INDIVIDUAL-DIFFERENCES IN SENSITIVITY TO BITTER-TASTING SUBSTANCES

Perception of several bitter-tasting compounds was tested in 52 subjects. Stable individual differences in the perceived intensity of the bitterness of suprathreshold concentrations of quinine sulfate (QSO(4)) and urea were found. Whereas 18 subjects judged selected concentrations 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). These reliable individual differences were significantly related to threshold 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 bitterness of PROP (6-n-propylthiouraci). However, QSO(4)-sensitive individuals tended to find the bitterness of suprathreshold caffeine and sucrose 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 compounds reported by other investigators. These results are consistent with the existence of multiple bitter transduction sequences and suggest that individual differences in response to various bitter compounds may reflect differences in the relative availability of specific transduction sequences.