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Taro Maeda, Hideyuki Ando, Maki Sugimoto; The spatial deviation of reaching to the same point under the different gaze directions. Journal of Vision 2003;3(9):692. doi: 10.1167/3.9.692.
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© ARVO (1962-2015); The Authors (2016-present)
It is an empirical phenomenon that the visual space is not homogeneous in the visible area. The retinal visual space and the eye-directional visual space should be correctly coincident in order to keep the equivalent continuity of the visual space under the free eye movements. It is a sensory integration process between eye directions and retinal spatial images, and under such sensory integration process, empirical phenomena of spatial deviation are observed frequently. In this report, the deviations between these visual spaces were measured psychophysically on the reaching tasks with upper limbs. Under the different eye directions, the reaching points are also different toward the same spatial point perceived not moving.
Following the spatial deviations, the temporal deviations were also measured under the reaching tasks via the fixation point In this experiment, Three points are arranged on the horizontal plane in front of the subject which are the start point, the target point and the fixation point. The subject starts his hand for the reaching task from the start point to the target point via the fixation point The subject has to fixate the point until the change of color on the point. After the change, the subject shifts the gaze to the target point before the end of reaching task. When the change is insufficiently earlier than the start of reaching, the hand reaches to the point as if the subject gaze the fixation point all time. When it is sufficiently earlier, the hand reaches to the point as if the subject fixated the target point all time.
From the results, it is observed that the shift of fixation before the start of hand is necessary to change the reaching point. It is supposed that this sensory integration process would have more direct connection to the motor command than the process of ordinarily visual spatial perception because of the short latency.
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