As soon as you taste it... Taste detection and discrimination responses vary with hedonic value.

The sense of taste is crucial for the evaluation of food, promoting the ingestion of nutrients, while helping us avoid possibly toxic substances. Humans are innately able to discriminate between taste categories (e.g. Cowart, 1981), yet it is unclear whether discrimination occurs instantaneously, or whether a general taste detection precedes taste category discrimination. Behavioral evidence suggests faster detection than discrimination in the gustatory system (e.g. Halpern, 1986), yet it is unclear whether such differences occur during early neural, or later decisional processes. We investigated this question using both behavioral responses and multivariate classification analysis of 64-channel scalp electrophysiological recordings obtained from 20 participants during two tasks: detection of salty, sour, sweet, or bitter and binary discrimination between sour and salty and between sweet and bitter. We found that both behavioral and neural responses were significantly faster in detection of salty and sour tastes than their discrimination, yet no such difference was observed for sweet and bitter tastes. One factor contributing to this contrast-dependent result is likely task difficulty, as accuracy rates were markedly higher for the detection of salty and sour tastes as compared to their discrimination, whereas sweet and bitter detection and discrimination accuracy was similar. The major difference between the two contrasts is the hedonic value of the tastes, such that salty and sour are similarly pleasant, whereas sweet and bitter differ significantly in pleasantness. Together, our findings suggest that the human gustatory system does not necessarily discriminate taste categories as quickly as it detects a taste event, but rather that it quickly discerns its hedonic value (cf. Sewards, 2004)