Post-exposure Settings Research Articles

Active and passive movement in the production of kinesthetic tilt after-effects.

A number of recent studies both in vision (Held, 1961) and in audition (Freedman 8: Pfaff, 1962) have demonstrated that, during rearranged or disarranged sensory input, self-induced movement by the observer is necessary to modify his perceptual-motor coordination. This experiment was a preliminary attempt to test this finding for another sense modality, kinesthesis. Method.-Blindfolded Ss palpated an adjustable rod tilted 20 to the left or right of the vertical in the mid-line of the frontoparallel plane. Before and after each exposure S set the rod to apparent vertical four times. Each S parricipated in rwo experimental sessions consisting of an alternating series of 11 tests and 10 15-sec. exposures. In each session exposures alternated between: (1) active, S moved his arm and hand up and down along the rod at a fixed rate; and (2) passive, S's relaxed arm was fixed to a mechanical device which moved it along the same path. The results were analyzed by calculating the changes from pre- to post-exposure settings for each exposure and comparing each consecutive pair of active and passive changes induced by exposure. Re~u1ts.--Our hypothesis was that active exposures would produce larger tilt after-effects than would passive exposures. Six Ss had two sessions each, making 108 active-passive comparisons possible. In 67 of these, active exposure produced greater after-effects than passive exposure; 39 comparisons showed the reverse; and 2 showed no difference. Thus there was a significant (z = 3.62, p < .002:) difference berween the effects of active and passive movement in producing the kinesthetic tilt after-effect. This experiment extends the finding that self-induced observer movement produces greater perceptual alteration under atypical stimulation than does passive movement.