“I spy with my little eye …”: Connectivity analyses of the illusory face perception network

Introduction Face pareidolia is the illusory perception of non-existent faces. Putatively, it is caused by matching high-dimensional sensory input with internal face templates, achieved through a top-down mediated coupling between prefrontal regions and brain areas in the ventral temporal cortex, the so-called “core system of face perception”. The objective of this study was to understand the coupling mechanisms between core and prefrontal regions in more detail.

Methods We conducted a functional magnetic resonance imaging study on face pareidolia. To trigger illusory face perception, subjects were shown pure noise images but were told that half of them contained a face. Network connectivity was assessed using psychophysiological interaction (PPI) analyses and Dynamic Causal Modeling (DCM).

Results Illusory face perception activated the bilateral core system, similar as for the processing of real faces. Contrary to the holistic processing ascribed to the right hemisphere when naturally perceiving a real face however, activity of the occipital face area (OFA) was atypically left-lateralized. Presumably, this arises due to the necessary and more fundamental feature-by-feature analysis of sensory input. Prefrontal activation was present within the inferior frontal gyrus (IFG), while the orbitofrontal cortex (OFC) was unexpectedly deactivated during the face perception condition, but activated when subjects could not detect a face. PPI analyses showed that the core system was stronger coupled with both prefrontal regions in the face detected compared to the no-face detected condition. DCM revealed in particular a stronger connectivity between OFA and OFC when subjects were unable to detect a face. This connectivity pattern was exhibiting a pronounced hemispheric asymmetry.

Conclusion Taken together, these findings suggest that while the IFG activity was face-sensitive, in line with current neuroanatomical models of face perception, the OFC served as a general, non-face specific matching point between external input and internal templates.