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Interaction Between Gaze and Pointing Toward Remembered Visual Targets

Department of Biophysics, University of Nijmegen, 6500 HB Nijmegen, The Netherlands

Submitted 5 May 2003; accepted in final form 15 June 2003

We examined the role of gaze in a task where subjects had to reproduce the position of a remembered visual target with the tip of the index finger, referred to as pointing. Subjects were tested in 3 visual feedback conditions: complete darkness (DARK), complete darkness with visual feedback of the finger position (FINGER), and with vision of a well-defined environment and feedback of the finger position (FRAME). Pointing accuracy increases with feedback about the finger or visual environment. In the FINGER and FRAME conditions, the 95% confidence regions of the variable errors have an ellipsoidal distribution with the main axis oriented toward the subjects' head. During the 1-s period when the target is visible, gaze is almost on target. However, gaze drifts away from the target relative to the subject in the delay period after target disappearance. In the FINGER and FRAME conditions, gaze returns toward the remembered target during pointing. In all 3 feedback conditions, the correlations between the variable errors of gaze and pointing position increase during the delay period, reaching highly significant values at the time of pointing. Our results demonstrate that gaze affects the accuracy of pointing. We conclude that the covariance between gaze and pointing position reflects a common drive for gaze and arm movements and an effect of gaze on pointing accuracy at the time of pointing. Previous studies interpreted the orientation of variable errors as indicative for a frame of reference used for pointing. Our results suggest that the orientation of the error ellipses toward the head is at least partly the result of gaze drift in the delay period.

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