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Paul McGraw, David Whitaker, Dennis Levi; Amblyopic eyes are particularly susceptible to motion-induced distortions of space. Journal of Vision 2008;8(6):431. doi: 10.1167/8.6.431.
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© ARVO (1962-2015); The Authors (2016-present)
When the internal structure of a stationary visual object moves, the object as a whole appears perceptually displaced in the direction of motion. In normal observers, the magnitude of this illusory offset can be dependably manipulated by systematically varying stimulus uncertainty. In this study, we investigate the role of neural uncertainty in the generation of motion-induced distortions of visual space. Nine subjects performed a 3-patch vertical alignment task using their amblyopic and non-amblyopic eyes. The central element consisted of a luminance grating (carrier frequency 4 cyc/deg) drifting either rightwards or leftwards (temporal frequency 6.3Hz) within a static contrast-defined envelope. The reference elements were luminance-defined patches, of the same size, located 2 degrees above and below the central element. In a separate control condition, subjects also performed an identical alignment task with the exception that the central carrier grating was stationary. For both stationary and moving carrier conditions the magnitude of the motion-induced positional offset was linearly related to the precision with which the central element could be localised. In subjects with amblyopia, where judgments of spatial position are less reliable, they become increasingly susceptible to an illusory shift in position. More importantly, when these motion-induced shifts are expressed in units of sensitivity, virtually all subjects show greater illusory offsets in their amblyopic eye relative to their non-non amblyopic eye. This result suggests there exists an additional deficit in position coding, over and above the well-documented sensitivity deficit. Due to the existence of positional deficits in amblyopia, location cues derived from the static contrast envelope may be down-weighted relative to motion cues arising from the carrier.
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