Taste perception arises from stimulation of taste receptors which are composed of modified epithelial cells and found most frequently on the papillae of the tongue throughout the oral cavity, on the hard and soft palates, the pharynx, the larynx, the epiglottis and the esophagus. The taste molecules that interact with these receptors after they dissolve in saliva can be separated into five primary taste qualities. For Toolbox, taste will be defined as sweet, salty, sour, bitter, or umami tastes arising from either whole-mouth stimulation of taste buds or regional stimulation of the front, sides, and rear of the tongue. Other qualities, that have been attributed to taste, are either due to stimulation of other sensory systems (e.g., chalky) or remain controversial as to how they are recognized (e.g., metallic, fatty).
Psychophysical measures of taste can provide data relevant to two separate aspects: the sensitivity of the system to chemical stimuli and the hedonic valence of the sensation. In studies on adults, the distinction between the two is usually unambiguous. Measures of sensitivity include thresholds, just noticeable differences, intensity judgments, sensory adaptation whereas measurements involving a hedonic dimension usually consist of estimates of pleasantness, liking or preference. In studies on children younger than 5 years of age, these two classes of responses to chemical stimuli can be more difficult to distinguish. That is, many response measures are associated with acceptance or rejection and, thus, presumably involve a hedonic component.