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Random-dot stereograms when used as adaptation stimuli can influence the perceived depth of similar test stimuli. Adaptation for 1 minute is sufficient to evoke this three-dimensional aftereffect for several seconds. This aftereffect must occur after stereopsis because prior to stereopsis no relevant monocular cues exist in these adaptation and test stimuli.
Animals with binocular single vision use disjunctive (vergence) eye movements to align the two eyes on a visual target. Several lines of evidence suggest that conjugate and vergence eye movement commands are generated independently and combined at the medial rectus motoneurons. If this were true, then a pure vergence eye-position signal should exist. This signal would be proportional to the horizontal angle between the eyes (vergence angle), without regard to the direction of conjugate gaze. The purpose of this experiment was to identify and study neurons that carry a pure vergence signal. Extracellular unit recordings were made from midbrain and pontine sites in monkeys trained to track visual targets moving in the horizontal, vertical, and depth (or target vergence) planes. The most commonly encountered neuron that had a vergence signal was the convergence cell. These units had a firing rate that was linearly proportional to the convergence angle; their activity was unaffected by changes in conjugate gaze. Changes in convergence cell activity preceded the change in vergence angle slightly. Convergence cell activity increased for increased convergence regardless of whether the change was in response to purely accommodative or disparity cues. Divergence cells were found far less frequently. These cells were similar to convergence cells except that they decreased their firing rate for increases in convergence. The activity of divergence cells was unaffected by changes in the direction of conjugate gaze. Both convergence and divergence cells were found, intermixed, in the mesencephalic reticular formation must outside the oculomotor nucleus. Most cells with a vergence signal were found within 1-2 mm of the nucleus. These results support the view that conjugate and vergence signals are generated independently and are combined at the extraocular motoneurons. Convergence cells seem ideally suited to provide the vergence signal required by the nearby medial rectus motoneurons.
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Biofeedback therapy refers to the process of gaining voluntary control over some bodily function by the immediate use of information regarding its physiological state. In this paper we review the use of oculomotor biofeedback therapy in three common ocular disorders: nystagmus, strabismus, and amblyopia. Experimental and clinical test results have been encouraging. We believe oculomotor biofeedback therapy should be attempted, either alone or in conjunction with orthoptic and/or surgical procedures, in these and other ocular disorders manifesting an abnormal oculomotor component.
Three experiments were conducted to replicate and extend Helmholtz's observation indicating vergence hysteresis. The two stimuli were presented dichoptically to the eyes in the mirror stereoscope and moved temporalward or nasalward. Helmholtz's finding was confirmed in Experiment 1, in which the critical separations were measured for the stimuli divergently moving temporalward when fusion of their images was abruptly broken (breakaway point) and when fusion was re-established (refusion point) for the stimuli moving nasalward. In Experiment 2, in which only the stimulus for one eye moved temporalward while the stimulus for the other eye was stationary, the breakaway point of the moving stimulus was found to be linearly dependent on the position of the stationary stimulus. Experiment 3 showed that, in the asymmetric divergent tracking as in Experiment 2, the change of the perceived visual direction of the fused image was smaller than the angular magnitude of the movement of the tracking eye. These results were discussed as evidence indicating the sensory and motor connection of the two eyes.
We examined the relationship between ventricular size and visual function in 50 children (36 males and 14 females) with hydrocephalus. The third and lateral ventricular sizes and the visual function scores did not significantly differ between the sexes. Ventricular enlargement was most pronounced at the trigones and least at the level of the foraminae of Monro. The visual function score correlated inversely with the size of the lateral ventricle measured at the levels of the anterior horn and the trigone and expressed as coronal diameter and "Modified" Evans' ratio (r = 0.49; P = 0.001 and r = -0.38, P = 0.01 for the anterior horn; r = 0.48, P = 0.001 and r = -0.35, P = 0.001 for the trigone). The size of the third ventricle did not correlate with visual function score. A "modified" anterior Evans ratio of 0.60 and a trigonal Evans ratio of 0.73 were associated with very low visual function score. Furthermore, there was significant inverse correlation between occipitofrontal circumference (OFC) and visual function (r = -0.6379, P = 0.001), but OFC was not valuable for predicting visual function before the onset of head enlargement.
Dark vergence depends on the vertical direction of gaze; it decreases with raised gaze and increases with lowered gaze. The vertical direction of gaze can be varied by means or raising or lowering the eyes or by way of tilting the head forward or backward. The effects of both manipulations on dark vergence are different. According to Heuer (1988) the effects of head tilt and eye inclination on dark vergence are almost, but not exactly, additive. In Exp. 1 the hypothesis of additive effects of gaze direction and eye inclination was tested and could not be rejected. The two additive hypotheses (head tilt and eye inclination vs. gaze inclination and eye inclination) result in different predictions for dark vergence with "compensatory" head and eye inclinations, which leave the direction of gaze in space invariant. In Exp. 2 it was shown that predictions from both hypotheses deviated from the observed values of dark vergence. Thus none of the two additive hypotheses provides exact predictions of dark vergence for all possible combinations of head tilt and eye inclination. For practical purposes the approximation might be sufficient. In particular, although mean dark vergence cannot be predicted exactly, individual differences can be predicted quite accurately.
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Orthoptic therapy was instituted in an adult, alternating esotrope with asthenopia who exhibited inaccurate static accommodative responses with adequate, clinically determined, accommodative facility. During and following therapy the patient showed considerable improvement in accommodative accuracy and related visual functions, such as contrast sensitivity, in the absence of any change in strabismic deviation. This case provides the first laboratory documentation of orthoptic effects on accommodation in an adult strabismic.
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The present paper exposes the shortcomings of orthoptics and proposes an original system of concomitant squint treatment named diploptics. This system is based on the new conception of the role of bifixation in the physiology and pathology of binocular vision. The major principle of diploptics is to induce diplopia under natural conductions and further to "enliven" or develope the ability to overcome it with the help of the optomotor fusion reflex and thus to recover the auto-control mechanism of bifixation - the basis of the normal binocular vision. To realize this principle a number of methods are suggested. A trial of these produced hopeful results.
Electrooculographic study on the movements of convergence among 53 young subjects clinically normal, in nine different conditions of symmetry, of laterality and of preponderance of the directing eye. The morphology of the graphs are described, the duration of latency, the velocities and the amplitudes were measured for the different types of response, and the statistical disturbances corresponding were compiled. For some of these characteristics were made unpublished acknowledgement.
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Thresholds for object-motion detection are significantly raised when concurrent self-motion perception is induced by either vestibular, or visual, or cervico-somatosensory stimulation. Active sinusoidal horizontal head oscillations with compensatory vestibulo-ocular reflex (VOR) and foveal or eccentrical target presentation; 'passive' head movements with fixation suppression of the VOR; pure body oscillations with the head fixed in space (cervical stimulation); optokinetically induced apparent self-motion (circularvection). This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue. It may reflect the disadventageous side effect due to unspecificness of an otherwise beneficial space constancy mechanism, which provides us with the image of a stable world during locomotion.