Does the vestibular apparatus play a role in the development of the visual system?

The effect of gravity on human recognition of disoriented objects

The role of non-visual cues, and particularly of signals tied to the direction of gravity, in the mechanisms of recognition of disoriented objects is reviewed. In spite of a limited number of studies, object recognition does not seem dramatically altered by weightlessness and astronauts can adapt to this novel environment. Particularly, mental rotation strategy can still be used in weightlessness with dynamic parameters relatively unchanged. Similarly, spatial coordinate assignment can be performed adequately under different gravitational conditions. However, signals related to gravity direction seem to be integrated in the early stages of visual processing. Thus, performances in symmetry detection tasks and visual search tasks are influenced by the gravito-inertial conditions in which experience are done. Functional roles of such a multisensory convergence on cortical visual neurons, partly confirmed by neurophysiological studies, are proposed.

Early sensory determinants of locomotor speed in adult cats: II. Effects of strobe rearing on vestibular functions

Cats raised under stroboscopic illumination are known to exhibit oculomotor and visuomotor deficits, but little is known about their locomotor abilities. Four strobe-reared cats with intact labyrinths were tested in a locomotor test involving various walking surfaces and various illumination conditions. Apart from their general slowness under all the experimental conditions, these strobe cats showed no special deficit on narrow rails, which indicates that their dynamic balancing abilities were normal. In these subjects, the decrease in the use of kinetic visual cues was roughly compensated for by an increase in the use of position cues. When tested after chronic bilateral labyrinthectomy, the strobe-reared cats' locomotor speeds were identical to those of control labyrinthectomized cats, except on wide platforms involving orientation towards a visual goal. These results show that in the absence of motion-vision, vestibular control of dynamic balance can mature normally, but they suggest that other aspects of locomotion involving the processing of vestibular and kinesthetic inputs may be impaired.

Role of eye movements in developmental processes of orientation selectivity in the kitten visual cortex

Six-week-old dark-reared kittens were exposed for 6 hr to a normal lighted environment in which they were free to move, but with eyes immobilized. Receptive field properties (orientation selectivity and ocular dominance) of the visual cortical cells (Area 17) were studied. No restoration of orientation selectivity could be observed when only the eyes were immobilized either by oculomotor nerve sections or by extraocular muscles removal, in contrast to what had been observed in intact free moving animals. From these results one can conclude that eye movements must be associated with vision to allow developmental processes of orientation selectivity in the primary cortex. These new results are compared to those obtained previously in paralyzed or restrained animals and those obtained in animals with interruption of orbital afferents.

Locomotion in adult cats with early vestibular deprivation: visual cue substitution

Four cats labyrinthectomized shortly after birth ( DELAB ) exhibited the classical vestibular syndrome and recovery, while their motor development was otherwise unimpaired. As adults, they were tested for visual vestibular substitution in a locomotor task with either orientation requirements (tilted platforms) or balance requirements (narrow platforms). Visual motion cues or static visual cues were controlled using normal or stroboscopic lighting, or darkness. Measurements of the average speed of locomotion showed that: - Although all cats increase their speed when more visual cues become available, a marked deficit occurs in darkness only in the DELAB cats. - With either vestibular cues alone or static visual cues alone, cats are able to reach the same level of performance in the tilted platform test, which suggests a total visual-vestibular interchangeability in orientation. - DELAB cats perform very poorly in the narrow rail test. - When continuous vision is allowed in the narrow rail test the DELABs ' performance rises but does not match that of the control group. - A specific deficit in balance for the DELAB group is thus reduced by normal continuous vision as compared to stroboscopic vision, suggesting a significant, though imperfect, substitution of motion visual cues for the missing dynamic vestibular cues. - Dynamic visual cues play only a minor role in most situations, when locomotory speed is high. This results support the view that both the vestibular and the visual system can subserve two distinct functions: - dynamic information may stabilize the stance in narrow unstable situations, during slow locomotion, - and static orientation cues may mainly control the direction for displacement. Possible interactions between head positioning and body orientation in the DELAB cats are discussed.

Kittens reared in a unidirectional environment: evidence for a critical period

1. Kittens were reared in the dark from birth except for a period each day when they were put inside a stationary transparent cylinder, around which a drum with vertical black and white stripes on the inside, rotated in one direction. After the end of the period of exposure, we recorded a sample of single cells from their visual cortices, and analysed each cell for direction and orientation sensitivity and other properties. 2. Two kittens were placed inside the drum, rotating rightward, for 2 hr each seekday from 3 1/2 to 7 weeks of age. A greater proportion of the directionally sensitive cells in their cortices showed a preference for rightward movement. 3. Six other kittens were placed inside the drug for 1 hr each weekday from 2 to 12 weeks of age with the drum rotating leftward up to a particular changeover age, then rightward until 12 weeks. The changeover point occurred at 21, 26, 28, 33, 35 and 51 days for different kittens. A changeover earlier than 4 weeks of age led to a preponderance of cells preferring rightward movement. A changeover later than 5 weeks of age led to a preponderance of cells preferring leftward movement. Comparison of these results with others on monocular deprivation suggests that the peak of the critical period for directional deprivation may occur earlier than the peak of the critical period for monocular deprivation. 4. None of the samples of cells showed a preponderance of cells specific for vertical orientations. It is unclear whether this negative effect resulted from the presence of some horizontal contours during exposure, or some more fundamental cause.

Modification of cortical orientation selectivity in the cat by restricted visual experience: a reexamination

Recent reports have stated that the orientation selectivity of cells in the cat's visual cortex can be biased by limiting the early visual environment to stripes of one orientation. Data obtained from seven kittens using systematic and quantitative sampling of preferred orientation, together with a blind procedure, do not show a bias toward the orientation presented in one type of restricted rearing environment.