Target similarity affects saccade curvature away from irrelevant onsets

Saccade curvature away from visual distractors is a measure of the salience of these distractors for the oculomotor system. Three experiments are reported in which the integration of luminance onset signals and target similarity signals is examined, using a saccade curvature paradigm. Observers made saccades to a no-onset colour target in one of two positions on the vertical meridian. On most trials, an abrupt onset distractor that was either similar or dissimilar to the target appeared left or right on the horizontal midline. Saccades curved away from the irrelevant onsets; however, the amount of curvature was modulated by target similarity only when the onset appeared before the target (experiment 2) or when saccade initiation was delayed (experiment 3). These results suggest that the initial response to the onset is stimulus-driven and mediated by its transient component. Over time, the response is integrated with and augmented by top-down inputs. Visual and non-visual signals converge onto a common motor map to determine an item's salience.