Comparative literature provides conflicting findings whether animals experience amodal completion. Five experiments were conducted to verify if baboons perceive partly occluded objects as complete. The first three experiments used a go/no-go procedure and a video monitor for stimulus presentation. These experiments failed to reveal amodal completion, suggesting that the stimuli were processed as 2-D images rather than 3-D objects. In contrast, completion was demonstrated in a fourth experiment with cardboard stimuli in a two-alternative forced-choice (2AFC) discrimination task presented in a Wisconsin General Test Apparatus. Although in experiment 5 the same 2AFC procedure was used as in experiment 4, completion was absent when the stimuli were shown with a computer graphic system. The results suggest that baboons share with humans the ability for amodal completion, but also underline some procedural factors that might affect the elicitation of this capacity.
From cockroaches to human beings, the presence of other members of the same species typically facilitates dominant (habitual/well-learned) responses regardless of their contextual relevance. This social facilitation requires special attention in animal species such as primates, given their evolved cognitive control mechanisms. Here we tested baboons who freely engaged in (computer-based) conflict response tasks requiring cognitive control for successful performance, and discovered that social presence does not only enhance dominant responses but also consumes cognitive control resources. Under social presence, the baboons experienced greater cognitive conflicts, were less able to inhibit a learned action in favor of a new one, and were also less able to take advantage of previous experience with response conflict, compared with isolation. These findings explain why inappropriate behaviors are not easily suppressed in primates acting in social contexts, and indicate a greater demand for cognitive control in social groups. This extra demand might represent a major evolutionary drive of human intelligence.
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