Tuesday, 22 July 2014
Rachael Jack and her colleagues developed computerised 3-D faces that began neutral and relaxed before transforming over one second into a random expression, created through a combination of different facial muscle movements. These standard facial actions were digitised from recordings of real people, then tweaked to create variants with different speeds of transformation (see video, above).
Sixty Western Caucasian participants (31 women) then categorised each random expression as either: happiness, surprise, fear, disgust, anger or sadness. When observers agreed in their categorisations it meant something was signalling emotional information, and a technique called reverse correlation was applied across all the expressions to establish which muscle movements were associated with which emotions, and when. Many of these were expected, such as perceiving happiness in a raised upper lip and a wide mouth, but other findings were more surprising.
Whereas happiness and sadness were identifiable early on, other emotions took time to be distinguished. For example, for both surprise and fear, the same two early facial signals were involved early - dropping of the jaw and raised eyelids. It was only with the later appearance of raised eyebrows that surprise was distinguished from fear. A similar pattern was found with anger and disgust, with facial actions common to both (wrinkled nose, funnelled lips) appearing early, and the differentiator (a sneered upper lip for disgust) appearing later. It is thanks to the researchers’ unique dynamic stimuli that these unfolding processes have been uncovered for the first time.
Jack and her team argue that the four emotions that take time to be distinguished (fear, surprise, anger and disgust) fall into two categories: a “what the heck” avoidance response to a sudden fast-approaching threat, and a “something needs dealing with” approach response to an interest or problem within our midst. They see each of these categories as a single basic emotion, with the later distinction (fear or surprise; anger or disgust) adding social information to the more fundamental biological signal. Their argument would suggest there are four basic human emotions (approach, avoidance, happiness, sadness), contradicting the existing emotion framework, which states there are six basic emotions.
The debate over the precise number of basic human emotions is likely to run for a while yet. For example, another taxonomy, based on analysis of voice, touch, and posture, claims that there are several basic forms of happiness, even before counting varieties of the other emotions.
Jack, R., Garrod, O., & Schyns, P. (2014). Dynamic Facial Expressions of Emotion Transmit an Evolving Hierarchy of Signals over Time Current Biology, 24 (2), 187-192 DOI: 10.1016/j.cub.2013.11.064
Thanks to Rachael Jack for permission to use the video and image from the study.
Post written by Alex Fradera (@alexfradera) for the BPS Research Digest.