Sensory factors are insufficient to define the ocular saccade goal in complex visual fields.

In most normal visual search situations, the environment is filled with a variety of stimuli, and selection among possible saccade targets is necessary. Current theories of visuomotor mechanisms must take into account not only the classical 'retinal error' input signal, but also perceptual and decisional factors as well as task-specific strategies adopted by the subjects. Experiments are reported in which eye movements are recorded in tasks requiring ocular saccades to be made onto target letters indicated by a peripherally visible mark or embedded within lines of homogeneous background letters. The results show how nonsensory factors interact with visual determinants in the preparation of the exploratory saccades. Expectations concerning the visibility of the sought-for target influence the spatial and temporal parameters of the eye movement which will be executed.