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S J Judge

Publications and source records attributed to S J Judge.

At least 19 recordsLinked to original sources
PubMed1996

How is binocularity maintained during convergence and divergence?

The geometrical requirements for binocular fusion are stated, and the main features of horizontal vergence eye movements are described, together with an influential schema of understanding the interaction between vergence and accommodation. The anatomy and physiology of the midbrain region implicated in vergence and accommodation control are discussed. The cortical areas from which suitable sensory signals might be derived are mentioned briefly, and a speculation is made about esotropia.

Animals↗
PubMed1993

Visual optics and retinal cone topography in the common marmoset (Callithrix jacchus).

The common marmoset (Callithrix jacchus) is a small, diurnal, New World monkey amenable to vision research. In this paper we describe the visual optics and cone photoreceptor topography of the normal adult marmoset. Paraxial optical ray-tracing shows that the marmoset eye is well represented as a scaled-down version of the human eye. The density of foveal and perifoveal cone photoreceptors in the marmoset is as high, and in peripheral retina higher, than those reported in humans and macaques. The foveal acuity predicted by the Nyquist limits set by the cone mosaic (30 c/deg) is in agreement with behavioral measures of visual acuity. Foveal depth of focus is remarkably small (< 0.2 D) for an eye of this size (axial length about 11 mm). Estimates of the amplitude of accommodation using infrared photorefraction indicate that the marmoset is capable of more than 20 D of accommodation.

Animals↗
PubMed1993

Ocular development and visual deprivation myopia in the common marmoset (Callithrix jacchus).

The normal postnatal ocular development of the common marmoset (Callithrix jacchus) and the effects of visual deprivation on eye growth and refractive state are described. The marmoset normally undergoes a developmental process of emmetropization from high hyperopia at birth. This emmetropization is easily disrupted by visual deprivation produced by lid-suture. Myopia and axial elongation of the vitreous chamber are induced by visual deprivations of 12, 5, and 3 weeks duration. The development of axial myopia after 3 weeks of visual deprivation differs from longer duration deprivations in that the experimental eyes are initially shorter than normal and hyperopic at the end of the visual deprivation period, but subsequently become longer than normal and myopic. Visual deprivation myopia in the marmoset persists even after the deprivation is discontinued and a visual signal is restored. In all experimental groups, the development of the eye in response to the cessation of visual deprivation shows no slowing of vitreous chamber enlargement; the axial enlargement relative to the control eye is either maintained or increases and produces significantly greater myopia. These results suggest that the visual control of postnatal eye growth in the marmoset may be unidirectional in its response to visual experience and able only to increase the growth rate of the vitreous chamber, possibly after an initial delay.

Animals↗
PubMed1992

Role of monkey midbrain near-response neurons in phoria adaptation.

1. One striking characteristic of the way in which accommodation and convergence of the eyes are organized is that although the two responses are usually tightly coupled, a brief period of binocular viewing through prisms that require extra convergence brings about a persistent, adaptive alteration in the relationship between the two responses: the vergence during monocular viewing of a target at a given distance is biased in a convergent direction. We sought to discover the role of the near-response neurons we have previously described in the monkey midbrain in such phoria adaptation. 2. Phoria adaptation was produced in two monkeys by having them view binocularly stereoscopic targets under conditions that mimicked prism viewing, i.e., the mirrors of the stereoscope were set so as to require more convergence than that associated with a real target at the same distance as the images seen in the stereoscope. The activity of 57 near-response neurons located dorsally and dorsolaterally to the oculomotor nucleus was recorded before and after adaptation while the monkeys monocularly viewed targets at a range of distances. 3. Comparison of a neuron's response in normal binocular viewing with the response when the accommodation and vergence stimuli were in conflict allowed us to distinguish 24 neurons that behaved as though they were related exclusively to the vergence response. 5 neurons that behaved as though they were exclusively related to the accommodation response, and 12 neurons whose firing was not so simply related to either response. We were unable to classify the remaining 16 near-response cells by this method. 4. In accommodation-related neurons, the relationship between firing rate and accommodation did not alter, or only altered slightly, when the animal's phoria was adapted. 5. The relationship between firing rate and vergence was unaltered by phoria adaptation in only a small proportion of vergence-related neurons, showing that most neurons do not carry the entire signal responsible for phoria adaptation. On the other hand, in the majority of vergence-related neurons the relationship between firing rate and accommodation was altered by phoria adaptation, showing that most neurons do carry part of the phoria adaptation signal. 6. The implication is that the increase in vergence observed after adaptation is mediated at more than one site. A proportion of the phoria adaptation signal is present at the level of the midbrain vergence-related neurons, with the remainder of the signal being added later, presumably at the motoneurons.

Accommodation, Ocular↗
PubMed1992

Binocular interactions in accommodation control: effects of anisometropic stimuli.

In binocular viewing of real targets, the accommodative demand in the two eyes is not in general identical, yet the accommodation response in the two eyes is equal. In order to investigate how the accommodative signals from the two eyes are combined, this study has examined the effects of several forms of dynamic anisometropic stimulation on the accommodation response in both man and the rhesus monkey (Macaca mulatta). All experiments were performed in a computer-controlled haploscopic apparatus to allow independent control of the accommodative stimuli to the two eyes and of the vergence stimulus. The vergence stimulus was held constant while the accommodation demand was modulated independently in each eye. Accommodation was monitored continuously with a dynamic infrared optometer. Four anisometropic conditions were used. In two of these conditions, accommodation demand was varied sinusoidally with time in both eyes, but with phases differing by 90 degrees or 180 degrees between the two eyes. In the two remaining conditions, accommodation demand in one eye varied sinusoidally, while the accommodation demand was constant in the other. In all cases, the form of the target pattern was identified in the two eyes. The accommodation responses observed with these stimulus conditions were similar in both man and the monkey. When presented with conflicting stimuli in the two eyes, the accommodation response appeared to be best described as a compromise between the inputs to the two eyes; there were no indications of a purely random alternation of eye dominance of the form seen in binocular contour rivalry. When the accommodation demand was modulated in only one eye, there was a modulated accommodation response of similar phase to the control condition (i.e., both eyes modulated in phase) but with a much smaller gain (mean, 39% of control gain). When the accommodation demand was modulated in both eyes with a phase difference of 180 degrees, no significant modulation was observed in the accommodation response at the stimulation frequency. When the interocular phase difference was 90 degrees, a modulated response was observed that showed a mean phase lag 41 degrees more than that observed in the control condition (both eyes modulated in phase) and an appreciably smaller gain (mean, 55% of control gain). The extent to which the results can be described by a linear vector average of the uniocular inputs is considered.

Accommodation, Ocular↗
PubMed1988

Do target angular size-change and blur cues interact linearly in the control of human accommodation?

Calculations made using the data of Kruger and Polar [J. opt. Soc. Am. A2, 1832-1835 (1985); Vision Res. 26, 957-971 (1986); Vision Res. 27, 555-567 (1987)] show that for three of the four subjects they studied, size-change and blur cues do not interact linearly in the control of accommodation. A simple non-linear interaction model is shown to fit the data for all four subjects.

Accommodation, Ocular↗
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↗