Event-related potentials of automatic imitation are modulated by ethnicity during stimulus processing, but not during motor execution

Abstract

This study investigated neural processes underlying automatic imitation and its modulation by ethnically diverse hand stimuli (Black, White) using event-related brain potentials (ERPs). Automatic imitation relies on motor stimulus-response compatibility (SRC), i.e., response conflict caused by motoric (in)congruency between task-irrelevant hand stimuli and the required response. Our novel task aimed to separate two distinct neuro-cognitive processing stages of automatic imitation and its modulation by ethnicity: the stage of stimulus processing (i.e. perception), comprising presentation of stimulus ethnicity and SRC, and the stage of response execution (i.e. action). Effects of ethnicity were observed in ERPs of different stages of stimulus processing - during presentation of ethnicity (LPP) and SRC (N190, P3). ERPs at response execution, Pre-Motion Positivity (PMP) and Reafferent Potential (RAP), were only sensitive to congruency. The N190 results may index visual self-other distinction, while the neural timecourse of P3 and PMP variation could reflect a dynamical decision process linking perception to action, with motor initiation reflected in the PMP component. The PMP might further index motor-related self-other distinction regardless of ethnicity. Importantly, overt motor execution was not influenced by ethnically diverse stimuli, which suggests generalizability of the automatic imitation effect across ethnicities.

Imitation or Polarity Correspondence? Behavioural and Neurophysiological Evidence for the Confounding Influence of Orthogonal Spatial Compatibility on Measures of Automatic Imitation

“…The general pattern of greater brain responses in the P3 window is consistent with previous studies: namely, greater positivity was observed in response to compatible relative to incompatible actions performed by all stimulus hands (Deschrijver et al, 2017a(Deschrijver et al, , 2017bRauchbauer et al, 2018). In contrast to the N190, stronger P3 responses also were observed in the right hemisphere for all stimuli.…”

“…To understand precisely how orthogonal compatibility influences performance on SRC tasks with rotated hand stimuli, future studies should extend our preliminary findings and assess the relative influence of these confounding effects on motor-related ERP components. For example, other neuroscientific investigations have revealed that (in) compatibility between observed and executed actions influences cortical indices of movement preparation (readiness potential; Deschrijver et al, 2017aDeschrijver et al, , 2017b and initiation (premotor positivity; Rauchbauer et al 2018).…”

“…In addition to assessing whether or not the pattern of AI observed in Experiment 1 can be reproduced when stimulus orientation is manipulated in a within-subject manner, providing a more systematic assessment of orthogonal spatialcompatibility effects, the second experiment employed electroencephalography (EEG) to investigate whether these effects also exert an influence on neurophysiological indices of AI. To permit comparisons with the handful of previous studies that have employed EEG to investigate the neural correlates of AI measured on the SCR task, we focus specifically on two stimulus-locked components of the event-related potential (ERP): the N190-a negative wave peaking at approximately 200 ms at lateral occipito-temporal regions, which has been localised within inferior temporal cortex (Thierry et al, 2006), and the P3-a positive wave peaking at 300-500 ms that occurs maximally over parietal regions (Deschrijver, Wiersema, & Brass, 2017b;Nishimura, Ikeda, & Higuchi, 2018;Rauchbauer, Pfabigan, & Lamm, 2018). A greater N190 in response to incompatible relative to compatible trials on the SRC task has been proposed to index low-level visual self-other distinction processes, while a larger P3 amplitude elicited by compatible compared with incompatible actions has been interpreted to reflect the cognitive processes recruited when resolving conflicts between internally and externally generated motor plans (Deschrijver et al, 2017b;Deschrijver, Wiersema, & Brass, 2017a;Rauchbauer et al, 2018).…”

“…For each condition, first we computed ERPs in sensor space. To be consistent with previous EEG investigations of the SRC task, we focused these analyses on temporal windows within which the N190 and P3 are expressed commonly: 170-220 and 310-430 ms post stimulus, respectively (Deschrijver et al, 2017b(Deschrijver et al, , 2017aRauchbauer et al, 2018). Trial segmentation included a 300 ms pre-stimulus baseline and 800 ms post-stimulus window.…”

Developmental trajectory of interpersonal motor alignment: Positive social effects and link to social cognition

“…If the irrelevant action matches the target movement, response execution is facilitated, while a mismatch requires inhibition of the perceived action representation to execute the target response and thus impairs execution. This paradigm has the advantage of high experimental controllability, implementation as a within-subject, repeated measures design and suitability for neuroscientific investigations, with, for example functional magnetic resonance imaging (fMRI) (e.g., Brass et al, 2005 ; Brass et al, 2009 ), electroencephalography (EEG) (e.g., Deschrijver et al, 2017 ; Rauchbauer et al, 2018 ), transcranial magnetic stimulation (TMS) (e.g., Catmur et al, 2011 ; Catmur et al, 2007 ; Mengotti et al, 2013 ; Sowden and Catmur, 2015 ) or transcranial direct current stimulation (e.g., Santiesteban et al, 2012 ). In the developmental literature the majority of studies refer to the effect of motor interference between target movement and task-irrelevant simultaneous movement as “motor interference task”.…”