Taste-acceptance and taste-aversion reflected by behavioral manifestations in man and animals

Abstract

Sensations and feelings, aroused by sensory stimuli are inaccessible to direct measurements. For collaborative human examinees, above verbal age, psychophysical testing methods can be used, in order to assess stimulus-identification as well as semiquantitative estimates reflecting on intensity and pleasurability (hedonics) of sensations.Taste- and odor-cues, for both man and animals, are known to be polarized between "pleasant" and "aversive" qualities. These hedonic differences were found to release in man distinct and differential, fixed oral and facial motor-behaviors. Since infants at perinatal age, prior to any food-intake experience, were found to respond differentially to sweet and bitter tastes, these behavioral displays can be seen as innate and probably even inherited competencies of the nervous system. Observations on infants, born with severe developmental malformations of the forebrain revealed identical reactivity to that found in the normal termborn neonate. It is, therefore, evident that taste-induced behaviors are primarily controlled by the brainstem. Further experiments revealed, that odor stimuli too can also trigger differential facial expressive behaviors. These reactions were termed: GUSTOFACIAL- and NASOFACIAL-REFLEXES, respectively. Using a multidisciplinary approach, both psychophysical and facial responses of young healthy human examinees were simultaneously recorded. These studies evinced that taste- and odor-induced facial expressions are as sensitive hedonic indicators as are semiquantitative psycho-physical hedonic estimates. Later studies revealed, that nonhuman primates, (monkeys and apes), as well as other mammals, and some other animal species display taste-induced oral or facial responses, similar and analogous to the human gustofacial reflex.