Physiological synchrony in brain and body as a measure of attentional engagement

Attentional engagement – the emotional, cognitive and behavioral connection with information to which the attention is focused – is important in all settings where humans process information. Measures of attentional engagement could be helpful to, for instance, support teachers in online classrooms, or individuals working together in teams. This thesis aims to use physiological synchrony, the similarity in neurophysiological responses across individuals, as an implicit measure of attentional engagement. The research is divided into two parts: the first investigates how different attentional modulations affect physiological synchrony in brains and bodies, the second explores the feasibility of using physiological synchrony as a tool to monitor attention in real-life settings.In Part I, the effect of different manipulations of attention on physiological synchrony in brain and body is explored. We find that physiological synchrony does not only reflect attentional engagement when measured in the electroencephalogram (EEG), but also when measured in electrodermal activity (EDA) or heart rate. Moreover, we find that physiological synchrony can reflect both sensory and top-down variations in attention, where top-down focus of attention is best reflected by synchrony in EEG, and where emotionally salient events attracting attention are best reflected by EDA and heart rate. Part II transitions into the practical applications of physiological synchrony in real-life contexts. Wearables are employed to measure physiological synchrony in EDA and heart rate, demonstrating comparable accuracy to high-end lab-grade equipment. The research also incorporates machine learning techniques, showing that physiological synchrony can be combined with novel unsupervised learning algorithms. Finally, measurements in classrooms reveal that physiological synchrony can be successfully monitored in real-life settings.While the findings are promising, the thesis acknowledges limitations in terms of sufficient data that are required for robust monitoring of attentional engagement and in terms of limited variance in attention explained by physiological synchrony. To advance the field, future work should focus on the applied, methodological and ethical questions that remain unanswered

The Effects of Stimulus Duration and Group Size on Wearable Physiological Synchrony

Physiological synchrony refers to the degree to which physiological measures such as heart rate and electrodermal activity (EDA) across multiple individuals uniformly change. Physiological synchrony has shown to be informative of attention among individuals presented with a narrative stimulus: higher physiological synchrony is often related with better attention to the narrative. However, results are strongly dependent on basic factors such as group size and recording length. In the current work we explore what group size and recording length are needed for robust physiological synchrony results.<br/

Robustness of Physiological Synchrony in Wearable Electrodermal Activity and Heart Rate as a Measure of Attentional Engagement to Movie Clips

Individuals that pay attention to narrative stimuli show synchronized heart rate (HR) and electrodermal activity (EDA) responses. The degree to which this physiological synchrony occurs is related to attentional engagement. Factors that can influence attention, such as instructions, salience of the narrative stimulus and characteristics of the individual, affect physiological synchrony. The demonstrability of synchrony depends on the amount of data used in the analysis. We investigated how demonstrability of physiological synchrony varies with varying group size and stimulus duration. Thirty participants watched six 10 min movie clips while their HR and EDA were monitored using wearable sensors (Movisens EdaMove 4 and Wahoo Tickr, respectively). We calculated inter-subject correlations as a measure of synchrony. Group size and stimulus duration were varied by using data from subsets of the participants and movie clips in the analysis. We found that for HR, higher synchrony correlated significantly with the number of answers correct for questions about the movie, confirming that physiological synchrony is associated with attention. For both HR and EDA, with increasing amounts of data used, the percentage of participants with significant synchrony increased. Importantly, we found that it did not matter how the amount of data was increased. Increasing the group size or increasing the stimulus duration led to the same results. Initial comparisons with results from other studies suggest that our results do not only apply to our specific set of stimuli and participants. All in all, the current work can act as a guideline for future research, indicating the amount of data minimally needed for robust analysis of synchrony based on inter-subject correlations.</p

Using Galvanic Vestibular Stimulation to Induce Post-Roll Illusion in a Fixed-Base Flight Simulator

INTRODUCTION: The illusions of head motion induced by galvanic vestibular stimulation (GVS) can be used to compromise flight performance of pilots in fixed-base simulators. However, the stimuli used in the majority of studies fail to mimic disorientation in realistic flight because they are independent from the simulated aircraft motion. This study investigated the potential of bilateral-bipolar GVS coupled to aircraft roll in a fixed-base simulator to mimic vestibular spatial disorientation illusions, specifically the “post-roll illusion” observed during flight.METHODS: There were 14 nonpilot subjects exposed to roll stimuli in a flight simulator operating in a fixed-base mode. GVS was delivered via carbon rubber electrodes on the mastoid processes. The electrical stimulus was driven by the high-pass filtered aircraft roll rate to mimic the semicircular canals’ physiological response. The post-roll test scenarios excluded outside visual cues or instruments and required subjects to actively maintain a constant bank angle after an abrupt stop following a passive prolonged roll maneuver. The anticipated outcome was an overshot in roll elicited by the GVS signal. RESULTS: The responses across subjects showed large variability, with less than a third aligning with the post-roll illusion. Subjective ratings suggest that the high-pass filtered GVS stimuli were mild and did not induce a clear sense of roll direction. However, uncontrolled head movements during stimulation might have obscured the intended effects of GVS-evoked illusory head movements. CONCLUSION: The mild and transient GVS stimuli used in this study, together with the uncontrolled head movements, did not convincingly mimic the post-roll illusion.</p

A usability study of physiological measurement in school using wearable sensors

Measuring psychophysiological signals of adolescents using unobtrusive wearable sensors may contribute to understanding the development of emotional disorders. This study investigated the feasibility of measuring high quality physiological data and examined the validity of signal processing in a school setting. Among 86 adolescents, a total of more than 410 h of electrodermal activity (EDA) data were recorded using a wrist-worn sensor with gelled electrodes and over 370 h of heart rate data were recorded using a chest-strap sensor. The results support the feasibility of monitoring physiological signals at school. We describe specific challenges and provide recommendations for signal analysis, including dealing with invalid signals due to loose sensors, and quantization noise that can be caused by limitations in analog-to-digital conversion in wearable devices and be mistaken as physiological responses. Importantly, our results show that using toolboxes for automatic signal preprocessing, decomposition, and artifact detection with default parameters while neglecting differences between devices and measurement contexts yield misleading results. Time courses of students' physiological signals throughout the course of a class were found to be clearer after applying our proposed preprocessing steps

Physiological synchrony in electrodermal activity predicts decreased vigilant attention induced by sleep deprivation

Introduction: When multiple individuals are presented with narrative movie oraudio clips, their electrodermal activity (EDA) and heart rate show significantsimilarities. Higher levels of such inter-subject physiological synchrony are relatedwith higher levels of attention toward the narrative, as for instance expressedby more correctly answered questions about the narrative. We here investigatewhether physiological synchrony in EDA and heart rate during watching ofmovie clips predicts performance on a subsequent vigilant attention task amongparticipants exposed to a night of total sleep deprivation.Methods: We recorded EDA and heart rate of 54 participants during a nightof total sleep deprivation. Every hour from 22:00 to 07:00 participants watcheda 10-min movie clip during which we computed inter-subject physiologicalsynchrony. Afterwards, they answered questions about the movie and performedthe psychomotor vigilance task (PVT) to capture attentional performance.Results: We replicated findings that inter-subject correlations in EDA and heartrate predicted the number of correct answers on questions about the movieclips. Furthermore, we found that inter-subject correlations in EDA, but not inheart rate, predicted PVT performance. Individuals’ mean EDA and heart rate alsopredicted their PVT performance. For EDA, inter-subject correlations explainedmore variance of PVT performance than individuals’ mean EDA.Discussion: Together, these findings confirm the association betweenphysiological synchrony and attention. Physiological synchrony in EDA doesnot only capture the attentional processing during the time that it is determined,but also proves valuable for capturing more general changes in the attentionalstate of monitored individuals.<br/

Understanding the combined effects of sleep deprivation and acute social stress on cognitive performance using a comprehensive approach

Background: Sleep deprivation (SD) and acute social stress are common, often unavoidable, and frequently co-occurring stressors in high-risk professions. Both stressors are known to acutely induce inflammatory responses and an increasing body of literature suggests this may lead to cognitive impairment. This study examined the combined effects of total SD and acute social stress on cognitive performance and took a comprehensive approach to explore their (shared) underlying mechanism leading to cognitive decline. Method: We recorded cognitive performance on a response inhibition task and a multitask and monitored a range of inflammatory, psychophysiological and self-reported markers in 101 participants, both before and after one night of either sleep (control group: N = 48) or SD (N = 53), and both before and after a social stressor (Trier Social Stress Test). Results: SD decreased cognitive performance. The social stress test also results in cognitive performance decline in the control group on the response inhibition task, but improved rather than decreased performance of sleep deprived participants on both tasks. The subjective ratings of mental effort also reflect this antagonistic interaction, indicating that the social stressor when sleep-deprived also reduced mental effort. In the inflammatory and physiological measures, this pattern was only reflected by IL-22 in blood. SD reduced blood IL-22 concentrations, and the social stress reduced IL-22 in the control group as well, but not in sleep-deprived participants. There were no interactive effects of SD and social stress on any other inflammatory or psychophysiological measures. The effects of the social stress test on autonomic measures and subjective results suggest that increased arousal may have benefited sleep-deprived participants’ cognitive performance. Discussion: SD generally decreased cognitive performance and increased required mental effort. By contrast, the isolated effects of a social stressor were not generic, showing a positive effect on cognitive performance when sleep deprived. Our study is the first that studied combined effects of sleep deprivation and acute social stress on cognitive performance and inflammatory markers. It provides a comprehensive overview of effects of these stressors on a range of variables. We did not show unequivocal evidence of an underlying physiological mechanism explaining changes in performance due to (the combination of) sleep deprivation and social stress, but consider IL-22 as a possible cytokine involved in this mechanism and certainly worth following up on in future research.</p