Three-month-old infants' sensitivity to horizontal information within faces.

Horizontal information is crucial to face processing in adults. Yet the ontogeny of this preferential type of processing remains unknown. To clarify this issue, we tested 3-month-old infants' sensitivity to horizontal information within faces. Specifically, infants were exposed to the simultaneous presentation of a face and a car presented in upright or inverted orientation while their looking behavior was recorded. Face and car images were either broadband (UNF) or filtered to only reveal horizontal (H), vertical (V) or this combined information (HV). As expected, infants looked longer at upright faces than at upright cars, but critically, only when horizontal information was preserved in the stimulus (UNF, HV, H). These results first indicate that horizontal information already drives upright face processing at 3 months of age. They also recall the importance, for infants, of some facial features, arranged in a top-heavy configuration, particularly revealed by this band of information. © 2016 Wiley Periodicals, Inc. Dev Psychobiol 58: 536-542, 2016.

Affective matching of odors and facial expressions in infants: shifting patterns between 3 and 7 months.

Recognition of emotional facial expressions is a crucial skill for adaptive behavior. Past research suggests that at 5 to 7 months of age, infants look longer to an unfamiliar dynamic angry/happy face which emotionally matches a vocal expression. This suggests that they can match stimulations of distinct modalities on their emotional content. In the present study, olfaction-vision matching abilities were assessed across different age groups (3, 5 and 7 months) using dynamic expressive faces (happy vs. disgusted) and distinct hedonic odor contexts (pleasant, unpleasant and control) in a visual-preference paradigm. At all ages the infants were biased toward the disgust faces. This visual bias reversed into a bias for smiling faces in the context of the pleasant odor context in the 3-month-old infants. In infants aged 5 and 7 months, no effect of the odor context appeared in the present conditions. This study highlights the role of the olfactory context in the modulation of visual behavior toward expressive faces in infants. The influence of olfaction took the form of a contingency effect in 3-month-old infants, but later evolved to vanish or to take another form that could not be evidenced in the present study.

Contextual odors modulate the visual processing of emotional facial expressions: An ERP study.

We studied the time course of the cerebral integration of olfaction in the visual processing of emotional faces during an orthogonal task asking for detection of red-colored faces among expressive faces. Happy, angry, disgust, fearful, sad, and neutral faces were displayed in pleasant, aversive or no odor control olfactory contexts while EEG was recorded to extract event-related potentials (ERPs). Results indicated that the expressive faces modulated the cerebral responses at occipito-parietal, central and central-parietal electrodes from around 100 ms and until 480 ms after face onset. The response was divided in different successive stages corresponding to different ERP components (P100, N170, P200 and N250 (EPN), and LPP). The olfactory contexts influenced the ERPs in response to facial expressions in two phases. First, regardless of their emotional content, the response to faces was enhanced by both odors compared with no odor approximately 160 ms after face-onset at several central, centro-parietal and left lateral electrodes. The topography of this effect clearly depended on the valence of odors. Then, a second phase occurred, but only in the aversive olfactory context, which modulated differentially the P200 at occipital sites (starting approximately 200 ms post-stimulus) by amplifying the differential response to expressions, especially between emotional neutrality and both happiness and disgust. Overall, the present study suggests that the olfactory context first elicits an undifferentiated effect around 160 ms after face onset, followed by a specific modulation at 200 ms induced by the aversive odor on neutral and affectively congruent/incongruent expressions.

Sex differences in interhemispheric communication during face identity encoding: evidence from ERPs.

Sex-related hemispheric lateralization and interhemispheric transmission times (IHTTs) were examined in twenty-four participants at the level of the first visual ERP components (P1 and N170) during face identity encoding in a divided visual-field paradigm. While no lateralization-related and sex-related differences were reflected in the P1 characteristics, these two factors modulated the N170. Indeed, N170 amplitudes indicated a right hemisphere (RH) dominance in men (and a more bilateral functioning in women). N170 latencies and the derived IHTTs confirmed the RH advantage in men but showed the reverse asymmetry in women. Altogether, the results of this study suggest a clear asymmetry in men and a more divided work between the hemispheres in women, with a tendency toward a left hemisphere (LH) advantage. Thus, by extending the pattern to the right-sided face processing, our results generalize previous findings from studies using other materials and indicating longer transfers from the specialized to the non-specialized hemisphere, especially in the male brain. Because asymmetries started from the N170 component, the first electrophysiological index of high-level perceptual processing on face representations, they also suggest a functional account for hemispheric lateralization and sex-related differences rather than a structural one.

Identity-expression interaction in face perception: sex, visual field, and psychophysical factors.

We investigated the psychophysical factors underlying the identity-emotion interaction in face perception. Visual field and sex were also taken into account. Participants had to judge whether a probe face, presented in either the left or the right visual field, and a central target face belonging to same person while emotional expression varied (Experiment 1) or to judge whether probe and target faces expressed the same emotion while identity was manipulated (Experiment 2). For accuracy we replicated the mutual facilitation effect between identity and emotion; no sex or hemispheric differences were found. Processing speed measurements, however, showed a lesser degree of interference in women than in men, especially for matching identity when faces expressed different emotions after a left visual presentation probe face. Psychophysical indices can be used to determine whether these effects are perceptual (A') or instead arise at a post-perceptual decision-making stage (B"). The influence of identity on the processing of facial emotion seems to be due to perceptual factors, whereas the influence of emotion changes on identity processing seems to be related to decisional factors. In addition, men seem to be more "conservative" after a LVF/RH probe-face presentation when processing identity. Women seem to benefit from better abilities to extract facial invariant aspects relative to identity.

Sex and hemispheric differences in facial invariants extraction.

This present study investigates sex differences in hemispheric cooperation during a facial identity matching task. The method used was a divided visual field paradigm in which the probe face was neutral or expressive and the target face was always neutral. Probe and target faces were presented both unilaterally and sequentially. A total of 28 right-handed women and 32 right-handed men participated in this study. The results confirm the women's advantage in face recognition and reveal symmetrical interhemispheric cooperation in women only. In men, processing time was faster when the probe face appeared in the left visual field-and encoded by the right hemisphere-and the target in the right visual field-projected to the left hemisphere-compared to the reverse direction. Interestingly, the data also show that women were not influenced by the expression of the probe face when matching identity, whereas men were always faster when the probe face was neutral, like the target, than when it was expressive. These results are discussed in light of Bruce and Young's (1986) model, and in terms of view-dependent and view-independent processes.

Sex differences in face processing: Are women less lateralized and faster than men?

The aim of this study was to determine the influence of sex on hemispheric asymmetry and cooperation in a face recognition task. We used a masked priming paradigm in which the prime stimulus was centrally presented; it could be a bisymmetric face or a hemi-face in which facial information was presented in the left or the right visual field and projected to the right or the left hemisphere. The target stimulus was always a bisymmetric face presented centrally. Faces were selected from Minear and Park's (2004) database. Fifty-two right-handed students (26 men, 26 women) participated in this experiment, in which accuracy (percentage of correct responses) and reaction times (RTs in ms) were measured. Although accuracy data showed that the percentage of correct recognition- when prime and target matched- was equivalent in men and women, men's RTs were longer than women's in all conditions. Accuracy and RTs showed that men are more strongly lateralized than women, with right hemispheric dominance. These results suggest that men are as good at face recognition as women, but there are functional differences in the two sexes. The findings are discussed in terms of functional cerebral networks distributed over both hemispheres and of interhemispheric transmission.