Written on the face - What facial expressions reveal about basic tastes

“Ugh, blah! That tastes terrible!” When you can see the person’s face as he eats, such exclamations are usually superfluous. Such spontaneous facial expressions speak an unequivocal language, one that is universally understood. But do these non-verbal facial reactions communicate their information when the tastes are more subtle and thus provide additional information to measuring responses in classical sensory tests? Swedish and Danish European Sensory Network researchers have taken a close look at the question.

Facial reactions to specific sensory stimuli are innate. This has been shown in studies using video recordings of new-born children who were given either sweet or bitter drops on their tongues. Regardless of the cultural circle from which the children came, they reacted with facial expressions that adults could recognize as corresponding to dislike or satisfaction. Adults likewise respond spontaneously to basic tastes in a very similar manner. Sweet and salty stimuli also elicit corresponding facial expressions. Up until now experts have believed these differences in expressions were not so strong that the observer could unequivocally link the taste quality to the corresponding facial expression. As part of a collaborative project between the Swedish Institute for Food and Biotechnology (SIK) and the Faculty of Life Sciences at the University of Copenhagen (KU-LIFE), visiting scientist Karin Wendin and co-workers from KU-LIFE have examined what expressions reveal about basic tastes and how the tastes’ perceived intensity and hedonic rating is reflected.

To this end the researchers presented to each person in a group of 21 trained sensory assessors three samples of sweet, salty, bitter, sour, umami (monosodium glutamate) water-based solutions, each sample with a different strength, and a single neutral sample containing pure water. This tasting in the observational laboratory at KU-LIFE was recorded on video. The assessors were asked to indicate the basic taste of each individual sample, rate its intensity, and, using a nine-point hedonic scale, indicate how pleasant or unpleasant the taste was. The facial expressions on the video recordings were coded and analyzed using facial recognition software. The assessors’ facial reactions were then rated separately by two trained observers. The observers identified twelve characteristic facial reactions that the assessors exhibited as they tasted the different samples and judged their quality and intensity.

Impact of taste intensity and (un)pleasantness

Thus it was clear that the facial reactions were not caused by the quality of the basic taste alone; intensity and pleasantness were also factors. With few exceptions, the facial reactions were the more pronounced the more intense and unpleasant the taste of the sample. However, even neutral-tasting water caused discernable facial reactions, such as pressing the lips together, frowning, and opening the mouth.

The reactions to bitter and sour were significantly different. The assessors reacted to the bitter stimuli by frowning, wrinkling the nose, eye widening, and squinting (eye diminishing). Their reaction to sour stimuli was frowning, pressing the lips together, pursing the lips, and lip corners turned down.

Differences in the facial reactions to bitter and salty stimuli were less pronounced. The sensory assessors reacted to both the bitter and the salty stimuli with frowning, nose wrinkling, eye widening, and eye diminishing. In this situation, more subtle differences were first recognizable when all the facial reactions were viewed together, comparing the relationship to each other using the Principal Component Analysis (PCA). This shows that the assessors tasting higher level salt samples also widened their nostrils and turned down the corners of their lips. They also did this when tasting light and medium bitter samples, but not when the sample had a very bitter taste.

Faces express dislike more clearly than positive sensations

The basic sample tastes of umami and sweet were both perceived as quite pleasant and evoked facial reactions that were of low intensity. At first glance these were scarcely different from the reactions to pure water. It was only after using the Principal Component Analysis that it was determined that the assessors had reacted more often with “lip corner up” to higher levels of umami and less often with “frowning” and “eyes diminishing” to the sweet stimuli.

Project leader Karin Wendin concluded that, “This study showed that facial expressions seemed suitable for measurement of dislike but not for measurements of liking or for neutral impressions. We were able to show for the first time that facial reactions may indicate differences in both the quality of the stimuli and their concentration. ” (isi / esn)

Source:
Karin Wendin, Bodil H. Allesen-Holm, Wender L.P. Bredie
Do facial reactions add a new dimeinsion to measuring sensory responses to basic tastes?
Food Quality and Preference, Volume 22, Issue 4, June 2011, Pages 346-354
doi:10.1016/j.foodqual.2011.01.002

The European Sensory Network (ESN; www.esn-network.com) is an international association of leading academic and research institutions in the field of sensory and consumer sciences. Presently the network comprises 26 member organisations from 21 countries. ESN members share their knowledge and work towards standard methodologies.

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