Neurophysiological Correlates of Featural and Spacing Processing for Face and Non-face Stimuli

Abstract

The peculiar ability of humans to recognize hundreds of faces at a glance has been attributed to face-specific perceptual mechanisms known as holistic processing. Holistic processing includes the ability to discriminate individual facial features (i.e., featural processing) and their spatial relationships (i.e., spacing processing). Here, we aimed to characterize the spatio-temporal dynamics of featural- and spacing-processing of faces and objects. Nineteen healthy volunteers completed a newly created perceptual discrimination task for faces and objects (i.e., the "University of East London Face Task") while their brain activity was recorded with a high-density (128 electrodes) electroencephalogram. Our results showed that early event related potentials at around 100 ms post-stimulus onset (i.e., P100) are sensitive to both facial features and spacing between the features. Spacing and features discriminability for objects occurred at circa 200 ms post-stimulus onset (P200). These findings indicate the existence of neurophysiological correlates of spacing vs. features processing in both face and objects, and demonstrate faster brain processing for faces.

Keywords: EEG; N170; P100; configural processing; face perception; holistic processing; object perception.

FIGURE 1

Experimental stimuli. Face (left) and house (right) stimuli adopted in the University of East London (UEL) face task. Parts (top) and spacing (bottom) manipulations are shown for both categories. Some of the face pictures have been obtained from www.beautycheck.de.

FIGURE 2

Example of trial structure.

FIGURE 3

Corresponding event related potentials (ERPs) traces (butterfly plots) for all electrodes as averaged across all trials (black: Face; red: House) after S1 (left panel) and S2 (right panel) presentation (“0” indicates stimulus onset).

FIGURE 4

Faces Vs. House comparison. Left: Topographical plots for S1-evoked ERP components (P100, N170, and P200) for Face and House conditions. Middle: t-statistic maps of the ERP amplitude Face vs. House differences. Crosses indicate significant channels (^∗: p < 0.01). Right grand-averaged ERPs traces for face and houses averaged across statistically significant electrodes (shades represent the SEM).

FIGURE 5

Features (FP) vs. spacing (FS) contrasts for the P100 as elicited by S2 faces. Top: Topographical plots of grand-averaged ERPs for the two Face conditions (Parts and Spacing), t-statistic map distribution (X: p < 0.05). Bottom: Grand-averaged ERPs traces as averaged across statistically significant electrodes (shades represent the SEM).

FIGURE 6

Features (HP) vs. spacing (HS) contrasts for the P200 as elicited by S2 houses. Topographical plots of grand-averaged ERPs for the two House conditions (Parts and Spacing) (left), t-statistic map distribution (^∗: p < 0.01) (middle), and grand-averaged ERPs traces as averaged across statistically significant electrodes (right) (shades represent the SEM).