Biomedical subjects

Terri L Lewis

Publications and source records attributed to Terri L Lewis.

10 recordsLinked to original sources

PubMed2007

Sleeper effects.

Early experience preserves and refines many capabilities that emerge prenatally. Here we describe another role that it plays -- establishing the neural substrate for capabilities that emerge at a much later point in development. The evidence comes from sleeper effects: permanent deficits when early experience was absent in capabilities that normally emerge long after birth. We provide evidence of sleeper effects for three aspects of vision, based on our research with children who were deprived of early visual input by congenital cataracts: contrast sensitivity for mid and high spatial frequencies, holistic face processing, and the ability to recognize the identity of faces based on small differences in the spacing among facial features.

Brain↗

PubMed2006

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.

Adult↗

PubMed2006

The development of sensitivity to biological motion in noise.

We investigated developmental changes in sensitivity to biological motion by asking 6-year-olds, 9-year-olds, and adults (twenty-four in each group) to discriminate point-light biological motion displays depicting one of a variety of human movements from scrambled versions of the same displays. When tested without noise dots, participants at all ages performed near ceiling levels and no differences in accuracy were found among the three age groups. Age differences emerged in the second task, in which we used a staircase procedure to determine threshold values of the number of noise dots that could be tolerated in producing a percentage correct value corresponding to a d' value of 1.4. Sensitivity to biological motion improved linearly with age (p < 0.01), with 6-year-olds performing significantly more poorly than adults. This immature performance contrasts with adult-like accuracy by 4 years of age for sensitivity to global motion (Parrish et al, 2005 Vision Research 45 827-837). The comparison implies an immaturity at 6 years of age in the neural networks involved specifically in the processing of biological motion, networks that may include the superior temporal sulcus (STS).

Adult↗

PubMed2005

Repeated measurements of contrast sensitivity reveal limits to visual plasticity after early binocular deprivation in humans.

Contrast sensitivity improves in visually normal children until 7 years of age and is impaired in children who experienced early visual deprivation from bilateral congenital cataracts. Here, we investigated whether the deficits after early visual deprivation change during childhood by retesting the contrast sensitivity of seven patients treated for bilateral congenital cataract who had been first tested before 7.5 years of age, and of two patients first tested after 11 years of age. For the younger group, contrast sensitivity at low spatial frequencies improved after 1- and 2-year intervals, while their sensitivity at mid and high spatial frequencies did not change. There was no systematic change in the two older patients. The results indicate that early visual input sets up the neural substrate for later improvement in contrast sensitivity at mid and high spatial frequencies. However, there is sufficient plasticity during middle childhood to allow some recovery at low spatial frequencies. The results shed new light on the role of early visual experience and the nature of developmental plasticity.

Cataract↗

PubMed2005

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.

Adolescent↗

PubMed2005

Missing sights: consequences for visual cognitive development.

The effects of early-onset blindness on the development of the visual system have been explained traditionally by the stabilization of transient connections through Hebbian competition. Although many of the findings from congenital cataract and congenital blindness are consistent with that view, there is inconsistent evidence from studies of visual cognition in children treated for visual deprivation from cataract, case reports of recovery of vision in adults, and studies of visual reorganization after late-onset blindness. Collectively, the data from congenital cataract and congenital blindness indicate that early visual experience sets up the infrastructure for later learning involving both the dorsal ("where") and ventral ("what") streams. Nevertheless, there is surprising residual plasticity in adulthood that can be revealed if vision is lost either temporarily or permanently. This has important implications for understanding the role of early visual experience in shaping visual cognitive development.

Adolescent↗

PubMed2004

A window on the normal development of sensitivity to global form in Glass patterns.

We studied the development of sensitivity to global form in 6-year-olds, 9-year-olds, and adults (n = 24 in each group) using Glass patterns with varying ratios of paired signal dots to noise dots. The developmental pattern was similar whether the global structure within the Glass patterns was concentric or parallel. Thresholds were equally immature for both types of pattern at 6 years of age (about twice the adult value) but were adult-like at 9 years of age. Together, the results indicate that the cortical structures involved in the processing of global form achieve functional maturity between 6 and 9 years of age. During middle childhood, the mechanisms mediating sensitivity to concentric structure develop at the same rate as those mediating sensitivity to parallel structure.

Adolescent↗

PubMed2003

Comparison of sensitivity to first- and second-order local motion in 5-year-olds and adults.

We compared sensitivity to first- versus second-order motion in 5-year-olds and adults tested with stimuli moving at slower (1.5 degrees s(-1)) and faster (6 degrees s(-1)) velocities. Amplitude modulation thresholds were measured for the discrimination of the direction of motion (up vs. down) for luminance-modulated (first-order) and contrast-modulated (second-order) horizontal sine-wave gratings. At the slower velocity (1.5 degrees s(-1)), the differences in threshold between 5-year-olds and adults were small but significant for both first- and second-order stimuli (0.02 and 0.05 log units worse than adults' thresholds, respectively). However, at the faster velocity (6 degrees s(-1)), the differences in threshold between the children and adults were 8 times greater for second-order motion than for first-order motion. Specifically, children's thresholds were 0.16 log units worse than those of adults for second-order motion compared to only 0.02 log units worse for first-order motion. The different pattern of results for first-order and second-order motion at the faster velocity (6 degrees s(-1)) is consistent with models positing different mechanisms for the two types of motion and suggests that those mechanisms mature at different rates.

Adult↗

PubMed2002

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.

Adolescent↗

PubMed2002

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.

Adolescent↗