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Biomedical subjects

C K Peck

Publications and source records attributed to C K Peck.

33 records · Page 2Linked to original sources
PubMed1981

Visual acuity in cats following surgically induced cyclotropia.

Visual acuity was measured, using a jumping stand technique, in cats which had undergone surgical cyclotorsion of one or both eyes. In cats with unilateral rotations acuity was depressed in the rotated eye and the extent of loss increased with larger amounts of rotation. Cats which had undergone bilateral rotations tended to have lower acuities than normal cats and there was a slight tendency for the eye with the greater rotation to show the larger deficit. Evidence is presented that the lowered acuities were not the result of peripheral damage and it is suggested that the defect may be considered as a form of strabismic amblyopia.

Amblyopia↗
PubMed1980

Visuo-oculomotor properties of cells in the superior colliculus of the alert cat.

Visual responses and eye movement (EM) -related activities were studied in single units of the superior colliculus (SC) of alert cats. Spontaneous EMs were encouraged by training. Throughout the SC (i.e., in intermediate and deep layers as well as in superficial layers), units were found to respond well to visual stimuli. Strong and consistent responses could be elicited by very dim, low-contrast stationary stimuli. Visual responses varied from phasic to tonic; some units responded tonically to stationary stimuli in the center of the receptive field, and phasically to peripheral stimuli. Many cells responded more vigorously to moving than to stationary stimuli, but very few responded exclusively to stimulus movement. The vast majority of cells were directionally selective. A small number of units were sensitive to the absolute, as well as the retinal, position of visual stimuli. These cells were activated by visual stimuli which fell in the receptive field only if the cat's gaze was fixated on one half of the screen. It seems that these cells must receive information about both eye position and the retinal (receptive field) position of the stimulus. It is possible that they reflect coding of target location within a head (or body) frame of reference. EM-related units were of two types: (1) about 20% of the sample responded prior to spontaneous or visually-triggered EMs, and (2) another 10% (or more) responded with, but not before, EMs. Some cells in the second group discharge almost synchronously with EMs and, thus, cannot plausibly be said to respond to the movement of images across the retina. All cells in the first group were directionally selective. The percentage of EM-related cells in the deep layers of SC is lower in cat than in monkey. Possible reasons for such differences are discussed.

Animals↗
PubMed1980

Visual responses of thalamic neurons depending on the direction of gaze and the position of targets in space.

Visual receptive field properties of neurons in the region of the thalamic internal medullary lamina were studied in alert cats while they fixated in various directions. In slightly more than 50% of the cells, the responsiveness of the cells was found to depend on the location of the stimulus with respect to the head-body axis (stimulus absolute position). A cell could ignore a stimulus outside its absolute field even if it was well placed within its receptive field. Three types of neurons were distinguished. Neurons with small central receptive fields were tonically activated when the animal fixated the stimulus in one half of the screen (usually contralateral). The firing rate of these cells was related to the stimulus absolute position measured along a preferred axis. Similarly, neurons with large receptive fields fired as a function of stimulus absolute position but stimulus fixation was not required. Neurons with eccentric fields responded to stimuli located in a target area defined in head-body coordinates. Such cells gave presaccadic bursts with eye movements terminating in the target area. The conclusion proposed is that neurons exist which code visual spatial information in a non-retinal frame of reference. This coding takes place at the time of stimulus presentation. Its role may be seen in the initiation of visually guided movements.

Animals↗
PubMed1979

Partial interocular transfer of brightness and movement discrimination by split-brain cats.

Interhemispheric transfer of discriminations of brightness and direction of movement, two types of stimuli which may be processed by midbrain visual areas, was compared to transfer of control patterns in cats with sections of the optic chiasm and forebrain commissures. Transfer in these split-brain cats was further compared to transfer in partially split-brain cats with sparing of either the splenium of the corpus callosum or the anterior commissure. An intact splenium was necessary for high levels of interhemispheric transfer of all of the discriminations, which implies a prominant role for cortical mechanisms in such tasks. However, animals with complete section of the corpus callosum often showed partial interocular transfer of both brightness and movement discriminations, which may reflect a limited but selective participation of subcortical areas in visual perception. Cats in which the anterior commissure was spared did not show greater transfer on any of these tasks than did cats with section of both callosum and anterior commissure.

Animals↗
PubMed1979

Pattern discrimination and visuomotor behavior following rotation of one or both eyes in kittens and in adult cats.

Sixteen cats, each of which had one or both eyes rotated at the time of natural eye opening (group K), were tested for visuomotor behavior and for learning and interocular transfer of two-choice visual discriminations. Their behavior was compared to that of two cats given monocular rotations in adulthood (group A) and to two normal controls (group N). These animals were all reared in the same colony. All cats, including those with monocular rotations up to 180 degrees and those with binocular rotations up to 80 degrees in each eye, showed good visuomotor behavior when using the rotated eye (i.e., with the normal eye covered). Both the group K and group A animals showed comparable visuomotor adaptation. All animals except those with monocular rotations of 180 degrees were able to learn several oriented pattern discriminations and showed considerable though incomplete interocular transfer of such information. The three animals with 180 degrees rotations were able to learn brightness, but not pattern discriminations. Seven further animals with large rotations were used for histological studies of the retina and primary visual pathways. Areas of reduced ganglion cell density were not observed in whole mounts of the retinae, nor were regions of reduced transport of 3H-proline from the retina to the lateral geniculate nuclei or superior colliculi detectable from autoradiographs.

Animals↗
PubMed1975

Modification of single neurons in the kitten's visual cortex after brief periods of monocular visual experience.

Kittens were deprived of form vision by suturing the lids of both eyes, except for a brief period (1, 6 or 20 hours) on the 29th day when the right eye was opened. 6 space and 20 hours of monocular vision produced a distinct shift in the ocular dominance of visual cortical neurons towards the experienced eye, and an increase in the proportion of cells with obvious orientation selectivity. These modifications in the visual cortex were enhanced by a period of "consolidation": they were somewhat less obvious if recordings were taken immediately after the exposure but were complete 2 days later. Although remarkably little visual experience was needed for these changes, the results contrast with the effects of rearing in an environment of vertical stripes, where only 1 hour of exposure produces much more striking effects. A normal visual environment may have a less powerful organizing influence on cortical neurons than such an environment containing only one orientation.

Animals↗