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Early Left Parietal Activity Elicited by Direct Gaze: A High-Density EEG Study

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ABSTRACT

Gaze is one of the most important cues for human communication and social interaction. In particular, gaze contact is the most primary form of social contact and it is thought to capture attention. A very early-differentiated brain response to direct versus averted gaze has been hypothesized. Here, we used high-density electroencephalography to test this hypothesis. Topographical analysis allowed us to uncover a very early topographic modulation (40–80 ms) of event-related responses to faces with direct as compared to averted gaze. This modulation was obtained only in the condition where intact broadband faces–as opposed to high-pass or low-pas filtered faces–were presented. Source estimation indicated that this early modulation involved the posterior parietal region, encompassing the left precuneus and inferior parietal lobule. This supports the idea that it reflected an early orienting response to direct versus averted gaze. Accordingly, in a follow-up behavioural experiment, we found faster response times to the direct gaze than to the averted gaze broadband faces. In addition, classical evoked potential analysis showed that the N170 peak amplitude was larger for averted gaze than for direct gaze. Taken together, these results suggest that direct gaze may be detected at a very early processing stage, involving a parallel route to the ventral occipito-temporal route of face perceptual analysis.

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Result of the fitting procedure for the two early maps (Map1 / Map 2) identified in the 41–80 ms time window.There was a significant interaction between MAP and GAZE in the BB picture condition. The fitting procedure showed that the Map 1 explained more variance in the direct than in the averted gaze condition and that Map 2 explained better the averted gaze condition than Map 1 did. In addition, post-hoc t-test showed that Map 1 explained better the direct gaze than the averted gaze condition, t(14) = 3.33, p < .005, and that Map 2 explained better the averted gaze condition than Map 1 did, t(14) = 2.73, p < .016. Since normality condition was not verified for this explained variance measure, we ran additional non-parametrical Wilcoxon signed-rank tests; this confirmed the results reported with Zs < -2.04, ps < .05.
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pone.0166430.g005: Result of the fitting procedure for the two early maps (Map1 / Map 2) identified in the 41–80 ms time window.There was a significant interaction between MAP and GAZE in the BB picture condition. The fitting procedure showed that the Map 1 explained more variance in the direct than in the averted gaze condition and that Map 2 explained better the averted gaze condition than Map 1 did. In addition, post-hoc t-test showed that Map 1 explained better the direct gaze than the averted gaze condition, t(14) = 3.33, p < .005, and that Map 2 explained better the averted gaze condition than Map 1 did, t(14) = 2.73, p < .016. Since normality condition was not verified for this explained variance measure, we ran additional non-parametrical Wilcoxon signed-rank tests; this confirmed the results reported with Zs < -2.04, ps < .05.

Mentions: We performed spatial clustering on the grand average ERPs in order to look for a possible early effect of gaze for the BB face pictures resulting in different scalp topographies. The microstate segmentation found 5 different maps of stable ERP topographies that explained 94.6% of the ERP data. Most interestingly, this analysis revealed a difference in the early maps identified for the direct and the averted gaze conditions of BB pictures between 41 and 80 ms. Later maps were similar across conditions and corresponded to the P1, N170, and P300 components of the ERP (see Fig 4C). In order to evaluate how much the early “prototypical” maps identified on the grand averaged data explains the individual scalp topographies obtained in each participant, we computed the GEV for the first two maps obtained in response to the direct and averted gaze in each spatial frequency range for each participant, and we performed an ANOVA on these GEV values with MAPS (map 1 / map 2, as numbered in Figs 4C and 5), GAZE (direct / averted) and FREQUENCIES (BB / LSF / HSF) as within-subject factors This analysis revealed a three-way interaction between MAPS, GAZE, and FREQUENCIES, F(2,28) = 7.72, p < .002, ηp2 = .35. This interaction reflected the MAP-by-GAZE interaction that was observed only for the BB pictures, F(1,14) = 8.85, p < .01, ηp2 = .38 (see Fig 4). In other terms, this analysis confirmed that the 2 maps identified between 41 and 80 ms were differentially represented in the direct and the averted gaze BB picture conditions across participants.


Early Left Parietal Activity Elicited by Direct Gaze: A High-Density EEG Study
Result of the fitting procedure for the two early maps (Map1 / Map 2) identified in the 41–80 ms time window.There was a significant interaction between MAP and GAZE in the BB picture condition. The fitting procedure showed that the Map 1 explained more variance in the direct than in the averted gaze condition and that Map 2 explained better the averted gaze condition than Map 1 did. In addition, post-hoc t-test showed that Map 1 explained better the direct gaze than the averted gaze condition, t(14) = 3.33, p < .005, and that Map 2 explained better the averted gaze condition than Map 1 did, t(14) = 2.73, p < .016. Since normality condition was not verified for this explained variance measure, we ran additional non-parametrical Wilcoxon signed-rank tests; this confirmed the results reported with Zs < -2.04, ps < .05.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5120811&req=5

pone.0166430.g005: Result of the fitting procedure for the two early maps (Map1 / Map 2) identified in the 41–80 ms time window.There was a significant interaction between MAP and GAZE in the BB picture condition. The fitting procedure showed that the Map 1 explained more variance in the direct than in the averted gaze condition and that Map 2 explained better the averted gaze condition than Map 1 did. In addition, post-hoc t-test showed that Map 1 explained better the direct gaze than the averted gaze condition, t(14) = 3.33, p < .005, and that Map 2 explained better the averted gaze condition than Map 1 did, t(14) = 2.73, p < .016. Since normality condition was not verified for this explained variance measure, we ran additional non-parametrical Wilcoxon signed-rank tests; this confirmed the results reported with Zs < -2.04, ps < .05.
Mentions: We performed spatial clustering on the grand average ERPs in order to look for a possible early effect of gaze for the BB face pictures resulting in different scalp topographies. The microstate segmentation found 5 different maps of stable ERP topographies that explained 94.6% of the ERP data. Most interestingly, this analysis revealed a difference in the early maps identified for the direct and the averted gaze conditions of BB pictures between 41 and 80 ms. Later maps were similar across conditions and corresponded to the P1, N170, and P300 components of the ERP (see Fig 4C). In order to evaluate how much the early “prototypical” maps identified on the grand averaged data explains the individual scalp topographies obtained in each participant, we computed the GEV for the first two maps obtained in response to the direct and averted gaze in each spatial frequency range for each participant, and we performed an ANOVA on these GEV values with MAPS (map 1 / map 2, as numbered in Figs 4C and 5), GAZE (direct / averted) and FREQUENCIES (BB / LSF / HSF) as within-subject factors This analysis revealed a three-way interaction between MAPS, GAZE, and FREQUENCIES, F(2,28) = 7.72, p < .002, ηp2 = .35. This interaction reflected the MAP-by-GAZE interaction that was observed only for the BB pictures, F(1,14) = 8.85, p < .01, ηp2 = .38 (see Fig 4). In other terms, this analysis confirmed that the 2 maps identified between 41 and 80 ms were differentially represented in the direct and the averted gaze BB picture conditions across participants.

View Article: PubMed Central - PubMed

ABSTRACT

Gaze is one of the most important cues for human communication and social interaction. In particular, gaze contact is the most primary form of social contact and it is thought to capture attention. A very early-differentiated brain response to direct versus averted gaze has been hypothesized. Here, we used high-density electroencephalography to test this hypothesis. Topographical analysis allowed us to uncover a very early topographic modulation (40&ndash;80 ms) of event-related responses to faces with direct as compared to averted gaze. This modulation was obtained only in the condition where intact broadband faces&ndash;as opposed to high-pass or low-pas filtered faces&ndash;were presented. Source estimation indicated that this early modulation involved the posterior parietal region, encompassing the left precuneus and inferior parietal lobule. This supports the idea that it reflected an early orienting response to direct versus averted gaze. Accordingly, in a follow-up behavioural experiment, we found faster response times to the direct gaze than to the averted gaze broadband faces. In addition, classical evoked potential analysis showed that the N170 peak amplitude was larger for averted gaze than for direct gaze. Taken together, these results suggest that direct gaze may be detected at a very early processing stage, involving a parallel route to the ventral occipito-temporal route of face perceptual analysis.

No MeSH data available.


Related in: MedlinePlus