Can you spot a face? Face pareidolia is enhanced by 40 Hz transcranial Alternating Current Stimulation (tACS) of the face perception network

Abstract

Pareidolia refers to the perception of ambiguous sensory patterns as carrying a specific meaning. In its most common form, pareidolia involves human-like facial features, where random objects or patterns are illusionary recognized as faces. The current study investigated the neurophysiological correlates of face pareidolia via transcranial Alternating Current Stimulation (tACS). tACS was delivered at gamma (40 Hz) frequency over critical nodes of the “face perception” network (the right lateral occipito-temporal and left prefrontal cortex) of 75 healthy participants while completing four face perception tasks (‘Mooney test’ for faces, ‘Toast test’, ‘Noise pareidolia test’, ‘Pareidolia task’) and an object perception task (‘Mooney test’ for objects). In this single-blind, sham-controlled between-subjects study, participants received 35 minutes of either Sham, Online, (40Hz-tACS_ON), or Offline (40Hz-tACS_PRE) stimulation. Results showed that face pareidolia was causally enhanced by 40Hz-tACS_PRE in the Mooney test for faces where, as compared to sham, participants more often misperceived scrambled stimuli as faces. In addition, 40Hz-tACS_PRE also caused faster responses to pareidolic faces in the visual noise stimuli of the Toast test. Similarly, in the Noise pareidolia test, 40Hz-tACS_ON induced slower rejections of face pareidolia responses. The current study shows for the first time that gamma-band (40 Hz) activity over the face perception network represents an important physiological substrate of face pareidolia. This has important implications for theories of human face perception and sheds light on basic pathophysiological mechanisms of clinical conditions where visual illusions and hallucinations represent core features.