A systematic study of personification in synaesthesia: Behavioural and neuroimaging studies

Abstract

In synaesthetic personification, personality traits and other human characteristics are attributed to linguistic sequences and objects. Such non-perceptual concurrents are different from those found in most frequently studied types of synaesthesia, in which the eliciting stimuli induce sensory experiences. Here, subjective reports from synaesthetes were analysed and the cognitive and neural mechanisms underlying personification were investigated. Specifically, the neural bases of personification were examined using functional MRI in order to establish whether brain regions implicated in social cognition are involved in implementing personification. Additional behavioural tests were used to determine whether personification of inanimate objects is automatic in synaesthesia. Subjective reports describing general characteristics of synaesthetic personification were collected using a semi-structured questionnaire. A Stroop-like paradigm was developed in order to examine the automaticity of object personification, similarly to the previous investigations. Synaesthetes were significantly slower in responding to incongruent than to congruent stimuli. This difference was not found in the control group. The functional neuroimaging investigations demonstrated that brain regions involved in synaesthetic personification of graphemes and objects partially overlap with brain areas activated in normal social cognition, including the temporo-parietal junction, precuneus and posterior cingulate cortex. Activations were observed in areas known to be correlated with mentalising, reflecting the social and affective character of concurrents described in subjective reports. Psychological factors linked with personification in previous studies were also assessed in personifiers, using empathy, mentalising and loneliness scales. Neither heightened empathy nor mentalising were found to be necessary for personification, but personifying synaesthetes in the study felt lonelier than the general population, and this was more pronounced in those who personified more. These results demonstrate that personification shares many defining characteristics with classical forms of synaesthesia. Ascribing humanlike characteristics to graphemes and objects is a spontaneous and automatic process, inducer-concurrent pairings are consistent over time and the phenomenological character of concurrents is reflected in functional neuroanatomy. Furthermore, the neuroimaging findings are consistent with the suggestions that synaesthetes have a lower threshold for activation brain regions implicated in self-projection and mentalising, which may facilitate the personification processes in synaesthesia.