Dynamics of neural representations when searching for exemplars and categories of human and non-human faces

Laurie Bayet,Benjamin Zinszer,Zoe Pruitt,Richard N Aslin,Rachel Wu

doi:10.1038/s41598-018-31526-y

Abstract

Face perception abilities in humans exhibit a marked expertise in distinguishing individual human faces at the expense of individual faces from other species (the other-species effect). In particular, one behavioural effect of such specialization is that human adults search for and find categories of non-human faces faster and more accurately than a specific non-human face, and vice versa for human faces. However, a recent visual search study showed that neural responses (event-related potentials, ERPs) were identical when finding either a non-human or human face. We used time-resolved multivariate pattern analysis of the EEG data from that study to investigate the dynamics of neural representations during a visual search for own-species (human) or other-species (non-human ape) faces, with greater sensitivity than traditional ERP analyses. The location of each target (i.e., right or left) could be decoded from the EEG, with similar accuracy for human and non-human faces. However, the neural patterns associated with searching for an exemplar versus a category target differed for human faces compared to non-human faces: Exemplar representations could be more reliably distinguished from category representations for human than non-human faces. These findings suggest that the other-species effect modulates the nature of representations, but preserves the attentional selection of target items based on these representations.

Highlights

Face perception abilities in humans exhibit a marked specialization for distinguishing individual human faces, along with a relative difficulty in distinguishing faces from another species or distinguishing between different human faces from another race or ethnicity
A first question is whether a different technique, multivariate pattern analysis (MVPA) of the EEG signal, could reveal neural differences reflecting the attentional selection of exemplar and category, human and non-human face targets
A second question is whether differences in the representation of human and other-species faces might be evidenced during exemplar- and category-based visual search either preceding or following attentional selection, as predicted from studies examining the processing of human or non-human faces presented in isolation

Summary

Introduction

Face perception abilities in humans exhibit a marked specialization for distinguishing individual human faces, along with a relative difficulty in distinguishing faces from another species (the other-species effect1,2) or distinguishing between different human faces from another race or ethnicity (the other-race effect[3]). A second question is whether differences in the representation of human and other-species (non-human) faces might be evidenced during exemplar- and category-based visual search either preceding or following attentional selection, as predicted from studies examining the processing of human or non-human faces presented in isolation. To examine these questions, we used time-resolved MVPA with a previously collected electrophysiological dataset[23] from 41 human adults performing a visual search task for human faces (N = 21) or non-human faces (N = 20; Table 1) to investigate the neural correlates of processing and selecting human versus non-human target faces. Given the greater difficulty of exemplar-level but not category-level processing of other-species and other-race faces[1,2,3,4,9], we directly tested for the effect of task-dependent processing (i.e. exemplar-level versus category-level target processing) on neural patterns when searching for human faces versus non-human faces

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Conclusion