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JI Prydal, DW Kennard; Relationship between Object and Image Location during Eye Movement . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4669.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Under conditions of high contrast stationary objects may seem to move in the visual field with saccadic eye movements, leaving a streak or blur. In earlier work this streak was reported to be an oscillating triphasic displacement. (1) Before eye movement: displacement of image in direction of movement to follow. (2) During eye movement: movement of image in the opposite direction, consistent with shift of image over retina. (3) After eye movement: return of image to baseline. Here we examine the relationship between the position of the perceived image and that of the stimulus during the middle phase - that of actual eye movement (2). Methods: (A) The position of an object was kept constant on the retina irrespective of the direction of gaze. A brief flash was delivered at the fixation point during a horizontal voluntary saccade through 16 degrees. Reported positions and the actual positions of the flash were recorded. (B) In the course of a horizontal saccade an oscilloscope spot moved from above to below two fixation points (16° separation) at approximately 33°/sec, the perceived vertical line passing through fixation wherever the eyes were looking. At the start of each spot traverse an auditory stimulus instructed subjects to perform a saccade between the two fixation points. The perceived curve was drawn on a transparent sheet over the screen. Subjects were two 26 year old males with normal vision, their heads supported by bite board and forehead rest. Results: (A) The flash was not necessarily perceived at fixation, the position at which it had been delivered. Mostly it was localized to the left (with left to right saccades). Some flashes were seen slightly to the right, displaced forward in the direction of movement. These were only at the beginning of eye movement. (B) Subjects clearly saw an S-shaped curve, not a vertical line. Throughout eye movement, images were perceived displaced to the left, towards the initial fixation point. Conclusion: The observations described here indicate that the perceived backward displacement of images during the phase of actual eye movement is not only the result of the physical shift of the image across the retina. There is another interacting factor, probably of central origin connected with pre-programmed processing of perceptual information which may help to maintain stability of the visual world.
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