Ocular perturbations and retinal extraretinal information: the coordination of saccadic and manual movements

Two experiments were conducted to examine the interactions between the ocular and manual systems during rapid goal-directed movements. A point-light array was used to generate Muller-Lyer configuration target endpoints (in-Muller, out-Muller,'X') for 30 cm aiming movements. Vision (of the limb and target), eye position, and the concurrence of eye movement were varied to manipulate the availability of retinal and extraretinal information. In addition, the Muller-Lyer endpoints were used to generate predictable biases in accuracy of these information channels. Although saccadic amplitude was consistently biased, manual bias in response to illusory targets only occurred in trials with concurrent eye movement and elimination of retinal target information on limb movement initiation; covariation of eye and hand displacement was also most prevalent in these trials. Contrary to previous findings, there was no temporal relation between eye and hand movements. In addition to any role in coordinated eye-hand action, the availability of vision of both the limb and target again had strong performance benefits for rapid manual aiming.