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By three years of age, children are skilled at assessing under which circumstances others can see things. However, nothing is known about whether they can use this knowledge to guide their own deceptive behaviour. Here we investigated 3-year-olds' ability to strategically inhibit or conceal forbidden actions that a nearby adult experimenter could see or hear. In the first experiment, children were more likely to disobey the adult when she did not have visual access to their activities than they were when she was looking at them. In the second experiment, in which the adult could never see the child, children refrained from making noise when engaging in a prohibited action that the adult might hear. These results suggest that by three years of age children use their knowledge of others' perceptual states to decide whether it is safe to commit a transgression and, moreover, actively conceal perceptual cues that could reveal to others their ongoing transgression.

We investigated whether great apes, like human infants, monkeys and dogs, are subject to a strong gravity bias when tested with the tubes task, and--in case of mastery--what the source of competence on the tubes task is. We presented 22 apes with three versions of the tubes task, in which an object is dropped down a tube connected to one of three potential hiding places and the subject is required to locate the object. In two versions, apes were confronted with a causal tube that varied in the amount of perceptual information it provided (i.e. presence or absence of acoustic cues). The third version was a non-causal adaptation of the task in which a painted line "connected" dropping and hiding places. Results indicate that apes neither have a reliable gravity bias when tested with the tubes, nor understand the causal function of the tube. Even though there is evidence that they can integrate tube-related causal information to localize the object, they seem to depend mainly on non-causal inferences when searching for an invisibly displaced object.

A key skill in early human development is the ability to comprehend communicative intentions as expressed in both nonlinguistic gestures and language. In the current studies, we confronted domestic dogs (some of whom knew many human "words") with a task in which they had to infer the intended referent of a human's communicative act via iconic signs--specifically, replicas and photographs. Both trained and untrained dogs successfully used iconic replicas to fetch the desired item, with many doing so from the first trial. Dogs' ability to use photographs in this same situation was less consistent. Because simple matching to sample in experimental contexts typically takes hundreds of trials (and because similarity between iconic sign and target item did not predict success), we propose that dogs' skillful performance in the current task reflects important aspects of the comprehension of human communicative intentions.

Although apes understand others' goals and perceptions, little is known about their understanding of others' emotional expressions. We conducted three studies following the general paradigm of Repacholi and colleagues (1997, 1998). In Study 1, a human reacted emotionally to the hidden contents of two boxes, after which the ape was allowed to choose one of the boxes. Apes distinguished between two of the expressed emotions (happiness and disgust) by choosing appropriately. In Studies 2 and 3, a human reacted either positively or negatively to the hidden contents of two containers; then the ape saw him eating something. When given a choice, apes correctly chose the container to which the human had reacted negatively, based on the inference that the human had just eaten the food to which he had reacted positively--and so the other container still had food left in it. These findings suggest that great apes understand both the directedness and the valence of some human emotional expressions, and can use this understanding to infer desires.

A nonverbal false belief task was administered to children (mean age 5 years) and two great ape species: chimpanzees ("Pan troglodytes") and bonobos ("Pan paniscus"). Because apes typically perform poorly in cooperative contexts, our task was competitive. Two versions were run: in both, a human competitor witnessed an experimenter hide a reward in one of two containers. When the competitor then left the room (version A) or turned around (version B), the experimenter switched the locations of the containers. The competitor returned and reached with effort, but unsuccessfully, towards the incorrect container. Children displayed an understanding of the competitor's false belief by correctly choosing the other container to find the reward. Apes did not. However, in version A (but not version B), apes looked more often at the unchosen container in false belief trials than in true belief control trials, possibly indicating some implicit or uncertain understanding that needs to be investigated further.

Human infants imitate others' actions "rationally": they copy a demonstrator's action when that action is freely chosen, but less when it is forced by some constraint (Gergely, Bekkering & Kiraly, 2002). We investigated whether enculturated chimpanzees (Pan troglodytes) also imitate rationally. Using Gergely and colleagues' (2002) basic procedure, a human demonstrator operated each of six apparatuses using an unusual body part (he pressed it with his forehead or foot, or sat on it). In the Hands Free condition he used this unusual means even though his hands were free, suggesting a free choice. In the Hands Occupied condition he used the unusual means only because his hands were occupied, suggesting a constrained or forced choice. Like human infants, chimpanzees imitated the modeled action more often in the Hands Free than in the Hands Occupied condition. Enculturated chimpanzees thus have some understanding of the rationality of others' intentional actions, and use this understanding when imitating others.

Understanding the intentional actions of others is a fundamental part of human social cognition and behavior. An important question is therefore whether other animal species, especially our nearest relatives the chimpanzees, also understand the intentional actions of others. Here we show that chimpanzees spontaneously (without training) behave differently depending on whether a human is unwilling or unable to give them food. Chimpanzees produced more behaviors and left the testing station earlier with an unwilling compared to an unable (but willing) experimenter. These data together with other recent studies on chimpanzees' knowledge about others' visual perception show that chimpanzees know more about the intentional actions and perceptions of others than previously demonstrated.

The recognition of iconic correspondence between signal and referent has been argued to bootstrap the acquisition and emergence of language. Here, we study the ontogeny, and to some extent the phylogeny, of the ability to spontaneously relate iconic signals, gestures, and/or vocalizations, to previous experience. Children at 18, 24, and 36 months of age (N = 216) and great apes (N = 13) interacted with two apparatuses, each comprising a distinct action and sound. Subsequently, an experimenter mimicked either the action, the sound, or both in combination to refer to one of the apparatuses. Experiments 1 and 2 found no spontaneous comprehension in great apes and in 18‐month‐old children. At 24 months of age, children were successful with a composite vocalization‐gesture signal but not with either vocalization or gesture alone. At 36 months, children succeeded both with a composite vocalization‐gesture signal and with gesture alone, but not with vocalization alone. In general, gestures were understood better compared to vocalizations. Experiment 4 showed that gestures were understood irrespective of how children learned about the corresponding action (through observation or self‐experience). This pattern of results demonstrates that iconic signals can be a powerful way to establish reference in the absence of language, but they are not trivial for children to comprehend and not all iconic signals are created equal. Four experiments investigated spontaneous comprehension of iconic gestures and vocalizations in human children and great apes. 24‐ and 36‐month‐olds, but not 18‐month‐olds and not great apes, spontaneously identified the referent of an iconic signal. Performance improved substantially with age. Overall, iconic gestures were more readily understood compared to iconic vocalizations. [ABSTRACT FROM AUTHOR]