Angela M. Brown, PhD - US grants

We propose to extend our basic knowledge and theoretical understanding of color vision development with three basic experiments. First, we plan to measure chromatic and luminance contrast thresholds as a function of age. We will follow the development of color vision from its inception at about age 3 months to whenever adult-like color vision is attained. The relative rates of development of chromatic and luminance contrast sensitivity may contribute to our understanding of why the color vision of young infants is so poor. Second, we plan to compare chromatic and luminance contrast sensitivity measured using sinusoidal grating stimuli (the usual stimulus) with chromatic and luminance contrast stimuli measured using edge stimuli, a stimulus that is increasingly being used in vision research. This will help us understand the relation between color vision and spatial vision during development. It is likely that edge stimuli could some day be used in clinical testing of infants, and if so the basic information from this kind of experiment will be important. Third, we plan to measure discrimination thresholds between white and stimuli differing in luminance and/or excitation purity from white. Those thresholds, measured as a function of age, will tell us whether the color vision of infants differs qualitatively from that of adults, or whether it is just uniformly less sensitive. Another set of those thresholds will measure the sensitivity of the individual receptor mechanisms, and, together with the results of the first experiment, will help us arrive at a quantitative understanding of why infants' color vision is poor.

biomedical equipment resource; biomedical equipment purchase;

biomedical equipment purchase;

DESCRIPTION: The vernier acuity of 3-month-olds is 50-150 times worse than that of adults, whereas resolution acuity is only about 10 times worse. Vernier acuity is a measure of fine spatial localization that requires additional perceptual processing beyond the simple detection of the stimuli. The overall goal of this research project is to understand which differences between infants and adults are critical immaturities that limit infant vernier acuity and which are not. These immaturities may be divided into two groups: those that lead to poor visual sensitivity and those that are specific to spatial vision. Visual sensitivity. When vernier stimuli are designed to "level the playing field" by being equally visible to infants and adults, are infant and adult vernier acuities similar? In Experiments I, II, and III, stimuli will be created from Fourier components that are equally visible to infants and adults. This will be accomplished by applying a combination of blur, contrast reduction, and added "white" noise to the adult stimuli. If these manipulations bring adult vernier acuity into the infant range, this will suggest that infants' poor vernier acuity is due to their visual insensitivity. In Experiment IV, vernier acuity will be studied using a sinusoidal stimuli and a trigonometric analysis. If infant and adult vernier acuity can be predicted from their contrast discrimination performance, that will be evidence that visual insensitivity is responsible for infants' poor vernier acuity. This analysis will also be applied to adult amblyopes to find out whether strabismic and anisometropic amblyopia are caused by an arrest of visual development. Spatial vision. If visual insensitivity alone cannot explain infants' poor vernier acuity, what is the nature of the additional immaturities? In Experiment V, spatial uncertainty or scrambling of the retinotopic map between stages of visual processing will be compared by examining infant sensitivity to "white" luminance noise and positional noise added to the vernier stimulus. Positional noise is introduced by randomly jittering the spatial positions of pixels in the stimulus. If positional noise has a bigger effect on vernier acuity than luminance noise does, that will be evidence that spatial uncertainty is partly responsible for the poor vernier acuity of infants. In Experiment VI, the offset segments of the vernier stimulus will be separated by a gap. The critical value of the width of that gap will be compared to the amount of intrinsic blur from Experiment I to determine whether the infant's visual representation of the vernier stimulus is significantly undersampled. Clinical relevance. In the course of this basic-science project, the PI will find out whether normal infant vernier acuity is poor simply because of poor visual sensitivity or whether, like strabismic amblyopes, infants also have important immaturities in their spatial vision. If normal infants behave like normal adults then a vernier acuity task is likely to be useful for diagnosing amblyopia in infancy; if normal infants behave like adult strabismic amblyopes, a clinical test of vernier acuity is less likely to be useful.

oxidoreductase; health science research; enzyme mechanism; model design /development; chemical models;

This project will improve our understanding of how human infants come to
appreciate the three-dimensional structure of the world by means of binocular disparity between the visual signals from the two eyes. This capability is exquisitely acute in normal adults, and it is known as "stereopsis". Stereopsis is the simplest emergent property of visual perception that cannot be performed using subcortical processes. Rather, stereopsis necessarily involves the cerebral cortex, not only in generating the final three-dimension stereoptic percept, but even in extracting the sensory information it is based upon, namely binocular disparity. Understanding the emergence and early development of stereopsis in human infants will improve our understanding of perceptual and cognitive
development in infancy.

Infants are not capable of stereopsis at birth, but rather become capable of stereopsis sometime between ages 2 and 6 months. Individual infants acquire stereopsis very suddenly, whereas other visual functions, such as contrast sensitivity and grating resolution acuity, develop gradually over this age range. A central issue in the study of infant visual development is to account for the sudden postnatal emergence of stereopsis. It is well known from much previous work in anatomy, physiology, and psychophysics, as well as from clinical experience, that normal maturation of stereopsis depends critically on normal binocular visual experience. However, this dependency of continuing develop-ment on experience does not necessarily mean that experience is necessary to establish the physiological bases of stereopsis to begin with, or that experience controls the timing and manner of its emergence. Another possibility is that the anatomical and physiological substrate of human stereo vision appears automatically as the infant matures, and never imposes any serious limit on behavior. Perhaps the known immaturity of the infant's contrast sensitivity function limits infant stereo behavior without limiting the maturation of the stereo vision mechanisms. A third possibility is that the infant visual nervous system is "wired up" in a fundamentally different way from those of older infants, children and adults. The project will be made up of a series of experiments on infants and adults that are designed to explore the limitations on infant stereopsis over the first months of life, just as it emerges. The experiments will test these general explanations of why newborn infants do not have stereopsis.

[unreadable] DESCRIPTION (provided by applicant): There is no compelling physiological theory that explains all eleven basic color categories in the English language. Linguistic relativists (following the Sapir-Whorf view) argue that no such theory is likely to be found, because they believe that color categories are acquired through language and culture, not physiology. This project will test that hypothesis by studying infants. (H1) If infants perceive colors categorically as soon as they have color vision, and before they are old enough to speak, then language is not necessary for colors to be perceived categorically. In that case, it will make sense for vision scientists to look for a physiological explanation of color categories. (H2) In contrast, if infants do not perceive colors categorically until well after they have acquired color vision, then categorical perception requires more than simply the ability to distinguish one color from another. That additional requirement might be the acquisition of language, as the linguistic relativists suggest. (H3) Finally, if infants perceive some colors categorically but not others, then it will make sense to look for a physiological basis of some basic color categories (those that infants see) but not others. This R21 project will establish a new paradigm for studying categorical perception of color in 4-month-old infants and adults. This will require two essential elements, based on eye movement data collected on the same eye-tracker apparatus, and using the same response measure: saccadic latency. These will be (1) a sensory element based on eye-movement Preferential Looking, and (2) a "preattentive" perceptual element based on Visual Search. After establishing the latency and spatial criteria for accepting a saccadic eye movement towards a stimulus, further experiments will determine whether "pop-out" (instantaneous) Visual Search is possible, using disks of color as targets and distracters. Next, eye movement preferential looking, the sensory component, will determine whether sensory color discrimination is a continuous function of chromatic- ity using blue and green stimuli. Finally, Visual Search, the perceptual component, will determine whether pre- attentive perception of blue and green colors is categorical. Depending on the results with blue and green stimuli, eye movement Preferential Looking and Visual Search experiments will be performed using other colors. The outcome will be one of three possibilities. Either (H1) infants perceive all colors categorically; (H2) infants perceive no colors categorically; or (H3) infants perceive some colors categorically, but they perceive some colors continuously. Depending on the results, color vision scientists can expect to find physiological explanations of (H1) all color categories, (H2) no color categories, or (H3) some color categories but not others. Although infant color vision has been studied extensively at the sensory level, much less is known about what infants "know" about color. This project will determine if infants group colors into "reds", "greens", "pinks", etc, as adults do, or whether they just perceive color on a continuum without categories. This project will increase our understanding of normal infant visual and perceptual development, and the methods can be applied to studies that distinguish between abnormal sensory versus cognitive development. [unreadable] [unreadable] [unreadable]

This research aims to understand the interaction of language and culture on the perception of color. The Standard Model of color vision asserts that the visual system of all humans with normal color vision is organized around six fundamental sensations in a color-opponent fashion: red vs. green, blue vs. yellow, and black vs. white. Yet most of the world languages do not have a specific term for the colors that English speakers call "blue." Some speakers use a word meaning black, others use the term gray to mean blue, and still others use a single word that means green-or-blue. In what sense, then, is the mental representation of color in these individuals "color-opponent" if identical names are given to two sensations that fall on two presumptively independent color dimensions? How do the language differences affect how people think about color? To answer this, color naming studies will examine in detail the structures of the named color categories in monolingual American English speakers and a group of recent immigrants from Somalia who now live in Columbus, OH. The Somalis, who do not yet speak English, do not use a specific word for blue. Experiments based on color sorting and similarity, which do not require a color name response, will examine the possibility that classical color-opponency is observable in their non-language representation of color. Control studies of spectral sensitivity and discrimination will test for the possible interplay between cultural and sensory factors (including congenital and acquired impairments in color vision) in shaping an individual's mental representation of color.

This research will contribute to understanding the foundational processes by which innate and cultural factors shape an individual's understanding of their world. In addition, it will bring the Somalis, who came to the US as refugees from political upheaval, into a research environment in a university and will give students a better understanding of people from a vastly different culture.