A Appendix
There are two distinct behavioral tendencies in intertemporal choice: Impulsiv-
ity and inconsistency. First, suppose the following Example 1 for demonstrating
impulsivity. Agent A who prefers ”one glass of beer available one year later”
over ”two glasses of beer available (one year plus one week) later” is more im-
pulsive than agent B who prefers ”two glasses of beer available (one year plus
one week) later” over ”one glass of beer available one year later”. In this Ex-
ample 1, most people tend to behave as the patient (less impulsive) agent B.
It is to be noted that both impulsive agent A and patient agent B may be
”rational” in terms of economic theory, because, in this example alone, there is
no inconsistency even in impulsive agent A’s behavior. Next, suppose the fol-
lowing Example 2 for intertemporal choice. There are two options: ”one glass
of beer available now” and ”two glasses of beer available one week later”. In
Example 2, most people (who planned to choose the larger but more delayed
option in Example 1) simultaneously tend to prefer smaller but immediate op-
tion: ”one glass of beer available now” over ”two glasses of beer available one
week later”. This phenomenon is referred to as ”preference reversal” over time,
and an instance of time-inconsistency in decision over time. It is important to
note that impulsivity and inconsistency corresponds to a large time-discount
rate and time-dependency of the time-discount rate, respectively.
B Appendix
Participants (N=9 male, N=12 female, mean age=21.4) were requested to select
among alternatives based solely on their free will, as if choices were about real
money. Instructions were written on the top of each page of the questionnaire
and expressed the temporal distance of delay (i.e., delays of 1 week, 2 weeks, 1
month, 6 months, 1 year, 5 years, 25 years, where each page included all delays
presented in exactly this order). Two columns of hypothetical money amounts
were listed below the instructions. The right column (standard amount) con-
tained 40 rows of a fixed magnitude of monetary gain or loss (10,000 yen, i.e.,
about 100 US dollars). The left column (adjusting amount) listed ascending or
descending magnitudes of money in 2.5% increments (= 10,000 yen × 0.025 =
250 yen) of the alternative in the right column. Participants were instructed
to choose between the two alternatives in each row of the questionnaire. Fur-
thermore, participants were directed to attend to the directions on the top of
each page (containing each delay) of the questionnaire, as the temporal dis-
tance would change over the course of the experiment. Thus, subjects chose
between the delayed-standard amount and the immediate-adjusted amount of
money. The order of the descending and ascending conditions was counterbal-
anced. The indifference points of delay discounting tasks were defined as the
means of the largest adjusting value in which the standard alternative was pre-
ferred and the smallest adjusting value in which the adjusting alternative was
preferred. Next, the mean of the indifference point in ascending and descending
adjusting amounts were calculated for the delay conditions (gain and loss) for
each participant.