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S J Judge

Publications and source records attributed to S J Judge.

31 records · Page 2Linked to original sources
PubMed1988

Adaptation to telestereoscopic viewing measured by one-handed ball-catching performance.

A one-handed ball-catching task was used to study the disturbance of depth judgement induced by telestereoscopic viewing (ie viewing with increased effective interocular separation), the recovery of performance with experience in the telestereoscope, and the errors that subsequently arose when the telestereoscope was removed. The ball's trajectory was variable so that subjects had to control both the position and the timing of the grasp in order to catch the ball. On first wearing the telestereoscope, subjects closed the hand when the ball was approximately twice as far away from the eyes as the hand was. After fewer than twenty trials in the telestereoscope subjects were closing the hand at approximately the correct time and place, although rather more trials were needed for ball-catching performance to recover to normal. When the telestereoscope was removed there was an aftereffect, with subjects making the opposite errors to when they began the task. The existence of an aftereffect shows that the process of adaptation involves reevaluation rather than neglect of the misleading binocular information. Helmholtz's theory that telestereoscopes cause the world to be perceived as a scale model is considered. Initial misreaching is roughly consistent with this theory, but there are insufficient data to test it rigorously. Data from the aftereffect phase are clearly inconsistent with the theory. The results confirm the importance of binocular information in dynamic motor tasks, such as ball catching.

Adaptation, Ocular↗
PubMed1987

Optically-induced changes in tonic vergence and AC/A ratio in normal monkeys and monkeys with lesions of the flocculus and ventral paraflocculus.

Monkeys wore either base-out prisms to promote changes in tonic vergence or periscopic spectacles to promote changes in the coupling between accommodation and vergence. Eye movements were recorded using the magnetic search coil technique and the monkeys were rewarded for accurate fixation. Two normal monkeys and two monkeys which had previously received lesions of the flocculus and ventral paraflocculus were studied. After 30 min of prism viewing the two normal monkeys had elevated phoria--increased by approximately 50% of the prism stimulus. The two lesioned monkeys also had phoria increases of a similar size after prism viewing. The effect of duration of prism viewing on the magnitude and time course of phoria elevation was studied in one normal monkey. The initial magnitude of phoria elevation and the time constant of relaxation of phoria both increased as the duration of prism exposure varied from 5 s to 30 min. Initial phoria increased approximately in proportion to the logarithm of duration of prism exposure whereas the time constant of phoria relaxation increased linearly with duration. In the same normal monkey it was shown that increasing vergence by means of accommodative-vergence did not induce phoria changes. The effect of periscopic spectacle viewing was studied in all four monkeys. After 30 min of periscopic spectacle viewing all four monkeys had a higher AC/A ratio. The magnitude of the changes was (paradoxically) greater in the two lesioned monkeys than in the one normal monkey studied fully.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed1987

Optically induced changes in the couplings between vergence and accommodation.

Vergence-induced accommodation (V-A) and accommodation-induced vergence (A-V) were measured in human subjects before and after they had worn various optical devices for 30 min. Laterally displacing periscopic spectacles, which increase the required change in vergence per unit change in accommodation, caused decreases and increases in the gain of V-A and A-V responses, respectively. These observations are consistent with the view that the gain of the neural cross-linkages between vergence and accommodation are subject to adaptive regulation. However, there were strong asymmetries: Medially displacing periscopes (cyclopean spectacles), which reduce the required change in vergence per unit change in accommodation to zero, were almost totally without effect. Base-out prisms, which increase the required convergence by an amount that is constant for all viewing distances, caused downward and upward shifts in the V-A and A-V response curves, respectively. Base-in prisms, which reduce the required convergence by a constant amount for all viewing distances, caused downward shifts of A-V curves but had no significant effect on V-A curves. These effects of prisms are in essential agreement with the work of others and confirm the existence of adaptive elements that regulate the bias in the vergence and/or accommodation control systems. Secondary effects of wearing periscopes and prisms indicated a certain lack of specificity in the sensing of gain and bias errors: vertical shifts of V-A and A-V curves (resembling those seen with base-out prisms) often occurred with the laterally displacing periscopes, and gain changes (generally resembling those seen with laterally displacing periscopes) often occurred with the base-out prisms.

Accommodation, Ocular↗
PubMed1986

Disparity-induced and blur-induced convergence eye movement and accommodation in the monkey.

The dynamics of vergence eye movement and of ocular accommodation were studied in two monkeys trained to track a haploscopically presented target that appeared to move in depth. The target was presented under four conditions: monocular viewing, normal binocular viewing, accommodation-open-loop binocular viewing, and "conflict" viewing, in which the accommodation and vergence stimuli did not correspond to those produced by any real target in three-dimensional space. The first and third conditions were chosen because in each case only one of the two primary cues that guide accommodation and vergence was operative: blur in the first case and disparity in the third. We usually studied responses to apparent target movement directly toward or away from the right eye, in which accommodation was measured. The latencies of the accommodation responses to steps toward the monkey were approximately 180 and 240 ms in the two monkeys, while in both monkeys the latencies of convergence were approximately 160 ms. Neither the vergence latencies nor the accommodation latencies were greatly different in monocular and binocular viewing. Responses to a sinusoidally moving target (frequencies 0.1-1.2 Hz; peak-to-peak amplitude 0.5-4 diopters or meter-angles) were studied in the first three of the above viewing conditions. In binocular viewing, even with accommodation open-loop, vergence and accommodation showed much smaller phase lags than in monocular viewing. Furthermore, in response to step changes, both vergence and accommodation velocities were higher in binocular viewing than in monocular viewing. Thus the dynamic control of both vergence and accommodation relies predominantly on disparity signals. At low frequencies (0.2 or 0.3 Hz) the monkeys showed only a modest ability to separate their accommodation and vergence responses when presented with conflicting blur and disparity cues. A simple linear calculation based on the data above was used to predict the responses in such situations. The predicted and observed responses were in reasonable agreement.

Accommodation, Ocular↗
PubMed1986

Neurons in the monkey midbrain with activity related to vergence eye movement and accommodation.

We recorded from neurons dorsal and dorsolateral to the third nerve nucleus of the monkey whose discharge rates modulated when the monkey tracked targets moving in depth but not when it tracked targets moving from side to side. The neurons' activity modulated equally well whether the target moved directly toward one eye or the other. For most neurons the amplitude of modulation was similar whether the monkey tracked monocularly (blur cue alone), binocularly with accommodation open-loop (disparity cue alone), or in normal binocular viewing. By comparing the modulation in normal binocular viewing with that when the blur and disparity cues were in conflict we were able to show that 19 neurons discharged in relation to the vergence response alone and not to accommodation. Eight neurons discharged exclusively in relation to accommodation. While the monkeys tracked targets moving in depth so that target vergence varied with a sinusoidal time course (frequency 0.1 or 0.2 Hz) the discharge modulations of identified vergence cells generally showed much more phase lead than expected of motoneurons. We examined the activity of a subset of these vergence cells in response to a range of stimulus frequencies to compare the dynamics of these neurons with motoneurons. The phase leads were larger than those expected of motoneurons over the entire frequency range tested. We speculate that vergence neurons may selectively activate (directly or indirectly) motoneurons with longer time constants than the mean.

Accommodation, Ocular↗
PubMed1985

Changes in the coupling between accommodation and vergence eye movements induced in human subjects by altering the effective interocular separation.

It has usually been thought that the coupling between accommodation and convergence of the eyes is fixed and not modifiable by experience. Experiments are reported which show that the ratio of accommodative vergence to the accommodation stimulus, the stimulus AC/A ratio (one measure of the coupling), is elevated by brief periods (approximately 30 min) of experience of viewing the world through periscopic spectacles which increase the effective interocular separation. Experience of viewing through 'cyclopean' spectacles, which superimpose the line of sight of the two eyes, reduced the stimulus AC/A ratio in one subject and increased it in another, while it remained hardly affected in a third.

Accommodation, Ocular↗
PubMed1977

Activity of neurones in the inferotemporal cortex of the alert monkey.

The activity of neurones in the inferotemporal cortex of the alert rhesus monkey was recorded while the monkey was shown visual stimuli, which included both food and non-food objects for comparison with the activity of neurones in the lateral hypothalamus and substantia innominata. In the anteroventral part of the inferotemporal cortex, neurones were found with visual responses which were sustained while the animal looked at the appropriate visual stimuli. The latency of the responses was 100 msec or more. The majority (96/142 or 68%) of these neurones responded more strongly to some stimuli than to others. These units usually had different responses when objects were shown from different views, and physical factors such as shape, size, orientation, colour and texture appeared to account for the responses of some of these units. Association of visual stimuli with a food reward (glucose solution) or an aversive taste (5% saline solution) did not affect the magnitude of the responses of the neurones to the stimuli either during the learning or after the period of learning. Nor did feeding the monkey to satiety affect the responses of the neurones to their effective stimuli.

Animals↗