Modulation of face-sensitive event-related potentials by canonical and distorted human faces: the role of vertical symmetry and up-down featural arrangement

Abstract

This study examined the sensitivity of early face-sensitive event-related potential (ERP) components to the disruption of two structural properties embedded in faces, namely, "updown featural arrangement" and "vertical symmetry." Behavioral measures and ERPs were recorded as adults made an orientation judgment for canonical faces and distorted faces that had been manipulated for either or both of the mentioned properties. The P1, the N170, and the vertex positive potential (VPP) exhibited a similar gradient in sensitivity to the two investigated properties, in that they all showed a linear increase in amplitude or latency as the properties were selectively disrupted in the order of (1) up-down featural arrangement, (2) vertical symmetry, and (3) both up-down featural arrangement and vertical symmetry. Exceptions to this finding were seen for the amplitudes of the N170 and VPP, which were largest for the stimulus in which solely vertical symmetry was disrupted. Interestingly, the enhanced amplitudes of the N170 and VPP are consistent with a drop in behavioral performance on the orientation judgment for this stimulus.

Figure 1

Examples of stimuli from the four categories used in the study. ST. Symmetrical Top-heavy canonical face. SB. Symmetrical Bottom-heavy scrambled face. AT. Asymmetrical Top-heavy face. AB. Asymmetrical Bottom-heavy face.

Figure 2

Mean efficiency scores for the four stimuli (n = 29). ST canonical faces gave rise to the most efficient performance and AT scrambled faces gave rise to the least efficient performance in the orientation judgment task. Error bars represent standard errors of the mean.

Figure 3

A. Grand-averaged ERPs, showing the P1 component at the left (O1) and right (O2) occipital electrodes for ST canonical faces and SB, AT, AB scrambled faces. B. Bar graph displays the overall mean amplitudes of the P1 component displayed for the four stimulus categories at O1 and O2. Note the linear increase in the voltage amplitude of the component for SB, AT and AB scrambled faces as compared to ST canonical faces.

Figure 4

A. The N170 obtained in response to ST canonical faces, SB, AT and AB scrambled faces at mastoid and temporal electrodes on left (A1 and T5) and right (A2 and T6) hemispheres. B. The overall mean latencies of the N170 for the four stimulus categories at the four electrodes. Note the linear increase in the latency of the component for SB, AT and AB scrambled faces as compared to ST canonical faces. C. The mean amplitudes of the N170 at the mastoid and temporal electrodes (A2/T6) on the right hemisphere. Note the larger N170 component for AT scrambled faces compared to the other three stimuli.

Figure 5

A. Grand-average waveforms showing the VPP component at the left (C3), medial (Cz) and right (C4) central leads for the four stimulus categories. B. The overall mean latencies of the VPP for the four stimulus categories at the three electrodes. Note the linear increase in the latency of the component for SB, AT and AB scrambled faces as compared to ST canonical faces. C. The overall mean amplitudes of the VPP for the four stimulus categories at the three electrodes. The VPP component is larger for AT scrambled faces compared to the other three stimuli.