Child Development, January/February 2009, Volume 80, Number 1, Pages 151 – 161 Time Course of Visual Attention in Infant Categorization of Cats Versus Dogs: Evidence for a Head Bias as Revealed Through Eye Tracking Paul C. Quinn, Matthew M. Doran, Jason E. Reiss, and James E. Hoffman University of Delaware Previous looking time studies have shown that infants use the heads of cat and dog images to form category representations for these animal classes. The present research used an eye-tracking procedure to determine the time course of attention to the head and whether it reflects a preexisting bias or online learning. Six- to 7-month- olds were familiarized with cats or dogs in upright or inverted orientations and then tested with a novel cat and novel dog in the same orientation. In the upright orientation, infants fixated head over body throughout familiarization; with inversion, no head preference was observed. These findings suggest that infant reliance on the head to categorize cats versus dogs results from a bias that pushes attention to the head. Looking time studies measuring the emergence of categorization during early development have demon- strated that young infants between the ages of 3 and 7 months will categorize nonhuman animals such as cats, dogs, and horses (Eimas & Quinn, 1994; Oakes & Ribar, 2005; Quinn, Eimas, & Rosenkrantz, 1993; Quinn, Westerlund, & Nelson, 2006; Younger & Fearing, 2000; Younger & Furrer, 2005). The infants are presented with multiple instances from a common category during familiarization (e.g., cats) and then with a preference test pairing a novel instance from the familiar category (e.g., a new cat) with a novel instance from a novel category (e.g., a new dog). Categorization is inferred if infants generalize their familiarization to the novel instance from the familiar category and display a pref- erence for the novel instance from the novel category. Although the evidence indicates that young infants can learn category representations on the basis of perceptual experience, an important question to con- sider is: What attributes are infants using to form the category representations? The answer to this question is not obvious, given that the exemplars of each category possess a number of common attributes such as a head, torso, four legs, and a tail. Quinn and Eimas (1996a) examined 3- to 4-month-olds’ abilities to categorize cats versus dogs when provided with the whole stimuli, just the heads (with the bodies occluded), or just the bodies (with the heads occluded) during both the familiarization and the preference test portions of the experiment. The results were that the infants categorized when presented with either the whole stimuli or just the heads but not when presented with just the bodies. These findings indicate that the head provided a sufficient basis for the infants to categorize cats versus dogs. The conclusion of Quinn and Eimas (1996a) was supported by an additional study in which infants were familiarized with whole cat or dog images and then preference tested with hybrid stimuli (i.e., cat head on dog body vs. dog head on cat body; Spencer, Quinn, Johnson, & Karmiloff-Smith, 1997). Infant preference during test followed the direction of the novel category head. Interestingly, adults also seem to emphasize the head when representing animal species (Reed, McGoldrick, Shackelford, & Fidopiastis, 2004). Use of the head could arise from a preexisting biasing mechanism that directs infant attention to the head information that is present in a visual scene (Johnson & Morton, 1991). Such a biasing mechanism would ensure that infants attend to and eventually recognize faces. It is also possible that the infants simply learn during the course of experience with the exemplars that the head is the most diagnostic part of the stimulus. In other words, the head feature may be flexibly created as the basis for the category repre- sentation in an online fashion (Quinn, Schyns, & Goldstone, 2006). This possibility seems reasonable given that the head may have fewer degrees of freedom relative to the body in terms of the various stances presented to the infants (Reed, Stone, & McGoldrick, 2005). As such, it might be more easily extracted as an invariant feature. This research was supported by National Institutes of Health Grants HD-42451 and HD-46526. The authors thank three anonymous reviewers for their comments on an earlier draft and also thank Laurie Yarzab and Erika Jordan for their assistance in testing participants. Correspondence concerning this article should be addressed to Paul C. Quinn, Department of Psychology, University of Delaware, Newark, DE 19716. Electronic mail may be sent to pquinn@udel. edu. # 2009, Copyright the Author(s) Journal Compilation # 2009, Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2009/8001-0013