Perception of partly occluded figures by baboons (Papio papio)

Comparative literature provides conflicting findings whether animals experi ence amodal completion. Five experiments were conducted to verify if baboon s perceive partly occluded objects as complete. The first three experiments used a go/no-go procedure and a video monitor for stimulus presentation. T hese experiments failed to reveal amodal completion, suggesting that the st imuli were processed as 2-D images rather than 3-D objects. In contrast, co mpletion was demonstrated in a fourth experiment with cardboard stimuli in a two-alternative forced-choice (2AFC) discrimination task presented in a W isconsin General Test Apparatus. Although in experiment 5 the same 2AFC pro cedure 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 so me procedural factors that might affect the elicitation of this capacity.