TASTE PSYCHOPHYSICS

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Taste stimuli in the real world (tap water, foods, beverages) contain substances that taste different to some individuals and taste different on different tongue locations. We propose to study this variability both to understand its origins and to characterize more accurately the taste world in which people live. Taste thresholds for the bitter substance PTC (phenylthiorcarbamide). PROP (6-n-prophylthiouracil) show a bimodal distribution, leading to the designation "tasters" for the more and "nontasters" for the less sensitive. Family studies suggest that nontasting is a simple Mendelian recessive trait. The taste worlds for these two groups are known to be different for certain bitter and sweet compounds (e.g., sucrose, saccharin and KCl). For example, in one study stimulating the front of the tongue, tasters perceived sucrose to be about twice as sweet as nontasters did. One of the major objectives of this proposal is to test additional compounds to characterize the differences between tasters and nontasters. The differences will be evaluated with both threshold and suprathreshold (e.g., magnitude estimation and magnitude matching) procedures. Topical exposure fo the tongue to constituents of the common globe artichoke (e.g., potassium chlorogenate) induces a sweet taste in water. This phenomenon occurs only in certain subjects but no family studies exist to support any particualr model of genetic transmission. Sensitivity to this phenomenon will be evaluated with the same methods used in the PTC/PROP studies. Taste perception varies with the locus of the stimulus in the oral cavity. A second major objective of this proposal is to evaluate the spatial properties of the tongue. This is an important research problem in its own right but, in addition, regional sensitivities may play a role in the differences between tasters and nontasters. Spatial properties of the tongue will be studied by stimulating limited areas and by selective application of a topical anesthetic. The information generated by these studies will be relevant to several health issues. Genetic variability in the perceived sweetness of sucrose and artificial sweetners impacts on dental as well as other medical problems. All the studies are relevant to the evaluation of taste loss. The threshold studies will contribute to the improved evaluation of trace tastes (e.g., "off" tastes in tap water).