The development of young infants' ability to detect stimuli in the nasal visual field

Asymmetries of the visual system and their influence on visual performance and oculomotor dynamics

Our representation of the visual field is not homogenous. There are differences in resolution not only between the fovea and regions eccentric to it, but also between the nasal and temporal hemiretinae, that can be traced to asymmetric distributions of photoreceptors and ganglion cells. We review evidence for differences in visual and attentional processing and oculomotor behaviour that can be traced to asymmetries of the visual system, mainly emphasising nasal-temporal asymmetries. Asymmetries in the visual system manifest in various measures, in basic psychophysical tests of visual performance, attentional processing, choice behaviour, saccadic peak velocity, and latencies. Nasal-temporal asymmetries on saccadic latency seem primarily to occur for express saccades. Neural asymmetries between the upper and lower hemifields are strong and cause corresponding differences in performance between the hemifields. There are interesting individual differences in asymmetric processing which seem to be related to the strength of eye dominance. These neurophysiological asymmetries and the corresponding asymmetries in visual performance and oculomotor behaviour can strongly influence experimental results in vision and must be considered during experimental design and the interpretation of results.

Naso-temporal asymmetry for signals invisible to the retinotectal pathway

Monocular viewing conditions show an asymmetry between stimuli presented in the temporal and nasal visual fields in their efficiency for automatically triggering eye saccades and grasping attention. For instance, observers free to make a saccade to one of two stimuli presented together orient preferentially to the temporal stimulus. Such naso-temporal asymmetry (NTA) has been assumed to reflect the asymmetry in the retinotectal pathway to the superior colliculus. We tested this hypothesis using S cone stimuli, which are invisible to the magnocellular and retinotectal pathways. The observed NTA in choice saccades to bilateral stimuli was no less present for S cone stimuli than for luminance stimuli. Additionally, the amplitude of the NTA can be enhanced when S cone signals are added to luminance signals. These results suggest that behavioral NTA in humans is not diagnostic of retinotectal mediation. Furthermore, we found no asymmetries in latency, suggesting that the NTA in saccade choice does not originate simply from a bottom-up asymmetry in any low level visual pathways.

The early development of visual attention and its implications for social and cognitive development

Looking behavior plays a crucial role in the daily life of an infant and forms the basis for cognitive and social development. The infant's visual attentional systems undergo rapid development during the first few months of life. During the last decennia, the study of visual attentional development in infants has received increasing interest. Several reliable measures to investigate the early development of attentional processes have been developed, and currently a number of new methods are giving fresh impetus to the field. Research on overt and covert as well as exogenously and endogenously controlled attention shifts is presented. The development of gaze shifts to peripheral targets, covert attention, and visual scanning behavior is treated. Whereas most attentional mechanisms in very young infants are thought to be mediated mainly by subcortical structures, cortical mechanisms become increasingly more functional throughout the first months. Different accounts of the neurophysiological underpinnings of attentional processes and their developmental changes are discussed. Finally, a number of studies investigating the implications of attentional development for early cognitive and social development are presented.

The human pulvinar and stimulus-driven attentional control

The present study compared the behavioral effects of sudden motion onsets or color changes (i.e., featural changes) with the effects of new objects (i.e., multiple changes). Experiments 1 and 2 showed that lesions of the pulvinar affect stimulus-driven attentional control only when it is triggered by featural changes, but not by new objects. Experiment 3 revealed that when appended on a new object, a featural change is processed as a part of a more massive new object: Its attentional effects are larger and remain undisturbed by lesions of the pulvinar. In Experiment 4 a temporal superiority effect was found for featural changes, but not for new objects in healthy subjects. These results suggest that featural changes and new objects may be processed through different pathways and that the pulvinar may be particularly involved in stimulus-driven attentional control by sudden events entailing featural changes.

Suppression of metabolic activity caused by infantile strabismus and strabismic amblyopia in striate visual cortex of macaque monkeys

INTRODUCTION

Suppression is a major sensorial abnormality in humans and monkeys with infantile strabismus. We previously reported evidence of metabolic suppression in the visual cortex of strabismic macaques, using the mitochondrial enzyme cytochrome oxidase as an anatomic label. The purpose of this study was to further elucidate alterations in cortical metabolic activity, with or without amblyopia.

MATERIALS AND METHODS

Six macaque monkeys were used in the experiments (four strabismic and two control). Three of the strabismic monkeys had naturally occurring, infantile strabismus (two esotropic, one exotropic). The fourth strabismic monkey had infantile microesotropia induced by alternating monocular occlusion in the first months of life. Ocular motor behaviors and visual acuity were tested after infancy in each animal, and development of stereopsis was recorded during infancy in one strabismic and one control monkey. Ocular dominance columns (ODCs) of the striate visual cortex (area V1) were labeled using cytochrome oxidase (CO) histochemistry alone, or CO in conjunction with an anterograde tracer ([H 3 ]proline or WGA-HRP) injected into one eye.

RESULTS

Each of the strabismic monkeys showed inequalities of metabolic activity in ODCs of opposite ocularity, visible as rows of lighter CO staining, corresponding to ODCs of lower metabolic activity, alternating with rows of darker CO staining, corresponding to ODCs of higher metabolic activity. In monkeys who had infantile strabismus and unilateral amblyopia, lower metabolic activity was found in (suppressed) ODCs driven by the nondominant eye in each hemisphere. In monkeys who had infantile esotropia and alternating fixation (no amblyopia), metabolic activity was lower in ODCs driven by the ipsilateral eye in each hemisphere. The suppression included a monocular core zone at the center of ODCs and binocular border zones at the boundaries of ODCs. This suppression was not evident in the monocular lamina of the LGN, indicating an intracortical rather than subcortical mechanism.

CONCLUSION

Suppression of metabolic activity in ODCs of V1 differs depending upon whether infantile strabismus is alternating or occurs in conjunction with unilateral amblyopia. Our findings reinforce the principle that unrepaired strabismus promotes abnormal competition in V1, observable as interocular suppression of ODCs.

Multiple sensitive periods in human visual development: Evidence from visually deprived children

Psychophysical studies of children deprived of early visual experience by dense cataracts indicate that there are multiple sensitive periods during which experience can influence visual development. We note three sensitive periods within acuity, each with different developmental time courses: the period of visually-driven normal development, the sensitive period for damage, and the sensitive period for recovery. Moreover, there are different sensitive periods for different aspects of vision. Relative to the period of visually driven normal development, the sensitive period for damage is surprisingly long for acuity, peripheral vision, and asymmetry of optokinetic nystagmus, but surprisingly short for global motion. A comparison of results from unilaterally versus bilaterally deprived children provides insights into the complex nature of interactions between the eyes during normal visual development.

A temporal/nasal asymmetry for blindsight in a localisation task: evidence for extrageniculate mediation

Some patients with hemianopia due to striate cortex lesions show above chance ability in reporting visual stimuli presented in the blind visual field, a phenomenon commonly known as blindsight. Here we report a patient with a dense right hemianopia whose blindsight shows a temporal/nasal asymmetry. MP was tested in a two-alternative forced-choice localisation task, with either the right eye or the left eye patched in separate blocks. When targets appeared in the contralesional temporal hemifield, MP's localisation performance was extremely accurate, whilst she performed at chance with targets in the contralesional nasal hemifield. This is the first demonstration of a temporal/nasal asymmetry for blindsight in a forced-choice paradigm, and is consistent with blindsight in MP's hemianopic field being mediated by a subcortical, extrageniculate route.

Visual response properties and visuotopic representation in the newborn monkey superior colliculus

Visual response properties and visuotopic representation in the newborn monkey superior colliculus. J. Neurophysiol. 78: 2732-2741, 1997. Visually responsive neurons were recorded in the superior colliculus (SC) of the newborn rhesus monkey. The receptive fields of these neurons were larger than those in the adult, but already were organized into a well-ordered map of visual space that was very much like that seen in mature animals. This included a marked expansion of the representation of the central 10 degrees of the visual field and a systematic foveal to peripheral increase in receptive field size. Although newborn SC neurons had longer response latencies than did their adult counterparts, they responded vigorously to visual stimuli and exhibited many visual response properties that are characteristic of the adult. These included surround inhibition, within-field spatial summation, within-field spatial inhibition, binocularity, and an adult-like ocular dominance distribution. As in the adult, SC neurons in the newborn preferred a moving visual stimulus and had adult-like selectivities for stimulus speed. The developmentally advanced state of the functional circuitry of the newborn monkey SC contrasts with the comparative immaturity of neurons in its visual cortex. It also contrasts with observations on the state of maturation of the newborn SC in other developmental models (e.g., cat). The observation that extensive visual experience is not necessary for the development of many adult-like SC response properties in the monkey SC may help explain the substantial visual capabilities shown by primates soon after birth.

Possible blindsight in infants lacking one cerebral hemisphere

Patients with damage to the striate cortex have a subjectively blind region of the visual field, but may still be able to detect and localize targets within this region. But the relative roles in this 'blindsight' of subcortical neural systems, and of pathways to extra-striate visual areas, have been uncertain. Here we report results on two infants in whom one cerebral hemisphere, including both striate and extra-striate visual cortex, needed surgical removal in their first year. Single conspicuous targets in the half-field contralateral to the lesion could elicit fixations, implying detection and orienting by a subcortical system. In contrast, binocular optokinetic nystagmus (OKN), for which a subcortical pathway has often been thought adequate, showed a marked asymmetry. In normal neonates, fixation shifts and OKN have both been taken to reflect subcortical control; our results are consistent with subcortical control for fixation but not for OKN.

The development of the temporal and nasal visual fields during infancy

We used static perimetry to measure the development of the monocular visual field during infancy. Infants from birth to 6 months of age, and adults, were shown a 3 or 6 degrees flashing light at various locations between 15 and 120 degrees in the temporal and nasal visual fields. We assumed that subjects could see a light if they moved their eyes toward it more often than they looked in the same direction on blank control trials. For both the 3 and 6 degrees lights, the visual field expanded with age from the center out, and development in the nasal visual field lagged behind development in the temporal visual field. Possible reasons for these findings are discussed.

Extrageniculate vision in hemianopic humans: saccade inhibition by signals in the blind field

The functional competence of extrageniculate visual pathways in hemianopic humans was demonstrated by showing that distractor signals in the blind half of the visual field could inhibit saccades toward targets in the intact visual field. This inhibitory effect of unseen distractors in patients occurred only when distractors were presented in the temporal half of the visual field, was specific to oculomotor responses, and did not occur in normal subjects. These results show that a peripheral visual signal activates retinotectal pathways to prime the oculomotor system and that these pathways can mediate orienting behavior in hemianopic humans.

Cortical Maturation and the Development of Visual Attention in Early Infancy

Bronson (1974) reviewed evidence in support of the claim that the development of visually guided behavior in the human infant over the first few months of life represents a shift from subcortical to cortical visual processing. Recently, this view has been brought into question for two reasons; first, evidence revealing apparently sophisticated perceptual abilities in the newborn, and second, increasing evidence for multiple cortica streams of visual processing. The present paper presents a reanalysis of the relation between the maturation of cortical pathways and the development of visually guided behavior, focusing in particular on how the maturational state of the primary visual cortex may constrain the functioning of neural pathways subserving oculomotor control.

Infant spatiotemporal vision: dependence of spatial contrast sensitivity on temporal frequency

Effects of temporal frequency on infant spatial contrast sensitivity were studied with forced-choice preferential looking, using localized 1.0 and 0.35 c/deg grating patches. Between 4 and 8 months, contrast sensitivity at 1.0 c/deg increased significantly at 8-17 Hz but showed little change at 2-4 Hz, so temporal tuning became increasingly bandpass with age. At 4 months, temporal tuning was lowpass at 1.0 c/deg and bandpass at 0.35 c/deg. Control data on adults indicate that the differences between the infant and adult data cannot be accounted for solely by reduced photoreceptor density and quantal catch, and suggest developmental changes in tuning and/or relative sensitivities of spatiotemporal mechanisms.

Visual field in dark-reared cats after an extended period of recovery

The visual field of dark-reared cats was behaviourally measured after several years of recovery in a normal environment. A reduction of the visual field was observed and affected the contralateral field as well as the ipsilateral field when tested in monocular viewing. The longer the deprivation period, the more reduced was the visual field. Our results suggest that binocular deprivation might have stabilized the visual system in an immature state.

Kinetic perimetry assessment of binocular visual field shape and size in young infants

Kinetic perimetry was used to measure the extent of the binocular visual field in 8 directions in 77 full-term infants tested as neonates, 4-week-olds, or 8-week-olds. The apparatus consisted of a black, 4-arm arc perimeter, a centrally-located 6-deg stationary white sphere, and an identical sphere that served as the peripheral target. Neonates showed larger visual fields than did 4- and 8-week-olds, perhaps due to the strength of the older infants' fixation of the central target. Infants at all ages showed significantly smaller fields than did adults. However, visual field shape was similar in infants and adults.

Effects on perceptual development of visual deprivation during infancy

We measured three aspects of vision in children treated for unilateral congenital cataract: visual resolution, the symmetry of optokinetic nystagmus (OKN), and peripheral vision. Good visual resolution was achieved by children who had had the earliest treatment and who had had the normal eye patched close to 50% of the waking time throughout early childhood. All children treated for unilateral congenital cataract showed a marked asymmetry of OKN regardless of the age of treatment. One child with early treatment who could be tested with the Goldmann perimeter also showed especially poor sensitivity in the nasal visual field of her aphakic eye. We found no such deficits in the vision of children who had had normal visual experience during early infancy and then later developed cataracts in one or both eyes. The limitations observed in children treated for congenital cataract are similar to those reported in normal human infants, in normal kittens, and in cats which were visually deprived early in life.