Inferences About Hidden Causes by 10- and 12-Month-Old Infants

Considerable evidence indicates that preverbal infants expect that only physical contact can cause an inanimate object to move. However, very few studies have investigated infants’ expectations about the source of causal power. In three experiments, we found that (a) 10and 12-month-old infants expect a human hand, and not an inanimate object, to be the primary cause of an inanimate object’s motion; (b) infants’ expectations can lead them to infer a hidden causal agent without any direct perceptual evidence; and (c) infants do not infer a hidden causal agent if the moving object was previously shown to be capable of self-generated motion. Causal attributions are central to human cognition, underlying representations of concepts and intuitive theories (Carey, 1985; Gopnik et al., 2004; Keil, 1989; Murphy, 2002), supporting prediction of future events, and allowing effective intervention in the service of goals. The capacity for causal attribution emerges early in infancy and is embedded in at least two distinct domains of reasoning, reasoning about inanimate objects for which the cause of motion must include contact (Ball, 1973; Cohen, Amsel, Redford, & Casasola, 1998; Cohen, Rundell, Spellman, & Cashon, 1999; Kosugi & Fujita, 2002; Kotovsky & Baillargeon, 2000; Leslie & Keeble, 1987) and reasoning about intentional agents in terms of their goals (Gergely, Nadasdy, Csibra, & Biro, 1995; Johnson, 2003; Kosugi, Ishida, & Fujita, 2003; Meltzoff & Brooks, 2001; Woodward, 1998; Woodward, Sommerville, & Guajardo, 2001). Previous studies of infants’ understanding of causal interactions have focused on the properties of the patient object (inert or animate) and on the spatiotemporal properties of the interaction. The studies show that infants expect an inert inanimate object to go into motion when and only when contacted by another moving object (Ball, 1973; Cohen et al., 1998; Kosugi et al., 2003; Kotovsky & Baillargeon, 2000; Oakes & Cohen, 1990, 1994; Spelke, Phillips, & Woodward, 1995; Wang, Kaufman, & Baillargeon, 2003), and that these expectations are suspended if the patient object is capable of self-generated motion (Kosugi & Fujita, 2002; Spelke et al., 1995). Adults, however, have expectations not only about the patient of a causal interaction, and about the interaction itself, but also about the causal agent. By ‘‘causal agent,’’ we mean the entity that is the purveyor of causal force, the source of motion or change, in an interaction (Leslie, 1994). Adults both distinguish between the roles of causal agent and patient in a visible interaction (e.g., one billiard ball hitting another) and expect a primary causal agent, usually an animate or intentional agent (e.g., the person holding the cue). The necessity of a primary cause can lead adults to infer the presence of a hidden causal agent, if none is visible. Imagine, for example, seeing a tennis ball or a shoe come flying over the backyard fence. Some evidence suggests that infants distinguish between the roles of causal agent and patient in simple, fully visible interactions by 7 to 10 months of age (Leslie, 1984; Leslie & Keeble, 1987; Oakes & Cohen, 1994). However, no previous studies have examined whether infants infer the presence of an agent from motion of an object they have categorized as inert. The present studies fill that gap. In these studies, we explored the following questions: Seeing only the motion of an inert object, do infants infer that something must have caused that motion (the causal agent)? Do infants have expectations about the potential causal agent? In particular, do they consider a person more likely to be a causal agent than an inanimate object?