Time-estimation error following Weber-Fechner law may explain subadditive time-discounting

Impulsivity in drug addicts have been associated with impatience in intertemporal choice, i.e., high degrees to which delayed rewards are discounted, indicating the importance of reducing the degree of discounting in drug addicts. Intertemporal choice (delay discounting) has been attracting attention in neuropsychopharmacology and behavioral neuroeconomics. Recently, behavioral economists have reported that impatience/impulsivity in intertemporal choice is increased if a delay period is presented as a sum of divided time-blocks, which is referred to as subadditive discounting (i.e., "total patience" over the delay period is larger than the "sum of patience" over divided delay periods). This finding implies that abstinent drug addicts may more readily relapse into addiction if an abstinence period is presented as a series of shorter abstinent periods, rather than a single block of a long abstinence period. Therefore, understanding of neuropsychological processing underlying subadditive discounting is important for establishing medical treatments of drug addiction, although to date, no study has addressed this question. In this study, we propose that time-estimation following Weber-Fechner law, formerly introduced for explaining hyperbolic discounting, may also explain subadditive discounting. Our present hypothesis also predicts that possibility of relapse into drug dependence can be decreased by helping abstinent patients to perceive time-duration of an abstinence/withdrawal period precisely.