Solving small spaces: investigating the use of landmark cues in brown capuchins (Cebus apella).

Some researchers have recently argued that humans may be unusual among primates in preferring to use landmark information when reasoning about some kinds of spatial problems. Some have explained this phenomenon by positing that our species' tendency to prefer landmarks stems from a human-unique trait: language. Here, we test this hypothesis-that preferring to use landmarks to solve such tasks is related to language ability-by exploring landmark use in a spatial task in one non-human primate, the brown capuchin monkey (Cebus apella). We presented our subjects with the rotational displacement task, in which subjects attempt to relocate a reward hidden within an array of hiding locations which are subsequently rotated to a new position. Over several experiments, we varied the availability and the salience of a landmark cue within the array. Specifically, we varied (1) visual access to the array during rotation, (2) the type of landmark, (3) the consistency of the landmark qualities, and (4) the amount of exposure to the landmark. Across Experiments 1 through 4, capuchins did not successfully use landmarks cues, suggesting that non-linguistic primates may not spontaneously use landmarks to solve some spatial problems, as in this case of a small-scale dynamic spatial task. Importantly, we also observed that capuchins demonstrated some capacity to learn to use landmarks in Experiment 4, suggesting that non-linguistic creatures may be able to use some landmarks cues in similar spatial tasks with extensive training.