Perception Versus Action Hypothesis And Selective Attention

Since the 90's of the 20th century, the relation between visual system and motorsystem which has become a hot issue in cognitive psychology has been received moreand more attention. Some psychologists proposed two visual systems, one for actionand the other for recognition or conscious perception, which corresponding to dorsalstream and ventral stream in our brain. The dorsal stream connects the primaryvisual cortex(striate cortex, orV1) with the posterior parietal cortex, while the ventralstream connects the primary visual cortex with the inferior temporal cortex.However, we found that the attentional demands in perceptual tasks and graspingtasks were not matched in many studies. The holistic attention was needed in theperceptual task while the selective attention was needed in the grasping task.Therefore, we proposed a hypothesis that the results of the perceptual task and thegrasping task would be the same if the subject's attention was led to part in theperceptual taskIn experiment 1, we asked the participants to judge the width of rectangularobjects which had been associated with different length. The result of experiment 1shows that the length has no influence on the judgement of the width. In experiment2,we carried out a grasping task to compare with experiment 1.Participants wereasked to reach out and grasp each rectangular object by its width. The rectangularobjects in experiment 2 are the same as the wood bars which are presented in screenin experiment 1.We compared the MGA of different rectangular objects which haddifferent length. The result of experiment 2 is consistent with experiment 1.The lengthof wood bar has no influence on the MGA of the width. The results of experiment 1and experiment 2 favored our hypothesis. If the attentional demhnds of perceptualtask and grasping task were matched, there will be no dissociation in perception andaction.At the same time, we noticed the chosen line of the width by subject was always smaller than the physical size of the width in the perceptual task of experiment1.Therefore we put forward a question: what was the reason? Are participantsconservative or there was a bias? We discussed this phenomenon in experiment 3 andexperiment 4.In experiment 3,the participants were asked to choose a line consistentwith the line presented above. The result of experiment 3 was compared withexperiment 1. We found that the difference between the judgements of the width andthe line was significant. The judgement of width is indeed smaller than its physicalsize. In experiment 4,the participants were asked to grasp the line .We found nodifference with the result of experiment 2.There is no bias in grasping task.