Alexithymia and socio-emotional processing : a multi-modal approach

• Main Author: Sou, Ka Lon
• Other Authors: Xu Hong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Social sciences::Psychology
• Online Access: https://hdl.handle.net/10356/137822
• Institution: Nanyang Technological University

Up to one out of five individuals in the general population has alexithymia, a deficit in processing one’s own and others’ emotions. The mechanism of the deficit in socio-emotional processing of alexithymia is poorly understood. Existing literature has shown that the high alexithymia individuals tend to pay less attention to the eye region of the face and have impaired self-awareness. Since these two processing are important for the evaluation of whether others’ emotions, as externalized by emotional faces, are relevant to oneself or not during social interaction, we hypothesize the high alexithymia individuals to have weaker evaluation of self-relevance during socio-emotional processing. More specifically, while the low alexithymia individuals process emotional faces with different gaze directions differently, the high alexithymia individuals might not differentiate emotional faces of different gaze directions in the same way. Therefore, in this thesis, one survey study and three experiments were conducted to examine whether and how alexithymia affects socio-emotional processing. Our investigation started with a survey study which aimed to explore the epidemiology of alexithymia in Singapore, and this was piloted in the university context. We found that about 1 out of 4 Singapore university students (24%) can be categorized as “alexithymic” (TAS-20 ≥ 61). This alexithymia rate is higher than the reported rate in the literature (10% to 19%; Franz et al., 2008; Mason, Tyson, Jones, & Potts, 2005; Parker, Taylor, & Bagby, 1989; Salminen, Saarijärvi, Äärelä, Toikka, & Kauhanen, 1999). The high alexithymia rate in our sample may due to its cultural orientation or its specific demographic, e.g., being student population rather than general population. On top of that, we further illustrated that alexithymia is closely related to other traits related to socio-emotional processing, such as autistic traits, anxiety and depression. These socio-emotional deficits may explain the previously reported interpersonal difficulties in alexithymia (Nicolò et al., 2011; Vanheule, Desmet, Meganck, & Bogaerts, 2007). Next, we further investigate how alexithymia affects socio-emotional processing. In Experiment 1, when being asked to rate how threatened one feel when perceiving the emotional faces, we found that the eye-contact effect of the angry faces was negatively correlated with alexithymia trait, such that the higher the alexithymia trait, the smaller the difference between the threat ratings given to an angry face with direct gaze and with averted gaze (i.e. weaker eye-contact effect in higher levels of alexithymia). This suggests that alexithymia affects the evaluation of self-relevance during social threat processing. After that, we explored one of the possible causes of the alexithymic impairment in the evaluation of self-relevance – reduced attention to the eye region. In Experiment 2, we showed that the high alexithymia individuals tended to fixate for shorter durations on the eye region of faces, and this eye avoidance was most prominent in the upright angry faces. The greater alexithymic eye avoidance tendency for angry faces indicates that the reduced attention to the eye region in alexithymia is mainly driven by aversion to potential threat that is indicated by eye contact. Furthermore, the result is coherent with our findings in Experiment 1 that alexithymia only affects the evaluation of self-relevance of angry faces. We thus raise the possibility that the alexithymic impairment in the evaluation of self-relevance is related to the reduced attention to eye information. Lastly, we explored the neural correlates of the alexithymic influences on the evaluation of self-relevance during socio-emotional processing. In Experiment 3, we recorded the EEG signals of subjects while they were perceiving emotional faces with different gaze directions. There were two major findings related to alexithymia. 1) The frontal N1 activation difference for gaze direction was reduced in high alexithymia individuals compared to low alexithymia individuals; and 2) the alexithymic influences on the evaluation of self-relevance during social threat processing was reflected at the frontal N2 component. That is, the frontal N2 activation of the low alexithymia individuals differentiated angry faces with different gaze directions, but the same neural differentiation was absent in the high alexithymia individuals. Summarizing our findings, we conclude that alexithymia is related to the impairment in the evaluation of self-relevance during social threat processing. This impairment is likely to be related to the reduced attention to eye information in high alexithymia individuals. At the neural level, our findings support that alexithymia is associated with deficit at the subcortico-frontal pathway. The findings are discussed with reference to existing models of socio-emotional processing, and a new model (adapted from existing models) is proposed to incorporate our novel findings on alexithymic influences in socio-emotional processing.