Chen, Sinead Hsi-Yi; (2018) An investigation of Laughter and Crying: 
from behavioural, physiological and neuroimaging studies. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This PhD investigates the perception of laughter and crying, two non verbal expressions of emotion, and how this perception is affected by the authenticity of the expressed emotions. Three separate approaches were used to address the perception of these stimuli by healthy participants: behavioural rating tasks, physiological responses recordings, and functional magnetic resonance imaging (fMRI) techniques. A series of behavioural ratings established that naïve listeners can reliably differentiate involuntary laughter from voluntary laughter, however, their performance was poorer when discriminating between involuntary crying and voluntary crying. In a larger set of behavioural ratings collected at the Science Museum (n=1723, age range = 3-76 years old), the ratings accuracy of voluntary and involuntary emotional vocalizations were both found to improve over age, however, the developmental trajectories of the voluntary expressions were shown to have a steeper slope throughout early adulthood than involuntary expressions. This difference may reflect a developmental learning process of perceiving voluntary emotional expressions through social interactions. The results of behavioural and developmental experiments consistently show that the involuntary crying was perceived as moe similar to voluntary crying than voluntary and involuntary laughter However the physiological responses (pupil size) shows a different pattern: listeners’ pupils were significantly more dilated for involuntary vocalizations than for voluntary ones, regardless of emotions. This discrepancy between physiological responses and behavioural ratings on crying suggests that social learning processes influence the perceivers’ judgments of involuntary crying, other than pure perceptual processes. In the fMRI study, we found that perceiving laughter and crying requires activation of similar areas in an emotional motor task as well as in a theory-of-mind task, suggesting that a shared interactive neural network of perceiving and interpreting emotions is involved. However, the cortical areas involved in differentiating voluntary and involuntary vocalizations are partly distinct for laughter and for crying, implying different neural networks may be responsible for the authenticity differentiation of different emotions. In summary, this thesis demonstrates the existence of emotion-specific differences in perception of non-verbal emotional vocalizations and these differences may be due to developmental factors. Moreover, multiple neural networks were shown to play important roles in perceiving and differentiating positive and negative emotions.

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