  We study the statistical properties of facial behaviour altered by the
regulation of brain arousal in the clinical domain of psychiatry. The
underlying mechanism is linked to the empirical interpretation of the vigilance
continuum as behavioral surrogate measurement for certain states of mind.
Referring to the classical scalp-based obtrusive measurements, we name the
presented method Opto-Electronic Encephalography (OEG) which solely relies on
modern camera-based real-time signal processing and computer vision. Based upon
a stochastic representation as coherence of the face dynamics, reflecting the
hemifacial asymmetry in emotion expressions, we demonstrate an almost flawless
distinction between patients and healthy controls as well as between the mental
disorders depression and schizophrenia and the symptom severity. In contrast to
the standard diagnostic process, which is time-consuming, subjective and does
not incorporate neurobiological data such as real-time face dynamics, the
objective stochastic modeling of the affective responsiveness only requires a
few minutes of video-based facial recordings. We also highlight the potential
of the methodology as a causal inference model in transdiagnostic analysis to
predict the outcome of pharmacological treatment. All results are obtained on a
clinical longitudinal data collection with an amount of 99 patients and 43
controls.
