Understanding how people make risky decisions is a promising target for basic scientific research. Although there is much debate on the compensatory rule, the family of compensatory theories has kept its dominant position. This is probably because the compensatory rule is appropriate when decisions will be played multiple times or are made for others. Using research methods and approaches developed in the fields of psychology and neuroscience, the present project explores the boundary of the compensatory and noncompensatory rules in the field of decision making under risk. The findings of this project are expected to gain a better understanding of the underlying mechanism of adaptive decision making under risk.