Henry P. Brent

Impairment in Holistic Face Processing Following Early Visual Deprivation

Unlike most objects, faces are processed holistically: They are processed as a whole rather than as a collection of independent features. We examined the role of early visual experience in the development of this type of processing of faces by using the composite-face task, a measure of holistic processing, to test patients deprived of visual experience during infancy. Visually normal control subjects showed the expected composite-face effect: They had difficulty perceiving that the top halves of two faces were the same when the top halves were aligned with different bottom halves. Performance improved when holistic processing was disrupted by misaligning the top and bottom halves. Deprived patients, in contrast, showed no evidence of holistic processing, and in fact performed significantly better than control subjects when top and bottom halves were aligned. These findings suggest that early visual experience is necessary to set up or maintain the neural substrate that leads to holistic processing of faces.

Better perception of global motion after monocular than after binocular deprivation

We used random-dot kinematograms to compare the effects of early monocular versus early binocular deprivation on the development of the perception of the direction of global motion. Patients had been visually deprived by a cataract in one or both eyes from birth or later after a history of normal visual experience. The discrimination of direction of global motion was significantly impaired after early visual deprivation. Surprisingly, impairments were significantly worse after early binocular deprivation than after early monocular deprivation, and the sensitive period was very short. The unexpectedly good results after monocular deprivation suggest that the higher centers involved in the integration of global motion profit from input to the nondeprived eye. These findings suggest that beyond the primary visual cortex, competitive interactions between the eyes can give way to collaborative interactions that enable a relative sparing of some visual functions after monocular deprivation.

The effect of early visual deprivation on the development of face processing

We evaluated the importance of early visual input for the later development of expertise in face processing by studying 17 patients, aged 10 to 38 years, treated for bilateral congenital cataracts that deprived them of patterned visual input for the first 7 weeks or more after birth. We administered five computerized tasks that required matching faces on the basis of identity (with changed facial expression or head orientation), facial expression, gaze direction and lip reading. Compared to an age-matched control group, patients’ recognition of facial identity was impaired significantly when there was a change in head orientation (e.g. from frontal to tilted up), and tended to be impaired when there was a change in facial expression (e.g. from happy to surprised). Patients performed normally when matching facial expression and direction of gaze (e.g. looking left or right), and in reading lips (e.g. pronouncing ‘u’ or ‘a’). The results indicate that visual input during early infancy is necessary for the normal development of some aspects of face processing, and are consistent with theories postulating the importance of early visual experience (de Schonen & Mathivet, 1989; Johnson & Morton, 1991) and separate neural mediation of different components of face processing (Bruce & Young, 1986).

Sensitivity to global form in glass patterns after early visual deprivation in humans.

To compare the effects of early monocular versus early binocular deprivation on the perception of global form, we assessed sensitivity to global concentric structure in Glass patterns with varying ratios of paired signal dots to noise dots. Children who had been deprived by dense congenital cataracts in one (n=10) or both (n=8) eyes performed significantly worse than comparably aged children without eye problems. Consistent with previous results on sensitivity to global motion [Vision Research 42 (2002) 169], thresholds in the deprived eyes were significantly better after monocular deprivation than after binocular deprivation of comparable duration, even when there had been little patching of the nondeprived eye after monocular deprivation. Together, the results indicate that the competitive interactions between a deprived and nondeprived eye evident in the primary visual cortex can co-occur with complementary interactions in extrastriate cortex that enable a relative sparing of some visual functions after early monocular deprivation.

Spatial and temporal vision in patients treated for bilateral congenital cataracts

Using the method of limits, we measured spatial and temporal vision in 13 children who had been deprived of patterned visual input during infancy until they were treated for dense central cataracts in both eyes. Spatial vision was assessed with vertical sine-wave gratings, and temporal vision was assessed with an unpatterned luminance field sinusoidally modulated over time. Under these testing conditions, spatial contrast sensitivity at low and medium spatial frequencies (0.33-2 c deg-1) was within normal limits, but sensitivity at higher spatial frequencies and grating acuity were reduced on average by 1.3 and 0.5 log units, respectively. Temporal vision was affected less severely, with losses in sensitivity only for low temporal frequencies (5 and 10 Hz), which averaged 0.4 log units. Thus, spatial and temporal vision are likely mediated by different neural mechanisms, that are differentially affected by deprivation.

Influence of monocular deprivation during infancy on the later development of spatial and temporal vision

Using the method of limits, we measured spatial and temporal vision in 15 patients, aged 4-28 years, who had been monocularly deprived of patterned visual input during infancy by a dense cataract. All patients showed losses in both spatial and temporal vision, with greater losses in spatial than in temporal vision. Losses were smaller when there had been more patching of the non-deprived eye. The results indicate that visual deprivation has smaller effects on the neural mechanisms mediating temporal vision than on those mediating spatial vision.

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.

Peripheral vision and optokinetic nystagmus in children with unilateral congenital cataract

The vision of cats which were monocularly deprived during early infancy, of kittens, and of young human infants shares two limitations: detection in the nasal visual field is far poorer than detection in the temporal visual field, and optokinetic nystagmus (OKN) is difficult to elicit when a pattern moves nasally to temporally. Here we report similar limitations on the vision of children who had a dense central cataract in one eye during early infancy. Extensive static perimetry with one of these children whose visual acuity was good in both eyes revealed that her threshold for detection all along the horizontal meridian was higher in her aphakic than in her normal eye, with this difference much more pronounced in the nasal visual field than in the temporal visual field. Three children who developed cataracts after 6 months of age showed no such discrepancy between thresholds in the temporal and nasal fields. We tested the symmetry of OKN in 12 children treated for unilateral congenital cataract. In every test of an aphakic (n = 4) or normal eye (n = 12), OKN occurred significantly more often when stripes moved temporally to nasally than when they moved nasally to temporally. In contrast, no asymmetry was observed in any of 13 children treated for traumatic cataracts incurred after 3 years of age. We conclude that children treated for unilateral congenital cataract, like young human infants and monocularly deprived cats, show asymmetric OKN and relatively poor detection in the nasal visual field.

Greater losses in sensitivity to second-order local motion than to first-order local motion after early visual deprivation in humans.

We compared sensitivity to first-order versus second-order local motion in patients treated for dense central congenital cataracts in one or both eyes. Amplitude modulation thresholds were measured for discriminating the direction of motion of luminance-modulated (first-order) and contrast modulated (second-order) horizontal sine-wave gratings. Early visual deprivation, whether monocular or binocular, caused losses in sensitivity to both first- and second-order motion, with greater losses for second-order motion than for first-order motion. These findings are consistent with the hypothesis that the two types of motion are processed by different mechanisms and suggest that those mechanisms are differentially sensitive to early visual input.

Contact lenses for the treatment of pediatric cataracts.

OBJECTIVE To evaluate the experiences, attitudes, and perceptions of the caregivers of children with cataracts who were visually rehabilitated with contact lenses. PARTICIPANTS One hundred twenty-three caregivers of children <8.1 years old treated for unilateral and bilateral cataracts at one pediatric hospital. DESIGN Survey by questionnaire. INTERVENTION Primary caregivers were asked to complete an anonymous questionnaire. MAIN OUTCOME MEASURES Caregiver responses to questions assessing background and demographic and clinical information, as well as perceptions, attitudes, levels of compliance, and anxiety with respect to treatment, were reviewed. Caregivers were also asked to choose between aphakic rehabilitation with contact lenses, aphakic glasses, or intraocular lenses, given various hypothetical scenarios differing in regard to their final visual prognosis, risks of treatment complications, and cost. RESULTS The response rate was 82.9%. Absolute average stress levels for contact lens use were 1.36 +/- 1.79 and 0.79 +/- 1.48 (scale, 0-5) for insertion and removal, respectively, compared with 4.03 +/- 1.64 and 2.40 +/- 1.92 for cataract surgery and patching therapy, respectively. Although average paired initial resistance to treatment (RT) levels for contact lens insertion and removal on a scale of 0 to 3 were high (2.09 +/- 1.15) and moderate (1.63 +/- 1.20), respectively, final RT levels were significantly lower (1.09 +/- 1.14 and 0.66 +/- 1.07, respectively; P < 0.0001). The vast majority of caregivers chose contact lens use in hypothetical scenarios that depicted realistic expectations for other forms of aphakic rehabilitation. CONCLUSIONS In our study, contact lenses seemed to be well tolerated by most patients, as assessed by caregivers. Although initial resistance to contact lens use is high, this decreases with time. Relative to other events in the treatment of pediatric cataracts, contact lens use is not a major stressor for most caregivers and patients. This study supports the notion that contact lenses should continue to receive serious consideration as a treatment option for pediatric cataracts.