Visual fields of cats reared with one eye intorted

Plasticity and stability of visual field maps in adult primary visual cortex

It is important to understand the balance between cortical plasticity and stability in various systems and across spatial scales in the adult brain. Here we review studies of adult plasticity in primary visual cortex (V1), which has a key role in distributing visual information. There are claims of plasticity at multiple spatial scales in adult V1, but a number of inconsistencies in the supporting data raise questions about the extent and nature of such plasticity. Our understanding of the extent of plasticity in V1 is further limited by a lack of quantitative models to guide the interpretation of the data. These problems limit efforts to translate research findings about adult cortical plasticity into significant clinical, educational and policy applications.

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.

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.

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.