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Optimal eye-gaze fixation position for face-related neural responses.

Zerouali Y, Lina JM, Jemel B - PLoS ONE (2013)

Bottom Line: It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses.However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features.We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion.

View Article: PubMed Central - PubMed

Affiliation: Ecole de Technologie Supérieure, Montreal, Canada ; Hôpital Riviere des Prairies, Montreal, Canada. youness.zerouali-boukhal.1@ens.etsmtl.ca

ABSTRACT
It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses. However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features. To address this issue, scalp electroencephalogram (EEG) and eye gaze-fixations were recorded simultaneously in a gaze-contingent paradigm while observers viewed faces. We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion. Interestingly, for inverted faces, this optimal fixation position was more variable, but mainly clustered in the upper part of the visual field (around the mouth). These observations extend the findings of recent behavioral studies, suggesting that the early encoding of a face, as indexed by the N170, is not driven by the eyes per se, but rather arises from a general perceptual setting (upper-visual field advantage) coupled with the alignment of a face stimulus to a stored face template.

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Sensitivity of the P100 waveform to fixation position.(a) P100 ERP responses to specific eye-gaze landing positions (fROI) are shown at occipital scalp sites (O1/O2) separately for upright and inverted faces. (b) P100 ERP waveforms recorded over O1 (in blue) and O2 (in red) electrodes are shown for fixated face regions along the horizontal meridian (left and right visual fields). (c) P100 ERP waveforms elicited by fixated face regions along the vertical meridian (upper in green, middle in red, and lower in blue).
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pone-0060128-g004: Sensitivity of the P100 waveform to fixation position.(a) P100 ERP responses to specific eye-gaze landing positions (fROI) are shown at occipital scalp sites (O1/O2) separately for upright and inverted faces. (b) P100 ERP waveforms recorded over O1 (in blue) and O2 (in red) electrodes are shown for fixated face regions along the horizontal meridian (left and right visual fields). (c) P100 ERP waveforms elicited by fixated face regions along the vertical meridian (upper in green, middle in red, and lower in blue).

Mentions: In order to test whether this effect is specific to the N170 or reflects a general visual bias, we also investigated an earlier visual ERP component, the occipital P100 component (fig. 4a). For both face orientations, the MANOVA did not yield a significant effect of fROIs on the amplitude of P100, measured over O1/2 and PO7/8 [F(6,11) <1.08; p>0.4]. However, as illustrated in fig. 4a, the amount of information distributed across the left and right hemifields modulated P100 amplitude over the left and right hemispheres. This was reflected by a significant fROI by Hemisphere interaction for both face orientations [F(6,11) >3.3; P = 0.042]. When the fixated fROIs are located in the left field of the face stimulus, much of the facial information covered the right peripheral visual field, leading to larger P100 responses over the left than over the right occipital scalp sites [P<0.008]. The reverse pattern was found when the fixated fROIs are located in the right field of the face stimulus. No hemispheric difference was found when the eye-gaze fell on the middle of the face. fig. 2c shows the effect of eye-position along the horizontal meridian on P100 amplitude, measured over electrode POz [F(2,15)  = 13.98; P<0.0004]. For upright faces, P100 was larger to foveated mouth feature than the nose [P = 0.036], and to foveated nose feature than the nasion [P = 0.003]. This pattern was reversed when faces were presented upside-down [F(2,15)  = 4.38; P<0.035].


Optimal eye-gaze fixation position for face-related neural responses.

Zerouali Y, Lina JM, Jemel B - PLoS ONE (2013)

Sensitivity of the P100 waveform to fixation position.(a) P100 ERP responses to specific eye-gaze landing positions (fROI) are shown at occipital scalp sites (O1/O2) separately for upright and inverted faces. (b) P100 ERP waveforms recorded over O1 (in blue) and O2 (in red) electrodes are shown for fixated face regions along the horizontal meridian (left and right visual fields). (c) P100 ERP waveforms elicited by fixated face regions along the vertical meridian (upper in green, middle in red, and lower in blue).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3675086&req=5

pone-0060128-g004: Sensitivity of the P100 waveform to fixation position.(a) P100 ERP responses to specific eye-gaze landing positions (fROI) are shown at occipital scalp sites (O1/O2) separately for upright and inverted faces. (b) P100 ERP waveforms recorded over O1 (in blue) and O2 (in red) electrodes are shown for fixated face regions along the horizontal meridian (left and right visual fields). (c) P100 ERP waveforms elicited by fixated face regions along the vertical meridian (upper in green, middle in red, and lower in blue).
Mentions: In order to test whether this effect is specific to the N170 or reflects a general visual bias, we also investigated an earlier visual ERP component, the occipital P100 component (fig. 4a). For both face orientations, the MANOVA did not yield a significant effect of fROIs on the amplitude of P100, measured over O1/2 and PO7/8 [F(6,11) <1.08; p>0.4]. However, as illustrated in fig. 4a, the amount of information distributed across the left and right hemifields modulated P100 amplitude over the left and right hemispheres. This was reflected by a significant fROI by Hemisphere interaction for both face orientations [F(6,11) >3.3; P = 0.042]. When the fixated fROIs are located in the left field of the face stimulus, much of the facial information covered the right peripheral visual field, leading to larger P100 responses over the left than over the right occipital scalp sites [P<0.008]. The reverse pattern was found when the fixated fROIs are located in the right field of the face stimulus. No hemispheric difference was found when the eye-gaze fell on the middle of the face. fig. 2c shows the effect of eye-position along the horizontal meridian on P100 amplitude, measured over electrode POz [F(2,15)  = 13.98; P<0.0004]. For upright faces, P100 was larger to foveated mouth feature than the nose [P = 0.036], and to foveated nose feature than the nasion [P = 0.003]. This pattern was reversed when faces were presented upside-down [F(2,15)  = 4.38; P<0.035].

Bottom Line: It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses.However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features.We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion.

View Article: PubMed Central - PubMed

Affiliation: Ecole de Technologie Supérieure, Montreal, Canada ; Hôpital Riviere des Prairies, Montreal, Canada. youness.zerouali-boukhal.1@ens.etsmtl.ca

ABSTRACT
It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses. However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features. To address this issue, scalp electroencephalogram (EEG) and eye gaze-fixations were recorded simultaneously in a gaze-contingent paradigm while observers viewed faces. We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion. Interestingly, for inverted faces, this optimal fixation position was more variable, but mainly clustered in the upper part of the visual field (around the mouth). These observations extend the findings of recent behavioral studies, suggesting that the early encoding of a face, as indexed by the N170, is not driven by the eyes per se, but rather arises from a general perceptual setting (upper-visual field advantage) coupled with the alignment of a face stimulus to a stored face template.

Show MeSH
Related in: MedlinePlus