonstrations

Unilateral neglect involves a spatial bias to one side of space, usually to the right. Perceptual and motor systems interact in the manifestation of this disorder, and there is also evidence that motor manipulative responses may have access to unique streams of information not available for non-motoric judgements. It is therefore predicted that the manifestation of neglect may be alterable by changing the purpose of otherwise very similar responses to spatially extended objects. In Experiment 1, neglect-based deviation to the right of centre was significantly less when subjects reached towards metal rods as if to pick them up in the centre, compared to when they pointed to their centres. In Experiment 2, subjects pointed to the centre of a rectangular box with a swivelled lid. They were then asked to place a coin at the centre of this lid, in a position sufficiently central to prevent the lid tilting and the coin falling into the box; in fact, the lid was fixed and subjects never received feedback. Responses were significantly more central with the balancing response than with the pointing one. These results suggest that prehensive movements towards objects allow 'leakage' of information about their spatial extent, via an unaffected stream of information available for motor-manipulative responses.