Westwood David A, Goodale Melvyn A
Department of Psychology, The University of Western Ontario, London, Ontario, Canada.
Spat Vis. 2003;16(3-4):243-54. doi: 10.1163/156856803322467518.
Participants were cued by an auditory tone to grasp a target object from within a size-contrast display. The peak grip aperture was unaffected by the perceptual size illusion when the target array was visible between the response cue and movement onset (vision trials). The grasp was sensitive to the illusion, however, when the target array was occluded from view when the response was cued (occlusion trials). This was true when the occlusion occurred 2.5 s before the response cue (delay), but also when the occlusion coincided with the response cue (no-delay). Unlike previous experiments, vision and occlusion trials were presented in random sequence. The results suggest that dedicated, real-time visuomotor mechanisms are engaged for the control of action only after the response is cued, and only if the target is visible. These visuomotor mechanisms compute the absolute metrics of the target object and therefore resist size-contrast illusions. In other situations (e.g. prior to the response cue, or if the target is no longer visible), a perceptual representation of the target object can be used for action planning. Unlike the real-time visuomotor mechanisms, perception-based movement planning makes use of relational metrics, and is therefore sensitive to size-contrast illusions.
参与者通过听觉提示，从大小对比显示中抓取目标物体。当目标阵列在反应提示和动作开始之间可见时（视觉试验），峰值抓握孔径不受感知大小错觉的影响。然而，当反应提示时目标阵列被遮挡而不可见时（遮挡试验），抓握对该错觉敏感。当遮挡在反应提示前2.5秒发生时（延迟）是这样，当遮挡与反应提示同时发生时（无延迟）也是这样。与先前的实验不同，视觉和遮挡试验以随机顺序呈现。结果表明，专门的实时视觉运动机制仅在反应提示后且目标可见时才参与动作控制。这些视觉运动机制计算目标物体的绝对度量，因此能抵抗大小对比错觉。在其他情况下（例如在反应提示之前，或者如果目标不再可见），目标物体的感知表征可用于动作规划。与实时视觉运动机制不同，基于感知的运动规划利用相对度量，因此对大小对比错觉敏感。
