Modulation of Face-sensitive Event-related Potentials by Canonical and Distorted Human Faces: The Role of Vertical Symmetry and Up-Down Featural Arrangement

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.

Illumination-Induced Apparent Shift in Orientation of Human Heads

Changing the position of a light source illuminating a human face induces an apparent shift of the perceived orientation of that face. The direction of this apparent shift is opposite to the shift of the light source. We demonstrated the illumination-induced apparent orientation shift (IAOS), quantified it in terms of the physical orientation shift needed to compensate for it, and evaluated the results in the context of possible mechanisms underlying orientation judgment. Results indicate that IAOS depends not only on the angle between the two light source positions, but also on the mean orientation of the face. Availability of cues coded in the visual texture of the face did not affect IAOS. The most effective cue was the location of the visible outline of the face. IAOS seems to be due to a shift of this outline when shadowed areas on the face merge with the black background. We conclude that an important mechanism for orientation judgment is based on a comparison of visible parts left and right of the profile line.