When foods or beverages are taken in the mouth, the resulting flavor perceptions emerge from sensory signals activated by stimulating several senses: taste (gustation), olfaction (retronasally, as air-borne particles reach olfactory receptors through the back of the mouth), and somatosensation (texture, warmth, cold, pungency). Flavor perception therefore involves the integration of signals from several modalities. Yet little is known about the mechanisms by which these multisensory signals combine and interact. The proposed research uses state-of-the-art behavioral (psychophysical) methods to test four quantitative hypotheses regarding the ways that gustatory and olfactory constituents of flavors interact in the human perception of flavor intensity and quality. (1) Using a standardized rating method, the first study tests the generality of, and limitations to, the hypothesis that taste and olfaction combine their signals additively in producing overall perceptions of flavor intensity. These experiments will test additivity in an experimental paradigm in which the relative concentrations of the gustatory and olfactory stimuli vary across test sessions to produce different degrees of contextual adaptation, thereby determining whether this adaptation affects additivity. (2) Using a simple response time procedure, the second study tests the hypothesis that the immediate sensory response to a flavor reflects the integration and interaction of signals from the gustatory and olfactory modalities. Integration yields facilitation (faster responses) when the two components are congruent (e.g., sucrose and citral), but less facilitation or even interference (slower responses) when the components are incongruent (e.g., MSG and citral). (3) The third study tests the hypothesis that increasing experience with (exposure to) incongruent flavor mixtures leads to greater facilitation as gauged by simple response time. (4) Using a choice response time method, the fourth study tests the hypothesis that the ability to distinguish different concentrations of a gustatory (or olfactory) flavorant is impaired when an olfactory (or gustatory) flavorant is added, the impairment being greater when the flavor combination is congruent (components less separable) rather than incongruent (more separable). The flavors of foods are important factors in food intake, and hence in the regulation of nutrition and body weight. A better understanding of flavor perception could contribute to the treatment of disorders of eating, nutrition, and body weight.
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