For many years, the standard object-choice test has posed a difficulty for chimpanzees, raising a significant question regarding their perception of human gestures. In the conventional test, an experimenter conceals a reward in one of two containers and indicates the correct one. Frequently, the chimpanzee’s selection is no better than chance, reinforcing the belief that chimpanzees do not understand that a point is meant to help.
Nonetheless, research conducted by Alicia Melis at University College London, Federico Rossano at the University of California, San Diego, and others, challenges this view. This study, carried out with nine chimpanzees at the Ngamba Island Chimpanzee Sanctuary in Uganda, and published in the journal iScience, revealed differing outcomes. When the experiment involved the chimpanzee’s name and food-related grunts accompanying the point, the chimpanzees performed well. Conversely, they did not show improved performance when the pointing was silent or when the experimenter simply looked and grunted without indicating.
This finding led researchers to suggest the attentional deficit theory: chimpanzees may fail traditional tests not due to an inability to understand cooperative intentions, but rather a lack of attention to the individual, especially in a foraging context. The new experimental setup, which included vocal cues, made the human hard to ignore, though it does not clarify which particular sound or gesture was effective.
The experiment featured two identical hiding containers, spaced 150 centimeters apart, with a collaboration box containing grapes. Tools necessary to obtain the grapes were hidden in one of the two boxes, while a key—a single-choice device—was placed three meters ahead. In the attention-enhanced scenario, the experimenter called the chimp’s name, made food-grunting sounds, and consistently pointed to the correct box, in contrast to a baseline pointing condition that lacked sounds and a non-intentional condition with food grunts without pointing.
Each chimpanzee participated in multiple sessions, with various trial types to balance conditions. All were acquainted with the setup; some had prior exposure to object-choice pointing tests. Collectively, the chimpanzees reached a 73% success rate in attention-enhanced trials, significantly above chance, unlike the silent-pointing (53%) and look-and-grunt (46%) trials.
This research indicates that capturing attention is crucial. Contrary to popular belief, non-enculturated chimpanzees can comprehend human pointing when appropriate attention cues are present. This finding disputes the traditional enculturation theory, implying that attentional engagement, rather than a background of learning from humans, may clarify differences in task understanding.
The researchers draw comparisons between their study and others, such as one by Hopkins et al., which similarly showed that vocalized pointing enhances performance. However, the Ngamba study emphasized targets across the body, preventing chimpanzees from simply reaching for the nearest hand, underlining the significance of attention instead of local enhancement.
The study aligns the chimpanzee group’s performance with that of human infants, observing comparable results in object-choice tasks during certain developmental phases. However, it refrains from directly equating the cognitive capabilities of chimpanzees with those of human children.
The study raises unresolved questions about which elements of the multimodal cue are vital and proposes that a combination of aspects may be important. Despite its limited sample size and inclusion of sanctuary-housed, previously exposed chimpanzees, the study advances the understanding of chimpanzee cognition, suggesting they can interpret human gestures when their attention is optimally engaged.