Hemispheric lateralisation and global precedence effects in the processing of visual stimuli by humans and baboons (Papio papio).

This paper examines the effect of global precedence (GPE: Navon, 1977) and its lateralisation from a comparative perspective. Using a divided field matching-to-sample task with compound stimuli, Experiment 1 demonstrated consistent patterns of lateralisation in humans and baboons, corresponding to a right-hemisphere advantage for global processing and a left- but nonsignificant advantage for local processing. Species differences emerged in terms of GPE; humans showed a global precedence effect, and baboons were better for local than for global matching. In Experiment 2, a visual search task was used to assess the origin of species differences in terms of GPE. Humans processed the global structure of the forms pre-attentively, whereas baboons used an attentional search strategy. From this finding, it is argued that lateralisation in Experiment 1 was rooted in early perceptual mechanisms. So far, consistent patterns of lateralisation for global/local processing have been found in baboons, chimpanzees, and humans, suggesting that this phenomenon has a long evolutionary history.