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M Cynader

Publications and source records attributed to M Cynader.

10 recordsLinked to original sources
PubMed1979

Stereoscopic subsystems for position in depth and for motion in depth.

We describe psychophysical evidence that the human visual system contains information-processing channels for motion in depth in addition to those for position in depth. These motion-in-depth channels include some that are selectively sensitive to the relative velocities of the left and right retinal images. We propose that the visual pathway contains stereoscopic (cyclopean) motion filters that respond to only a narrow range of the directions of motion in depth. Turning to the single-neuron level we report that, in addition to neurons turned to position to depth, cat visual cortex contains neurons that emphasize information about the direction of motion at the expense of positional information. We describe psychophysical evidence for the existence of channels that are sensitive to change size, and are separate from the channels both for motion and for flicker. These changing-size channels respond independently of whether the stimulus is a bright square on a dark ground or a dark square on a bright ground. At the physiological level we report single neurons in cat visual cortex that respond selectively to increasing or to decreasing size independently of the sign of stimulus contrast. Adaptation to a changing-size stimulus produces two separable after-effects: an illusion of changing size, and an illusion of motion in depth. These after-effects have different decay time constants. We propose a psychophysical model in which changing-size filters feed a motion-in-depth stage, and suppose that the motion-in-depth after-effect is due to activity at the motion-in-depth stage, while the changing-size after-effect is due to to activity at the changing-size and more peripheral stages. The motion-in-depth after-effect can be cancelled either by a changing-size test stimulus or by relative motion of the left and right retinal images. Opposition of these two cues can also cancel the impression of motion in depth produced by the adapting stimulus. These findings link the stereoscopic (cyclopean) motion filters and the changing-size filters: both feed the same motion-in-depth stage.

Animals↗
PubMed1979

Interocular alignment following visual deprivation in the cat.

Kittens were placed in the dark just after birth and then removed at various ages for the study of interocular alignment. It was found that kittens dark-reared for 4 months or longer were characteristically incyclotorted with respect to normal animals. Deprivation periods of less than 2 months were ineffective in producing these changes. Divergence of the visual axes was also observed in some dark-reared cats. Pupillary constriction in response to light was much more pronounced in dark-reared cats than in normal cats. This enhanced pupillary reaction persisted for at least 3 weeks after the deprived animals were brought into an illuninated environment. When dark-reared cats were allowed a recovery period in a normally lit visual environment, their ocular alignment changed markedly. The incyclotorsion and divergence of the visual axes disappeared, and instead cats allowed recovery from deprivation could display excyclotorsion and/or convergence of the visual axes. These anomalies of ocular alignment associated with the recovery from visual deprivation could occur following periods of initial deprivation as short as 30 days or as long as 2 years. The mechanisms and possible significance of such anomalies are considered.

Animals↗
PubMed1979

Role of visual cortex in interocular alignment.

The role which the visual cortex plays in the development of interocular alignment in the cat was examined by removing this structure bilaterally in 4 groups of subjects. These included (1) kittens 10 to 14 days of age, (2) 10- to 14-day-old kittens in which one eyelid was sutured shut at the same time, (3) normally reared adult cats, and (4) cats dark-reared until 4 months of age. If the cortex is removed in young kittens, interocular alignment appears to develop normally until the kittens are 60 to 80 days of age. At this time, an abrupt change in alignment resulting in incyclotorsion of the optic axes is observed. If binocular vision is prevented in kittens with neonatal visual cortex lesions by suturing one eyelid shut, convergent strabismus and/or incyclotorsion are frequently observed. This characteristic incyclotorsion does not develop if similar lesions are made in adult cats; no significant alterations of eye alignment occur in these animals even after postoperative survival times of more than 6 months. Incyclotorsion characterizes dark-reared cats when they are first brought into the light, but this diminishes with time and may even be replaced by excyclotorsion after the animals spend a few weeks in the light. If dark-reared cats are decorticated on being brought into the light, these changes are largely prevented. Such animals remain permanently incyclotorted relative to normal cats. The results indicate that the visual cortex plays an important role in the development of torsional alignment of the eyes.

Animals↗
PubMed1978

Neurones in cat parastriate cortex sensitive to the direction of motion in three-dimensional space.

1. On psychophysical grounds, Beverley & Regan suggested that in man different neural mechanisms mediate the binocular perception of movement in depth and the binocular perception of positional (static) depth. They proposed that the human visual pathway contains several neural mechanisms, each sensitive to a different direction of motion in space. These mechanisms compute the direction of motion from the relative speeds and directions of movement of the left and right retinal images.2. We have recorded from 101 units in area 18 of cat visual cortex, searching for neurones tuned to the direction of motion in three dimensions, with properties that could account for the proposed directionally tuned binocular motion detectors in man. The cat's left eye viewed one bar, while its right eye simultaneously viewed a second bar. Single units were stimulated by independently oscillating the bars from side to side. The apparent direction of movement in three dimensions was altered by varying the relative speeds of the bars and their relative directions of motion. The mean (positional) disparity of the bars could also be varied.3. For one class of neurone (twenty cells), binocular stimulation inhibited firing for trajectories parallel to the frontoparallel plane over a large volume of space. Strong firing was produced by oppositely directed bar movements. Some of these neurones were especially narrowly tuned to the direction of movement in depth, responding only to a range of 2-3 degrees , i.e. to moving bodies that would hit or only narrowly miss the cat. These cells emphasized the direction of movement at the expense of positional information.3. These units occurred in clusters. On the perpendicular penetrations in which they were found, they comprised a substantial majority of all cells encountered.5. For a second class of neurone (nine cells), binocular facilitation produced selective responses to objects moving along trajectories that missed the head.6. The two classes of neurone provide a basis for four proposed directionally tuned binocular motion detectors.7. A third class of neurone (seventeen cells) was selectively sensitive to movements parallel to the frontoparallel plane. There was strong binocular facilitation when the bars moved at the same speeds in the same directions: oppositely directed movements might be more than 100 times less effective. These neurones may signal positional disparity.8. These three classes of neurone cut across established categories. Only when both eyes were stimulated simultaneously with targets moving in different speeds and directions was it possible to demonstrate the binocular interactions described here.

Action Potentials↗
PubMed1976

Abolition of direction selectivity in the visual cortex of the cat.

Cats were reared in a stroboscopically illuminated environment, which deprived them of expereience with visual movement but allowed them form vision. In these cats, neurons of the visual cortex displayed normal orientation selectivity, but direction selectivity was virtually abolished. The effect remained unaltered by long periods of normal visual exposure.

Animals↗