INDIVIDUAL-DIFFERENCES IN SENSITIVITY TO BITTER-TASTING SUBSTANCES

Perception of several bitter-tasting compounds was tested in 52 subjec ts. Stable individual differences in the perceived intensity of the bi tterness of suprathreshold concentrations of quinine sulfate (QSO(4)) and urea were found. Whereas 18 subjects judged selected concentration s of these compounds to be equally bitter, 17 found QSO(4) to be more bitter than urea, and 17 found urea to be more bitter than QSO(4). The se reliable individual differences were significantly related to thres hold sensitivity to QSO(4); that is, individuals who perceived QSO(4) to be more intense than urea at suprathreshold concentrations also had lower QSO(4) thresholds than did those who perceived urea to be more intense than QSO(4). There appeared to be no relationship between the relative perceived intensities of these compounds and rating of the bi tterness of PROP (6-n-propylthiouraci). However, QSO(4)-sensitive indi viduals tended to find the bitterness of suprathreshold caffeine and s ucrose octaacetate to be greater than that of suprathreshold magnesium sulfate, whereas the reverse was true for urea-sensitive individuals. This pattern parallels the pattern of cross-adaptation among these co mpounds reported by other investigators. These results are consistent with the existence of multiple bitter transduction sequences and sugge st that individual differences in response to various bitter compounds may reflect differences in the relative availability of specific tran sduction sequences.