Word learning is a critically important component of cognitive development. Learning words not only facilitates communication but the mere exposure to linguistic input appears to help young infants organize their world. While various mechanisms have been proposed to account for the developmental changes in word learning and to explain the reported effects of words on cognitive development, it is unclear how these proposed mechanisms map onto recent findings examining cross-modal processing;a necessary component of word learning. Specific aim 1 of the proposed research is to further examine how auditory input affects visual processing and binding of auditory-visual pairings. Specific aim 2 is to directly test the ability of the proposed attentional mechanisms to account for effects of words on categorization. Based on research investigating the dynamics of attention in cross-modal processing, the current application will test a non-trivial hypothesis;some of the initial effects of words on cognitive tasks stem from auditory input decreasing visual processing. Attenuated processing of the details of a visual stimulus may help infants to automatically reduce a perceptually-rich environment in favor of more abstract, generic representations (e.g., overall shape, whole object, etc.). This reduction may in turn facilitate early generalizations, such as categorization of entities and induction of hidden properties. The proposed research consists of three experiments examining early word learning and effects of auditory input on categorization. Using methodologies derived from microgenetic studies, Experiment 1 will employ a novel word learning procedure that will teach infants word-object and sound-object associations and then monitor comprehension of these associations at various points throughout training. By manipulating the type and familiarity of the auditory input, Experiment 1 will examine factors affecting binding of arbitrary, auditory-visual stimuli, such as words and potential referents. It is expected that familiarity of the auditory stimulus, rather than the type of auditory stimulus (word vs. sound), will initially be the best predictor of binding. Experiment 2 will examine how a word learning context affects encoding of the referent. It is expected that infants in Experiment 1 will map words and sounds onto referents, however, it is likely that the word learning context will attenuate processing of the referent (i.e., infants are expected to encode more details of a visual stimulus when it is presented in silence than when paired with an auditory stimulus). Experiment 3 will determine whether attenuated visual processing can provide a low-level account for some of the early effects of words on category learning, with words facilitating category responding by decreasing the discriminability of labeled referents. By examining how infants allocate their attention to cross-modal stimuli, the current application will not only have implications for word learning in typical and atypical populations but the information gained from this research will be fundamental for understanding the early interactions between language and thought. By examining how infants pay attention to simultaneously presented words and pictures, the proposed research will help researchers, parents and teachers better understand early word learning and factors that can facilitate word learning. The information gained from this research will also be fundamental for understanding how exposure to a language influences the way infants perceive their world.