Brain Activity Related to the Judgment of Face-Likeness: Correlation between EEG and Face-Like Evaluation

Abstract

Faces represent important information for social communication, because social information, such as face-color, expression, and gender, is obtained from faces. Therefore, individuals' tend to find faces unconsciously, even in objects. Why is face-likeness perceived in non-face objects? Previous event-related potential (ERP) studies showed that the P1 component (early visual processing), the N170 component (face detection), and the N250 component (personal detection) reflect the neural processing of faces. Inverted faces were reported to enhance the amplitude and delay the latency of P1 and N170. To investigate face-likeness processing in the brain, we explored the face-related components of the ERP through a face-like evaluation task using natural faces, cars, insects, and Arcimboldo paintings presented upright or inverted. We found a significant correlation between the inversion effect index and face-like scores in P1 in both hemispheres and in N170 in the right hemisphere. These results suggest that judgment of face-likeness occurs in a relatively early stage of face processing.

Keywords: ERP/EEG; face inversion effect; face perception; face-like patterns; pareidolia.

Figure 1

Example stimuli for each category and the timeline of stimulus presentation during a single trial. The face category was selected from the FACES database (Max Planck Institute for Human Development, Berlin; Ebner et al., 2010). Only faces with neutral expression were chosen (interrater agreement N 0.90, as published for the reference sample). The car category was selected as representing artificial objects, and the insect category was selected as representing natural objects. The Arcimboldo paintings were selected for observing holistic and feature processing, as described by Caharel et al. (2013) and Rossion et al. (2011). Images for each condition were randomly presented, and the participants performed the face-likeness evaluation task.

Figure 2

(A) Each bar indicates the mean face-likeness score for each category in the upright (fill) and inverted (no fill) orientations. (B) Each bar indicates the mean reaction times for each category in the upright (fill) and inverted (no fill) orientation.

Figure 3

The grand average of ERP waveforms elicited by each category in the upright and inverted orientations at the left and right pooled occipito-temporal electrode sites (waveforms averaged for electrodes P5/P9/PO7, P6/P10/PO8). In addition, the waveforms of inversion effect was calculated (see Supplementary Data Sheet 1, Supplementary Figure 1).

Figure 4

Peak amplitude of the P1 (Top), N170 (Middle), and N250 component (Bottom) measured at the left and right pooled occipito-temporal electrode sites (averaged for electrodes P5/P9/PO7 and P6/P10/PO8), displayed for 4 categories in the upright (fill) and inverted (no fill) orientations.

Figure 5

The inversion effect index for peak amplitude of the P1 (Top), N170 (Middle), and N250 (Bottom) components, measured at the left and right pooled occipito-temporal electrode sites (averaged for electrodes P5/P9/PO7 and P6/P10/PO8) and displayed for 4 categories.

Figure 6

Correlation map between the inversion effect index and the face-likeness score of P1 (Top), N170 (Middle), and N250 (Bottom) components, calculated for the left (left side) and right (right side) hemispheres. The vertical axis indicates the inversion effect index value, and the horizontal axis indicates the face-likeness scores. Underlines indicate significant correlations.