The effect of head orientation on face detection in natural images as evidenced by fast periodic visual stimulation

Abstract

Face detection is typically fast and accurate, but some faces are detected faster and better than others in natural images. While some studies have shown that low-level visual cues contribute to rapid face detection, there is less information concerning the contribution of high-level factors. Here, we tested whether face detection differs for full-front vs. 3/4 head views using fast periodic visual stimulation (FPVS). This approach can isolate cortical responses for the detection of faces – as compared to other object categories – objectively, rapidly and implicitly in natural images, without contribution from low-level visual cues (Rossion et al., 2015). High-density electroencephalogram (EEG) was recorded from 16 observers presented with 40-s sequences containing natural images of objects sinusoidally contrast-modulated at a fixed rate of 12.0 Hz (F). Natural face images were introduced at fixed intervals of F/9 (‘oddballs’, 1.33 Hz). In Condition 1, all faces were posed full-front. In Condition 2, they were at 3/4 views (either left or right, but only in one orientation within a sequence). In Condition 3, the oddball alternated between full-front and 3/4 views throughout the sequence (frequency of each view, F/18 = 0.67 Hz). In all conditions, significant responses were recorded at 1.33 Hz and its harmonics, mainly over the right occipito-temporal region, indicating a high-level face-detection response. Interestingly, Condition 3 also showed significant responses at 0.67 Hz and its harmonics over the same cortical region, implying a differentiable face-detection response to full-front vs. 3/4 views. Analysis in the time domain revealed a sequence of face-selective components, with peak latencies approximately 12 ms earlier for full-front than 3/4 views emerging as early as the first face-selective component (130-150 ms). These findings indicate that a full-front view presents an advantage in face detection, arising in part from a faster high-level brain response. Meeting abstract presented at VSS 2015