Behavioural mimicry refers to an unconscious and automatic tendency for people to copy each other’s actions and mannerisms, while engaging in an interaction. Behavioural mimicry in dyadic interactions leads to an increase in liking, rapport and prosocial behaviour. Given that behavioural mimicry carries a social benefit within the dyad, in the first experiment, we wanted to explore the social consequence of behavioural mimicry in a larger social environment by introducing a third person. The third person was in the background of an interacting dyad (consisting of the participant and a neutral in demeanour confederate) and either (1) mimicked the participant, (2) anti-mimicked the participant, or (3) kept a neutral position throughout the interaction. The results indicated that when one of the interacting partners is anti-mimicked, they report liking their non-mimicking interaction partner more than in either of the other two conditions. In experiment two, we set out to determine whether motor similarity of movement or temporal contingency of movement led to the affiliative judgements often reported in the mimicry literature. We had a research assistant either anatomically mimic (same effector), specularly mimic (different effector) or anti-mimic the participant during a task at either a short or long time delay, and collected participant’s likeability judgements of the research assistant. We discovered that anatomical mimicry leads to higher affiliative judgement at short time delay compared to long time delay, that specular mimicry leads to a higher affiliative judgement at long time delay compared to short time delay, and that anti-mimicry leads to the same affiliative judgement regardless of time delay. In experiment three, we wanted to explore the neurocognitive significance of behavioural mimicry. A previous study demonstrated that anodal transcranial direct current stimulation (tDCS) to the inferior frontal cortex (IFC) increased mimicry in a subsequent interaction. We wanted to replicate this finding with one change: we used a computer task rather than a naturalistic interaction. Following anodal tDCS to the IFC, control site or sham stimulation, the participants watched a video of a female model that touched her face every few seconds. We wanted to determine whether the participant would touch their face more often following the IFC stimulation compared to the other two conditions. Our results were not similar to the previous finding: participants touched their face at similar rates regardless of the stimulation site. Nonetheless, in this thesis, we report a novel social manipulation of behavioural mimicry (mimicry emanating from outside the interacting dyad) that impacts the affiliative feelings within the interacting dyad. We also report a novel form of a mimicking behaviour, that goes beyond the traditional definition, to impact the perception of the interaction partner at a longer time delay. / Thesis / Master of Science (MSc) / This thesis describes empirical research that explores the nature of behavioural mimicry and the impact it has on how people perceive one another. Behavioural mimicry refers to the natural tendency for people to copy one another’s behaviours and mannerisms in an interaction. This tendency builds rapport and likeability between the interacting pair. Across three experiments, we expand on previous behavioural mimicry literature. By using novel mimicry manipulations, we demonstrate that behavioural mimicry detection (experiment one) and recognition (experiments two and three) systems are more complex than previously believed.