Nature vs. Nurture in Vision: Evidence from Typical and Atypical Development
Friday, May 7, 1:00 – 3:00 pm
Royal Ballroom 6-8
Organizers: Faraz Farzin, University of California, Davis
Presenters: Karen Dobkins (Department of Psychology, University of California, San Diego), Rain G. Bosworth (Department of Psychology, University of California, San Diego), Melanie Palomares (University of South Carolina), Anthony M. Norcia (The Smith-Kettlewell Eye Research Institute), Janette Atkinson (Visual Development Unit, Department of Developmental Science, University College London), Faraz Farzin (University of California, Davis)
The interplay between genetics and the environment is a rapidly advancing area in vision, yet it is a classic question in developmental research. In this symposium, each speaker will present empirical evidence supporting the contribution of genetic and/or environmental factors on specific visual processes, and will collectively discuss how these factors affect human visual development. The symposium has three aims: (1) to provide the opportunity for developmental researchers to come together and engage in collaborative dialogue in a single session at VSS, which has been neglected in recent years, (2) to synthesize a working knowledge of the biological and environmental influences on the functional and anatomical organization of the typically and atypically developing visual system, and (3) to advance the role of development in understanding visual mechanisms. Bringing together prominent scientists as well as young investigators, we anticipate that this symposium will appeal to those who share a common interest in understanding the nature of early vision and the factors which shape its development.
Infant Contrast Sensitivity: Contributions of Factors Related to Visual Experience vs. Preprogrammed Mechanisms
Karen Dobkins, University of California, San Diego; Rain G. Bosworth, University of California, San Diego
In order to investigate potential effects of visual experience vs. preprogrammed mechanisms on visual development, we have investigated how well variation in contrast sensitivity (CS) across a large group of typical infants (n = 182) can be accounted for by a variety of factors that differ in the extent to which they are tied to visual experience. Using multiple regression analyses, we find that gestational length and gender, which are unlikely to be tied to visual experience, predict Luminance CS (thought to be mediated by the Magnocellular pathway). Other factors, which might be tied to either preprogrammed mechanisms or visual experience, specifically, birth order and small variations in postnatal age, predict Chromatic CS (thought to be mediated by the Parvocellular pathway) and Luminance CS. In addition, we have investigated effects of visual experience vs. preprogrammed mechanisms by studying CS in infant twins (n = 64). Our results show that the CS of both monozygotic (Mz) and dizygotic (Dz) twin pairs are significantly correlated with one another (accounting for ~35% of the variance in CS), which could be due to either shared environment or genetic preprogramming. More data will allow us to determine whether correlations are significantly stronger in Mz vs. Dz twins, which would provide direct evidence of effects of genetic preprogramming. Based on our multiple regression studies (above), as well as our studies of premature infants (presented in this symposium), we predict that genetic preprogrammimg will be more influential for Luminance (Magnocellular pathway) CS than Chromatic (Parvocellular pathway) CS.
Chromatic and Luminance Contrast Sensitivity in Fullterm and Preterm Infants: Effects of Early Visual Experience on Magnocellular and Parvocellular Pathway Processing
Rain G. Bosworth, University of California, San Diego; Karen Dobkins, University of California, San Diego
Study of healthy preterm infants affords an opportunity to investigate the contributions of visual experience vs. preprogrammed mechanisms on visual development. By comparing the developmental trajectories of contrast sensitivity (CS) in preterm vs. fullterm infants, we can determine if development is primarily tied to postterm age, in which visual maturation is governed by preprogrammed mechanisms timed to conception. By contrast, if development is tied to postnatal age, then visual maturation may be affected by visual experience. Using forced-choice preferential looking methods, data from 57 preterm (born 5-9 weeks early) and 97 fullterm infants were collected between 1–6 months postterm age (2-7 month postnatal age). Our visual measures were luminance (light/dark) and chromatic (red/green) CS, which are thought to be mediated by the Magnocellular and Parvocellular subcortical pathways, respectively. In the first few months, luminance CS was found to be predicted by postterm age, suggesting that preprogrammed development is sufficient to account for luminance CS. By contrast, chromatic CS significantly exceeded that predicted by postterm age, which suggests that time since birth (and by extension, visual experience) confers a benefit on chromatic CS. In sum, early Parvocellular pathway development appears to be more influenced by early postnatal visual experience than Magnocellular pathway development. We will present results comparing preterm infants born at different gestational ages, to determine if the slope of postnatal development changes with gestational length at birth. Finally, data will be compared to very preterm infants with retinopathy of prematurity.
Visual Evoked Potentials in Texture Segmentation: Are Boys and Girls Different?
Melanie Palomeres, University of South Carolina; Anthony M. Norcia, The Smith-Kettlewell Eye Research Institute
Texture-defined objects are shapes defined by boundaries based on discontinuities along a feature dimension (Nothdurft, 1993). Psychophysical studies in pediatric observers showed that detecting texture discontinuities based on orientation have been found to appear at 4-6 months of age mature in adolescence (Rieth & Sireteanu, 1992). We evaluated the neural correlates of texture-segmentation across development by measuring high-density visual-evoked potentials in typically-developing children and adults. We found that the formation of texture-defined form elicited VEP responses earlier in adults than in children. While there were no sex differences in VEP responses in adults, we found that response amplitudes in girls were much smaller than in boys of the same age. These results suggest that the neural responses in girls were more adult-like than in boys. This presentation will discuss the possible cortical substrate of this sex difference (e.g. Sowell, et al, 2007).
Experience Dependent Plasticity of human Form and Motion Mechanisms in Anisometropic Amblyopia
Anthony M. Norcia, The Smith-Kettlewell Eye Research Institute; Sean I. Chen, The Galway Clinic, Galway, Ireland; Arvind Chandna, Royal Liverpool Childrens Hospital, Liverpool, UK
Deprivation of visual input during developmental critical periods can have profound effects on the structure of visual cortex and on functional vision (Hubel and Wiesel 1963). Converging evidence from studies in human and animal models of amblyopia suggests that visual deprivation can have differential effects on different cortical pathways, consistent with the presence of multiple critical periods within the visual system as a whole (Harwerth, Smith et al. 1986). Anisometropia (unequal refractive error between the two eyes) is a common clinical condition in humans that can lead to very deep amblyopia if not treated. We studied the effects of visual deprivation secondary to anisometropia in a group of children before and after treatment for amblyopia. We recorded Visual Evoked Potentials (VEPs) evoked by vernier offsets of different sizes. This VEP paradigm (Norcia, Wesemann et al. 1999) elicits two qualitatively dissimilar response components, one associated with relative alignment or spatial position cues (form) and the other with transients due to motion or contrast change (motion) . Prior to treatment, the non-deprived eye shows supernormal form responses and normal motion responses. The amblyopic eye shows markedly reduced form responses and moderately reduced motion responses. Treatment via patching and glasses partially normalized the form responses in both eyes but had less of an effect on motion responses. The results indicate that form mechanisms are differentially susceptible to deprivation of high spatial frequency inputs during a developmental critical period.
Dorsal Stream Vulnerability: Interaction of Intrinsic Programmes and Acquired Developmental Disorders
Janette Atkinson, University College London; Oliver Braddick, University of Oxford
Global motion and global form sensitivity can provide a developmental indicator of extra-striate processing in the dorsal and ventral streams respectively, and measures of spatial cognition, visuo-motor co-ordination and control of attention offer higher level indicators of the integrity of the dorsal cortical stream. We will provide an overview of our own work and others using these measures to show that ‘dorsal stream vulnerability’ is a feature of many neurodevelopmental disorders, both genetic (Williams syndrome, fragile-X, and probably autism and dyslexia) and acquired (perinatal brain injury, prematurity, congenital cataract). Follow up of prematurely born infants at 6-7 years allows the distinct impacts of white matter injury, weeks gestation, and prematurity per se on different visuo-cognitive measures to be assessed.
Since both genetic and acquired disorders show differential effects on dorsal stream processing, this vulnerability cannot be considered either a direct effect of gene expression or of specific environmental impact. Rather, the unfolding programme by which the visual system is built, with genetic control in an environmental context, appears to make dorsal stream function vulnerable either to interaction with other genetic effects, or to various environmental disruptions. We will consider the developmental demands on dorsal stream function that may be responsible for this vulnerability. We will also review our findings, using novel high-density VERP measures, on the normal development of global motion processing and the reorganization of its cerebral basis between infancy and adulthood, which may help to understand the period(s) of development when the system is vulnerable to disruption.
The Role of the FMR1 Gene in Infant Contrast Sensitivity
Faraz Farzin, University of California, Davis and Center for Mind and Brain; David Whitney, University of California, Berkeley and Center for Mind and Brain, Davis; Flora Tassone, M.I.N.D. Institute; Susan M. Rivera, University of California, Davis, Center for Mind and Brain, Davis, and M.I.N.D. Institute
Fragile X syndrome (FXS) is characterized by the expansion of a CGG trinucleotide repeat within the FMR1 gene located on the X chromosome. Depending on the size of the CGG expansion, the mutation can be categorized as full (> 200 CGG repeats), which is associated with gene silencing and little to no FMR1 protein (FMRP) production, or premutation (55 – 200 CGG repeats), which is associated with high levels of FMR1 mRNA and decreased FMRP levels particularly in the upper permutation range. Several previous studies have reported impaired processing of temporally dynamic stimuli in infants, adolescents and adults with the FXS full mutation (Kogan et al, 2004, Farzin et al, 2008), and most recently in adult premutation carriers (Kéri and Benedek, 2008). Here, we assessed contrast sensitivity for second-order static and dynamic stimuli in male and female infants with the full mutation and the premutation, and compared their performance to mental age-matched typically developing infants. Our goal was to examine the molecular correlates of this visual deficit in infants with the disorder.
A forced-choice preferential looking paradigm was presented on an eye tracker to measure contrast sensitivity for second-order (texture-defined) static and dynamic stimuli. Michelson contrast levels were varied at four points between 10 and 42%. Infants’ looking time to the side of the display that contained the stimulus, relative to their overall looking time, was measured to calculate a Visual Preference (VP) score. Logistic psychometric functions were fitted to the mean VP score at each contrast level to determine the minimum contrast value at which a 0.75 VP score was demonstrated. Our results revealed a significant difference in contrast sensitivity for second-order dynamic stimuli between TD infants and infants with the full mutation. Importantly, a significant negative correlation was found between contrast sensitivity for second-order dynamic stimuli and CGG repeat length, but not for sensitivity for second-order static stimuli. These findings confirm the role of the FMR1 gene in infant visual development, and specifically its involvement in sensitivity for parietally-mediated, attention-based dynamic stimuli. Critically, no molecular link was present for sensitivity for static stimuli. This is the first study to correlate performance on a psychophysical visual detection task with molecular measures in individuals with fragile X spectrum disorders. These results support the hypothesis that an abnormal molecular phenotype of the FMR1 gene is associated with the specific visual deficit of processing dynamic stimuli.