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Younes Zerouali, Boutheina Jemel; Optimal eye-fixation positions for face perception: A combined ERP and eye-tracking study. Journal of Vision 2011;11(11):658. doi: 10.1167/11.11.658.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has outlined the existence of a saliency map among facial features, with the eye region being the most salient feature in a face. In addition, event-related potential (ERP) studies showed that the face-sensitive N170 component is larger in response to isolated eyes relative to other face features, and even to a whole face. Although these results suggest that the N170 could be mainly triggered by the eye-region, there is as yet no direct investigation of the N170 response profile when viewers fixate specific facial features within a whole face context. To address this question, EEG and eye-tracking measurements were recorded and monitored simultaneously to allow an accurate sampling of electrical brain signals from fixated face regions, while participants viewed faces in upright or inverted presentations. ERPs were averaged by gaze location (eyes, inion, eyebrows, nose, mouth and jaws). We also introduce a novel analysis procedure, neuroelectrical heat maps, that allowed mapping the amplitude of the N170 responses associated to specific eye-gaze fixations (measured by the eye-tracker) on face displays. Our results revealed that the optimal fixation position on an upright face (i.e., eliciting the largest N170s) is located around the nasion (triangle between to two eyes and the upper ridge of the nose). Interestingly for inverted faces, the optimal positions are mainly clustered in the upper part of the visual field (around the mouth). Our results suggest that the N170 is not driven by the eyes per se, but could rather arise from a general perceptual setting (upper-visual field advantage). It is also possible that the upper part of faces (eyes) serves as an artificial horizon to align a face stimulus on a stored face template.
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