ABSTRACT
When a person makes a voluntary saccade, the location of visually perceived objects remains undisturbed even though the image of these objects on the retina is displaced. In order to account for this discrepancy between what occurs in perception and on the retina, a number of theories have been proposed (Helmholtz, 1962; James, 1950; Sherrington, 1918; von Holst, 1954) which in general suggest that the brain, via an extraretinal signal, assigns a visual direction (local sign) to each retinal locus. During a saccade, according to this viewpoint, the extraretinal signal changes causing a shift in the relation of visual direction to retinal locus. It is implied that the shift has the same direction, time-course, and magnitude as retinal image displacement and thus "cancels" or "nulls" the displacement in perception.
