Bridging Sensory Extraction and Decision Dynamics: Face Pareidolia Emergent from Bottom-Up and Top-Down Interactions

Face pareidolia-the illusory perception of faces in everyday objects-provides a unique window into how the human brain resolves visual ambiguity. Whether pareidolia arises from bottom-up sensory processing or top-down, expectation-driven feedback, is currently debated. Here we recorded electroencephalography (EEG) while participants viewed rapid serial visual presentation (RSVP) streams of images, each of which was an object-to-face morph generated along a 21-image continuum via text-to-image diffusion models. Time-resolved representational similarity analyses revealed a clear spatiotemporal dissociation, in which early occipitotemporal areas tracked physical feature changes linearly, while later frontocentral channels collapsed this structural gradient into a sharp, sigmoidal profile reflecting discrete categorical decisions (face-like versus object-like). To characterise information transmission between these regions, we implemented a novel transformation-based representational connectivity analysis. These analyses uncovered an initial feedforward flow of information that transferred and transformed posterior linear traces into anterior sigmoidal representations. Crucially, partitioning the image continuum revealed that unambiguous stimuli (faces or objects) were predominantly resolved via feedforward information flow, whereas ambiguous pareidolic images recruited prolonged top-down feedback. Furthermore, perceptual decision sensitivity was biased by animacy priors and directly predicted individual behavioural reaction times during the task. Together, the findings help reconcile prior debate by establishing that face pareidolia is neither a feedforward process nor an isolated top-down projection, but an active, multi-stage recurrent process driven by feedforward feature extraction and top-down categorical resolution.