Gustofacial and olfactofacial responses in human adults.

Adults' facial reactions in response to tastes and odors were investigated in order to determine whether differential facial displays observed in newborns remain stable in adults who exhibit a greater voluntary facial control. Twenty-eight healthy nonsmokers (14 females) tasted solutions of PROP (bitter), NaCl (salty), citric acid (sour), sucrose (sweet), and glutamate (umami) differing in concentration (low, medium, and high) and smelled different odors (banana, cinnamon, clove, coffee, fish, and garlic). Their facial reactions were video recorded and analyzed using the Facial Action Coding System. Adults' facial reactions discriminated between stimuli with opponent valences. Unpleasant tastes and odors elicited negative displays (brow lower, upper lip raise, and lip corner depress). The pleasant sweet taste elicited positive displays (lip suck), whereas the pleasant odors did not. Unlike newborns, adults smiled with higher concentrations of some unpleasant tastes that can be regarded as serving communicative functions. Moreover, adults expressed negative displays with higher sweetness. Except for the "social" smile in response to unpleasant tastes, adults' facial reactions elicited by tastes and odors mostly correspond to those found in newborns. In conclusion, adults' facial reactions to tastes and odors appear to remain stable in their basic displays; however, some additional reactions might reflect socialization influences.