Human gestures trigger different attentional shifts in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

To examine how gestural cues trigger shifts in attention, two chimpanzees and ten humans participated in a computer-controlled target-detection experiment. Before presenting the target at either a left or right location, a photograph of a human gesturing towards or away from the forthcoming target location was presented on a CRT display monitor. Humans exhibited faster response times in the trials in which the gestural cue signalled the target location (valid trials) as opposed to the opposite location (invalid trials) when the cue–target interval (stimulus onset asynchrony, SOA) was 100 ms but not when the SOA was 500 ms. However, chimpanzees showed faster response times in valid trials than in invalid trials only when the SOA was 500 ms. The reflexive mechanism is known to activate attention quickly, while the slow onset of the cueing effect can be considered a sign of voluntary control of attentional shift. The present study used the cueing paradigm and a comparative cognitive perspective to clarify the effect of directional gestural cues for the first time. The results suggested that different mechanisms underlie the attentional shift triggered by gestural cues in humans and chimpanzees.