Multisensory and Gaze-Contingent Stimulation of the Own Face

When observers’ own face is stroked in synchrony, but not in asynchrony with another face, they tend to perceive that face as more similar to their own and report that it belongs to them. This “enfacement effect” appears to be a compelling illusion and also modulates social cognitive processes. This thesis further examined the effect of such synchronous multisensory stimulation on physical and psychological aspects of the self. Chapter 2 explored whether multisensory facial stimulation can reduce racial prejudice. White observers’ faces were stroked with a cotton bud while they watched a black face being stroked in synchrony. This was compared with a no-touch and an asynchronous stroking condition. Across three experiments, observers consistently reported an enfacement illusion after the synchronous condition. However, this effect did not produce concurrent changes in implicit or explicit racial prejudice. Chapter 3 explored whether a similar enfacement effect can be elicited with a novel gaze-contingent mirror paradigm. In this paradigm, an onscreen face either mimicked observers’ own eye-gaze behaviour (congruent condition), moved its eyes in different directions to observers’ eyes (incongruent condition), or remains unresponsive to the observers’ gaze (neutral condition). Observers experienced a consistent enfacement illusion after the congruent condition across two of three experiments. However, while the mimicry of the onscreen face affected observers’ phenomenological experience, it did not alter their perceptual self-representations. A final experiment, in Chapter 4, further investigated the cognitive locus of the enfacement effect by using ERPs. Observers were exposed to blocks of synchronous and asynchronous stimulation. ERPs were then recorded while observers were presented with images of (a) a synchronously stimulated face, (b) an asynchronously stimulated face, (c) their own face, (d) one of two unfamiliar filler faces and (e) an unfamiliar target face. Observers consistently reported an enfacement illusion after the synchronous condition. However, this enfacement effect was not evident in ERP components reflecting early perceptual encoding of the face (i.e., N170) or subsequent identity- and affect-related markers, such as the N250 and the P300. Altogether the results of this thesis show that it is possible to enface a face, even when it belongs to a different ethnic group to that of the observer. This effect is such that observers report that the enfaced face belongs to them. Interestingly, a similar phenomenological enfacement experience can be obtained with gaze-contingent mirror paradigm. However, this enfacement effect seems to be too short-lived to be reflected in ERP components

Multisensory stimulation of other-race faces and the reduction of racial prejudice

This study investigated whether multisensory stimulation with other-race faces can reduce racial prejudice. In three experiments, the faces of Caucasian observers were stroked with a cotton bud while they watched a black face being stroked in synchrony on a computer screen. This was compared with a neutral condition, in which no tactile stimulation was administered (Experiment 1 and 2), and with a condition in which observers' faces were stroked in asynchrony with the onscreen face (Experiment 3). In all experiments, observers experienced an enfacement illusion after synchronous stimulation, whereby they reported to embody the other-race face. However, this effect did not produce concurrent changes in implicit or explicit racial prejudice. This outcome contrasts with other procedures for the reduction of self-other differences that decrease racial prejudice, such as behavioural mimicry and intergroup contact. We speculate that enfacement is less effective for such prejudice reduction because it does not encourage perspective-taking

Two face masks are better than one: congruency effects in face matching.

Although the positive effects of congruency between stimuli are well replicated in face memory paradigms, mixed findings have been found in face matching. Due to the current COVID-19 pandemic, face masks are now very common during daily life outdoor activities. Thus, the present study aims to further explore congruency effects in matching faces partially occluded by surgical masks. Observers performed a face matching task consisting of pairs of faces presented in full view (i.e., full-view condition), pairs of faces in which only one of the faces had a mask (i.e., one-mask condition), and pairs of faces in which both faces had a mask (i.e., two-mask condition). Although face masks disrupted performance in identity match and identity mismatch trials, in match trials, we found better performance in the two-mask condition compared to the one-mask condition. This finding highlights the importance of congruency between stimuli on face matching when telling faces together

Face masks affect emotion categorisation, age estimation, recognition, and gender classification from faces

Although putting on a mask over our nose and mouth is a simple but powerful way to protect ourselves and others during a pandemic, face masks may interfere with how we perceive and recognize one another, and hence, may have far-reaching impacts on communication and social interactions. To date, it remains relatively unknown the extent to which wearing a face mask that conceals the bottom part of the face affects the extraction of different facial information. To address this question, we compared young adults' performance between masked and unmasked faces in four different tasks: (1) emotion recognition task, (2) famous face recognition and naming test, (3) age estimation task, and (4) gender classification task. Results revealed that the presence of face mask has a negative impact on famous face recognition and emotion recognition, but to a smaller extent on age estimation and gender classification tasks. More interestingly, we observed a female advantage in the famous face recognition and emotion recognition tasks and a female own-gender bias in gender categorisation and age estimation tasks. Overall, these findings allude to the lack of malleability of the adulthood face recognition and perceptual systems

The role of inversion and face masks on simultaneous and delayed face matching tasks.

Although it is generally accepted that face recognition relies on holistic processing, it has been suggested that the simultaneous face matching task may depend on a more analytical or featural processing approach. However, empirical evidence supporting this claim is limited. In two experiments, we further explored the role of holistic and featural processing on simultaneous face matching by manipulating holistic processing through inversion and presenting faces with or without face masks. The results from Experiment 1 revealed that both inversion and face masks impaired matching performance. However, while the inversion effect was evident in both full-view and masked faces, the mask effect was only found in upright, but not inverted, faces. These results were replicated in Experiment 2 but, the inversion and mask effects were stronger in delayed face matching than in simultaneous face matching. Our findings suggest that simultaneous face matching relies on holistic processing, but to a smaller extent compared to higher memory-demanding identification tasks

A more featural based processing for the self-face: An eye-tracking study

Studies have suggested that the holistic advantage in face perception is not always reported for the own face. With two eye-tracking experiments, we explored the role of holistic and featural processing in the processing and the recognition of self, personally familiar, and unfamiliar faces. Observers were asked to freely explore (Exp.1) and recognize (Exp.2) their own, a friend's, and an unfamiliar face. In Exp.1, self-face was fixated more and longer and there was a preference for the mouth region when seeing the own face and for the nose region when seeing a friend and unfamiliar faces. In Exp.2, the viewing strategies did not differ across all faces, with eye fixations mostly directed to the nose region. These results suggest that task demands might modulate the way that the own face is perceived and highlights the importance of considering the role of the distinct visual experience people have for the own face in the processing and recognition of the self-face

No modulation effects of depressive traits on the self-face advantage

The self-face advantage (SFA) is reflected through a faster recognition of a self-face compared to other faces. It has been suggested that this effect is prompted by one's positive self-evaluations. However, it is unclear whether negative self-concepts (depressive traits) also affect the SFA. The present study explored this possibility using a visual-search task. In Experiment 1, participants with low and high depressive traits were asked to search for frontal view images of self and unfamiliar faces among arrays of unfamiliar faces. Regardless of group, participants were better and faster in searching for the own face compared to the unfamiliar face. Similar findings were observed in Experiment 2, but the participants were more accurate when searching for their happy self-face compared to their sad and neutral faces. These results suggest that SFA is not modulated by depressive traits (i.e., negative self-concepts) and that familiarity effects for the own face could be implicated as an underlying factor for an attentional prioritization of the own face

Cultural modulation effects on the Self-Face Advantage: Do Caucasians find their own faces faster than Chinese?

The self-face advantage (SFA) is reflected through a faster recognition of a self-face compared to familiar and unfamiliar faces. Nevertheless, as Westerners and East Asians tend to present differences in self-concept styles, it is possible that the SFA is modulated by culture. The present study explored this possibility using a visual search task. British Caucasians and Malaysian Chinese participants were asked to search for frontal view images of self, friend, and unfamiliar faces among an array of unfamiliar faces. Regardless of race, participants were more accurate and faster in searching for the own face and friend's face compared to an unfamiliar face, with no differences in the search between the own and friend's face, and these findings could not be accounted by the cultural differences in self-concept (i.e., operationalized by SCS and HCIV scores). Altogether our results suggest that culture does not modulate the SFA and that this effect is better explained by a familiar face advantage

Holistic and featural processing’s link to face recognition varies by individual and task

While it is generally accepted that holistic processing facilitates face recognition, recent studies suggest that poor recognition might also arise from imprecise perception of local features in the face. This study aimed to examine to what extent holistic and featural processing relates to individual differences in face recognition ability (FRA), during face learning (Experiment 1) and face recognition (Experiment 2). Participants performed two tasks: (1) The “Cambridge Face Memory Test-Chinese” which measured participants’ FRAs, and (2) an “old/new recognition memory test” encompassing whole faces (preserving holistic and featural processing) and faces revealed through a dynamic aperture (impairing holistic processing but preserving featural processing). Our results showed that participants recognised faces more accurately in conditions when holistic information was preserved, than when it is impaired. We also show that the better use of holistic processing during face learning and face recognition was associated with better FRAs. However, enhanced featural processing during recognition, but not during learning, was related to better FRAs. Together, our findings demonstrate that good face recognition depends on distinct roles played by holistic and featural processing at different stages of face recognition

High-frequency transcranial random noise stimulation enhances unfamiliar face matching of high resolution and pixelated faces.

Face identification is useful for social interactions and its impairment can lead to severe social and mental problems. This ability is also remarkably important in applied settings, including eyewitness identification and ID verification. Several studies have demonstrated the potential of Transcranial Random Noise Stimulation (tRNS) to enhance different cognitive skills. However, research has produced inconclusive results about the effectiveness of tRNS to improve face identification. The present study aims to further explore the effect of tRNS on face identification using an unfamiliar face matching task. Observers firstly received either high-frequency bilateral tRNS or sham stimulation for 20 min. The stimulation targeted occipitotemporal areas, which have been previously involved in face processing. In a subsequent stage, observers were asked to perform an unfamiliar face matching task consisting of unaltered and pixelated face pictures. Compared to the sham stimulation group, the high-frequency tRNS group showed better unfamiliar face matching performance with both unaltered and pixelated faces. Our results show that a single high-frequency tRNS session might suffice to improve face identification abilities. These results have important consequences for the treatment of face recognition disorders, and potential applications in those scenarios whereby the identification of faces is primordial