Showing papers on "Monocular vision published in 1986"

Multiple sensitive periods in the development of the primate visual system.

Abstract: Early in life, abnormal visual experience may disrupt the developmental processes required for the maturation and maintenance of normal visual function. The effects of retinal image deprivation (monocular form deprivation) on four psychophysical functions were investigated in rhesus monkeys to determine if the sensitive period is of the same duration for all types of visual information processing. The basic spectral sensitivity functions of rods and cones have relatively short sensitive periods of development (3 and 6 months) when compared to more complex functions such as monocular spatial vision or resolution (25 months) and binocular vision (greater than 25 months). Therefore, there are multiple, partially overlapping sensitive periods of development and the sensitive period for each specific visual function is probably different.

Binocular vs. monocular task performance.

Abstract: Functional advantages of binocularity were investigated by having 13 subjects perform a group of occupational-type tasks under monocular and binocular conditions. Significant binocular advantages ranging from 29.5% (pointers in straws) to 3.7% (reading speed) were measured. Tasks with many disparity cues showed the greatest binocular advantage. This shows that patients with normal binocular vision use binocular cues, most likely stereopsis, to enhance performance. In a second experiment, three subjects with normal binocular vision underwent monocular occlusion for 5 days to investigate whether monocular skills improved to compensate for the loss of binocular vision. During that period binocular performance was consistently better than monocular performance, and both monocular and binocular performance improved, even though the subjects were only gaining monocular experience. Although the 5 day occlusion period does not simulate the long-term denial of normal binocularity that strabismics or monocular patients experience, it shows that binocular superiority remains after short-term loss of binocularity.

Monocular acuity in normal infants: the acuity card procedure.

Abstract: An "acuity card" technique has been developed for rapid assessment of visual acuity in infants. In this procedure an adult observer shows the infant a series of cards that contain gratings of various spatial frequencies and estimates acuity as the highest spatial frequency that the infant is judged to see. The present paper shows that the acuity card procedure can be used in a laboratory setting to estimate both monocular and binocular acuity in infants 1 to 12 months of age. Four monocular and two binocular acuity estimates were obtained on 36 normal infants, six each at ages 4, 8, and 16 weeks and 6, 9, and 12 months. Acuity estimate means and SD's agreed well with previously established preferential looking (PL) norms for each of the test ages. Time required for a monocular or a binocular test averaged 3 to 6 min.

Recovering viewer-centered depth from disparity, occlusion, and velocity gradients

Abstract: Two experiments were conducted to assess the effects of corresponding and conflicting binocular and monocular information on the recovery of depth order (signed depth). Subjects viewed displays in which the same or opposite depth orders were indicated by disparity and occlusion, in one experiment, or by disparity and velocity gradients, in a second experiment. The same 36 subjects, 17 who had failed a Random Dot E test and 19 who had passed, were run in both experiments. When binocular and monocular information indicated conflicting depth orders, most subjects responded in accordance with the monocular information on some trials in both experiments. This was true even for a subgroup who always responded in accordance with the stereoscopic information on control trials that did not provide monocular information for depth order. For this subgroup, the impact of conflicting monocular information in the velocity gradient task correlated with performance on the uncrossed version of the Random Dot E test. We also found that some subjects who failed static tests of stereoscopic depth perception could respond accurately to continuously changing disparities.

Monocular aniseikonia: a motion parallax analogue of the disparity-induced effect.

Abstract: Mayhew and Longuet-Higgins have recently outlined a computational model of binocular depth perception1 in which the small vertical disparities between the two eyes' views of a three-dimensional scene are used to determine the ‘viewing parameters’ of fixation distance (d) and the angle of asymmetric convergence of the eyes (g) (refs 2, 3). The d/g hypothesis, as it has been called4, correctly predicts that a fronto-parallel surface, viewed with a vertically magnifying lens over one eye, should appear to be rotated in depth about a vertical axis1,3–5. We report here a comparable illusion for surfaces specified by monocular motion parallax information, which can be explained more simply by considering the differential invariants of the optic flow field. In addition, our observations suggest that the disparity-induced effect is not a ‘whole field’ phenomenon nor one limited to small magnification differences between the eyes1,4.

Effect of ecological viewing conditions on the Ames' distorted room illusion.

Abstract: Ecological theory asserts that the Ames' distorted room illusion (DRI) occurs as a result of the artificial restriction of information pickup. According to Gibson (1966, 1979), the illusion is eliminated when binocular vision and/or head movement are allowed. In Experiment 1, to measure the DRI, we used a size-matching technique employing discs placed within an Ames' distorted room. One hundred forty-four subjects viewed the distorted room or a control apparatus under four different viewing conditions (i.e., restricted or unrestricted head movement), using monocular and binocular vision. In Experiment 2, subjects viewed binocularly and were instructed to move freely while making judgments. Overall, the main findings of this study were that the DRI decreased with increases in viewing access and that the DRI persisted under all viewing conditions. The persistence of the illusion was felt to contradict Gibson's position. Language: en

Accommodation in anuran Amphibia and its role in depth vision

Abstract: 1. In order to analyse the mechanism of accommodation in anurans, drugs (miotic or atropine) were applied to the cornea of anaesthetized animals to change the refractive state of their eyes. During such changes, the lens and cornea were photographed and the refractive state of the eye was measured using laser speckle refractometry. Measurements taken from the photographs confirmed suggestions by Beer (1898) that accommodation is achieved by moving the lens and not by changing the shape of the lens or cornea. The change in refractive state induced by pharmacological manipulation was about 10 diopters with an accompanying shift in lens position of about 150 μm. Calculations based on a schematic eye suggest a disparity between the amount of lens movement theoretically needed to produce a 10 D shift in refractive state and the amount actually observed. 2. The lens is probably moved by two protractor lentis muscles which are positioned so as to pull the lens towards the cornea (Tretjakoff 1906, 1913). Dissection and HRP preparations revealed that these muscles are innervated by fibres of the oculomotor nerve which relay in the ciliary ganglion. InR. esculenta andR. pipiens, the ciliary ganglion consists of only 8 to 12 nerve cells. 3. MS222 anaesthesia and lymphatic injection of curare cause the lens to move away from the cornea, presumably because they destroy the resting tonus of the protractor lentis muscles. We discuss this finding in relation to the frog's ‘resting’ accommodative state, and conclude that unparalysed frogs are likely to be myopic, and not emmetropic as previous work suggests. 4. Prey capture was analysed inR. pipiens after the disruption of accommodation by bilateral section of the oculomotor nerve. Estimates of prey distance remained accurate when vision was binocular. However, during monocular vision, when the oculomotor nerve was sectioned on one side and the other eye was either occluded or had its optic nerve cut, frogs consistently underestimated the distance of their prey. This result suggests, in agreement with earlier evidence, that accommodation is used for judging depth when vision is limited to one eye, but that binocular information predominates when it is available. 5. Atropine applied to the cornea of monocular frogs also causes distance to be underestimated. It is argued from this that frogs assess distance by monitoring the motor commands sent to their accommodative muscles, rather than by using sensory information from the muscles themselves.

Positional Acuity without Monocular Cues

Abstract: The accuracy with which human observers can determine the spatial location of a shape boundary was measured by vernier alignment. The vernier targets were presented as random-dot stereograms, with varying amounts of camouflage in the monocular image. Camouflage decreased vernier acuity, but when the camouflage was broken by stereoscopic disparity, acuity was improved. In the limiting case when the shape boundaries were defined by disparity information alone, vernier thresholds (75% correct, binary forced-choice) were in the region of 40 s visual angle. This is poor acuity in comparison to vernier thresholds with monocular contour, but if the limited resolution acuity for stereopsis is taken into account, cyclopean and monocular positional acuities can be considered quite similar in relation to their respective resolution limits.

Binocular stereo vision system using an eye and neuron model

Abstract: Humans have two eyes and see objects binocularly. The three-dimensional sensing capacity of humans depends both on the eyes and the neuron system controlling them. In this article, we made a model of the human visual system, including eye movement, and tried to realize the capacity in an artificial sensor. For this, the visual system is separated into two parts—the Eye System and the Neuron System. The former is realized by the sensor mechanisms that are similar to human eyes and the latter by the Neuron Simulator which consists of sixty-four microprocessors. This system can be used as a passive three-dimensional sensor in unarranged surroundings such as the outdoors.

Binocular optical instruments and binocular vision

Abstract: Many visual optical instruments provide the facility for binocular viewing instead of restricting viewing to monocular vision. The main advantage of binocular viewing is the reduction in fatigue likely to occur if one eye is occluded while viewing monocular instruments. This is particularly important for prolonged viewing periods. Also, binocular systems have the potential for stereopsis with an increase in stereoscopic acuity in some cases; although not all binocular instruments provide stereoscopic imagery. In spite of these advantages, some observers have difficulty with binocular instruments. The problems arise when there are alignment errors in the optical components leading to displaced or rotated images. There may also be a conflict between the amount of convergence of the binocular tube axes and the AC/A ratio of the observer, and the amount of accommodation required under those viewing conditions. These factors are discussed in detail along with a case example.

The topology of visual appearance

Abstract: There has been a long, and at times acrimonious, debate in the philosophy of perception over the question of whether depth is seen 'directly' Berkeley notoriously held that it was not1 Much depends, of course, on how one understands the notion of 'direct' or 'immediate' (visual) perception, assuming indeed that one admits such a notion at all Berkeley's notion of indirect perception is essentially an inferential one: something is perceived indirectly just in case it is in some sense only 'inferred' (perhaps only unconsciously) from what is perceived directly2 Direct perception is accordingly non-inferential Rather than enter this debate, I want to show that there is a clear sense in which 'visual appearances' are only tworather than three-dimensional; the epistemological significance of this is another matter I shall deal first with the monocular case and then with the binocular Consider, then, the following simple 'experiment' in monocular vision, to perform which we require a small loop of thin wire, A, and a small length of flexible thin wire, B Suppose x and y are any two objects which visually appear to be separated (eg, they might be two distant houses, one situated to the left of the other from where the observer stands, or they might be opposite corners of a matchbox viewed at arm's length) Then it must be possible to position the loop A in such a fashion that if the two ends of B visually appear to touch jc and y respectively, then B must visually appear to intersect A (see figure 1) But this just reflects the following theorem of the topology of two dimensional surfaces: if x and y are any two separate points on a surface, it must be possible to draw a closed curve A on the surface in such a fashion that any open curve B on the surface whose end-points coincide with x and y must intersect A From this we may conclude that in monocular vision, at least, there certainly is a use of the notion of 'visual appearance' according to which the spatial properties that objects visually appear to have obey a two-dimensional geometry3 (This is the sense in which, for instance, one may say that a small coin viewed face-on at arm's length appears the same size as the moon as seen from the earth) Of course it does not