Susan Wardle¹, Jessica Taubert^1,2, Malcolm Udeozor^1,3, Chris Baker¹; ¹National Institute of Mental Health, ²University of Queensland, ³University of Cincinnati

Face pareidolia (the perception of illusory faces in objects) engages cortical areas in the fusiform gyrus and on the lateral occipital surface in the human brain (Wardle et al., 2020, Nature Communications). In the macaque, face pareidolia also activates the amygdala (Taubert et al., 2022, Social Cognitive & Affective Neuroscience). Although emotional expressions are attributed to illusory faces by human observers (Wardle, Paranjape et al., 2022, PNAS), it is unknown whether the human amygdala responds to face pareidolia, and whether its response is mediated by emotional expression. Here we measured the BOLD response to human faces and illusory faces in cortical and subcortical human brain regions using 7 Tesla fMRI (1x1x1mm voxels, TR = 2s). Participants (N = 21) viewed photographs of 21 human faces with natural and candid emotional expressions (happy, angry, and neutral), and 21 examples of face pareidolia with the same expressions. For each illusory face, we included a matched control image of a similar object that did not elicit any face perception (21 images). Each of the 63 images was shown once per run for 300ms with a 5.7s ISI; participants completed 6-7 runs. We used a 1-back task to maintain attention in the scanner. We defined face-responsive regions of the amygdala and cortical face areas in occipitotemporal cortex using independent localizer runs containing different emotional face and object photographs. Human faces produced the strongest response in the amygdala, regardless of their emotional expression. The response to illusory faces was stronger than that of similar objects without a face, and in the amygdala this was modulated by the perceived emotional expression. Together, the results demonstrate a subcortical response to face pareidolia in the human brain and show that illusory faces share emotional expression processing mechanisms with real human faces.

Acknowledgements: This research was supported (in part) by the Intramural Research Program of the NIMH (ZIAMH002909).