Developmental and postural changes in children's visual access to faces.

Developmental and postural changes in children’s visual access to faces Michael C. Frank, Kaia Simmons, Daniel Yurovsky, & Guido Pusiol {mcfrank,kaias,yurovsky,pusiol}@stanford.edu Department of Psychology Stanford University Abstract Campos (under review) noted robust correlations between children’s ability to walk and their vocabulary, both recep- tive and productive. On the basis of an observational study of parent input, they speculated that the emergence of walking may change the ability of the child to access social informa- tion (because walking toddlers see more of the social world than crawling infants). Accessing more social information may in turn allow children to discover word meanings more effectively. The faces of other people are a critical information source for young children. During early development, children un- dergo significant postural and locomotor development, chang- ing from lying and sitting infants to toddlers who walk inde- pendently. We used a head-mounted camera in conjunction with a face-detection system to explore the effects of these changes on children’s visual access to their caregivers’ faces during an in-lab play session. In a cross-sectional sample of 4–20 month old children, we found substantial changes in face accessibility based on age and posture. These changes may translate into changes in the accessibility of social information during language learning. Keywords: Social development; face processing; head- camera. Recent methodological developments have the potential to provide data that would allow this hypothesis to be tested. The availability of head-mounted cameras and eye-trackers allows for the measurement of children’s naturalistic envi- ronment in a way that was not previously possible. Yoshida and Smith (2008) gave the first demonstration of the radi- cal differences between toddler and adult perspectives on the social world, with toddlers’ visual field being dominated by hands and objects much more than that of adults. More re- cent work has used head-mounted eye-tracking methods to measure young toddlers’ fixations (Franchak, Kretch, Soska, & Adolph, 2011), also finding that children look relatively infrequently at their mothers’ faces in naturalistic play. Introduction A father offers his young daughter a novel object: a bright yellow feather duster. A few moments after she accepts the toy, he remarks, “Isn’t the zem funny?” Her father may still be talking about the feather duster, or he may be describing a new object. To find out she has access to a simple and reliable method: she can look to his face to infer the direction of his attention. The ability to follow social signals like eye-gaze is an im- portant part of early social cognition (Scaife & Bruner, 1975) and a strong predictor of children’s early language develop- ment. For example, Brooks and Meltzoff (2005) found that children who followed an experimenter’s gaze better before their first birthday had larger vocabularies at 18 months. Sim- ilarly, Carpenter, Nagell, and Tomasello (1998) found that children’s level of joint engagement (as well as the degree to which mothers followed the child’s focus of attention in their labeling) predicted vocabulary growth in both language pro- duction and comprehension. These studies suggest that chil- dren’s social environment plays a powerful supportive role in language learning. But at the same time as children are beginning to learn their first words, their view of the world is changing radically (Adolph & Berger, 2007). As speechless infants, they are un- able to locomote independently. Before their first birthday, they begin crawling; soon after, they begin to walk indepen- dently. Infants’ visual field is subject to the whims of their caregivers, but caregivers often place them in positions con- ducive to joint attention. In contrast, toddlers determine their own input to a much greater degree, but as a consequence they spend much of their time in a world primarily populated by knees. These postural and locomotor changes may have a profound effect on what children see. A recent study suggests the possibility of links between motor milestones, social cognition, and language. Walle and These methods are now being applied to understand inputs to language acquisition. Work by Yu, Smith, and colleagues suggests that word learning is facilitated when parents and children create moments in which the visual field is domi- nated by a single object (Smith, Yu, & Pereira, 2011; Yu & Smith, in press). Some data even suggest that young chil- dren’s restricted viewpoint may be more effective for learn- ing words than the comparable adult perspective (Yurovsky, Smith, & Yu, in press). Together, this body of evidence suggests that measuring infants’ perspective—and how it changes in motor development—is a critical part of under- standing early language learning. In the current study we took a developmental approach to understanding the relationship between perspective and ac- cess to social information. We recorded head-camera data from a group of infants and children across a broad age range as they played with their caregivers during a brief laboratory visit. We then hand-annotated these data for the child’s pos- ture and parents’ naming behavior and used face-detection algorithms to measure the frequency of faces in the child’s vi- sual field. The resulting dataset allows us to analyze changes in access to faces according to children’s age, posture, and linguistic input.