Perceptual and motor effects elicited by a moving visual stimulus below the forearm: an example of segmentary vection.

It has been shown in man that movement of a visual stimulus under the forearm may induce illusory sensations of movement (segmentary vection) and motor activity in the same direction, such that, for example, a sensation of elbow flexion is accompanied by EMG activity in biceps brachialis. The characteristics of these two types of activity, perceptual and motor, are analyzed and compared with analogous phenomena described for the whole body. These comparisons bring out two essential features: the effectiveness of stimuli of small surface area applied to central regions of the retina, and the non-compensatory character of the motor phenomena. The results are discussed with respect to the participation of vision in the control and regulation of limb movements.