Showing papers on "Monocular vision published in 1983"

Binocular stereopsis in an insect

Abstract: Binocularity in insects is generally assumed to have the same function as in many vertebrates—the perception of depth. Evidence for this hypothesis stems from the observation that one-eyed dragonfly larvae, tiger beetles, praying mantids and water scorpions rarely catch prey1–5 but no definitive evidence is available. Depth perception and catching behaviour depend on visual attention and visual behaviour and it is difficult to assess what is impaired when one eye is occluded6. A more promising approach to studying the importance of binocular disparity is one that does not interfere with normal binocular vision, and allows potential monocular depth cues to be controlled carefully. These criteria were met in the present study by the use of prismatic lenses placed in front of the compound eyes of the praying mantis, thus creating a conflict between binocular disparity and monocular cues. The results demonstrate that mantids do indeed rely on binocular triangulation when estimating the distance of prey, and thus provide the first unequivocal evidence for stereoscopic vision in an invertebrate.

Involvement of GABAergic mechanisms in the optokinetic nystagmus of the frog.

Abstract: Frog optokinetic nystagmus (OKN) was studied before and after an intravitreal injection of picrotoxin, a specific non-competitive GABA antagonist. In monocular vision, the OKN displayed a directional asymmetry favouring the Temporal-Nasal (T-N) stimulation. In that case, the nystagmus extinction frequency (NEF) is low, about 2 frames/s. In binocular vision, the OKN is symmetrical with a facilitation of performances compared to monocular vision (NEF = 3 frames/s). In monocular as in binocular vision, an intravitreal injection of picrotoxin (between 1×10−4 and 5×10−3 M) provoked the disappearance of the injected eye OKN and a spectacular facilitation in the performances of the intact eye, with the appearance of a N-T component and the increase of the NEF value reaching 7 or 11.5 frames/s according to the experimental conditions. This contralateral facilitation was no longer observed after the optic nerve of the injected eye had been cut, indicating that such a facilitation can only be explained by alterations of a central process triggered by the visual input. It is concluded that GABAergic mechanisms might be responsible for the inhibition of the N-T component in the frog OKN and might be involved in the control of the power of temporal resolution in this animal.

Non-fusable stimuli and the role of binocular inhibition in normal and pathologic vision, especially strabismus

Abstract: Stimuli on corresponding points of both retinae that cannot be fused may cause binocular rivalry: the stimuli suppress each other alternately. This effect was used to study the influence of image sharpness upon binocular inhibition. Blurring an image means decreasing its contrast and attenuating its high spatial frequencies. Both factors diminish the time that a stimulus is perceived during rivalry. This fact has implications both for normal vision - as objects off the horopter are normally blurred - and for disturbed vision when the image of one or both eyes is (locally) deteriorated. In both cases, the binocular field of view can be combined from the ‘good’ parts of both eyes. Hence, the field of view may consist, in a piece-meal fashion, of parts stemming from the right or the left eye exclusively and others where both images are superimposed. We present evidence for the hypothesis that there is a common neural mechanism causing both binocular rivalry and functional amblyopia in anisometropia and strabismus. Consequences of the results on rivalry suppression for the pathophysiology and therapy of strabismic amblyopia are discussed.

Sighting from the cyclopean eye: the cyclops effect in preschool children

Abstract: The behavior of preschoolers in two sighting tasks was observed. In one task, the child was asked to sight a target through a tube, and, in the other, to point to a target. In addition to monocular sighting, the “cyclops effect” was observed; the child positioned the tube or finger in line with the target and a point between the eyes and left it there. Observation of both types of response suggests a developmental shift from central sighting, which reflects the visual direction basis of sighting tasks, to monocular sighting, which reflects the monocular alignment required by the tasks.

A model for the monocular line orientation analyzer

Abstract: A model for monocular line perception by humanSs is based on three basic assumptions: (a) the line's inclination is coded by the maximally excited orientation detector's number; (b) the inclination of the perceived line is equivocally determined by the excitation vector in the subjective space; (c) the analyzer has a maximum differential sensitivity over the whole range of the line inclinations. This simple model for the line inclination analyzer, taking into account the optimization of its sensitivity, provides incomplex explanations for a wide range of psychophysical and neurophysiological data obtained from human and animal experiments.

Surgical procedure for restoration of the physiological alignment of the eyes following muscular dysfunction

Abstract: Eight adult patients suffering from bilateral or unilateral N VI paralysis of more than one year's standing, and from rupture of the inferior rectus muscle due to accident underwent transposition of the muscle venter, a method which has been practiced now for five years. In all these patients the starting point of eyeball movement was shifted either outward or downward with the result that the primary position of the yeses could be used for either full or intermittent binocular vision. Where the patient had monocular vision either unilateral or alternating, at least spatial orientation was improved, as a result of the restored physiological alignment of the visual axes with the sagittal plane of the body.