# Camera-Sourced Heart Rate Synchronicity: A Measure of Immersion in Audiovisual Experiences
## 1 Introduction  
This paper sets out to apply and evaluate a novel means of measuring immersion using a camera within a study that aims to better understand the true influence of audio presentation methods on audiovisual experiences. The term _immersion_ is applied here as a means of labelling the extent to which a participant feels they are placing their full attention within a mediated world. The term _audio presentation_ refers to a holistic concept that includes the soundtrack, all aspects of the system utilised for its reproduction, and the acoustics of the room where it is presented.  
The opening scene of the film _Gravity (2013)_[1] is consistently theorised as evoking a feeling of immersion when experienced with a faithful reproduction of the Dolby Atmos soundtrack [2; 3; 4; 5; 6]. In the original experimental work presented in this paper, we conduct a between-subjects study in which this scene is experienced with either high-end audio presentation or basic audio presentation. In the high-end condition, the moving image is accompanied by a lossless _Dolby Atmos_[7] version of the soundtrack, reproduced using 12 _Genelec_  loudspeakers. In the basic audio condition, the same moving image is accompanied by a _Dolby Digital 2.0_ (320 kbps) stereo version of the soundtrack, reproduced using the built-in television (TV) loudspeakers [8].  
To measure immersion in this study, we apply a novel camera-sourced physiological feature alongside an established self-report method. The camera-sourced feature captures the extent to which a participant's heart rate (HR) rises and falls synchronously with the rest of the cohort in response to the evolving narrative. This feature, known as HRinter-subject correlation (ISC-HR), has been shown to index immersion [9; 10], attentional engagement [11; 12], and flow [13] when acquired using an electroencephalogram (ECG). However, no research has been conducted that attempts to obtain this feature using a camera. To properly evaluate the camera-sourced feature, an ECG is also used in this study. We propose that the camera may be deployed without an ECG in future research. The camera-based method is considered advantageous as it avoids the discomfort and obtru-siveness of physical sensors. Moreover, this method is promising due to its potential for simultaneously capturing other experientially indicative features, such as facial movements and gaze direction.  
The overarching hypothesis for this study is that the increase in immersion influenced by a high-end audio presentation, compared with a basic audio presentation, can be measured using a camera-sourced ISC-HR feature. Retrospectively, the primary contribution of this research is the documentation of the camera-based method. This method may be used to inform research across various domains concerned with the assessment of the human psychological condition at a distance, including telemedicine and affective computing. While a detailed discussion of the broader applications and ethical considerations of using cameras for physiological data extraction is beyond the scope of this manuscript, this lab-based psychophysiological investigation, conducted with explicit consent, demonstrates the potential of non-contact methods for evaluating audiovisual experiences.