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159Mimicry and pair-bonding9and economically. By employing a controlled laboratory environment, wethus allow for a space where multiple individuals can engage in brief dateswith several potential partners, allowing for a structured and standardizeddata collection (Eastwick & Finkel, 2008b; Finkel et al., 2007; Finkel & Eastwick, 2008). Thus, speed-dating paradigms provide an ecologically valid wayto study human mate choice (e.g., see Roth, Samara, & Kret, 2021a; Samaraet al., 2021). We expected that when both couple members were interestedin their partner, they would mimic more subtle expressions indicating attraction (i.e., coy smiles and eyebrow flushes). We also explored whetherthe mimicry of nonverbal expressions indicating positive affect (i.e., smiles,such as genuine smiles and polite smiles) predict attraction.MethodsParticipantsGiven that we opted for a Bayesian analysis framework, which offers moreflexibility with optional stopping during data collection, we did not conductan a-priori power calculation (van Doorn et al., 2021). Eighty (N = 80)Dutch heterosexual participants between the ages of 18-30 were recruitedvia online platforms (e.g., Sona Systems, https://www.sona-systems.com)and on-campus advertisements for a speed-dating experiment. Ten participants failed to attend the experimental sessions, and three participants (2men) withdrew from the study prior to the speed dating sessions. Therefore, the final sample consisted of 67 participants (N = 67; 35 women; Mage= 22.03, SD = 2.26; men: Mage = 22.61, SD = 1.75). Participants registered via a Qualtrics form, where they were provided with an informationletter and criteria questions to participate in the experiment. Only participants who met the criteria (i.e., heterosexual, fluent in Dutch, 18-30 yearsold, with normal or corrected-to-normal vision and normal colour vision,normal hearing acuity, and no psychological disorders) were allowed to register for the experimental session. Participants were further instructed notto wear jewelry, heavy make-up, perfume, and revealing clothes during thetesting sessions. As compensation for their participation, participants wereprovided with a ticket to Apenheul Primate Park located in Apeldoorn, theNetherlands. The study received approval from the Leiden University EthicsCommittee (CEP: 2020-02-20-M.E. Kret-V1-2169).Speed-datesParticipants were divided into groups of 20 (10 men) and were asked to complete a series of cognitive tasks (for a full description of the methods, seeRoth et al., 2021). Following the tasks, the participants took part in a maximum of 10 speed dates with all opposite-sex participants, which resultedIliana Samara 17x24.indd 159 08-04-2024 16:36