Investigating the perceptual-motor system : a novel test of the directionality-of-guidance model
Lucas, Donald R.
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The purpose of the present study was to test hypotheses derived from a theory of intersensory coordination known as the directionality-of-guidance (DOG) model. The present study, involving perceptual adaptation, tested the theory by using a novel experimental method which provided test data that are independent of those experimental data from which the theory was initially derived. Twenty subjects performed pointing tasks in the dark; they were able to detect prismatically induced errors only during a flash of stroboscopic illumination which occurred at the end of their pointing movements. They performed two tasks. One task (E -> H) required subjects to look at some self-selected position either to the left or right of center in the horizontal plane and then point to that same position. In this task the eye-head sensori-motor subsystem is guiding the hand- head sensori-motor subsystem. The DOG model predicts that adaptation should occur in the hand-head sensorimotor subsystem yielding manual adaptation. The other task (H -> E) required subjects to point their hand at some self-selected position either to the left or right of center in the horizontal plane at arm's length and then look to that same position. In this task the hand-head sensori-motor subsystem is guiding the eye- head sensori-motor subsystem. The DOG model predicts adaptation should occur in the eye-head sensori-motor subsystem yielding visual adaptation. The present results are consistent with the DOG model's prediction that the E -> H task should yield more manual adaptation than the H -> E task. The present results are not consistent with the DOG model's prediction that the H -> E task should yield more visual adaptation than the E -> H task. However, an analysis of the results suggests that this was due to the differences in difficulty between the two tasks; that is, the more difficult E -> H task often became a E -> H -> E task.