Orientation advantage in human face recognition : why so horizontal?

Abstract

Face processing is a core component of human social interactions, from the ability to detect a face to the comprehension of what it conveys, in terms of age, identity, emotion... This work aims at further the understanding of the diagnostic information at play in such essential processes. Previous studies demonstrated that face processing differed as a function of the orientation of face information, with an advantage for the horizontal range. In line with these results, we focused on the orientation of face information, to determine how this advantage could be explained. Along 4 different angles, we aimed at extending the comprehension of the horizontal advantage through thorough investigation of oriented face information. First, we focused on the reference frame of this horizontal advantage. More specifically, we dissociated the observer’s reference frame and the face’s reference frame during a face recognition task. We found that albeit a small influence of the observer reference frame, the horizontal advantage of face identity categorization is image centered. Having determined that it was the face information and not the orientation per se that was important, we then focused in the two following chapters on this oriented information, and why it is more diagnostic of identity than other ranges. First, in an identity recognition task, through the use of inversion and negation, disrupting shape and surface-shading cues processing, we found that the horizontal was the orientation range that was the most affected by these manipulations. As shape and surface-shading cues have been demonstrated to be essential sources of information in face identity categorization, we demonstrated that the horizontal range, more than other orientation ranges of information, conveys essential face perception cues. In a second phase, through analysis of the orientation dependency of identity recognition across views, we showed that it was the horizontal range that yielded best view-tolerant recognition. Further analysis of the image content enabled to conclude that the horizontal range conveys the most informative identity cues at frontal views, and the most stable ones across different views. Finally, we tested whether the horizontal preference was solely found at finer categorization levels like identity and emotion processing, or whether basic-level categorization was also tuned to the horizontal information. Using fast periodic visual stimulation coupled with EEG and a similar behavioral experiment, to measure face categorization amongst various stimuli, we found that the horizontal and neighboring ranges yielded better basic-level categorization. These results suggest that the horizontal and neighboring ranges of face information convey better diagnostic cues for basic-level face categorization than the vertical range. In summary, the horizontal face information conveys face processing essential cues to a greater extent than other orientation ranges. This information is also the most informative at full front views as well as the most stable, enabling view-tolerant face recognition, thus accounting for the horizontal preference of face processing. As this horizontal advantage is found at multiple levels of face processing, the horizontal range seems to conveys diagnostic cues enabling the recruitment of face specialized mechanisms.(PSYE - Sciences psychologiques et de l'éducation) -- UCL, 202