Terri L. Lewis

Development of spatial and temporal vision during childhood

Using the method of limits, we measured the development of spatial and temporal vision beginning at 4 years of age. Participants were adults, and children aged 4, 5, 6, and 7 years (n = 24 per age). 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 every frequency increased by at least 0.5 log units between 4 and 7 years of age, at which point it was adult-like. Grating acuity reached adult values at 6 years of age. Temporal vision was more mature: at 4 years of age temporal contrast sensitivity at higher temporal frequencies (20 and 30 Hz) and critical flicker fusion frequency were already adult-like. Sensitivity at lower temporal frequencies (5 and 10 Hz) increased by 0.25 log units after the age of 4 to reach adult levels at age 7. The results suggest that temporal vision matures more rapidly than spatial vision during childhood. Thus, spatial and temporal vision are likely mediated by different underlying neural mechanisms that mature at different rates.

What Aspects of Face Processing Are Impaired in Developmental Prosopagnosia

Developmental prosopagnosia (DP) is a severe impairment in identifying faces that is present from early in life and that occurs despite no apparent brain damage and intact visual and intellectual function. Here, we investigated what aspects of face processing are impaired/spared in developmental prosopagnosia by examining a relatively large group of individuals with DP (n = 8) using an extensive battery of well-established tasks. The tasks included measures of sensitivity to global motion and to global form, detection that a stimulus is a face, determination of its sex, holistic face processing, processing of face identity based on features, contour, and the spacing of features, and judgments of attractiveness. The DP cases showed normal sensitivity to global motion and global form and performed normally on our tests of face detection and holistic processing. On the other tasks, many DP cases were impaired but there was no systematic pattern. At least half showed deficits in processing of facial identity based on either the outer contour or spacing of the internal features, and/or on judgments of attractiveness. Three of the eight were impaired in processing facial identify based on the shape of internal features. The results show that DP is a heterogeneous condition and that impairment in recognizing faces cannot be predicted by poor performance on any one measure of face processing.

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 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.

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.

Long trajectory for the development of sensitivity to global and biological motion

We used a staircase procedure to test sensitivity to (1) global motion in random-dot kinematograms moving at 4° and 18° s(-1) and (2) biological motion. Thresholds were defined as (1) the minimum percentage of signal dots (i.e. the maximum percentage of noise dots) necessary for accurate discrimination of upward versus downward motion or (2) the maximum percentage of noise dots tolerated for accurate discrimination of biological from non-biological motion. Subjects were adults and children aged 6-8, 9-11, and 12-14 years (n = 20 per group). Contrary to earlier research, results revealed a similar, long developmental trajectory for sensitivity to global motion at both slower and faster speeds and for biological motion. Thresholds for all three tasks improved monotonically between 6 and 14 years of age, at which point they were adult-like. The results suggest that the extrastriate mechanisms that integrate local motion cues over time and space take many years to mature.

Putting order into the development of sensitivity to global motion

We studied differences in the development of sensitivity to first-versus second-order global motion by comparing the motion coherence thresholds of 5-year-olds and adults tested at three speeds (1.5, 6, and 9 degrees s(-1)). We used Random Gabor Kinematograms (RGKs) formed with luminance-modulated (first-order) or contrast-modulated (second-order) concentric Gabor patterns with a sinusoidal spatial frequency of 3c deg(-1). To achieve equal visibility, modulation depth was set at 30% for first-order Gabors and at 100%, for second-order Gabors. Subjects were 24 adults and 24 5-year-olds. For both first- and second-order global motion, the motion coherence threshold of 5-year-olds was less mature for the slowest speed (1.5 degrees s(-1)) than for the two faster speeds (6 and 9 degrees s(-1)). In addition, at the slowest speed, the immaturity was greater for second-order than for first-order global motion. The findings suggest that the extrastriate mechanisms underlying the perception of global motion are different, at least in part, for first- versus second-order signals and for slower versus faster speeds. They also suggest that those separate mechanisms mature at different rates during middle childhood.

Developmental changes in attention: the effects of endogenous cueing and of distractors

We used two reaction time tasks to examine age differences in the ability to use an endogenous cue to shift attention covertly and to ignore distractors. In Experiment 1, 8-year-olds, 10-year-olds and adults (n = 24 per age) were asked to push a button as soon as they detected a target that was presented in a cued, miscued or non-cued peripheral location at 100, 400 or 800 ms after the appearance of a central cue. In Experiment 2, 10-year-olds and adults (n = 24 per age) were asked to indicate which of two shapes appeared in the periphery 400 ms after a central cue, with those shapes surrounded by compatible or incompatible distractors. Unlike previous studies, the data were corrected for a reaction time bias that can inflate the apparent effect of cueing. Children were slower and more variable than adults overall. However, there were no age differences in the effects of the cues in either experiment: at all ages, the speed of responding was increased similarly by correct cueing and slowed similarly by incorrect cueing. Thus, under these conditions, the ability to use endogenous cues to orient covertly to the periphery is already adult-like by 8–10 years of age, although there may be subsequent changes in the consistency of responding. In Experiment 2, 10-year-olds were slowed more than adults by incompatible distractors. Thus, the ability to ignore distracting information is not adult-like even by 10 years of age. The findings suggest different rates of development for the ability to shift attention following an endogenous cue and for the ability to filter out irrelevant information.

Visual acuity: the role of visual input in inducing postnatal change

Abstract Some crude visual abilities are present at birth, and hence, do not depend on visual experience. However, there are substantial and rapid postnatal improvements. For example, the acuity of newborns is 40 times worse than that of normal adults, largely because of retinal immaturities. Between birth and 6 months of age, there is a five-fold increase in acuity, followed by slow improvement to adult levels by 6 years of age. This review examines the role of visual experience in inducing those improvements by comparing the visual development of normal children with that of children treated for congenital cataracts that blocked patterned visual input until the cataracts were removed surgically and the eyes were given a compensatory optical correction. The acuity of children treated for congenital cataracts does not improve before they receive patterned visual input, but then increases rapidly to reach normal limits by 1 year of age. However, the patients later show permanent deficits in acuity, presumably because the initial deprivation caused damage to the visual cortex. Studies of children who developed cataracts after birth indicate that visual input is also necessary to consolidate cortical connections. Moreover, the deleterious effects of visual deprivation are worse if there was also uneven competition between the eyes — because the deprivation was monocular and there was little patching of the non-deprived eye — but only at some points during development. Thus, the development of visual acuity is shaped by experience-dependent and competitive mechanisms that have different temporal parameters.