Showing papers on "Monocular vision published in 1982"

The precision of gaze. A review.

Abstract: This paper reviews advances in our knowledge about the stability of the human being's line of sight while fixating objects stationary with respect to himself. Recent technological developments made it possible to measure gaze with a high degree of accuracy when the head was free of artificial support. Measurements made with the head free while the subject sat, as still as possible, show that gaze is half as stable as when the head is held rigidly. Precision deteriorates by an additional factor of five when the head is moved actively or passively within a range of natural physiological frequencies and amplitudes. Fixation errors and retinal image motions associated with such imprecision of gaze under natural conditions would not be expected to degrade monocular vision in light of current psychophysical evidence. Binocular fixation errors and differences in retinal image motions in each of the eyes, associated with imprecision of vergence under natural conditions, cannot, however, be reconciled with current psychophysical knowledge of binocular vision attained thus far only under artificial conditions.

The organization of binocular cortex in the primary visual area of the rabbit.

Abstract: A conscious rabbit which crouches in the ‘freeze’ position has an unequivocal 24° wide binocular field formed by the overlap of the two 12° sectors of uniocular optical field which extend nasal of its midline. Although this investigation reveals that the horizontal representation of the uniocular visual field in cortical visual area I extends more nasal than in earlier reports, it is found to terminate at the midline when the eyes are set in the standard freeze position. The 12° sectors of uniocular field nasal of the midline were not represented in spite of being served by retina. The binocular field of the rabbit in the freeze posture thus appears to have no binocular representation in visual area I. Nevertheless, the presence of a binocular region was confirmed in rabbit visual area I but the projections to it, via the contralateral and ipsilateral eyes, deal with the nonoverlapping sectors of monocular field when the eyes are in the freeze position. The maps of the visual field obtained in one hemisphere via the contralateral and ipsilateral projections were subject to a horizontal divergent disparity of some 18°. The presence of binocular single units in these regions was also confirmed but their two receptive fields were necessarily located in different visual hemispheres and again subject to an 18° mean horizontal divergent disparity. They could not be simultaneously stimulated by any localized feature of an object and are thus precluded from involvement in binocular single vision during the freeze position. The systematic, rather than reportedly random, topography of the ipsilateral projection to visual area I ensured that it could be well fused with the similarly organized contralateral projection by means of an 18° vergence of the eyes from the freeze position. The horizontal receptive field disparity of binocular single units is then brought to a zero mean value which enables their receptive fields through each eye to be simultaneously stimulated by the same part of an image. Tested units then evinced response summation; a minimum requirement for binocular vision. In this equivalent primary position of the eyes, the entire binocular visual field is completely represented in visual area one of both hemispheres. The rabbit thus appears to employ a two-state cortical system for forward vision. In the freeze position the visual field attains a cyclopean extent of 360° but the receptive fields of cortical binocular units are widely divergent. The classic binocular optical field may then project to some other region of brain which subserves binocular vision. Upon examination of a frontal object the animal must verge its eyes in order to obtain binocular single vision in visual area I; it then temporarily surrenders part of its rear visual field. An explanation in terms of ocular image quality is suggested.

Blur-induced changes in the visual evoked potential.

Abstract: Binocular vision has several advantages as compared with monocular vision. In this study, objective recordings of binocular functioning were studied with visual evoked potentials (VEP's). Lenses from plano through +1.50 D were added to reduce acuity monocularly and binocularly. Results indicate that the VEP, while sensitive to binocularly induced blur, does not reflect the changes in binocular vision which are produced by monocularly induced blur. The high contrast of the visual stimulus pattern (97%) may be responsible for the absence of attenuation during binocular viewing while one eye is blurred.

Normal binocular vision.

Abstract: All vertebrates have two eyes. They are thus able to observe a wider panorama than would be the case if they had only one. Binocular vision also offers a second advantage, namely depth perception. This “stereoscopic vision” arises from the fact that the two eyes observe the world from slightly different positions. Panoramic vision and stereoscopic vision involve conflicting requirements. For the widest panorama, the visual fields of the two eyes must meet, but without overlapping. Depth perception in as large as possible an area of the visual field, by contrast, requires that the visual fields overlap as far as possible. Some animals have opted for panoramic binocular vision and thus for laterally positioned eyes. These are mainly the herbivores, which need to escape as soon as they scent danger in their surroundings. Other species have abandoned panoramic vision in favor of depth perception in as large a binocular field of vision as possible; their eyes have adopted a frontal position. This group consists mainly of predatory animals, which must be able to accurately estimate the distance to their prey, and tree-dwelling species, which need to know how far it is to the next branch if they are to jump successfully. Among the animal species, the apes have the most highly developed visual co-ordination of front leg movements.

Binocular vision in normal and stereoblind subjects.

Abstract: This article describes several different psychophysical strategies that have been applied to the study of binocular vision in normal persons and people with deficient stereopsis. Results from these three techniques--binocular summation, interocular transfer, and utrocular discrimination--are considered in terms of the properties of neural mechanisms that integrate inputs from the two eyes.