Retinal image motion alone does not control disconjugate postsaccadic eye drift

Abstract

1. In these experiments, postsaccadic ocular drift was induced by postsaccadic motion of the visual scene. In the most important case, the scene was moved in one eye but not the other. Six human subjects viewed the interior of a full-field hemisphere filled with a random-dot pattern. During training, eye movements were recorded by the electrooculogram. A computer detected the end of every saccade and immediately moved the pattern horizontally in the same or, in different experiments, in the opposite direction as the saccade. The pattern motion was exponential with an amplitude of 25% of the size of the antecedent saccade and a time constant of 50 ms. Before and after 3-4 h of such training, movements of both eyes were measured simultaneously by the eye coil-magnetic field method while subjects looked between stationary targets for calibration, explored the visual pattern with saccades, or made saccades in the dark to measure the effects of adaptation on postsaccadic ocular drift. The amplitude of this drift was expressed as a percentage of the size of the antecedent saccade. 2. In monocular experiments, subjects viewed the random-dot pattern with one eye. The other eye was patched. With two subjects, the pattern drifted backward in the direction opposite to the saccade; with the third, it drifted onward. The induced ocular drift was exponential, always in the direction to reduce retinal image motion, had zero latency, and persisted in the dark. After training, drift in the dark changed by 6.7% in agreement with our prior study with binocular vision, which produced a change of 6.0%. 3. In a dichoptic arrangement, one eye regarded the moveable random-dot pattern; the other, through mirrors, saw a different random-dot pattern (with similar spacing, contrast, and distance) that was stationary. These visual patterns were not fuseable and did not evoke subjective diplopia. In this case, the induced change in postsaccadic drift in the same three subjects was only 4.8%. In all cases the changes in postsaccadic drift were conjugate--they obeyed Hering's law. 4. Normal human saccades are characterized by essentially no postsaccadic drift in the abducting eye and a pronounced onward drift (approximately 4%) in the adducting eye. After training, this abduction-adduction asymmetry was preserved in the light and dark with monocular or dichoptic viewing, indicating again that all adaptive changes were conjugate. 5. When the subjects viewed the adapting stimulus after training, the zero-latency, postsaccadic drift always increased from levels in the dark.(ABSTRACT TRUNCATED AT 400 WORDS)

Unequal saccades produced by aniseikonic patterns: a model approach

“…Prisms (Henson & North, 1980;Oohira & Zee, 1992), anisometropic spectacles (Henson & Dharamshi, 1982;Erkelens, Collewijn & Steinman, 1989;Lemij & Collewijn, 1991a,b, 1992Oohira, Zee & Guyton, 1991) and muscular weakening (Snow, Hore & Vilis, 1985;Viirre, Cadera & Vilis, 1988;Inchingolo, Optican, Fitzgibbon & Goldberg, 1991) have been extensively used to address this issue. More recently, both post-saccadic drift adaptation (Kapoula, Optican & Robinson, 1990;Kapoula, Eggert & Bucci, 1994) and fast disconjugate saccadic adaptation induced by aniseikonia (Van der Steen, 1992Bush, Van der Steen & Miles, 1994;Eggert & Kapoula, 1992;Eggert, Kapoula & Bucci, 1995) has been studied with dichoptically presented images.…”

Influence of afferent synaptic innervation on the discharge variability of cat abducens motoneurones

“…Extraocular motoneurones, in contrast to other cells such as cortical neurones (Stevens & Zador, 1998; Salinas & Sejnowski, 2000), fire highly regular spike trains. Firing stability ensures the correct eye position and it is, therefore, necessary for visual accuracy during eye movements (Easter, 1973; Kapoula et al 1990). Nevertheless, during an eye fixation, motoneurone interspike intervals (ISI) show a certain degree of variability (Gómez et al 1986).…”

Proprioceptive and Retinal Afference Modify Postsaccadic Ocular Drift

“…The reason for the discrepancy between their results and our findings is uncertain. Although the incongruency between retinal and proprioceptive afferent signals in the paradigm used by Kapoula et al (1990) may be partially responsible for their findings, we have demonstrated that ocular deafferentation does not inhibit visually mediated disconjugate adaptation of drift. Thus this form of oculomotor adaptation does not require a congruence between retinal and extraretinal afferent signals.…”

“…In normal human subjects, if postsaccadic retinal image motion is presented to one eye while the other eye views a stationary, nonfusible pattern, a conjugate pattern of postsaccadic drift adaptation occurs (i.e., changes in drift are approximately equal in the 2 eyes) (Kapoula et al 1990). These authors suggested that binocular fusion is required for disconjugate adaptation of drift, although subsequent similar experiments using fusible dichoptic visual stimuli failed to induce substantial vertical disconjugate postsaccadic drift (Kapoula et al 1996b).…”