Exploring the Use of Thermal Infrared Imaging in Human Stress Research

Abstract

High resolution thermal infrared imaging is a pioneering method giving indices of sympathetic activity via the contact-free recording of facial tissues (thermal imprints). Compared to established stress markers, the great advantage of this method is its non-invasiveness. The goal of our study was to pilot the use of thermal infrared imaging in the classical setting of human stress research. Thermal imprints were compared to established stress markers (heart rate, heart rate variability, finger temperature, alpha-amylase and cortisol) in 15 participants undergoing anticipation, stress and recovery phases of two laboratory stress tests, the Cold Pressor Test and the Trier Social Stress Test. The majority of the thermal imprints proved to be change-sensitive in both tests. While correlations between the thermal imprints and established stress markers were mostly non-significant, the thermal imprints (but not the established stress makers) did correlate with stress-induced mood changes. Multivariate pattern analysis revealed that in contrast to the established stress markers the thermal imprints could not disambiguate anticipation, stress and recovery phases of both tests. Overall, these results suggest that thermal infrared imaging is a valuable method for the estimation of sympathetic activity in the stress laboratory setting. The use of this non-invasive method may be particularly beneficial for covert recordings, in the study of special populations showing difficulties in complying with the standard instruments of data collection and in the domain of psychophysiological covariance research. Meanwhile, the established stress markers seem to be superior when it comes to the characterization of complex physiological states during the different phases of the stress cycle.

How good is this food? A study on dogs' emotional responses to a potentially pleasant event using infrared thermography

“…In hens there is a significant drop in comb surface temperature in response to anticipation and consumption of a palatable food reward [36] but also during exposure to unpleasant events [73]. This contrasting effect on body temperature can be explained in terms of activation of the sympathetic branch of the ANS which induces an increase in core temperature, reflected in the eye, and a decrease in more peripheral body area, such as nose, face and ears, due to vasoconstriction [49,50,74,75].…”

Automated mental stress recognition through mobile thermal imaging

“…With advancements in commercial thermal imaging technologies, thermography has begun to extend its application context to the analysis of people's physiological processes and affective states. Indeed, it has been shown that physiological signatures, such as thermal directional changes (e.g., [4], [12]- [14]), cardiac (e.g., [11]), perspiratory (e.g., [15]) and respiratory (e.g., [8]) indices, and muscular activations related to facial expressions (e.g. FACS decoding [20]), can be captured through thermal imaging.…”

“…FACS decoding [20]), can be captured through thermal imaging. Researchers have investigated thermal signatures of one's face in relation to mental stress, (e.g., [4], [13], [21]- [23]). For example, it was found that a person's nose tip could show temperature drops under cognitive load inducing mental stress [4].…”

“…In addition, studies have shown that different types of autonomic nervous system activities can be simultaneously read through the use of thermal imaging (e.g. temperature direction in [4], respiration in [8], heart rate in [11]). …”

“…Although earlier approaches provided initial evidences of the relation between affect and temperature, a variety of body regions and their thermal signatures have been much less investigated than thermal directionality of facial and palm regions [4], [12]- [17]. Little is indeed known about how such areas respond to stress level.…”