Visual field deficits in cats reared with cyclodeviations of the eyes

Geometry of the projection of the visual field onto the superior colliculus of the wallaby (Macropus eugenii). II. Stability of the projection after prolonged rearing with rotational squint

At about the time of eye opening, one eye of seven tammar wallaby pouch young was surgically rotated about the optic axis by approximately 90 degrees. In adulthood the projection of the visual field through the rotated eye onto the contralateral superior colliculus was mapped electrophysiologically. Although apparently distorted, the projection could be coherently re-rotated mathematically to a reasonable copy of the normal projection from the opposite eye of the same animal, including details such as regional variations of the magnification factor. The same was true of three adult animals in which the eye rotation was done after anaesthesia immediately before the electrophysiological mapping. In animals in which the visual field seen through one eye, the other being normal, was rotated for the entire period of visual experience, there was no sign of compensation or rearrangement of the topographic map. Retinocollicular synaptic connections appear unmoved by such discordant visual experience.

Human amblyopia: structure of the visual field

Kittens raised with different kinds of abnormal early visual experience (monocular and binocular deprivation, convergent strabismus, eye rotation, asymmetric alternating occlusion, early callosal split) show systematic deficits in the nasal visual field of the affected eye. To test whether abnormal visual experience produces similar deficits in the human visual system, we measured the monocular visual field of humans with subnormal binocular vision (strabismic and anisometropic amblyopes, strabismics with alternating fixation). Eight amblyopes were tested with a computer-assisted static perimetry (Octopus 2000). Twenty other subjects were tested with kinetic perimetry (Goldmann 940), 11 subjects with static perimetry (Goldmann 940). In some of these subjects, we measured the latency of saccades and the accuracy of visually guided pointing toward stimuli presented in the peripheral visual field. Both strabismic and anisometropic amblyopes frequently showed deficits of visual sensitivity in the central part of the visual field, but no systematic deficits in the peripheral field of the amblyopic eyes. Strabismic alternators had practically equal fields in the two eyes. Neither saccadic latency nor pointing accuracy showed a systematic impairment in the nasal visual field. The discrepancy between the field losses in strabismic humans and in cats raised with a surgically induced squint cannot be due to methodological differences, but rather to anatomical differences, or to the different origin of strabismus in the two species.

Small lateral suprasylvian cortex lesions produce visual neglect and decreased visual activity in the superior colliculus

Previous experiments in cats have shown that complete contralateral visual neglect is produced by removing all known visual cortex on one side of the brain, which can then be reversed by damaging the opposite superior colliculus. Presumably, descending facilitatory influences from the visual cortex to the ipsilateral superior colliculus are counterbalanced by intercollicular inhibition (Sprague: Science 153:1544-1546, '66). However, not all of visual cortex or all of the superior colliculus needs to be involved in this circuit. It is the deep rather than the superficial laminae of the superior colliculus that are primarily involved in visual attentive and orientation behaviors, and these laminae are largely independent of primary visual cortex. However, they do depend on corticotectal influences from a comparatively small extraprimary visual area of the posterior region of the lateral suprasylvian cortex (PSSC-Ogasawara et al: J. Neurophysiol. 52:1226-1245, '84). The present experiments demonstrate that lesions only a few millimeters in diameter in this corticotectal zone of the PSSC can produce profound visual neglect. While damage to this area has little, if any, effect on superficial laminae visual activity, it produces a dramatic decrease in the visual activity of the deep laminae. These cats with PSSC lesions fail to orient to a visual stimulus that is introduced suddenly into the contralateral visual field, yet they respond on nearly 100% of the trials to this same stimulus when it is presented in the ipsilateral visual field. The lesion-induced visual neglect produced by PSSC lesions is long-lasting but can be abruptly ameliorated by a midbrain lesion that primarily involves, or undercuts, the deep laminae of the contralateral superior colliculus. Thus, 1) visual neglect can be produced by depriving the deep laminae of the superior colliculus of visual inputs from the cortex, even when the principal visual cortical regions (17, 18, and 19) and their target structures are intact, and 2) visually guided behavior can be restored by eliminating afferents originating in, or passing through, the deep laminae of the contralateral superior colliculus.

Neuronal organization underlying visually elicited prey orienting in the frog--I. Effects of various unilateral lesions

We have studied the effects on frog orienting behavior of three lesions: unilateral optic nerve section, unilateral tectal lobe ablation, and unilateral transverse hemisection of the neuraxis at a level just caudal to the optic tectum. Unilateral optic nerve section and unilateral tectal lobe ablation produce very similar deficits in visually elicited responses to prey items, an absence of responses for stimuli at locations within the monocular field of one eye. Unilateral hemisection, in contrast, results in abnormalities in visually elicited responses over a wider area, encompassing the entire ipsilateral visual hemifield. The hemisection deficit also differs in character from that following optic nerve section or tectal lesion. Within the affected hemifield, frogs do not fail to respond to stimuli but rather respond with abnormally directed movements. The movements, regardless of stimulus eccentricity on the horizontal, are always forwardly directed. While not varying with horizontal eccentricity, the movements do vary with stimulus elevation and distance. The variation with stimulus distance in the affected hemifield is somewhat different from that in the opposite hemifield. We conclude from the behavior that remains after hemisection lesions that there must exist bilateral descending tectofugal paths capable of triggering movements which vary with stimulus elevation and distance, and a crossed descending tectofugal path capable of triggering turns into one visual hemifield. That the deficit area is larger following a hemisection than following tectal lobe ablation indicates that the hemisection has affected the ability of both tectal lobes to trigger turns in one direction. A possible interpretation of this finding is that the lesion has interrupted not only the crossed descending tectofugal path from one tectal lobe but an uncrossed descending tectofugal path from the other. This hypothetical pathway as well as the others mentioned is incorporated in a model of the organization of the post-tectal circuitry involved in orienting.

Optically induced strabismus results in visual field losses in cats

Kittens were reared using goggles containing a prism that simulated a convergent strabismus. A bilateral loss of 30 degrees of the contralateral monocular visual field resulted, indicating that the components of the visual pathways representing the nasal visual field are more sensitive to spatially conflicting visual inputs than the components representing the temporal field. Differences in the extent of binocular visual fields occurred, with alternating fixators demonstrating a full field and unilateral fixators demonstrating a binocular field reduction ipsilateral to the deviating eye.

Visual orienting deficits in frogs with various unilateral lesions

We have studied the visual prey acquisition behavior of frogs with unilateral optic nerve section, unilateral tectal lobe ablation, and unilateral transverse hemisection at a level between the tectum and the cerebellum. The first two groups of animals oriented normally to stimuli throughout the region of visual field overlap and failed to respond to more peripheral stimuli on one side. Hemisected animals responded to stimuli at all positions in the visual field. For stimuli located contralateral to the lesion, the frogs oriented normally. For ipsilateral stimuli, the frogs oriented forward.

The development of the kitten's visual field

We tested the monocular visual field of 16 kittens aged 13-56 days, by observing their unreinforced visual orienting. At 13-14 days the kittens oriented toward stimuli out of 45 degrees in the nasal field. Until 7-8 weeks, performance was significantly poorer in the nasal field than in the temporal field. This delayed development of the nasal field may be related to the relatively slow development of the uncrossed retino-geniculate projection and of the pathway through the visual cortex to the superior colliculus.