Thesis title: Somatosensory processing in social cognition: from an individualistic to an interactionist approach
The purpose of this thesis is to provide empirical and theoretical work to expand the current understanding of the role of the somatosensory system in processing social information.
The thesis is organised in two sections, reflecting two different conceptual frameworks to investigate social cognition. In the first section, traditional ‘individualistic’ paradigms have been used to elucidate how the somatosensory system contributes to our understanding of other’s emotions, and how this mechanism might operate differently in autistic individuals. In Chapters 2 and 3, I will outline two empirical studies which aimed at investigating the role of the somatosensory system in processing emotional information in individuals with or without autism spectrum disorder (ASD), and its relationship with interoception.
Within the first experiment, I collected EEG data from two groups of ASD and typically developing (TD) individuals while they observed stimuli depicting facial emotional expressions and recognised either the emotion (emotion task) or gender (gender task) of the stimuli. In 50% of trials, participants received task-irrelevant tactile taps which evoked somatosensory evoked potentials (SEP) during emotion or gender discrimination. Moreover, we subtracted pure visual responses from visual and somatosensory activity to isolate SEP from visual carryover effects (Sel et al., 2014, 2020; Galvez-Pol et al., 2020). Results showed increased amplitude of the P100 SEP component during emotion processing in TD compared to ASD, revealing reduced engagement of the somatosensory system during emotion discrimination in ASD. Interestingly, the amplitude of SEP correlated with the strength of autistic traits.
In the second experiment, we administered a heartbeat counting task to two groups of ASD and TD individuals, who were previously recruited for the first experiment, with the purpose to investigate the relationship between somatosensory embodiment of emotional expressions and interoception. Results showed a significant association between interoceptive accuracy (IAcc), SEP amplitudes during emotion processing, and the strength of autistic traits. Taken together, these two experiment provide novel evidence of altered responses of the somatosensory system during emotion processing in ASD, and suggest this phenomenon might have important implications also for difficulties in interoception.
The second section of this thesis is dedicated to developing conceptual and methodological tools to investigate social cognition within an ‘interactionist’ framework (Gallotti & Frith, 2013). In Chapter 4, I hypothesize that plastic reorganisations of the body schema and the peripersonal space (PPS) may underlie interpersonal coordination during joint action. Specifically, I propose that, during motor interactions, our PPS is temporarily extended to our partner’s body, to create a shared representation supporting interpersonal coordination.
In Chapter 5, I outline an experimental paradigm which was designed to test experimentally the hypothesis of an ‘entangled’ body schema (Soliman et al., 2015) as a consequence of joint action. In this experiment, we planned to record brain activity with EEG after participants engaged in a joint task (sawing a candle with a tight rope) or a solo task (observing the confederate sawing the candle). The experimental paradigm consisted in a tactile stimuli detection task, while task-irrelevant visual stimuli were delivered to the partner’s hand either in a congruent (same finger) or incongruent (opposite finger) condition. We expected to observe stronger multisensory integration between visual and tactile stimuli after the joint task compared to the solo task, reflected in higher accuracy and lower reaction times at a behavioural level, and in enhanced SEP amplitude at a neural level, in the congruent condition compared to the solo condition. These results would provide behavioural and neural evidence of plastic reorganisations of the body schema onto a joint, interpersonal representation. Hopefully, the experiment will start as soon as the social distancing situation related to the Covid-19 pandemic improves.
This work provides novel evidence of the role of the somatosensory system in social cognition and how it might operate differently in individuals with ASD. Moreover, it develops methodological and conceptual tools for future investigations of the role of the somatosensory system in facilitating interpersonal coordination during joint action.