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Jeffrey B. Mulligan, Scott B. Stevenson; A comparison of the dynamics of visually-controlled head and hand movements. Journal of Vision 2009;9(8):846. doi: 10.1167/9.8.846.
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© ARVO (1962-2015); The Authors (2016-present)
Brueggemann and Stevenson compared tracking of a randomly moving target by eye gaze and hand, using a joystick-controlled cursor (2007 OSA Fall Vision Meeting). In this study, we extended their work by comparing motor control of a tracking cursor using either the hand or the head. A Polhemus Fastrak 6-DOF space tracker was used to provide inputs; in the case of the hand, position was used to control the cursor, with up and right in space naturally mapping to up and right on the screen. In the case of the head, angular measures of pitch and yaw were used, as if a virtual laser pointer were attached to the subject's nose. The primary difference between these two cases is that, in the case of head rotations, the vestibulo-ocular reflex (VOR) causes compensatory eye movements to be made, stabilizing the scene on the retina in spite of the movement of the head. Under normal circumstances, the VOR effectively compensates for head movements, the world appears stable, and similar results are obtained for head and hand correlograms. Observed latencies are in the neighborhood of 400 milliseconds, with the head around 50 milliseconds faster than the hand. The method is expected to reveal more striking differences, however, under abnormal gravitational conditions such as those encountered during aircraft maneuvers or space flight, where lack of visual stability is often observed. We have examined adaptation of the VOR (using modified visual feedback) as a possible analog of these conditions. We have also measured period-versus-delay (PVD) functions of oscillations induced by delayed visual feedback. We have previously reported PVD slopes near 1.6 for eye movements, suggesting a control system using both position and velocity inputs. PVD functions obtained for head tracking show steeper slopes, suggesting a different weighting of visual signals is used for control.
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