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Biomedical subjects

C G Gross

Publications and source records attributed to C G Gross.

At least 73 records · Page 4Linked to original sources
PubMed1979

Visual areas in the temporal cortex of the macaque.

Visual receptive fields and responsiveness of neurons to somesthetic and auditory stimuli were studied in the inferior temporal cortex and adjacent regions of immobilized macaques. Neurons throughout cytoarchitectonic area TE were responsive only to visual stimuli and had large receptive fields that almost always included the center of gaze and usually extended into both visual half-fields. There was no indication of any visuotopic organization within area TE. Neurons in an anterior and in a dorsal portion of TE tended to have larger receptive fields. By contrast, dorsal, ventral and anterior to area TE, units often responded to somesthetic and auditory as well as to visual stimuli. In these regions visual receptive fields were even larger than in TE and often included the entire visual field. Posterior to TE the neurons were exclusively visual and had much smaller receptive fields that were confined to the contralateral visual field and were topographically organized.

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PubMed1979

Role of inferior temporal cortex in interhemispheric transfer.

Neurons in inferior temporal cortex of the rhesus monkey usually have large receptive fields that extend well across the midline into both visual half-fields. The responsiveness of these neurons to stimuli in the ipsilateral visual half-field depends on the splenium and anterior commissure, the same pathways necessary for interhemispheric transfer of visual habits. Since inferior temporal neurons have the same trigger features in both half-fields and are usually binocular, they may be the site of the interhemispheric neural convergence that underlies interhemispheric transfer. If so, bilateral removal of inferior temporal cortex should interfere with interhemispheric transfer even when the commissures are intact. To test this, monkeys were trained on pattern discriminations with one eye and then tested for transfer with the other eye. Five experimental monkeys received bilateral inferior temporal lesions and, to restrict input from each eye to one hemisphere, section of the optic chiasm. Ten controls received either bilateral temporal lesions alone, chiasm section alone or remained unoperated. Only the experimental animals showed impaired transfer. These results suggest that inferior temporal neurons mediate interhemispheric transfer by providing perceptual equivalence for patterns in the left and right visual fields, and, by implication, perhaps also for patterns in different parts of the same field.

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PubMed1979

Color categories in macaques.

This experiment investigated whether macaque monkeys partition the photic spectrum into the same four basic hue categories that humans do, i.e., blue, green, yellow, and red. Monkeys were trained to respond in the presence of one chromatic stimulus and were tested, in extinction, for generalization to others. In extinction, the monkeys responded at similar and high levels to stimuli that fell in the same basic human hue category as the training stimulus and at similar and much lower levels to stimuli that fell in a different human hue category from the training stimulus. It was concluded that macaques and humans categorize the spectrum in a similar fashion.

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PubMed1978

Localization and detection of visual stimuli following superior colliculus lesions in rhesus monkeys.

Rhesus monkeys were trained to fixate a central stimulus and to detect and localize a 50 msec light flash presented 6-80 degrees on either side of the central stimulus. Following large lesions of the superior colliculus, they showed persistent deficits in localizing flashes presented 43-80 degrees from the fixation stimulus. However, they were not consistently impaired when the flashes were presented more centrally, and their performance with peripheral stimuli improved when the stimulus duration was 1 sec. Thus, the superior colliculus appears to be necessary for the localization of brief visual stimuli in the far periphery.

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PubMed1978

Inferior temporal lesions do not impair discrimination of rotated patterns in monkeys.

Ablation of inferior temporal cortex in the rhesus monkey produces a visual discrimination learning deficit. The severity of this deficit has often been found to be a function of task difficulty. This report concerns a type of visual discrimination problem that, although difficult, is not sensitive to inferior temporal lesions. Monkeys with anterior, posterior, and complete inferior temporal lesions were repeatedly unimpaired or only slightly impaired in learning to discriminate a pattern from the same pattern rotated 90 degrees or 180 degrees; yet they were very severely impaired in learning equally or more difficult discriminations of two different patterns. This demonstration that discrimination of orientation of patterns is relatively spared after inferior temporal lesions helps specify the pattern-recognition processes that require inferior temporal cortex.

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PubMed1977

Contributions of the corpus callosum and the anterior commissure to visual activation of inferior temporal neurons.

Most neurons in the inferior temporal cortex of the rhesus monkeys have visual receptive fields that extend across the vertical meridian well into both the contralateral and ipsilateral visual half-fields. We examined the role of different portions of the forebrain commissures in providing the ipsilateral input with the following results. (1) Combined section of the splenium and anterior commissure eliminated visual activation from the ipsilateral visual half-field. (2) Section of the splenium, with sparing of the anterior commissure, reduced the incidence of ipsilateral activation by about one-half. (3) Section of the anterior commissure, with sparing of the splenium, did not alter the incidence of ipsilateral activation. (4) Section of the non-splenial portions of the corpus callosum had no effect on the laterality of the receptive fields. Thus, both the splenium and the anterior commissure but not the non-splenial callosum can provide information from the ipsilateral visual field to neurons in inferior temporal cortex. These results are interpreted as suggesting that the converging input from the two visual half-fields onto single inferior temporal neurons provided by the forebrain commissures may mediate interhemispheric transfer of visual habits.

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PubMed1976

A visual deficit after superior colliculus lesions in monkeys.

The superior colliculus has been implicated in visual orientation and localization in several mammalian species. To examine this possibility in rhesus monkeys, we trained monkeys to respond to one of six locations signaled by a small light of 5 s duration that was turned off immediately before they were allowed to respond. The locations were directly behind the light. After tectal lesions they continued to perform this task normally, but showed a severe deficit when the duration of the signal was reduced to 1 s. However, when the stimulus remained on throughout the trial and the site of the stimulus and response were further separated, performance of the animals with tectal lesions was normal. We suggest that this deficit in the accuracy of reaching guided by a transient visual stimulus may be related to the role of the superior colliculus in the control of eye movements.

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PubMed1975

Visual activation of neurons in inferotemporal cortex depends on striate cortex and forebrain commissures.

Neurons in inferotemporal cortex respond only to visual stimuli and a majority have receptive fields that extend well into both visual half-fields. After bilateral removal of striate cortex, no inferotemporal neurons responded to visual stimuli. After unilateral removal of striate cortex, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the intact striate cortex. After section of the corpus callosum and anterior commissure, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the recording site. These results indicate that inferotemporal cortex visual information from striate cortex and that the pathway from striate cortex to the contralateral inferotemporal cortex includes the forebrain commissures. This same striate-temporal pathway is also necessary for normal discrimination learning. We suggest that the converging input onto single inferotemporal neurons from widely separated retinal areas may provide a mechanism for stimulus equivalence over different parts of the visual field, and it may be the absence of such a mechanism that contributes to the visual discrimination deficit that follows inferotemporal lesions.

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