Monocular Facilitation Implicates Subcortical Involvement in Holistic Processing of Faces

Holistic processing (HP) refers to obligatory processing of the entirety of a visual stimulus rather than independent parts. In particular, HP has been implicated in face processing. Given that HP of faces has evolutionary significance, and subcortical structures generally being evolutionarily older than neocortex, the present research tests whether subcortical structures might contribute to the composite face effect (CFE), a common indicator of HP. According to the CFE, identical top halves of faces are more likely to be judged as different when the two bottom halves are from different faces, and differing top halves are less likely to be noticed as different given identical bottom halves (and vice versa for judging the bottom). Using a mirror stereoscope, we tested whether the CFE is greater when the images are presented to a single eye (monocularly) as opposed to different eyes (binocularly) sequentially, which would indicate HP outside cortical involvement. This study contributes to the literature on subcortical mechanisms in face processing, and, ultimately, has implications for our understanding of the evolutionary history of face processing.