Discrimination of proprioceptive and visual spatial information is a prerequisite for the learning of visuo-motor transformations. This study investigated the individual's capability to discriminate the directions of seen cursor motions and felt hand movements under a visuo-motor rotation paradigm and its age-related variation. Young and older participants performed 3-stroke arm movements on a digitizing tablet without seeing their arm. The visual feedback of the second stroke was rotated randomly by various angles ranging from -30° to 30° and displayed on a monitor. Older adults were poorer in discrimination than young adults. In both age groups, the felt hand direction was shifted toward the seen cursor direction (i.e., visual capture) by approximately 25% to 30% of the rotation of the visual feedback. Older adults also showed an enhanced visual capture. The results suggest that both the increased sensory noise and the increased assimilation of the bimodal information cause the reduction of discrimination capability in older adults. These findings provide underlying reasons for age-related changes in learning a new visuo-motor transformation.
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