Emotional contagion to vocal smile revealed by combined pupil reactivity and motor resonance

Abstract

The interplay between the different components of emotional contagion (i.e. emotional state and facial motor resonance), both during implicit and explicit appraisal of emotion, remains controversial. The aims of this study were (i) to distinguish between these components thanks to vocal smile processing and (ii) to assess how they reflect implicit processes and/or an explicit appraisal loop. Emotional contagion to subtle vocal emotions was studied in 25 adults through motor resonance and Autonomic Nervous System (ANS) reactivity. Facial expressions (fEMG: facial electromyography) and pupil dilation were assessed during the processing and judgement of artificially emotionally modified sentences. fEMG revealed that Zygomaticus major was reactive to the perceived valence of sounds, whereas the activity of Corrugator supercilii reflected explicit judgement. Timing analysis of pupil dilation provided further insight into both the emotional state and the implicit and explicit processing of vocal emotion, showing earlier activity for emotional stimuli than for neutral stimuli, followed by valence-dependent variations and a late judgement-dependent increase in pupil diameter. This innovative combination of different electrophysiological measures shed new light on the debate between central and peripherical views within the framework of emotional contagion.

Keywords: Emotional contagion; Motor resonance; Pupil reactivity; Vocal smile; fEMG.

Fig. 1

Zygomaticus major (ZM) and Corrugator supercilii (CS) activity. A: Effect of filter (upper panel) and choice (lower panel) on ZM; B: Effect of filter (upper panel) and choice (lower panel) on CS; Effect of filter (C) and of the given choice (D) on CS and ZM -mean response amplitude in the window 2900-3400ms (in grey in A and B time series). Shaded areas represent standard error of the mean. *p < .05; **p < .01.

Fig. 2

Effect of Filter and Choice on pupil activity. A: Effect of emotional filters on pupil dilation B: Effect of Filter on pupil dilation C: Effect of Choice on pupil dilation (without neutral sentences); D: Effect of Filter, Choice and Response on pupil dilation (neutral sentences excluded). Shaded areas represent standard error of the mean. Barplots represent mean pupil dilation in the window 2100-2600ms (mean ± standard error of the mean) (in grey in time series). PD: Pupil Dilation* p < .05.

Fig. 3

Effect of Filter and Choice on pupil dilation kinetic. A: Effect of Filter and Choice on pupil dilation with Neutral sentences (no matter the judgement for them) with time windows chosen for slopes analysis. B: 1- Effect of emotional content; 2- Effect of Filter; 3- Effect of Choice. PD: Pupil Dilation.

Fig. 4

A: Timeline of a trial in the experimental sequence. Tone 1 indicated the beginning of a new trial, tone 2 indicated the time when the subject should rate the sentence. B: Rating scale displayed on screen throughout the duration of the task; PD: Pupil Dilation; fEMG : facial ElectroMyoGraphy.