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Gerrit Maus, Richard Ivry, David Whitney; The flash-lag effect is reduced in patients with cerebellar atrophy. Journal of Vision 2012;12(9):155. doi: 10.1167/12.9.155.
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The cerebellum is known to implement predictive forward models for the motor system (Wolpert et al. 1998). These models generate spatiotemporal predictions about the consequences of motor commands to aid in the control of movements. Similar spatiotemporal prediction may be involved in overcoming transmission delays in the visual system, e.g. for more accurately perceiving the positions of a moving object. Two possible examples of a spatiotemporal prediction in visual perception are the flash-lag effect, in which a moving object is seen ahead of a co-localized flash (Nijhawan 1994), and the De Valois effect, in which stationary drifting Gabors are perceived as shifted in the direction of internal motion (De Valois & De Valois 1991). Here, we test the hypothesis that the cerebellum also contributes to the generation of spatiotemporal predictions in the visual system. Four patients with cerebellar ataxia due to degenerative cerebellar atrophy and six healthy control subjects were tested on both effects. For the flash-lag effect, they judged the perceived position of a flashed bar in relation to another bar moving towards the fovea in a 2-alternative forced-choice (2AFC) task. For the De Valois effect, we presented Gabor patches arranged vertically and drifting in opposite directions. Patients and controls judged the perceived alignment in another 2AFC task, while the physical alignment was varied. Cerebellar patients showed typical spatial shifts for drifting Gabors in the De Valois effect. However, patients showed, on average, a markedly reduced flash-lag effect compared to controls. Sensitivity (i.e., the slopes of psychometric functions) was reduced for both tasks in patients. These results provide initial evidence that the cerebellum is involved in the spatiotemporal perception of moving object trajectories (in the flash-lag effect), but not in motion-induced spatial shifts of stationary objects (in the De Valois effect).
Meeting abstract presented at VSS 2012
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