Effects of kinesthetic information from body movements on accuracy in perception and cognition of object motion

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We investigated the relative importance of vision and proprioception in estimating target locations in a dynamic environment. Subjects performed a position estimation task in which a target moved horizontally on a screen at a constant velocity and then disappeared. Study results indicate that proprioceptive localization of the hand included systematic biases under dynamic conditions. When visual feedback was not given, the hand tended to overshoot target positions during tracking movements. This characteristic is approximately similar to those in past studies using hitting or reaching tasks. In the other experiments, study participants significantly underestimated their actual hand displacements without visual feedback, if they were asked to estimate the dynamic hand position in visual space. There seems to be a strong relationship between these two phenomena. Overshooting the target position in such a motor task would be attributed to underestimation of own hand movements, but not overestimation of target movements. In fact, study participants consistently underestimated the target displacements, even when the overshooting behaviours took place. These findings lead us to hypothesize that while humans are consciously aware of the position change of the various parts of the limb during ongoing movement without vision, the brain might interpret the limb movement as if more distal end of the limb (e.g., hand or the tip of finger) transferred less than it actually did relative to the extrapersonal space. So we need to know why estimates of the dynamic hand position are biased toward as if the extent of limb movement is reduced, but not extended. Moreover, for attainment of a motor task interacting with an object, how do people adjust or correct, in conscious or subconscious level, errors in estimation of their hand movements that could occur as they more rely on proprioceptive information. These problems remain to be examined in future studies.