We examined the effect of 4-month-old infants' previous experience with dogs, cats, or both and their online looking behavior on their learning of the adult-defined category of "cat" in a visual familiarization task. Four-month-old infants' (N = 123) learning in the laboratory was jointly determined by whether or not they had experience with pets at home and how much they shifted their gaze back and forth between the stimuli during familiarization. Specifically, only infants with pets at home who also exhibited high levels of switching during familiarization remembered the individual cat exemplars or formed a summary representation of those cats. These results are consistent with recent theorizing about the processes of how infants' categorical representations are formed, and provide new understanding into how infants' categorization unfolds over time. (Contains 2 figures and 3 tables.)