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.