Do observers use the same facial movements that encode pain when inferring pain in others?

In this issue you will find a paper by Roy et al., entitled ‘Efficient information for recognizing pain in facial expressions’ (Roy et al., 2015). In this study, the authors tried to identify which are the critical facial features that trigger the accurate inference of pain by human observers, a topic we know very little about. The process of communicating pain through facial expressions has been conceptualized into an ‘encoding process’, where the experience of pain is encoded in particular facial muscle movements and a ‘decoding process’ where these facial movements are broadcasted into the social world where they may be decoded by others. With regard to the encoding process, extensive research has already been conducted and we know that there is a small subset of facial movements that reliably occur in the context of experimental and clinical pain. This subset encompasses the tightening of the muscles surrounding the eyes, furrowed brows, raising the upper lip/nose wrinkling, eye closure as well as opening the mouth and raising the eyebrows (Prkachin, 1992; Kunz and Lautenbacher, 2014). We also know that this subset does not represent an invariant and uniform facial activity pattern of pain but that individuals often display only parts of this subset, with the tightening of the muscle surrounding the eyes being the most prominent facial movement occurring during pain (Kunz and Lautenbacher, 2014). Roy et al. (2015) are now interested in whether observers use the same subset of facial movements that have been shown to encode pain when inferring pain in others. They tried to answer this question by choosing a very interesting experimental approach, namely by using the Bubbles technique to identify which parts of the face are used by observers to accurately recognize facial expressions of pain. The authors used photos showing posed (actor portrayals) facial expressions of pain and the six basic emotions, and used the Bubble technique to alter these photos so that varying facial features of the face were revealed, while most of the face was hidden (see examples displayed in Roy et al., 2015). The main finding was that the accurate inference of pain by human observers mostly relied on the features ‘furrowed brows’ in addition to the mouth region. This is a somewhat surprising finding because the overlap between facial movements which are encoding pain and those which are used for decoding pain is rather small. Out of the subset of six facial responses that accompany the pain experience (Prkachin, 1992; Kunz and Lautenbacher, 2014), it is mostly only one movement, namely ‘furrowed brows’ that trigger the accurate inference of pain by human observers. And whereas the tightening of the muscle surrounding the eyes is the most frequent movement for the encoding of pain, this movement does not seem to be important at all for the accurate decoding of pain. Roy et al. (2015) findings that the facial movements accompanying pain are not identical with the facial movements that trigger the accurate recognition of pain have important clinical implications, especially for pain assessment in patients with dementia, who are no longer able to provide selfreport ratings. Many observational pain scales for assessing pain in patients with dementia have been developed in the last decade and all of these scales include facial items (Corbett et al., 2014). Despite the agreement that facial items are essential when trying to infer pain in others, the items used to describe pain-indicative facial responses vary substantially between observational scales. Many include items like ‘frowning’, ‘opened mouth’ or ‘narrowing eyes’. This selection is based on findings from encoding studies. Given that Roy et al. could now demonstrate that observers do not necessarily use the same facial movements that encode pain in the decoding process, it is possible that present observational scales for pain assessment do not contain the best facial items.