Action-specific extrapolation of target motion in human visual system.

Full Abstract

Neuropsychological studies have indicated two distinct visual pathways in our brain, one dedicated to conscious perception and one to visuomotor control. Some psychophysical results support this idea with normal subjects, but they are still controversial. This study provides new psychophysical evidence for the dissociation by showing action-specific extrapolation of the visual target trajectory. When a moving target disappears, the perceived final position is liable to be shifted forward (representational momentum). In experiment 1, larger and more robust forward shifts were found when the position was directly touched without seeing the screen (open-loop pointing) than when the position was judged perceptually. The most striking dissociation was that fixation did not affect the forward shift in open-loop pointing while it almost abolished the shifts in perceptual judgements. In experiment 2, this action-specific result was found to disappear after a response delay of 4000 ms. Experiments 3 and 4 confirmed that the results were not affected by the external reference frames. The specific forward shifts found in open-loop pointing suggest that the visuomotor system compensates for the neural delays by extrapolating the target motion. The results, together with earlier findings, lead to a psychophysical double dissociation of the two visual pathways.

Author information

Author/s: Ashida, Hiroshi (H);

Affiliation: Graduate School of Letters, Kyoto University, Kyoto 606-8501, Japan. ashida(-atsign-)bun.kyoto-u.ac.jp

Journal and publication information

Publication Type: Journal Article; Research Support, Non-U.S. Gov't

Journal: Neuropsychologia (Neuropsychologia), published in England. (Language: eng)

Reference: 2004-; vol 42 (issue 11) : pp 1515-24

Dates: Created 2004/07/12; Completed 2004/09/17; Revised 2009/11/11;

PMID: 15246289, status: MEDLINE (last retrieval date: 11/11/2009, IMS Date: )

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