New Frontiers for Applications of Thermal Infrared Imaging Devices: Computational Psychopshysiology in the Neurosciences

Abstract

Thermal infrared imaging has been proposed, and is now used, as a tool for the non-contact and non-invasive computational assessment of human autonomic nervous activity and psychophysiological states. Thanks to a new generation of high sensitivity infrared thermal detectors and the development of computational models of the autonomic control of the facial cutaneous temperature, several autonomic variables can be computed through thermal infrared imaging, including localized blood perfusion rate, cardiac pulse rate, breath rate, sudomotor and stress responses. In fact, all of these parameters impact on the control of the cutaneous temperature. The physiological information obtained through this approach, could then be used to infer about a variety of psychophysiological or emotional states, as proved by the increasing number of psychophysiology or neurosciences studies that use thermal infrared imaging. This paper presents a review of the principal achievements of thermal infrared imaging in computational psychophysiology, focusing on the capability of the technique for providing ubiquitous and unwired monitoring of psychophysiological activity and affective states. It also presents a summary on the modern, up-to-date infrared sensors technology.

Keywords: autonomic nervous system; computational psychophysiology; microbolometers; thermal detectors; thermal imaging systems.

Figure 1

A thermal imaging system whose output is provided in temperature units (Fahrenheit, Celsius, Kelvin, or Rankine) (Adapted from [38]).

Figure 2

Temperature calibration: (a) Voltage output as a function of temperature obtained in a laboratory. (b) The temperature as a function of voltage. This calibration appears in a look-up table. Although the output is shown as an analog voltage, most systems operate in the digital domain [38].

Figure 3

Thermal signal extracted from right and left nostrils regions [48].

Figure 4

Screenshot of the breathing signature processing interface for visible and thermal dual-mode imaging system [54].

Figure 5

(a) Raw thermal image of a human wrist. (b) The corresponding blood flow rate visualization image. The color bars at the bottom index colors to values from the minimum to the maximum of the respective ranges [56].

Figure 6

Facial thermal changes in a representative subject. On the left: the average temperature before the acoustic stimulation; on the right: soon after the acoustic stimulation. A general temperature drop can be observed over the whole face, with the onset of sudomotor response as highlighted by the dotted pattern of the temperature associated with the emotional sweating response. In particular, while the cheeks do not change their average temperature values and pattern, nose tip, perioral, maxillary and forehead regions clearly present a temperature decrease due to the appearance of colder dotted spots. The temperature decrease is particularly appreciable on the nose tip, where blue areas can be easily spotted. The circles over the face are paper markers put on to facilitate the tracking of the region of interest along the procedure. The black-contour circular region on the nose tip is the region of interest from which the temperature data have been extracted [61].

Figure 7

Facial thermal imprints of one of the mother–child dyads [71].

Figure 8

Graphical representation of group temperature variations of the nasal tip and maxillary area during the experimental phases as well as during the neutral baseline period [71].