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PubMed1984

Parallel-alleys and distance-alleys on horopter plane in the dark.

On each of three frontoparallel planes at distances of about 98, 186, and 276 cm from the subject, two series of light points running horizontally in the dark, one above the other, were constructed by six subjects: a P-alley in which the two series appear as two straight lines that are parallel, and a D-alley in which each pair of points appear equally separated in the vertical direction. Luneburg's mapping functions between visual space and physical space have been used to obtain estimates of K (curvature) and sigma (a constant related to depth perception). In addition, ratios of perceptual distances were assessed by four out of the six subjects with eleven triplets of points on the alleys and values of K were estimated (and the fits of theoretical equations were tested) without the use of the mapping functions. In contrast to experiments with P-alleys and D-alleys on the horizontal plane, K was not unequivocally negative in either of the two experiments.

Depth Perception↗

PubMed1995

Fast perceptual learning in hyperacuity.

We investigated fast improvement of visual performance in several hyperacuity tasks such as vernier acuity and stereoscopic depth perception in almost 100 observers. Results indicate that the fast phase of perceptual learning, occurring within less than 1 hr of training, is specific for the visual field position and for the particular hyperacuity task, but is only partly specific for the eye trained and for the offset tested. Learning occurs without feedback. We conjecture that the site of learning may be quite early in the visual pathway.

Analysis of Variance↗

PubMed1992

Prevalence of disabled stereopsis in a class of optometry students.

Stereopsis is said to be disabled when the third dimension (3-D) cannot be perceived during everyday life but can be when viewing conditions are appropriately arranged. To discover a test suitable for detecting disabled stereopsis, I measured stereoacuity, stereolatency, and the subjective difference in depth perception between monocular and binocular vision of a group of 41 optometry students. Only 2 students showed no sign of this disability. A predictive value for each test was calculated from the results of 14 students whose disability was confirmed by another means. Stereoacuity had the worst predictive value (43%) and stereolatency the best (100%). The prevalence of disabled stereopsis in this group was no less than 34% and might have been as great as 95%.

Depth Perception↗

PubMed1989

A physiological correlate of the Pulfrich effect in cortical neurons of the cat.

When a swinging pendulum is viewed with a light-attenuating filter before one eye, the pendulum bob is perceived to move in an elliptical path in depth. It is believed that the filter causes this illusion, the Pulfrich effect, by delaying processing of the image in the filtered eye relative to that of the unfiltered eye. We sought a physiological correlate of this effect by studying binocular integration in cortical neurons of cats while they viewed moving stimuli. Special attention was focused on single unit disparity tuning because it is widely believed that depth perception is related to the responses of disparity selective neurons in visual cortex. We found that placing a filter before one of the cat's eyes produced a temporal delay in the cortical response. The temporal delay was always associated with a shift in the neuron's spatial disparity tuning. The observed temporal delays and disparity shifts are comparable with the magnitude of the Pulfrich effect in humans.

Action Potentials↗

PubMed1982

Systematic studies with amoxapine, a new antidepressant.

Amoxapine, a tricyclic dibenzoxazepine is an antidepressant which in the dosage range of 150-300 mg/day is notable for its rapid onset of action. Because of the rather long, approximately 30-hour, half-life of 8-hydroxyamoxapine, the active metabolite of amoxapine, the possibility was raised that amoxapine therapy may be carried out with single daily dosages. Such a dosage schedule may improve compliance and, if appropriately timed, decrease perception of some of the unwanted effects of the drug. To test the hypothesis that there may be no disadvantages and perhaps even advantages of a once-a-day regimen as compared to a divided dosage schedule, a 6-week double-blind clinical trial was carried out in 35 hospitalized patients with major (18 patients) and minor (17 patients) depressive disorders. While no statistically significant difference was found in overall therapeutic and adverse effects between the groups treated with single or divided daily doses, onset of therapeutic effect appeared a bit faster in the group treated with single daily doses. Of particular relevance for drugs which can be given in single daily doses is their effect on psychomotor performance tests. In view of the findings that a once-a-day dosage regimen with amoxapine may have advantages over divided daily doses, a second study was carried out in which the effects of amoxapine (50 and 100 mg) were compared to an inactive placebo and amitriptyline (50 mg) with and without ethanol in 8 normal male volunteers. The study was double-blind and followed a latin square design. Since the effects of amoxapine on motor reflex, visual-motor coordination and depth perception did not differ significantly from placebo, the results suggest that the effects of amoxapine on the performances measured are clinically insignificant. No significant interaction with ethanol was noted.

Adult↗

PubMed2003

Disparity-based coding of three-dimensional surface orientation by macaque middle temporal neurons.

Gradients of binocular disparity across the visual field provide a potent cue to the three-dimensional (3-D) orientation of surfaces in a scene. Neurons selective for 3-D surface orientation defined by disparity gradients have recently been described in parietal cortex, but little is known about where and how this selectivity arises within the visual pathways. Because the middle temporal area (MT) has previously been implicated in depth perception, we tested whether MT neurons could signal the 3-D orientation (as parameterized by tilt and slant) of planar surfaces that were depicted by random-dot stereograms containing a linear gradient of horizontal disparities. We find that many MT neurons are tuned for 3-D surface orientation, and that tilt and slant generally have independent effects on MT responses. This separable coding of tilt and slant is reminiscent of the joint coding of variables in other areas (e.g., orientation and spatial frequency in V1). We show that tilt tuning remains unchanged when all coherent motion is removed from the visual stimuli, indicating that tilt selectivity is not a byproduct of 3-D velocity coding. Moreover, tilt tuning is typically insensitive to changes in the mean disparity (depth) of gradient stimuli, indicating that tilt tuning cannot be explained by conventional tuning for frontoparallel disparities. Finally, we explore the receptive field mechanisms underlying selectivity for 3-D surface orientation, and we show that tilt tuning arises through heterogeneous disparity tuning within the receptive fields of MT neurons. Our findings show that MT neurons carry high-level signals about 3-D surface structure, in addition to coding retinal image velocities.

Animals↗

PubMed1973

Evidence for the existence of neural mechanisms selectively sensitive to the direction of movement in space.

1. Visual sensitivity to movement in depth was measured as a function of the relative distances through which the left and right retinal images moved. This relative distance (left:right ratio) provides a sensitive cue to the direction along which a target moves in three-dimensional space.2. Gazing at a target which moved along a fixed direction in space produced a gross reduction of visual sensitivity to movements in depth along that direction. For other directions of movement, visual sensitivity was not affected.3. Sensitivity to depth movement rapidly rose almost to the preadaptation level within the first 20-60 sec after removing the adapting target, but recovery was not complete until 100-300 min had elapsed.4. Any adapting target whose left:right ratio fell within a definite range gave similar reductions of visual sensitivity to movements in depth. There were five such ranges.5. The effects of adapting to movement in depth suggest that eight mechanisms underlie depth perception. These mechanisms are ;tuned' to the direction of movement in three-dimensional space. Four mechanisms are wholly concerned with movements along directions very close to the line which cuts midway between the eyes, and do not respond to movements whose direction departs by more than 1.5 degrees from the preferred direction.6. Neural mechanisms ;tuned' to different left:right ratios could provide a physiological basis for sensing the direction in which an object moves in three-dimensional space.

Adaptation, Ocular↗

PubMed1997

Experience with perceptual and motor skills in rhythmic gymnastics.

Based on the notion of measuring motor performance, an experiment with three groups of 20 elite rhythmic gymnasts (N = 60), 9 to 10 yr., 11 to 12 yr., and 13 to 15 years of age (national level), with children of the same size and age was conducted, to identify the important abilities for the achievement of excellence in this sport. Motor abilities (whole-body coordination, dynamic balance, static balance, sense of kinesthesis, whole-body movement time, and eye-hand coordination) as well as perceptual abilities (whole-body reaction time, anticipation of coincidence, and depth perception) were compared. Analysis showed that scores on measures of whole-body coordination, dynamic balance, and static balance were higher for elite groups of athletes than for corresponding control groups. Moreover, elite athletes in the oldest group scored higher than those in the youngest group on anticipation of coincidence, on eye-hand coordination, and on static balance. These findings indicate the presence of systematic differences between elite athletes and nonathletes on motor abilities related to experience in this sport.

Adolescent↗

PubMed1995

Extent and limits of callosal plasticity: presence of disconnection symptoms in callosal agenesis.

Although earlier studies have emphasized the absence of 'split-brain' symptoms in callosal agenesis patients, the notion of an 'asymptomatic' acallosal brain has lately been challenged. We report a number of findings that are indicative of an interruption of interhemispheric communication and integration in individuals lacking the corpus callosum. Several groups of patients with callosal pathology (acallosals, patients with commissurotomy or callosotomy, either complete or partial) were compared to matched controls. Interhemispheric transfer was tested in two different experiments involving pointing to a light source while maintaining central fixation. In the first experiment, a learning paradigm was used to measure transfer of a motor skill from the trained to the untrained hand. In the second experiment, subjects pointed to visual targets at different locations on a perimeter. Midline fusion, a recurrent theme when describing callosal function, was assessed using tasks which included depth perception with binocular and/or monocular cues, two-point discrimination thresholds and sound localization in the peri-central and lateral fields. Subjects with callosal pathology were impaired on all tasks involving transfer of motor and visuo-spatial skills and on some of the tasks requiring sensory integration of visual and tactile information across the body midline. We conclude that these functions require an intact corpus callosum since none of these deficits were seen in controls equated for IQ.

Adolescent↗

PubMed2002

Acquired monocular vision: functional consequences from the patient's perspective.

PURPOSE: The study is conducted to determine the effect of acquired monocular vision (enucleation, phthisis) on the daily activities of patients. METHODS: Sixty-five patients in a case series completed a 30-question survey evaluating the functional consequences of monocular vision. RESULTS: Patients with sudden visual loss adapted more slowly than those with gradual loss (8.8 versus 3.6 months). Difficulties with depth perception and cosmesis were prevalent. Unexpected consequences included neck pain, strain with reading, employment change, depression, car accidents, and alcoholism. Ninety-one percent of patients had no formal training to help them adapt. CONCLUSIONS: More than previously appreciated, there are many obstacles that patients face in making the transition to monocular vision. Few patients receive any formal instruction to help them adapt, yet many indicate that it would be beneficial.

Activities of Daily Living↗

PubMed2000

Three-dimensional analysis of object properties during active electrolocation in mormyrid weakly electric fishes (Gnathonemus petersii).

Weakly electric fishes are nocturnal and orientate in the absence of vision by using their electrical sense. This enables them not only to navigate but also to perceive and recognize objects in complete darkness. They create an electric field around their bodies by producing electric signals with specialized electric organs. Objects within this field alter the electric current at electroreceptor organs, which are distributed over almost the entire body surface. During active electrolocation, fishes detect, localize and analyse objects by monitoring their self-produced electric signals. We investigated the ability of the mormyrid Gnathonemus petersii to perceive objects three-dimensionally in space. Within a range of about 12 cm, G. petersii can perceive the distance of objects. Depth perception is independent of object size, shape and material. The mechanism for distance determination through electrolocation involves calculating the ratio between two parameters (maximal slope and maximal amplitude) of the electrical image which each object projects onto the fish's skin. During active electrolocation, electric fishes cannot only locate objects in space but in addition can determine the three-dimensional shape of an object. Up to certain limits, objects are spontaneously categorized according to their shapes, but not according to their sizes or the materials of which they are made.

Animals↗

PubMed2002

A stereoscope for image-guided surgery.

A method of image guidance for neurosurgery using the surgeon's binocular depth perception is described. Magnetic resonance volume acquisitions and surface rendering software were used to produce stereoscopic pairs of images of the surface of the heads of patients with brain tumours. Stereoscopic pairs of the surface rendering of the tumour were also produced. The two pairs of images were colour-coded and combined into one pair of 35-mm slides. A stereoscopic viewer was constructed to allow simultaneous viewing of the pair of slides and the patient's head. Registration was achieved by moving the stereoscope in space until the virtual images of the rendered surface of the head coincided with the real head. The stereoscope was then locked in position and the virtual image of the tumour was projected 'into' the patient's head to allow the surgeon to locate the tumour. The instrument was used in six cases. A lateral accuracy of 10-15 mm was achieved and a depth accuracy of 5-10 mm.

Brain Neoplasms↗

PubMed1976

[The 3- and 4-point experiments and a test of homogeneity in binocular visual space (author's transl)].

The variability of the 2 parameters in the Luneburg model, sigma (the degree of depth perception) and K (the curvature of binocular visual space), was examined. The 3- and 4-point experiments were performed to estimate these parameters by using various sized stimulus configurations. For 2 of the Os used, it was found that the value of K was inversely related to the size of stimulus configuration (SSC) while the value of sigma was constant. This finding was discussed referring to previous investigations and problems: The discrepancy in the estimated values of K between the alley experiment and 3- and 4-point experiments, equidistance tendency, and angular separation problem in the traditional size constancy experiment.

Depth Perception↗

PubMed1990

The processing of object and self-motion in the tectofugal and accessory optic pathways of birds.

This paper reviews electrophysiological studies of motion processing in the tectofugal and accessory optic systems (AOS), and suggests these are specialized respectively for the analysis of object motion and self motion. Evidence is presented which shows that directionally specific neurons in the tectofugal system process local motion and are inhibited by wholefield motion. These cells respond to kinematograms and moving occlusion edges and may therefore also be involved in figure-ground segregation and depth perception. In contrast, cells in the nucleus of the basal optic root (nBOR), a component of the AOS, respond best to large slowly moving patterns. These cells are directionally selective preferring either upward, downward or backward directions. In the posterior region of the nBOR some cells have been found which are binocular and prefer either the same or opposite directions of motion in the two eyes. Thus, these cells are tuned to respond optimally to either translational or rotational components of wholefield motion and it is suggested these may be involved in the control of posture and locomotion.

Animals↗

PubMed1985

Early postnatal lead exposure: behavioral effects in common tern chicks (Sterna hirundo).

Exposure to lead early in life is known to affect behavioral and intellectual development. To develop an animal model we chose the common tern, Sterna hirundo, a species whose early developmental landmarks are well known. One potential for avian models lies in the reliance of birds on visual and acoustic rather than olfactory (and ultrasonic) modes of communication. One randomly chosen member of each of 8 pairs of young common tern chicks was injected with lead nitrate solution at a concentration of 0.2 mg/g. The pairs were not siblings but were matched for age (+/- 1 d) and weight (+/- 3 g). The second member of each pair was injected with an equal volume of sterile saline. Behavioral tests performed examined locomotion, balance and righting response, feeding tasks and begging, depth perception and response on a visual cliff, and behavioral thermoregulation. In each pair the control chick was heavier at 4 wk of age. For most behavioral measures, except begging and movement on a stationary incline, the lead-injected chicks performed less well than the control chicks. When presented with a novel feeding situation (reversal of fish position), the lead-injected chicks required significantly more time to eat the same number of fish. The single injection of lead thus affected a variety of behavioral patterns, with effects apparent within 5 d after injection.

Analysis of Variance↗

PubMed1981

[Functional aniseikonia: clinical study of 110 cases (author's transl)].

A clinical study was conducted in 110 cases of subjective aniseikonia, a syndrome that is often neglected. After in practice summarizing the different distortions composing the phenomenon of aniseikonia, a description of the prototype apparatus used for the experiments is given: it is eikonometric stereo-projector the originality of which lies in the measuring system, constituted by the projected stereograms. Three parameters were studied: depth-perception, peerception threshold of anseiikonic disparity, and value of the found aniseikonia. The results are presented in relation to 3 groups of subjects: 14 emmetropic, 32 isometropic, and 64 anisometropic, 32 isometropic, and 64 anisometropic patients, including 24 monocular aphakic. The author shows the advantage of contact lens correction in the last cases: with an average of 3.5 p. cent, the found aniseikonia was always inferior to 6 p. cent and to the theorectical levels currently accepted. Finally, the phenomenon of "cortical malleability" arises in the adaptation of the patient to his optical correction and could regularly and progressively be increased.

Aniseikonia↗

PubMed1989

[Difficulty in the implantation of intraocular lenses by "hidden" parallax].

Although this is not the intent of the surgeon, many posterior chamber lenses are nevertheless placed asymmetrically--one loop in the sulcus and the other in the capsular bag. Difficulties can arise during implantation of even the first loop, which is mostly done in the 6 o'clock position. In this situation, a deficit or loss in steroscopic vision is observed. According to the law of Garten, depth perception is increasingly disturbed as the angle between the connection line of the two observer eyes and two smooth, stretched contours being steroscopical objects diminishes to zero. The reason is not a loss of parallaxis, but the fact that there are no structures that can be matched for stereopsis in a horizontal direction. Thus, stereoscopic vision can be improved dramatically by: (1) twisting the axis of the IOL loops into the five to four o'clock direction; (2) enlarging the magnification of the operating microscope until the grain of the structures is visible. It will then be possible to implant the IOL into the capsular bag (or the ciliary sulcus), which is what was intended.

Depth Perception↗

PubMed1971

Development behaviors: delayed appearance in monkeys asphyxiated at birth.

Developmental behaviors were studied in monkeys subjected to asphyxia at birth. Visual depth perception, visual pla ing, and locomotion appeared significantly later than in nonasphyxiated monkeys. After these behaviors had been established in asphyxiates, however, there was little difference from those observed in normal monkeys. These results were compared with reports of permanent learning deficits that occur in monkeys asphyxiated at birth for similar periods of time. Such comparison suggests that the neural structures responsible for the developmental behaviors studied are not damaged by asphyxia to the same extent as those for acquisition. Delay in development may be an early indication of brain damage with subsequent mental retardation.

Amnesia↗