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Masashi Yamaguchi, Hirohiko Kaneko; Eccentric head and eye positions affect proprioceptive pointing. Journal of Vision 2005;5(8):118. doi: https://doi.org/10.1167/5.8.118.
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To perceive the location of a stationary object to be constant, visual system should estimate head and eye positions as well as the retinal image position. Although previous studies indicated that eye position affects perceptual direction of a stimulus (J.Lewald, 2000), the effect of head position on the perceptual direction is not systematically shown. In this study, we investigated the effect of static positions of head and eye and movement of head on proprioceptive pointing.
Subjects put on a helmet that could be rotated about the vertical axis. Seven green light emitting diodes (LEDs) were arranged from 15 degree left to 15 degree right at eye level on a cylindrical surface (radius 0.5 m) in front of the subject and a red LED was mounted below the central green LED on the surface. In a trial, first, one of the green LEDs (randomly selected) was presented and subject fixated it. After two second from the onset of fixation point, a red LED was presented and subjects responded the perceptual position of the red LED using an unseen pointer with both hands. In one condition, subjects made the head movement before the response. In another condition, subjects kept their head directed to one of the three positions (15 degree left, center or 15 degree right).
The direction of pointing bias was opposite to that of the position of eye-in-head. This result is consistent with the previous study (J.Lewald, 2000). Moreover, the direction of pointing shifted to opposite to that of the position of head-in-space. These pointing errors generated by head and eye positions were simply added when both head and eye positions were eccentric. The results suggest that the error is not due to the position of eye-in-space but the individual positions of eye-in-head and head-in-space.
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