Kanetaka Mori

Individual taste sensitivity influences food preferences, nutritional control, and health, and differs greatly between individuals. The purpose of this study was to establish a method of measuring and quantifying an individual's taste sensitivity and to evaluate the relationship between taste variation and genetic polymorphisms in humans using agonist specificities of the bitter taste receptor gene, TAS2R38, with the bitter compound 6-n-propylthiouracil (PROP). We precisely detected the threshold of PROP bitter perception by conducting the modified two-alternative forced-choice (2AFC) procedure with the Bayesian staircase procedure of the QUEST method and examined genetic variation in TAS2R38 in a Japanese population. There were significant differences in PROP threshold between the three TAS2R38 genotype pairs for 79 subjects: PAV/PAV vs AVI/AVI, p < 0.001; PAV/AVI vs AVI/AVI, p < 0.001; and PAV/PAV vs PAV/AVI, p < 0.01. Our results quantified individual bitter perception as QUEST threshold values: the PROP bitter perception of individuals with the PAV/PAV or PAV/AVI genotypes was tens to fifty times more sensitive than that of an individual with the AVI/AVI genotype. Our analyses provide a basic model for the accurate estimation of taste thresholds using the modified 2AFC with the QUEST approach.

We investigated whether individual differences in visual updating function are important in solving arithmetic word problems. First, undergraduate and graduate students (n = 47) solved area word problems, some presented with extraneous information. We measured several components of reading time for the problems (e.g., integration time) and tested participants' updating functions in the phonological and visual domains. The results indicated that a stronger phonological or visual updating function reduced the effect of extraneous information on integration time, showing that both phonological and visual updating contributed to the integration process. Second, participants (n = 49) solved area problems presented in a figure format. The results suggested that only the visual updating function made a significant contribution to reducing integration difficulty. We infer that individual differences in the visual updating function are important to arithmetic problem solving when the category of problem or problem format requires problem-solvers to manipulate visual information.