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Chien-Chung Chen, Rung-Yu Tseng; The role of external head contours in face processing in the human occipitotemporal cortex. Journal of Vision 2008;8(6):164. doi: https://doi.org/10.1167/8.6.164.
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While a human observer can easily recognize a face with only internal face features, such as eyes, noses or mouths, the presence of an external head contour can affect the face recognition greatly. We used fMRI technique and the well-known face inversion effect, or impaired recognition performance on upside down faces, to investigate how the human occipitotemporal cortex processes internal and external face information.
BOLD activations were collected from eight observers in a 3T Bruker scanner (EPI, TR=3s, TE=40ms) with block design runs (epoch length: 18s, 6 cycles per run). We used seven types of face stimuli: whole faces with both internal features and external head contours, external contour-only and internal feature-only and their inverted version, and a face with upright internal features but an inverted external contour. The fusiform and the occipital face areas (FFA and OFA respectively) were first identified by contrasting BOLD activation to upright faces and their phase scrambled versions.
Contrasted with their own inverted versions, the whole faces showed greater activation in both the OFA and FFA. The internal feature-only produced greater activation than their inverted counterparts in the OFA and posterior the FFA while the external contour-only produced greater activation in the anterior FFA than their inverted versions. The whole faces showed greater activations in the FFA than internal feature only. The differential activations were observed both in the FFA and the when contrasted between the whole faces and the faces with only external contour inverted. The result suggests that face processing in the OFA mainly utilizes information from internal features. The external contour information plays a significant role in face processing only in the FFA.
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