Effects of Target Eccentricity on Temporal Costs of Point of Gaze and the Hand in Aiming

This experiment addresses the coordination of point of gaze (PG) and hand movements in a speeded aiming task to predictable targets of three different eccentricities (35, 40, and 45 cm). In each condition subjects moved the eyes, head, trunk, and hand freely. Performance was assessed on 5 blocks of 5 trials. Analyses were conducted for (a) frequencies for initiation order of PG and the hand, (b) correlation between initiation latencies of PG and the hand, and (c) initiation, movement, and response times of PG and the hand. PG always arrived on target in advance of the hand and at approximately 50% of the response time of the hand (proportional time).Varying eccentricity increased initiation time of PG but not of the hand. With learning there was an initial temporal improvement and decreased variability of response within the first 10 trials, and with additional practice response times were further reduced. The importance of proportional time and its relationship to the first submovement in aiming are discussed.