A hyperbolic decay of subjective probability of obtaining delayed rewards.
BACKGROUND
Hyperbolic discounting of delayed and probabilistic outcomes has drawn attention in psychopharmacology and neuroeconomics. Sozou's evolutionary theory proposed that hyperbolic delay discounting may be totally attributable to aversion to a decrease in subjective probability of obtaining delayed rewards (SP) which follows a hyperbolic decay function. However, to date, no empirical study examined the hypothesis, although this investigation is important for elucidating the roles of impatience, precaution, and uncertainty aversion in delay discounting processes.


METHODS
In order to (i) determine the functional form of the relation between delay until receipt and SP, and (ii) examine whether delay discounting is attributable to a decrease in SP, we assessed the subjects' SP and their delay and probability discounting. We examined the fitness of hyperbolic and exponential functions to the assessed SP, and relations between the SP, and delay/probability discounting, and subjective-probability discounting for delayed rewards.


RESULTS
The results demonstrated (a) SP decayed hyperbolically as delay increases, (b) a decay of SP was associated with delay discounting, and (c) subjective-probability discounting did not significantly correlate with delay discounting.


CONCLUSIONS
Our results demonstrated (i) hyperbolic decay of SP is related to delay discounting, and (ii) delay discounting is, however, not attributable to precautious foresight in intertemporal choice. Further, a novel parameter of pure time preference is proposed.
Takahashi
Taiki
T
Department of Life Sciences, Unit of Cognitive and Behavioral Sciences, School of Arts and Sciences, The University of Tokyo, 21 COE office, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902, Japan. taiki@ecs.c.u-tokyo.ac.jp.
Ikeda
Koki
K
Hasegawa
Toshikazu
T