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Differential facial responses to four basic tastes in newborns
1Department of Psychology, University of Pennsylvania, Philadelphia 19104.
Insights
Newborns display distinct facial expressions for sweet, sour, and bitter tastes, differentiating them from salt. Adults could identify sweet responses but struggled with nonsweet tastes, suggesting innate taste communication in infants.
Area of Science:
- Developmental Psychology
- Neuroscience
- Sensory Science
Background:
- Taste perception is crucial for survival, guiding nutrient intake and avoiding toxins.
- Facial expressions are a primary mode of communication in infants.
- Understanding infant facial responses to taste provides insights into early sensory processing and communication.
Purpose of the Study:
- To investigate the distinctiveness and recognizability of taste-elicited facial expressions in human newborns.
- To determine if newborns can differentiate between sweet, salty, sour, and bitter tastes through facial expressions.
- To assess adult observers' ability to interpret these infant facial responses.
Main Methods:
- Two studies were conducted with 12 infants within 2 hours of age, presented with sucrose, sodium chloride, citric acid, and quinine hydrochloride solutions.
- Study 1 utilized the Facial Action Coding System adapted for infants (Baby FACS) to objectively analyze videotaped facial responses.
- Study 2 involved untrained adults judging videotaped infant reactions and rating their hedonic tone.
Main Results:
- Newborns exhibited specific facial expressions for sweet (relaxation, sucking), sour (lip pursing), and bitter (mouth gaping) tastes.
- Responses to salty, sour, and bitter stimuli shared negative upper-face components but differed in lower-face actions.
- There was no distinct facial expression for sodium chloride (salty).
- Adult judges accurately identified sucrose responses but made errors with nonsweet stimuli; however, they correctly rated the hedonic tone of bitter responses.
Conclusions:
- Newborns can differentiate sweet from nonsweet tastes and discriminate between sour and bitter stimuli.
- Infant facial expressions for taste are partially recognizable by untrained adults, particularly for sweet and bitter tastes.
- These findings suggest innate, communicative functions for taste-elicited facial expressions in early infancy.
Abstract:
The distinctiveness and recognizability of taste-elicited facial expressions in newborns were examined in 2 studies. Sucrose, sodium chloride, citric acid, and quinine hydrochloride solutions were presented to 12 infants at 2 hours of age. In Study 1, the anatomically based Facial Action Coding System adapted for infants (Baby FACS) was used to obtain detailed, objective descriptions of the infants' videotaped facial responses to each solution. Facial responses to sucrose were characterized primarily by facial relaxation and sucking. The responses to salty, sour, and bitter solutions shared the same hedonically negative upper- and midface components but differed in the accompanying lower-face actions: lip pursing in response to sour and mouth gaping in response to bitter. There was no distinctive facial expression for sodium chloride. These findings demonstrate that newborns differentiate sour and bitter from each other and from salt, as well as discriminating sweet versus nonsweet tastes. In Study 2, untrained adults viewing videotapes of the infants' facial reactions made forced-choice judgments identifying the stimuli presented and rated the hedonic tone of the infants' responses. While the judges accurately identified the newborns' responses to sucrose, there were systematic errors in their judgments of the 3 nonsweet stimuli. The judges' hedonic ratings, on the other hand, clearly differentiated between the infants' responses to the bitter stimulus and the other 3 tastes. The findings are discussed in terms of the possible functional origins and communicative value of taste-elicited facial expressions in infants.