An analysis of the saccadic system by means of double step stimuli.

Abatrac-The characteristics of saccadic reactions to double steps of a target were analysed as a function of the time lapse between the second target step and the onset of the response. The analysis suggests that goal-directed saccades are prepared in two steps; first a decision as to their direction is taken which requires a randomly varying time, and subsequently their amplitude is calculated as a time average of the fixation error. In addition. the analysis demonstrates that the preparatory processes of two different saccades may overlap in time (“parallel programming”) and that. although reacting in a discontinuous manner, the saccadic system continuously processes the afferent visual information. A conceptual model based on an internal predictive feedback pathway and on a non-linear decision mechanism is proposed that accounts for the observed behaviour.