Pupillometry has been one of the most widely used response systems in psychophysiology. Changes in pupil size can reflect diverse cognitive and emotional states, ranging from arousal, interest and effort to social decisions, but they are also widely used in clinical practice to assess patients' brain functioning. As a result, research involving pupil size measurements has been reported in practically all psychology, psychiatry, and psychophysiological research journals, and now it has found its way into the primatology literature as well as into more practical applications, such as using pupil size as a measure of fatigue or a safety index during driving. The different systems used for recording pupil size are almost as variable as its applications, and all yield, as with many measurement techniques, a substantial amount of noise in addition to the real pupillometry data. Before analyzing pupil size, it is therefore of crucial importance first to detect this noise and deal with it appropriately, even prior to (if need be) resampling and baseline-correcting the data. In this article we first provide a short review of the literature on pupil size measurements, then we highlight the most important sources of noise and show how these can be detected. Finally, we provide stepby-step guidelines that will help those interested in pupil size to preprocess their data correctly. These guidelines are accompanied by an open source MATLAB script (available at https://github.com/ElioS-S/pupil-size). Given that pupil diameter is easily measured by standard eyetracking technologies and can provide fundamental insights into cognitive and emotional processes, it is hoped that this article will further motivate scholars from different disciplines to study pupil size.

Cooperation is pivotal for society to flourish. To foster cooperation, humans express and read intentions via explicit signals and subtle reflections of arousal visible in the face. Evidence is accumulating that humans synchronize these nonverbal expressions and the physiological mechanisms underlying them, potentially influencing cooperation. The current study is designed to verify this putative linkage between synchrony and cooperation. To that end, 152 participants played the Prisoner’s Dilemma game in a dyadic interaction setting, sometimes facing each other and sometimes not. Results showed that synchrony in both heart rate and skin conductance level emerged during face-to-face contact. However, only synchrony in skin conductance levels predicted cooperative success of dyads. Crucially, this positive linkage was strengthened when participants could see each other. These findings show the strong relationship between our bodily responses and social behavior, and emphasize the importance of studying social processes between rather than within individuals in real-life interactions.

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in press). How effortful is cognitive control? Insights from a novel method measuring singe-trial evoked beta-adrenergic cardiac reactivity. International Journal of Psychophysiology. AbstractThe ability to adjust attentional focus to varying levels of task demands depends on the adaptive recruitment of cognitive control processes. The present study investigated for the first time whether the mobilization of cognitive control during response-conflict trials in a flanker task is associated with effort-related sympathetic activity as measured by changes in the RZinterval at a single-trial level, thus providing an alternative to the pre-ejection period (PEP) which can only be reliably measured in ensemble-averaged data. We predicted that response conflict leads to a physiological orienting response (i.e. heart rate slowing) and increases in effort as reflected by changes in myocardial beta-adrenergic activity (i.e. decreased RZ interval). Our results indeed showed that response conflict led to cardiac deceleration and decreased RZ interval. However, the temporal overlap of the observed heart rate and RZ interval changes suggests that the effect on the latter reflects a change in cardiac pre-load (Frank-Starling mechanism). Our study was thus unable to provide evidence for the expected link between cognitive control and cardiovascular effort. However, it demonstrated that our single-trial analysis enables the assessment of transient changes in cardiac sympathetic activity, thus providing a promising tool for future studies that aim to investigate effort at a single-trial level.

Humans are social animals whose mental wellbeing is shaped by the ability to attract and connect with each other. In a dating world, in which success can be determined by brief interactions, apart from physical features, there is a whole choreography of movements, physical reactions and subtle expressions that drive humans' sexual attraction. To determine what drives attraction, we measured nonverbal dynamics between people during real-life interactions outside the laboratory, where dating is most relevant. Participants wore eye-tracking glasses with embedded cameras, and devices to measure physiological signals including heart rate and skin conductance. Crucially, visible signals that can be controlled, such as facial expressions or gaze, did not predict attraction. Instead, attraction was predicted by synchrony in heart rate and skin conductance between partners, which are unconscious and difficult to regulate. Our findings suggest that shared emotionality is vital for mutual attraction. Moreover, physiological synchrony may provide a medium for translating visible expressions into embodied emotions, which can turn into intentions via somatosensory simulation. Significance StatementIn our modern world where millions of people meet online without interacting face-to-face, the question "what defines attraction" has become very relevant. In this study, we used modern technologies to lay down a foundation for the processes that drive human attraction during reallife interactions. Contrary to common belief, we found that attraction is not predicted by a frequency of expression or eye fixation duration, nor is linearly related to the participant's autonomic nervous system activity. Importantly, we found that the more a participant synchronized their heart rate and skin conductance with their partner, the more they felt attracted toward that person. This study reveals a fundamental physiological process that plays a role in the formation of romantic relations.