Friends of the Nonverbal Communication Blog, this week we present the paper “Assessing pain by facial expression: Facial expression as nexus” de Prkachin, K. M. (2010) in which the author makes a revision about what are the movements that scientifically have been associated with pain through recent research.

When it comes about the study of nonverbal expressions of emotions, there is great interest in identifying the exact movements that represent each one of them.

The reality is that there is no completely precise answer, and there are many elements to pay attention to if we want to be able to say that we infer the presence of one or another emotion. Nevertheless, it is true that over recent years research with scientific validity has been carried out, in which we can observe a series of movements that are repeated in the expression of emotions.

Consequently, the author of this article wants to make a review of facial movements that have been associated with the emotion of pain.

Evolution has equipped us with complex systems for treating injuries, many of which depend on our behavior.

In the case of adults, there is a language that allows us to talk about pain, its causes, and the options to deal with it in the best way. If we talk about babies, it will be the parents who would have to describe the behaviors they use to infer whether their child is in pain or not. We can therefore affirm that behaviors related to pain are mainly communicative.

Charles Darwin, to whom we owe the first research about the facial expressions of emotions, mentioned that when it came about pain the mouth could be compressed, the lips were retracted, the teeth clenched, and the eyes opened with horror.

However, Darwin’s contribution to the study of pain expression, as well as his much broader contribution to the study of facial expressions, was largely forgotten for many years.

And although interest in studying emotional facial expressions was lost for a few years, there were some experts who took over from Darwin. For example, Hollander studied pain experimentally, placing a metal grater under a cuff to measure blood pressure and inflating it, watching the subjects wince at pain.

On the other hand, Chapman and Jones also conducted experimental studies on pain and observed a contraction of the eyelids in the outer area of ​​the eyes, even when they asked the subjects to try not to make any movement.

In a later work, also by Chapman, it was suggested that neurotic patients had a pain reaction to milder stimuli than other subjects.

These studies show that almost all inferences about pain arise from observations of behavior, so research focused on it and how to measure it.

As the behavior that was most recognized as a manifestation of pain was facial expression, it was the one that the experts chose to carry out most of the investigations. It thus offered a basis for establishing more objective measurement rules.

Among the attempts to classify facial expressions, the most influential and used by experts is the Facial Action Coding System (FACS) by Ekman and Friesen. In it, they describe facial expressions in 44 action units, which are changes produced by movements of facial muscles. From its creation, it was a way of measuring facial expressions that gradually gained strength among experts, who used it for their studies.

LeResche used the FACS to describe the facial expressions depicted in real photographs of people in extreme pain. He concluded that there was a characteristic expression of pain, which included the lowering of the eyebrows, the tight skin around the eyes and an open mouth, stretched horizontally, with a deepening of the nasolabial fold.

Craig and Patrick, on the other hand, and also using the FACS, reported that they observed, in pain, an elevation of the cheekbones, squeezing of the eyelids, elevation of the upper lip, and pulling of the corners of the lips.

As there was a relative coherence between all the empirical research on facial expressions associated with pain, the idea that there was a possibly universal expression for it gained weight.

Noting the success of the FACS, Grunau and Craig developed the Neonatal Facial Coding System (NFCS) for newborn children. These subjects have a skin and a neuromuscular system whose differences with those of adults make the application of the FACS complicated for both.

With this system, some elements that were associated with pain in young babies were identified, such as a bulging of the forehead, the contraction of the eyes, the deepening of the nasolabial fold or the opening of the lips.

There are, therefore, similarities between the facial actions associated with pain in adults and in newborns, which is why it is suggested that there is a continuity in the expression of this emotion from birth to maturity.

And since most of the actions associated with pain require the participation of the corrugator muscle, the orbicularis oculi, and the elevator, it is suggested that researchers interested in evaluating the expression of pain can focus their attention on this area of the face, where the key information concentrates.

One limitation of the FACS is that it takes a considerable amount of time to train on it. In addition, a quality observation time is also needed.

However, it is one of the most useful tools to study, know, identify and research on facial expressions so far.


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