Deep thought and cold noses

Non-obtrusive thermal cameras help researchers confirm a significant link between the two

A generic eye tracker. Photo: Maurizio
Pesce. CC BY 2.0

Facial temperatures, which can be measured with a thermal camera, and the diameter of the pupil of the eye are strongly correlated to mental workload.

That is what the data says, according to researchers at the University of Nottingham’s Institute for Aerospace Technology (IAT), together with academic staff from the Bioengineering and Human Factors research groups. The effect seen was strongest above the sinuses around the nose, with facial temperatures dropping as participants carried out tasks of increasing difficulty.

The results also show that when people are fully focused on a task, their breathing rates change as the autonomic nervous system takes over. It suggests that there may also be diversion of blood flow from the face to the cerebral cortex as mental demand increases.

Non-invasive monitoring is important in fields where excessive cognitive demands on an operator can contribute to oversights and use errors – particularly when these errors can have tragic results. The study, published in Human Factors, explores how advances in performance and resolution in thermal cameras have made this a reality.

An earlier study had provided evidence that blink duration and frequency, and the distance the eye moves its rapid shifts, and and pupil diameter are all good measures of mental workload.

A thermal image from the study.
Image: Human Factors. CC BY-NC 4.0

Other studies have shown that a drop in the temperature of the skin around the forehead and the tip of the nose when there is more mental workload. The drop in nose temperature was linked to blood capillaries constricting in the face of stress.

Modern digital thermography relies on cameras that are light and small enough to be placed in an aircraft’s cockpit. In addition, improvements in resolution and computing power will allow the implementation of expert systems that can be programmed to recognize the operator and how he or she will react to varying mental demands.

The test involved having undergraduates play a video game in which they had to use a joystick to target and shoot a particular kind of ball dropping from the top of the screen. The idea was stop those kind of balls from falling upon and dragging down a yellow line that lay below.

There were two levels of the game – one in which the target balls were red, the other in which they had odd numbers on them (a fact that made it cognitively more difficult).

Besides facial temperature, posture, eye movements, and heart and breathing rates, were also measured. The subjects studied were few: the researchers started with 14 people (11 men and three women) and ended with 11 because of a data collection problems.

Adrian Marinescu, who has been examining physiological responses to workload in his PhD in aerospace human factors, and the first author of the paper, said “Our goal is to estimate workload using non-invasive and non-intrusive physiological monitoring. Of all the approaches we’ve tried, facial thermography is the least intrusive, and has proved to be an excellent method.”

Sharah Sharples, who initiated
the study. Photo:
University of Nottingham

Sarah Sharples, professor of human factors, and supervisor and initiator of the study said, “The measurement of workload without needing to interrupt people to ask them to report how busy they are, has been challenging human factors specialists for many years. By bringing together our expertise in bioengineering, human factors and machine learning, we have developed a much better understanding of how physical changes associated with workloads manifest themselves as physiological symptoms – and how these symptoms translate into the parameters that we can measure.”

Alastair Campbell Ritchie of the Bioengineering Research Group, said, “We expected that mental demands on an operator would result in physiological changes, but the direct correlation between the workload and the skin temperature was very impressive, and counter-intuitive – we were not expecting to see the face getting colder. With this accurate way to estimate workload, we can develop methods that will assist the operator at times of maximum stress.”