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

Two experiments were conducted to examine the interactions between the ocul ar and manual systems during rapid goal-directed movements. A point-light a rray was used to generate Muller-Lyer configuration target endpoints (in-Mu ller, out-Muller,'X') for 30 cm aiming movements. Vision (of the limb and t arget), eye position, and the concurrence of eye movement were varied to ma nipulate the availability of retinal and extraretinal information. In addit ion, the Muller-Lyer endpoints were used to generate predictable biases in accuracy of these information channels. Although saccadic amplitude was con sistently biased, manual bias in response to illusory targets only occurred in trials with concurrent eye movement and elimination of retinal target i nformation on limb movement initiation; covariation of eye and hand displac ement was also most prevalent in these trials. Contrary to previous finding s, there was no temporal relation between eye and hand movements. In additi on to any role in coordinated eye-hand action, the availability of vision o f both the limb and target again had strong performance benefits for rapid manual aiming.