The Importance of Eyes: How Infants Interpret Adult Looking Behavior

Gaze following occurs when a person looks where another person just looked. Among adults, detecting the direction of another’s gaze is a crucial component of social interactions (Argyle & Cook, 1976; Kleinke, 1986; Langton, Watt, & Bruce, 2000). Gaze following is important from a developmental perspective (Butterworth, 1991; Scaife & Bruner, 1975); for example, individuals with autism have profound deficits in gaze following (Baron-Cohen, 1995; Dawson, Meltzoff, Osterling, Rinaldi, & Brown, 1998; Sigman & Ruskin, 1999). Gaze following has been implicated as a building block for developing a “theory of mind” (Baldwin & Moses, 1994; Lee, Eskritt, Symons, & Muir, 1998; Meltzoff & Brooks, 2001). In particular, it is relevant for understanding the meaning of an emotional display because a person’s emotion is often “about” what he or she sees in the external world (e.g., that object is pleasant vs. dangerous). One needs to be able to follow gaze to understand the cause and meaning of a person’s emotional behavior (Moses, Baldwin, Rosicky, & Tidball, 2001; Repacholi, 1998). Language acquisition is also facilitated by understanding another’s line of regard. In the prototypical case, a verbal label refers to the object being looked at and not the other objects that may be in the room (Baldwin, 1995; Bloom, 2002; Tomasello, 1995). The act of looking at something may take on a referential meaning even to infants (Scaife & Bruner, 1975). The common-sense view is that infants look at the same object as the adult because they want to see what the adult is seeing. From this perspective, infants implicitly understand that the other person is directing his or her own attention to something (Baron-Cohen, 1995; Carpenter, Nagell, & Tomasello, 1998). This interpretation grants a complex interpersonal understanding to infants because it implies that infants interpret the triadic relationship of seeing or attention between themselves, the adult, and the object (Perner, 1991). Some researchers have offered a more conservative or “leaner” interpretation of infants’ gaze following (Langton et al., 2000; Moore, 1999; Moore & Corkum, 1994; Povinelli, 2001). Researchers have suggested that “looking at an object” can be processed as merely an observable movement—the movement of the gazer’s head draws the infant’s attention to a section of space. This would not require any understanding about the gazer’s attention or a reference to the object. Infants may coincidently look at the same object as the adult because they notice the most salient object in the hemifield to which they have been drawn (Butterworth & Jarrett, 1991). It should be noted that there are several debates being intertwined here. One is about the psychological attributions infants make to the adult. The other concerns the necessary and sufficient cues for eliciting gaze following. These are correlated but not identical debates. The natural alliances are for those advocating the lean interpretation about cues to also be conservative about attributions. After all, if infants are merely swept to a hemifield of space by another’s head movement, there is little reason to argue that gaze following is bound up with the attribution of mental states. No single study about cues, no matter how well-designed, is likely to provide definitive conclusions about infants’ attributions. As shown repeatedly in the history of psychology and philosophy, in schools of thought such as behaviorism, arguments can be mustered to show that even adults (no less infants) are simply smart readers of others’ behavior and need not rely on making attributions of mind to other humans (Ryle, 1949). Nonetheless, empirical work provides grist for the debate. If young infants simply follow global head movements to a hemifield but older infants do more than this and selectively follow only when an adult can see the target, this begins to raise questions about the young child’s developing understanding of “seeing” as psychological connectedness between observer and object (e.g., Flavell, 1988, 2001). Researchers have explored whether head movement is sufficient to elicit infant gaze following by manipulating the head-turn angle and the placement of targets. Between 6 and 12 months of age, infants follow another person’s gaze, especially if the targets are within their visual field (Butterworth & Jarrett, 1991; Deak, Flom, & Pick, 2000; D’Entremont, 2000; Morissette, Ricard, & Decarie, 1995). However, careful examination of infants’ gaze following reveals that in many cases they do not look at the same target as the adult, but rather match the general direction of the adult turn. Specifically, when given a choice between two potential targets in the correct half of the room, infants usually stopped searching for a target when they arrived at the first available target on their own scan path (Butterworth, 1991). Because of this response pattern, some theorists have argued that the adult’s head turn pulls infants in the generally indicated direction, providing support for the leaner interpretation of gaze following (Butterworth & Grover, 1990; Moore, 1999). Researchers have also investigated which features (e.g., head, eyes) are necessary for gaze following. For example, Johnson, Slaughter, and Carey (1998) presented 12-month-old infants with a round, furry toy animal. The animal either had a face or not and either interacted contingently with the infant or not. The results showed that the 12-month-old infants turned in the same direction as the faceless, eyeless animal as long as it had previously interacted with them in a contingent manner. The authors interpreted these findings to mean that adult eye gaze was not necessary for infant turning. In another study, Corkum and Moore (1995) pitted the direction of head movement against eye movement to assess which one elicited a response from infants. They tested whether 6- to 19-month-old infants follow eye gaze in conditions such as (a) turns of the eyes (with head remaining forward), (b) turns of the head (with eyes forward), and (c) head and eyes turning in opposite directions. The youngest infants to reveal a significant turning pattern were the 12-month-olds, and they matched the direction of head orientation rather than eye orientation. In this study, there was no age at which infants followed the adult’s gaze when only eyes were turned in the absence of head movement. On the basis of these results and others (Caron, Butler, & Brooks, 2002), a number of authors have suggested that the adult’s head movement often directs where infants look because it is distinct and salient enough to override eye-gaze information (Corkum & Moore, 1995; Farroni, Johnson, Brockbank, & Simion, 2000; Moore & Corkum, 1998). It is important to realize, however, that when head and eyes point in different directions, this presents young infants with a conflict between cues. For example, showing the eyes turning left while the head moves to the right provides an unnatural and potentially confusing display. If we design a test in which the head and eyes are not in conflict, we may find that infants are more sensitive to the role of eyes than previous studies suggest. We designed a study comparing infants’ reactions to an adult who either had open or closed eyes as she turned toward a target. This controls for the head movement, because the movement is identical whether the eyes are open or closed. Surprisingly, few studies of human infants have assessed gaze following in open-versus closed-eyes conditions (for an exception, see Caron et al., 2002). The closed-eyes stimulus has been used to test older children’s understanding (O’Neill, 1996) and has also been used by Povinelli (2000) in work with chimpanzees. Povinelli argued that chimpanzees do not understand the meaning of eye closure inasmuch as they are as likely to direct food-begging gestures to an adult with an unobstructed view of objects as to an adult with an obstructed view (i.e., closed eyes, a blindfold, or a bucket-over-the-head). Systematic tests with human infants seemed worthwhile. We also reasoned that progress could be made in addressing questions about the meaning of infant gaze following and the attributions legitimately credited to infants if we moved beyond narrow data collection strategies. The focus has traditionally been on whether infants follow the adult’s gaze. It became apparent to us in pilot studies, however, that gaze following is only one component of a richer envelope of social behavior. It is this cluster that is so striking in face-to-face adult interaction and so absent in children with autism and in other animals. For example, infants typically use a rich repertoire of behaviors to indicate objects when adults are present, including vocalizing and pointing (Franco & Butterworth, 1996; Moore & D’Entremont, 2001). Humans may be the only species that uses their index finger to draw a conspecific’s attention to a location or object in space (Butterworth, 1991). In addition to measuring infants’ looking behavior, we investigated whether infants would use pointing and vocalizing more often when the adult turned to look at a distal object with open rather than closed eyes.