The involvement of monocular channels in the face pareidolia effect

Studies examining the neural mechanisms of face perception in humans have mainly focused on cortical networks of face-selective regions. However, subcortical regions are known to play a significant role in face perception as well. For instance, upon presenting pairs of faces sequentially to the same eye or to different eyes, superior performance is observed in the former condition. This superiority was explained by monocular, pre-striate processing of face stimuli. One of the intriguing face-related effects is the face pareidolia phenomenon, wherein observers perceive faces in inanimate objects. In this study, we examined whether face pareidolia involves similar low-level neural substrates to those that are involved in face perception. We presented participants with pairs of houses or face-like houses using a stereoscope to manipulate the information presented to each eye and asked them to determine whether the stimuli were similar or different. We managed to examine the contribution of monocular channels (mostly subcortical) in processing face-like stimuli. We hypothesized that besides their involvement in actual face perception, subcortical structures are engaged in face pareidolia as well. To test our hypothesis, we conducted three experiments to replicate and strengthen the reliability of our results and rule out alternative explanations. We demonstrated a perceptual benefit when presenting similar face-like houses to the same eye in comparison to their presentation to different eyes. This finding matches previous results found for images of real faces and indicates subcortical involvement not only in face perception but also in processing face-like objects.