Closed-loop and open-loop accommodative vergence eye movements

Exploring Binocular Visual Attention by Presenting Rapid Dichoptic and Dioptic Series

This study addresses an issue in attentional distribution in a binocular visual system using RSVP tasks under Attentional Blink (AB) experimental protocols. In Experiment 1, we employed dichoptic RSVP to verify whether, under interocular competition, attention may be captured by a monocular channel. Experiment 2 was a control experiment, where a monoptic RSVP assessed by both or only one eye determines whether Experiment 1 monocular condition results were due to an allocation of attention to one eye. Experiment 3 was also a control experiment designed to determine whether Experiment 1 results were due to the effect of interocular competition or to a diminished visual contrast. Results from Experiment 1 revealed that dichoptic presentations caused a delay in the type stage of the Wyble's eSTST model, postponing the subsequent tokenization process. The delay in monocular conditions may be further explained by a visual attenuation, due to fusion of target and an empty frame. Experiment 2 evidenced the attentional allocation to monocular channels when forced by eye occlusion. Experiment 3 disclosed that monocular performance in Experiment 1 differs significantly from conditions with interocular competition. While both experiments revealed similar performance in monocular conditions, rivalry conditions exhibit lower detection rates, suggesting that competing stimuli was not responsible for Experiment 1 results. These findings highlight the differences between dichoptic and monoptic presentations of stimuli, particularly on the AB effect, which appears attenuated or absent in dichoptic settings. Furthermore, results suggest that monoptic presentation and binocular fusion stages were a necessary condition for the attentional allocation.

Symmetrical horizontal vergence contributes to the asymmetrical pursuit of targets in depth

When a target travels slowly and smoothly along the line of sight of one eye, the eye that is aligned with the target remains stationary while the other eye adducts. The mechanism that is commonly invoked is that commands signaling conjugate pursuit and symmetrical vergence are combined. The two signals are in the same direction in the adducting eye but are in the opposite direction in the stationary eye and, so, cancel. Recent data have challenged this view and the idea that the two eyes are controlled independently has been resurrected. Pursuit and vergence movements are difficult to separate when they occur together because they have similar latencies and dynamics. We have developed a method where horizontal vergence is "tagged" by training it to have a vertical vergence component that can then be identified in combined pursuit-vergence movements. Four subjects trained eye movements to have a vertical vergence component by fusing vertical disparities that varied in association with horizontal convergence. Following training, the vertical vergence aftereffect was found whenever horizontal vergence was stimulated regardless of whether the horizontal vergence resulted from movement of the target in the midsagittal plane (symmetrical vergence) or from movement of the target along the line of sight of one eye (asymmetrical vergence). The vertical vergence aftereffect was never observed in association with conjugate movements indicating that asymmetrical slow eye movements are not controlled monocularly but contain a vergence component along with symmetrical smooth pursuit.

What does the dominant eye dominate? A brief and somewhat contentious review

We examine a set of implicit and explicit claims about the concept of eye dominance that have been made over the years and note that the new literature on eye dominance does not reflect the old literature from the first half of the last century. We argue that the visual and oculomotor function of the dominant eye--defined by such criteria as asymmetry in acuity, rivalry, or sighting--remains unknown and that the usefulness of the concept for understanding its function is yet to be determined. We suggest that the sighting-dominant eye is the eye used for monocular tasks and has no unique functional role in vision.

The cyclopean eye in vision: the new and old data continue to hit you right between the eyes

We argue against recent claims by Erkelens and van Ee (Vision Res., in press) and by Erkelens (Vision Res. 40 (2000) 2411) that "the concept of the cyclopean eye is em leader always irrelevant as far as vision is concerned" (p. 1157) [corrected] and that "perceived direction during monocular viewing is based on the signals of the viewing eye only" (p. 2411), respectively. In Experiment 1, we presented a pair of small lights on a visual axis and measured the absolute visual direction of the near light with reference to different parts of the face. The near light appeared in front of the bridge of the nose or very near it, contrary to what was expected from Erkelens and van Ee's claim that monocular stimuli are seen in their correct locations. In Experiment 2, we replicated Erkelens' experiments with measurements of phoria and analyses of eye movements. The results confirmed his finding that the cyclopean illusion occurred rarely in the monocular condition, but our phoria and eye movement data provided the basis for a very different interpretation. Our data show that the oculomotor signal in his particular monocular condition was considerably weaker than in his binocular condition; therefore, the rarity of the monocular cyclopean illusion is not surprising. Moreover, since both claims above are based on an over-generalization of the results of Erkelens' study, neither claim is persuasive.