KINESTHETIC FIGURAL AFTEREFFECTS: SATIATION OR CONTRAST

Does limb proprioception drift?

The hypothesis that proprioceptively perceived limb position drifts during visual occlusion was re-examined by combining some of the protocols used in previous experiments. Sixteen adult subjects made judgements of static limb position during visual occlusion lasting up to 2 min. In addition, the effect of brief 250 ms "glimpses" of the limb, occasional proprioceptive stimulation and directed attention were examined. Despite, conflicting evidence from earlier experiments, there was clear evidence of a drift in perceived limb position, towards the body, during visual occlusion. This drift was halted if brief glimpses of the limb were provided, or minor re-positioning (without vision) was allowed. In neither case, however, did the supplementary cues reset limb position to its originally perceived position. Drift was amplified when subjects attempted to attend to limb position rather than perform a secondary tracking task. The results are not easily accounted for if drift is considered purely as an effect of peripheral sensor adaptation. A notion of central-drift between visual and proprioceptive maps is suggested as an alternative hypothesis.

Influence of repated testing and of starting poition in kinesthetic aftereffect

The purposes of this experiment on kinesthetic aftereffects were to determine whether test (T) trials inserted between inspection (I) periods affected the magnitude of effect and to examine the influence of wedge starting position on single judgment and cumulative effect on averaged judgments using the method of average error. 60 experimental Ss had 1-min. I periods separated by rests or by T trials. A control group had T trials without I periods. Each S had 4 trials per test period and started each trial at a different wedge position (A, B, C., or D). Starting position order was varied within groups (ADCB, BADC, CDAB, or DABC). Results indicate: (a) T trials may decrease aftereffect; (b) starting position highly influences single PSE choice; and (c) effects of starting position are not a simple function of starting position per trial since the impact of each start is modified by the first in a series. Therefore, averaging settings made on the basis of starting positions above and below POE does not eliminate the bias created by the initial starting position.