Induced changes in oculocentric visual direction when saccades are recalibrated
Classically, Oculocentric visual direction (the angular direction associated with a particular retinal locus) has been considered innately specified and immutable. This study examined whether, in contrast to the classical viewpoint, a target's Oculocentric visual direction is affected uhen the magnitude of saccades to that target is changed. For normal adults, saccades to a monocularly viewed target, initially 8.5 deg right of fixation, were made artificially inaccurate by Surreptitiously shifting the target 2.15 deg inward or outward during saccades to it. On separate trials the visual direction of the unshifted target was specified by matching its direction (relative to a fixated stimulus) with a target in the left field. When the right field target was shifted during saccades, each subject showed an appropriate adjustment of saccadic magnitude. Statistically significant but smaller changes occurred in the visual direction of the left field matching target. The changes in visual direction occurred more slowly than the adjustment of saccadic magnitude. Although induced changes of saccadic magnitude were larger than induced changes in the target's Oculocentric direction, changes were comparable when normalized to their respective variabilities. The results show that small changes of a peripheral target's Oculocentric direction can occur in normal adults.