PAPER Carryover effect of joint attention to repeated events in chimpanzees and young children Sanae Okamoto-Barth, Chris Moore, Jochen Barth, Francys Subiaul and Daniel J. Povinelli Department of Cognitive Neuroscience, Maastricht University, The Netherlands Abstract Gaze following is a fundamental component of triadic social interaction which includes events and an object shared with other individuals and is found in both human and nonhuman primates. Most previous work has focused only on the immediate reaction after following another’s gaze. In contrast, this study investigated whether gaze following is retained after the observation of the other’s gaze shift, whether this retainment differs between species and age groups, and whether the retainment depends on the nature of the preceding events. In the social condition, subjects (1- and 2-year-old human children and chimpanzees) witnessed an experimenter who looked and pointed in the direction ofa target lamp. In the physical condition, the target lamp blinked but the experimenter did not provide any cues. After a brief delay, we presented the same stimulus again without any cues. All subjects looked again to the target location after experiencing the social condition and thus showed a carryover effect. However, only 2-year-olds showed a carryover effect in the physical condition, 1-year-olds and chimpanzees did not. Additionally, only human children showed spontaneous interactive actions such as pointing. Our results suggest that the difference between the two age groups and chimpanzees is conceptual and not only quantitative. Introduction By the end of their first year, human infants become sen- sitive to information specifying where others are looking. The ability to follow the gaze of other individuals is a critical component of joint attention, defined as looking toward the object of others’ attention. Infants show a specific developmental trajectory in this ability (see Moore, 2008). In this first year, human infants follow their mother’s gaze to the appropriate side (e.g. Scaife & Bruner, 1975), at first when there are objects already in their immediate field of view (e.g. D’Entremont, Hains & Muir, 1997), and later even when objects are outside their immediate field of view (e.g. Corkum & Moore, 1995). By the beginning of the second year, infants will follow their mother’s gaze towards particular objects even when vari- ous objects are present, and between 12 and 18 months they can direct their attention to objects that are located behind them or in containers (e.g. Butterworth & Coch- ran, 1980; Butterworth & Jarrett, 1991; Moll & Tomasello, 2004). Joint attention is considered by some to be an early social cognitive ability leading to the later development of the ability to infer others’ mental states (cf. Baron-Cohen, 1995; Tomasello, 1995). However, eye-gaze is not the only cue to another’s focus of attention. The orientation of the whole head, body, and hand (e.g. pointing) are similarly good indi- cators of attention and interest, and are used in our daily interactions with others. Pointing in particular is con- sidered an important component of joint attention as an indicator of particular objects, locations, or events. At about 12 months, infants begin to follow pointing to distant locations (Butterworth & Jarrett, 1991; Desro- chers, Morissette & Ricard, 1995; Lempers, 1979; Leung & Rheingold, 1981; Murphy & Messer, 1977). Gaze following is also found in a number of nonhu- man primates. The use of gaze shifts as social cues has various evolutionary advantages. For instance, gaze shifts may index the location of predators, dominants, potential mates or food sources. Several field studies suggest that primates follow the gaze of conspecifics (e.g. Chance, 1967; Menzel & Halperin, 1975; Whiten & Byrne, 1988). A number of laboratory studies have also investigated gaze following in nonhuman primates. Within a gaze-following task paradigm, various stud- ies with chimpanzees have demonstrated that they follow the gaze direction of other individuals (e.g. Itakura, 1996; Povinelli & Eddy, 1996; Tomasello, Call & Hare, 1998; Okamoto-Barth, Call & Tomasello, 2007; see Emery, 2000, for review). However, interpreting this behavior is not straightforward, as it may represent either a simple reflexive tendency to visually orient in the D E S C 9 9 6 B Dispatch: 26.7.10 Journal: DESC CE: Blackwell Journal Name Manuscript No. Author Received: No. of pages: 13 PE: Bhagyalakshmi Address for correspondence: Sanae Okamoto-Barth, Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands; e-mail: s.barth@maastrichtuniversity.nl Ó 2010 Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. Developmental Science (2010), pp 1–13 DOI: 10.1111/j.1467-7687.2010.00996.x 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58