Aging related responses to conflicting proprioceptive and visual information about initial position during reaching

INTRODUCTION: The purpose of the current study was to examine whether age-related differences are exhibited in the relative contributions of vision and proprioception with initial hand position to the control of movement distance of single-joint reaching movements. METHODS: We use a virtual reality display to systematically change the relationship between the actual hand position and the displayed hand position (virtual position) as subjects' positioned a cursor within a start circle. Visual feedback of the reaching hand was only available before movement onset. Two groups of subjects (older and young) reached to two different visual targets (115º and 125º elbow angle) from four possible starting locations (90º, 95º, 100º, 105º elbow angle) under four virtual/actual dissociation conditions (0º, 5º, 10º, 15º). RESULTS: For the mismatched conditions movement distance was generally longer for the older adults as compared to the younger. Also, the younger group better scaled their movement extent with cursor initial location, whereas, the older group showed scaling with hand location. Our results indicate age-related differences in the effects of initial position information when vision and proprioception initial information were dissociated. CONCLUSION: The young were able to completely rely on visual information through feedforward mechanism applying acceleration amplitude manipulation for controlling movement distance. In contrast, older subjects relied on proprioceptive information for the scaling of peak velocity with movement distance, suggesting more reliance on feedback-mediated error-correction mechanisms during the course of movement