A Nonlinear Analysis Of Event-Related Brain Potentials Of The Thatcher Illusion

In the Thatcher illusion, a face with inverted eyes and mouth looks abnormal when upright but not when inverted. Behavioral studies have shown that thatcherization of an upright face disrupts perceptual processing of the local configuration, while face inversion disrupts global configural processing.The author recorded electroencephalographs (EEGs) from normal observers to study event-related potentials (ERPs) of the illusion and the wavelet entropy (WE) of the ERPs, to determine whether inversion and thatcherization affect similar neural mechanisms. Observers viewed faces in eight conditions (upright vs. inverted, normal vs. tratcherized, and male vs. female) while performing an orientation-decision task.Thatcherization delayed the N170 component to upright faces and resulted in shorter N170 latency to inverted faces, proving that global and local configural processing can be distinguished on a functional as well as neural level. Smaller P1 to inverted thactheriazed faces was also observed in the present study, indicating that local configural processing may be more active after inversion. Moreover, thatherization decreased the WE of ERPs to inverted faces, showing that frequency modulation occurred with feature inversion of inverted faces. Finally, the WE analysis within a time window demonstrated that local configural processing started earlier, while global configural processing was most active in the temporal region of N170.These results describe the processing mechanism of face perception in a more detailed way, and prove that the WE method fits the ERP study with potentials to show the research of cognitive psychology a new direction.