Effect of manipulating visual feedback parameters on eye and finger movements.

Thirteen healthy subjects were asked to maintain a constant index finger position in Experiment 1 or a constant eye position in Experiment 2 using visual feedback. The finger or eye position along with a stationary baseline target was displayed on an oscilloscope placed in front of the subject. Experiments 1 and 2 were carried out under sixteen combinations of delay and amplification of displacement on the screen (i.e., gain). In Experiment 1, increasing the gain in the visual feedback decreased the Root Mean Square (RMS) errors while increasing the delay increased these errors. An interaction between gains and delays was also observed in Experiment 1. In Experiment 2, the RMS errors were systematically higher than those recorded in Experiment 1 for the finger. No systematic pattern was recognized across all conditions of gains and delays for eye movements in Experiment 2. This study clearly illustrates differences in dynamics of motor control systems regulating eye and finger positions, respectively.