森 兼隆

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.

We investigated how the updating function supports the integration process in solving arithmetic word problems. In Experiment 1, we measured reading time, that is, translation and integration times, when undergraduate and graduate students (n = 78) were asked to solve 2 types of problems: those containing only necessary information and those containing extraneous information. The results indicated that participants required more integration time to solve extraneous-information problems than necessary-information problems. However, the higher the updating, the smaller the increment of integration time. In Experiment 2, we investigated whether different problem models were provided by undergraduate and graduate students (n = 73) with different updating functions. Participants executed a lexical-decision task immediately following an integration process. The lexical-decision task comprised 3 conditions: necessary-information word, extraneous-information word, and novel word conditions. The RTs for both necessary-and extraneous-information word conditions were faster than that for the novel word condition. The facilitation amount in an extraneous-information word became weaker as the problem solver's updating function increased. These results suggest that individuals with a high updating function provide a problem model that maintains only task-relevant information, while those with less-effective updating use an approach that also considers extraneous information. These 2 experiments indicate that updating is an important contributor to the integration process and different updating abilities result in different problem models.