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S.J. Bennett, G.R. Barnes; Oculo–Manual Pursuit During Transient Target Occlusion . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2919.
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© ARVO (1962-2015); The Authors (2016-present)
Smooth ocular pursuit decays following target occlusion, but often recovers if there is an expectancy the target will reappear. It is suggested the visuomotor drive to the eyes is inhibited by the loss of visual feedback, but is reinstated in anticipation of target reappearance. It is also well documented that the latency and gain of smooth ocular pursuit to a self–moved target is enhanced compared to pursuing with the eye alone. The present study examined whether visual and/or proprioceptive feedback of concurrent manual pursuit movement influenced smooth ocular pursuit during transient occlusion of externally generated target motion.
Eye movements were recorded from four participants using infrared video–oculography. Hand movement recordings were obtained from a manipulandum. The pursuit target (red) moved from –20o (left) with a rightward velocity of 10 or 20o/s for 800ms. The target was then extinguished for 400 or 800ms, and subsequently reappeared for 400ms. Visual feedback of the hand movement could be provided by illuminating a green cursor. Participants performed pursuit movements in 5 conditions: eye alone – transient target occlusion (EA); eye and hand – transient target and cursor occlusion (EH); eye and hand – target occlusion only (EHvis); eye and hand – no hand cursor (EHno–vis); eye and hand – no cursor or target occlusion (EHall). Each combination of target velocity and occlusion interval was presented 8 consecutive times to enhance the predictability.
Eye velocity at the moment of target occlusion was similar across conditions. Eye velocity decayed following the loss of visual feedback, resulting in a reduced gain over the occlusion interval compared to when the eye and hand targets remained visible. The average gain of smooth ocular pursuit was not influenced by the availability of visual feedback of hand movement.
mooth pursuit eye velocity decayed when visual feedback was occluded, and was not influenced by concurrent hand movement. These results indicate that neither efference copy nor afferent feedback from hand movement enabled smooth ocular pursuit gain to be maintained during transient target occlusion.
Acknowledgement: UK MRC.
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