The Psychological Record, 2005, 55, 439-460
DELAY OF GRATIFICATION AND DELAY DISCOUNTING: A UNIFYING
FEEDBACK MODEL OF DELAY-RELATED IMPULSIVE BEHAVIOR
BRADY REYNOLDS
The University of Chicago
RYAN SCHIFFBAUER
West Virginia University
Delay of Gratification (DG) and Delay Discounting (DO)
represent two indices of impulsive behavior often treated as
though they represent equivalent or the same underlying
processes. However, there are key differences between DG and
DO procedures, and between certain research findings with each
procedure, that suggest they are not equivalent. In the current
article, evidence is presented to support the argument that DG and
DO measure discrete, yet related, processes involved in delayrelated impulsive behavior. Also presented is a theoretical
"feedback model" for the relation between DG and DO. In the
model, it is proposed that the processes measured by DG are less
cognitive and less learning-mediated than those measured by DO.
However, as proposed, ability to sustain choices for delayed
rewards (DG) is still represented in the choice processes
measured by DO through an individual's learning history with DG
types of situations; that is, the less a person is able to sustain
choices for delayed rewards the more likely he or she will be to
choose immediate rewards when given choices between larger
delayed and smaller but more immediate options. The proposed
model is consonant with observed consistencies and differences
between DG and DO measures. From the proposed model, new
research questions arise that would be lost in a continued
conceptualization of DG and DO as equivalent measures.
One of the goals of this article is to outline a theoretical framework for
the relation between the behavioral processes measured by delay of
gratification (DG) and delay discounting (DO) procedures. Generally, DG
is a model and measure of impulsive behavior originating out of the fields
of developmental and personality psychology. This procedure assesses
an individual's "willpower" in sustaining choices for delayed rewards
without defecting during a delay-to-reward period to an initially less
preferred, nondelayed option. By contrast, the psychological study of DO,
Correspondence may be sent to Brady Reynolds, PhD., Columbus Children's
Research Institute, Department of Pediatrics, The Ohio State University, 700 Children's
Drive, J1401, Columbus, OH 43205. (E-mail : reynoldb@ccri.net).
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REYNOLDS AND SCHIFFBAUER
also considered a model and measure of impulsive behavior, came from
the field of behavior analysis and was originally based on nonhuman
animal research. Human DD procedures have been developed to assess
discounting behavior through initial choice preference between larger,
delayed and smaller, nondelayed rewards. However, interpretations of
DD findings have typically emphasized stimulus control (e.g., reward
quality or delay lengths) instead of internal governing processes.
Given some of the impulsivity/delay-related similarities between
these measures, it is not surprising that many researchers who publish
w ithin the relevant literatures treat the two procedures as though they are
equivalent (e.g. , Evenden & Ryan, 1996; Green, Fry, & Myerson, 1994;
Johnson & Bickel, 2002; Mischel, Shoda, & Rodriguez, 1989; Schweitzer
& Sulzer-Azaroff, 1995); or, in some instances, unambiguously assert that
DG and DD should be regarded as measuring the same processes
(Rachlin , 2000). However, perhaps due in part to these procedures
originating from different subdisciplines of psychology, DG and DD have
not been studied in humans in a manner allowing direct comparisons
between the two procedures. Therefore, very little actual data exist that
specify the relation between these two models of impulsivity.
The thesis of the current article will be that DG and DD procedures
measure discrete, yet related, aspects of impulsive behavior. As will be
expanded on in following sections , DG and DD as measures of
impulsivity are undoubtedly related; however, even without direct human
laboratory comparisons, there are still "real world" circumstances under
which these two procedures appear to reflect different underlying
processes . These apparent differences may hold promise for a more
complete and useful understanding of delay-related impulsive behavior.
The present article is intended to (a) serve as a review of the DG and
DD assessment procedures and the processes believed to influence
behavior during each procedure, (b) demonstrate through illustrative
argument and example that DG and DD procedures measure different
aspects of impulsive behavior, and (c) propose a theoretical framework
for the relation between the different processes measured by DG and DD.
From the proposed framework, novel research questions will emerge that
should lead to a more complete analysis of delay-related impulsive
behavior as defined by DG and DD.
Delay of Gratification and Delay Discounting
Delay of Gratification
As already described, the DG procedure is a measure of ability to
sustain a choice for a delayed reward while a smaller immediate reward
is continually available (e .g., Mischel, 1966). In the most common DG
procedure for children, primary reinforcers (cake, cookies, etc.) are
normally used. In th is procedure, participants are seated at a table and
presented with a choice between a larger or more preferred reward and
a less preferred reward (e.g., Mischel & Baker, 1975; Mischel & Ebbesen ,
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
441
1970). Once participants choose the preferred option, they are instructed
that they may have their preferred-choice item when the experimenter
returns (the delay to which is not specified but is usually 15 to 20 min) or
that they may have the less preferred option immediately or at any time
during the delay period by ringing a bell that is on the table. If a participant
rings the bell and receives the less preferred option, he or she can no
longer receive the initially preferred delayed option. Interindividual
differences in the length of time participants are able to wait before
ringing the bell are taken to reflect individual differences in "self-control"
or "willpower," with shorter delay periods indexing impulsivity.
In interpreting findings with this DG procedure, Mischel and colleagues
have focused on behavioral inhibition on the part of the individual as the key
determinant of interest (e.g. , Metcalfe & Mischel, 1999; Mischel et aI., 1989).
Attributing causality to personal-agency variables, olr determinants within the
organism, is consistent with personality theory, which emphasizes the
analysis of interindividual differences in behavior independent of what might
be considered stimulus control (e.g., Allport, 1961 ; Grant & Dweck, 1999;
Mischel, 1990; Reynolds & Karraker, 2003). Though considerable DG
research has explored the impact of situational manipulations on DG
performance (see below), the underlying emphasis in interpreting the
resultant effects has been on how these manipulations influence internal
processes invoked by the DG procedure.
Metcalfe and Mischel (1999) have described a two-system model
composed of "hot" and "cool" systems that characterize the underlying
processes believed to determine performance in the DG procedure. Their
model parallels in some ways the development and functioning of the
human brain. The hot system in their model does not represent selfcontrol, but rather reflects pure, unmediated responding to environmental
stimuli. They suggest that this system may be represented in the
amygdala, which is functional at birth. Conversely, the cool system in their
model represents the development of self-control, or the ability to inhibit
responses by the hot system to salient environmental stimuli. They posit
that this cool system may be represented in the hippocampus and frontallobe structures of the brain, which develop and become increasingly
functional later in childhood.
The cool system in this model of impulsive behavior (Metcalfe &
Mischel, 1999; Mischel, Cantor, & Feldman, 1996; Mischel et aI., 1989;
Sethi , Mischel, Aber, Shoda, & Rodriguez, 2000) represents an active
process on the part of the individual to resist the "temptations" of the
highly stimUlus-responsive hot system . Interindividual differences in
ability to delay gratification, as measured by the DG procedure, constitute
differences in cool-system functioning. Those individuals who have weak
cool systems in terms of behavior inhibition are more impulsive and have
a harder time willfully delaying gratification.
To support their model, Mischel and colle,agues cite a number of
findings that conform to predictions derived from the model. For example,
younger children are clearly less capable of delaying gratification than
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REYNOLDS AND SCHIFFBAUER
older children (e.g ., Mischel, 1966), which is consistent with the
maturational aspect of the model. Also, having the stimulus present
during the delay period decreases ability to delay gratification compared
to not having the stimulus present (Mischel & Ebbesen, 1970). This
finding did not support the original hypothesis that having the stimulus
present would lead to longer DG times rather than shorter times. It was
hypothesized that having the stimulus present would serve to remind
participants of what they were waiting for, thus making it easier to sustain
the original choice. Finding that DG times were actually reduced by
having the stimulus present suggests that there may have been
properties of the stimulus (e.g., smell) that made it more difficult to resist
when present. Interestingly, having a life-size color photograph of the
stimulus instead of the actual stimulus did lead to DG times that were
twice as long when compared to having a similar photograph of a neutral
object (Mischel & Moore, 1973). This finding supports the hypothesis of
the earlier studies. Therefore, these photograph findings actually support
the interpretation that DG times were shorter when the stimulus was
present because of certain properties of the stimulus that made it more
difficult to resist.
Another interesting finding involves the development of effective selfregulatory strategies (Mischel & Mischel, 1983). When 4-year-old children
are given the option of either obscuring or not obscuring the salient
features of a stimulus during the delay period of the DG procedure, they
typically choose to have the stimulus present, thus undermining their own
efforts to delay gratification. However, 5- or 6-year-olds (and older
children) more often choose to obscure the saliency of the stimulus
during the delay period. It appears that children generally learn at a
relatively early age that it is important to reduce the saliency of the
stimulus in their efforts to delay gratification. In terms of individual
differences in DG performance, research focusing on strategic attention
deployment has shown that those children who spontaneously look away
from the stimulus object or distract themselves in other ways have
consistently longer delay times (e.g., Peake, Hebl, & Mischel, 2002;
Rodriguez, Mischel, & Shoda, 1989). Further, this type of attention
deployment has even been observed through mother-toddler interactions
in which the toddler distracts himself or herself during what are typically
distressing separation periods from the mother. Even at such an early
age, high levels of toddler attention diversion during separations from the
mother have been found to be significantly related to DG performance
later in preschool, with those who diverted attention more as a toddler
delaying gratification longer in preschool (Sethi et aI. , 2000).
The ability to delay gratification in preschool also has been a
remarkably robust predictor of later developmental outcomes.
Longitudinal research using DG procedures has revealed predictive
positive relations between a preschooler's ability to sustain a choice and
later parental ratings during adolescence for academic and social
competency, ability to deal with stress and frustration, and ability to pursue
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
443
goals (Mischel , Shoda, & Peake, 1988). Significant positive relations also
have been found between an earlier ability to delay gratification and later
verbal and quantitative SAT scores (Shoda, Mischel, & Peake, 1990).
Longitudinal links have even been found between measures of DG in
preschool and later measures of social and cognitive competencies and
ability to self-regulate in early adulthood (Ayduk, Mendoza-Denton, Mischel ,
Downey, Peake, & Rodriguez, 2000). These deve~opmental findings (i.e.,
that DG can be measured at such an early age and that these early
measures are predictive of individual differences into early adulthood)
suggest that an individual's capacity to sustain choices for delayed rewards
may be a person characteristic (similar to other person characteristics like
intelligence or activity level) that is influential in shaping long-range
developmental outcomes (e.g. , Scarr, 1997). In other words, the above
research findings are consistent with the notion that ability to sustain choices
for delayed consequences is an early-emerging personality characteristic
foundational to subsequent developmental outcomes involving delayed
consequences. As will be described in later sections, this characterization of
DG processes as a developmentally foundational person characteristic will
become important in conceptualizing the relation between the processes
measured by DG and DD.
Delay Discounting ·
In contrast to DG procedures, DD procedures focus on initial-choice
responses . These "commitment-choice" procedures typically present
choices between larger delayed and smaller but more immediate
reinforcers. Once a choice has been made, the participant is committed
to it until the next trial-that is, there is no requirement to sustain a choice
in that there is no opportunity to defect to the more immediate option after
having made a choice for the delayed reward.
With DD research originating largely in the field of behavior analysis,
which emphasizes stimulus control and overt behavior (e.g., Skinner,
1938), DD researchers have historically avoided performance
interpretations involving specific internal processes or person
characteristics (e.g., Ostaszewski & Karzel, 2002; Rachlin, 2000).
However, some researchers have begun to explore the underlying
cognitive processes involved in DD (Hinson, Jameson, & Whitney, 2003) ,
developmental topics related to DD (Green et aI., 1994; Reynolds,
Karraker, Horn , & Richards, 2003) , and specific brain mechanisms
implicated in DD performance (e.g., Cardinal, Pennicott, Sugathapala,
Robbins, & Everitt, 2001; Wade , de Wit, & Richards, 2000) . These
research efforts are more recent, and the fact that DD research has
traditionally emphasized stimulus control and overt behavior and avoided
the internal processes emphasized in most DG research has likely
precluded a better understanding of the relation between DG and DD .
Procedures for assessing DD in humans usually take the form of
hypothetical choices in which a participant is asked to choose between
different monetary alternatives (one delayed and one immediate). More
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REYNOLDS AND SCHIFFBAUER
specifically, DD procedures are intended to assess the pattern of
devaluation that occurs for an individual when a delay is added to the
delivery of a particular reward. For example, consider two choice options:
$5 or $10. All things being equal, it can be assumed that most individuals
would choose the latter option . However, if a delay to the delivery of the
$10 were added and incrementally increased, the $10 reward would
begin to decrease in subjective value with increasing delay. Eventually,
with the addition of a sufficient delay, the $10 would actually be of less
subjective value than the alternative $5, causing a preference shift
towards the smaller reward. For example, an individual may prefer $10 to
$5 when the $10 is delayed by a week, but instead prefer the $5 when
the $10 is delayed by a year. Individuals who shift their preference earlier
(i.e. , with a shorter delay) are considered more impulsive.
By analyzing the points at which shifts in preference occur (also
called indifference points) over multiple delays, the rate at which
discounting occurs as a function of increasing delay can be quantified.
Curves representing rate of discounting as a function of delayed rewards
are best represented by a hyperbolic function (Mazur, 1987),
Value = A/(1+kO) ,
(1 )
where Value represents the value of the delayed reward , A and 0 are the
amount of reward and length of delay to its delivery, respectively; and k
is a free parameter. The k parameter, which represents the steepness of
an individual's discounting curve, serves as a parametric value
operationalizing impulsivity, with higher k-values indicating greater
discounting and impulsivity. Some authors also have included an
exponent, which can yield a more precise fit to the data (e.g. , Green et
aI., 1994).
Conceptually, the Hyperbolic Temporal Discounting Model - (e.g.,
Rachlin, 2000) is the model used to represent the processes measured
by DD procedures. Generally, this model, as represented by Persons A
and B in Figure 1, illustrates the subjective values (the curves of the
graphs) for smaller more immediate rewards relative to more delayed but
larger rewards. From left to right, both graphs show the value of a given
reward as the time to its attainment draws near. In both graphs, and for
each reward , the model illustrates the observation that a reward
increases in value shortly before it is to be obtained, but that it decreases
in value (hyperbolically) when its delivery is more temporally distal.
More specifically from Figure 1, to represents the point at which a
particular smaller-sooner reward (e.g., $5) is to be given , whereas tE
represents the point at which a larger more delayed reward (e.g., $10)
may be obtained. The top panel of Figure 1 shows that Person A has a
relatively steep discounting curve for the larger delayed reward, where k
= 0.2 . For this individual, the functions for the two choice options cross
before the availability of either option. Therefore, because of the
crossover of the functions, if a choice were made at any time after the
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
445
Person A
k= .2
Person B
k= .02
Q)
::J
en
>
-----;.;
Time ----------+~
Figure 1. The Hyperbolic Temporal Discounting Mode. For both upper and lower panels ,
subjective value for rewards is shown to increase from left to right (curves) as the time to
their delivery draws near. The top panel (Person A) represents a relatively impulsive
individual whose preference shifts from a larger delayed reward to a smaller more
immediate reward as it is about to become available. The bottom panel (Person B)
represents a less impulsive individual whose preference does not shift from the larger
delayed reward.
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REYNOLDS AND SCHIFFBAUER
preference reversal, at tc for example, the smaller-sooner reward would
be preferred because of its close temporal proximity (compared to the
delayed reward), even though in terms of absolute magnitude it is a less
valuable option. However, if for the same individual a choice were made
at t B , the larger-later reward would be preferred.
In the bottom panel of Figure 1, no preference reversal occurs for
Person B because of the less steep discounting curve for the larger more
delayed reward, thus resulting in a smaller k-value of .02. Because this
individual does not discount delayed rewards as steeply as Person A, at
no time does the smaller-sooner reward become more valuable to that
person than the larger-later one. By definition, Person B would be
considered less impulsive than Person A.
Measurement procedures for this DD model typically aim to
determine the steepness of the discount curve for the larger delayed
reward as represented in Figure 1 by use of adjusting-amount or
adjusting-delay procedures. In an adjusting-amount procedure, the tD
parameter of Figure 1 is adjusted in two ways: amount of reward and the
temporal distance between it and the larger reward. Figure 2 shows a
schematic of indifference pOints for five different delays to receiving $10.
To arrive at these indifference points, the participant would be asked a
series of chOice-preference questions between $10 to be received after
$10
$9
$7
Q)
$4
::J
CO
>
$1
365 days
160 days
90 days
30 days
2 days
to $10
to $10
to $10
to $10
to $10
Figure 2 . Five different indifference points for money to be delivered after five specified
delays (2, 30, 90, 160, & 365 days) . Each indifference point represents the smallest amount
of money a person chooses to receive immediately instead of waiting for the larger amount
of money to be delivered after the specified delay. Such indifference points are plotted and
fit to a curve-fitting function to derive k-values (see Equation 1).
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
447
one of the specified delay intervals (e.g., 160 days) and a smaller
adjusting amount of money available immediately. An indifference point in
this instance is the smallest dollar amount a participant chooses to
receive immediately instead of waiting for the delayed $10. For example,
from Figure 2, the indifference point for $1 0 in 160 days is $2 . This means
that for this participant, receiving $10 in 160 days is of equal value to
receiving $2 immediately. From plotting such indifference points over a
series of delays, k-values from Equation 1 can be obtained.
Using discount functions as described above, relations have been found
between higher k-values and excessive alcohol consumption (Vuchinich &
Simpson, 1998), opioid dependence (Madden, Petry, Badger, & Bickel,
1997; Petry & Casarella, 1999), and the clinical diagnoses of substance
abuse and dependence, borderline personality disorder, and bipolar
disorder (Allen , Moeller, Rhoades, & Cherek, 1998; Crean, deWit, &
Richards, 2000). Similarly, research with adult smokers has shown that
those who smoke Cigarettes chronically discount delayed monetary rewards
more on average than those who have never smoked (e.g., Mitchell, 1999;
Reynolds, Richards, Horn, & Karraker, 2004) or those who have quit
smoking (e.g. , Bickel, Odum, & Madden, 1999). These findings point to the
ecological validity of DD as a measure of impulsivity.
Specific Differences Between Delay of Gratification and Delay Discounting
Although a number of researchers discuss DG and DD findings as
though they were derived from equivalent measures (see introduction),
only Rachlin (2000) has attempted to articulate specifically how DG and
DD measure the same behavioral processes. In that discussion, Rachlin
contended that the DG procedure is actually measuring DD- a reduction
in subjective value for delayed rewards purely as a function of the delay.
This would mean that defections occur in the DG procedure because
rewards decrease in subjective value the longer a participant waits. In this
account, there is no allowance for the role of personal agency, or
behavior inhibition, in what is measured during the DG procedure.
A critical aspect of the DG procedure that fits into this reasoning is
that participants do not know how long they must wait before the
experimenter returns and gives them the preferred reward (see earlier
description of the DG procedure). It was suggested, given this condition,
that the longer the experimenter is away, the longer still the participant
believes he or she will have to wait before receiving the preferred reward.
From this perspective, defections occur during the delay-to-reward period
of the DG procedure because the delay to reward is perceived by a
participant as becoming longer, which. leads to a delay-related reduction
in subjective value for the initially preferred reward.
This account of the processes measured by the DG procedure may
play a role in performance during such a procedure; however, it is
inconsistent with a number of behavioral observations, some of which
have already been discussed. We contend that these inconsistencies
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REYNOLDS AND SCHIFFBAUER
between DG and DD warrant further consideration and believe that they
may hold promise for a more complete conceptualization of delay-related
impulsive behavior. Some of these differences are outlined below:
1. Developmental onset differences. An interesting difference
between the DD and DG procedures is that the ability to perform the
procedures emerges at different ages. Mischel and Metzner (1962)
conducted a study involving a DD procedure with children ranging in ages
from 5 to 12 years old. They asked each child participant a single
question about choice preference between smaller amounts of candy
available immediately and larger amounts of candy that were delayed.
The question was asked verbally, thus not requiring any reading ability;
and all of the candy-choice options were visible during the procedure,
therefore not requiring participants to consider hypothetical rewards. It
was not until 9 to 10 years of age and older that participants started
making choices in a manner reflecting sensitivity to the delays (i.e.,
logical discounting). Younger participants made no differentiation
between different delays and therefore did not truly demonstrate
discounting as a function of delay. The findings of this study are
particularly important in comparing DG and DD because the procedure
was similar to most DG procedures, except there was no requirement to
sustain choices for delayed candy.
Similarly, with an "experiential" delay-discounting task developed by
the authors (Reynolds & Schiffbauer, 2004) , which involves multiple
choice trials with actual delays (ranging from 0 to 60 seconds) and nickels
for reinforcers , children younger than 8 or 9 years of age have not been
able to perform the procedure in a manner reflecting discounting, or a
sensitivity to different delays. However, 9-year-old and older children
demonstrated discounting as a function of delay and showed expected
age differences in k-values between 9- and 12-year-olds (Reynolds,
Schiffbauer, Richards, & Karraker, 2003; Reynolds, Schiffbauer,
Swenson , & Karraker, 2001).
In that younger children do not consistently demonstrate delay
discounting in a manner similar to older children or adults , it seems likely
that the choice behaviors measured by DD procedures require
participants to have a certain level of cognitive function ing to evaluate
contingencies associated with the choice options, which younger children
may not have. One possible developmental explanation for this agerelated difficulty in discounting may come from the cognitive-development
literature. Cognitively, children develop what are considered concreteoperational abilities between 7 and 11 years of age (e.g., Piaget &
Inhelder, 1969; Lutz & Sternberg , 1999). The ages at which concreteoperational thinking emerges have been shown to vary, with younger
children demonstrating some concrete-operational-like abilities (e.g. ,
Pears & Bryant, 1990; Rogoff, 1990). Yet a number of researchers hold
that recent findings with younger children neglect certain aspects of
Piaget's procedures and therefore do not de-validate Piaget's accounts
(e.g., Chapman, 1988; Smith, 1982). Concrete-operational thinking is
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
449
characterized by a child's increased ability to perform internalized mental
manipulations with non hypothetical, concrete subject matters. For
example, prior to concrete-operational thinking, children are incapable of
the mental operations required to take the perspective of another person
or to understand that the volume of a substance may stay constant even
if the shape of the substance changes. Concrete-operational thinking also
involves more mature spatial operations, including the comprehension of
distance, time, velocity, and space. In relation to DD procedures, it is
possible younger children who have not yet achieved concreteoperational thinking, especially related to the perception of time, may
have trouble conceptualizing the temporally related contingencies
associated with DD choice options, therefore leading to a general
insensitivity to different delay lengths in DD procedures.
However, children are able to perform the DG procedure as early as
3 1/2 to 4 years of age in a manner predictive of long-range developmental
outcomes (e.g., Mischel, Ebbesen, & Zeiss, 1972; Mischel et aI., 1989).
With these age differences in measurement feasibility of DG and DD, it
seems unlikely that the two procedures are measuring the exact same
processes, and it seems even less likely that they both reflect the lateremerging processes measured by DD procedures. When compared to
DG from a developmental perspective, the DO procedure appears to
include the assessment of more mature cognitive processes than DG and
is therefore, to some extent, measuring something different from what is
measured by DG.
2. ''Real-world'' situations. As DG and DD are currently measured , it
appears that they both hold ecological validity to real-world
ci rcumstances regarding behavior inhibition and choice. However, each is
likely applicable to different aspects of such situations. In other words, it
is unlikely that under more ecologically valid conditions, as opposed to
laboratory conditions, that the processes underlying either DG or DO
alone determine delay-related impulsive behavior entirely. For example, a
person who is trying to lose weight by restricting caloric intake is required
to (a) make the initial choice to lose weight and (b) resist eating high
calorie foods that are frequently available. Personally evaluating the
relevant contingencies to make the initial choice to lose weight by
restricting caloric intake is obviously an important factor in actually losing
weight, which would perhaps reflect the choioe behaviors measured by
DD procedures. However, as time goes by, and especially if the person
does not initially see favorable results, he or she is required to sustain
that choice by resisting the temptation to eat high calorie foods that are
often immediately available (e.g., in the refrigerator at home or vending
machines at work). In this example, the ability to sustain an earlier choice
to lose weight clearly requires the ability to inhibit defecting to
immediately available options , which would ultimately lessen the
likelihood that weight would be lost. A similar example is the recovering
alcoholic who arrives at a party and says "no" to the offer of an alcoholic
beverage. This individual must not only say "no" to a drink upon arrival but
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REYNOLDS AND SCHIFFBAUER
also must sustain the choice of abstinence by continuing to say "no" to
immediately available drinks while at the party.
These examples illustrate the importance of being able to sustain a
choice for a preferred, but delayed, reward. They do not fit conceptually with
the idea that the entire underlying process driving behavior in such situations
is the delay (or a perception of increasing delay, as described above) either
to losing weight or to maintaining abstinence from alcohol. This is apparent
in that the individuals described in the examples should not be under the
impression that the longer high-calorie foods are successfully avoided or the
longer drinks are declined while at the party will lead to even longer delays
before the desired outcomes are obtained (i.e., weight loss or abstinence
from alcohol while at the party). Rather, these examples suggest that
perhaps certain features of the immediate stimuli (i.e. , high-calorie foods or
alcohol) are tempting and may require behavior inhibition on the part of the
individual, as appears to be measured in the DG procedure. More generally,
these examples highlight the likelihood that choice preference or initial value
(as emphasized in DD measures) and ability to sustain a choice (as
emphasized in DG measures) may represent different aspects of delayrelated impulsive behavior relevant to different contextual conditions.
3. Nonhuman-animal research comparing DG and DO. A recent study
(Reynolds, de Wit, & Richards, 2002) compared a DG procedure and a
DD procedure developed for rats. In the DG procedure, the rats made
multiple choices between a delayed larger reward and an immediate
adjusting (usually smaller) reward. During the delay-to-reward period
following responses to the delayed option, a rat could defect to the
smaller immediate option and receive that reward immediately but then
would no longer receive the delayed larger option for that trial. For the DD
animals, the procedure was the same except that there was no
opportunity to defect during the delay-to-reward periods. For both DG and
the DD procedures, responses made to the immediate adjusting option
during the delay-to-reward periods were recorded, even though such
defection-like responses were not reinforced in the DD procedure. For the
DD procedure, only the first defection-like response was recorded for a
specific choice trial , which controlled for possible differences in number of
opportunities to defect between the procedures. Results showed that the
DG rats made significantly fewer defection responses than the DD rats
made defection-like responses. This find ing showed that behavior
inhibition was an aspect of behavior summarized by the DG procedure
but not by the DD procedure. These nonhuman animal findings point to
DG and DD measuring different aspects of impulsive behavior-behavior
inhibition versus choice behavior, respectively.
Using similar procedures to measure DG and DD in rats ,
comparisons also were made to determine the effects of serotonin (5HT)
lesions on each (Richards, Chock, & de Wit, 1998). It was found that only
the DG group was impaired by the 5HT lesion. The increase in impulsive
behavior in the DG procedure (and the absence of an increase in the DD
procedure) after serotonin (5HT) lesions indicates that the requirement of
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
451
sustaining a choice for a delayed alternative may be an important
determinant of impulsive behavior in some types of situations-independent
of choice behavior. In a subsequent study, which involved a different type of
DD procedure and no DG comparison procedure, there was some
disruption from serotonin (5HT) lesions on task performance (Mobini,
Chiang, Ho, Bradshaw, & Szabadi, 2000). However, this latter study did not
provide a comparison for lesion effects between DD and DG procedures;
therefore, it cannot be known to what extent animals in a DG procedure
would have been affected by these same lesions. The nonhuman animal
data that do compare DG and DD procedures generally suggest these
procedures measure different aspects of impulsive behavior. This research
also suggests different underlying neural mechanisms between the
procedures, with a greater role of 5HT in DG.
4. Development of strategies. As described earlier, certain findings
with the DG procedure are not consistent with the notion that the chief
behavioral determinant in the DG procedure is a perception of increasing
delay (Rachlin, 2000). That children have longer DG times when a
stimulus is not present (Mischel & Ebbesen, 1970), and that they also
develop the strategy of obscuring the saliency of a stimulus in efforts to
improve DG performance (Mischel & Mischel, 1983), does not fit with a
purely "delay-driven hypothesis" of the underlying processes measured
by DG. As already described, however, these findings do support the
notion that DG assesses the ability to resist (or inhibit responding to) the
temptation of a salient, immediately available stimulus.
Taken together, these points of apparent difference between DG and
DD suggest that (a) ability to delay gratification may be an earlier
emerging, more foundational aspect of impulsive behavior when
compared to the processes measured by DD, (b) the processes
measured by DG and DD may relate to different aspects of ecologically
valid, delay-related situations, and (c) some preliminary research
suggests that DG and DD procedures measure behaviors mediated by
different underlying neural mechanisms. The remainder of this article will
focus on the ways in which DG and DD may be related.
A Unifying Feedback Model of Delay-Related Impulsive Behavior
As described in previous sections, DG and DD appear to reflect
somewhat different aspects of impulsive behavior, with DG measuring
behavior inhibition and DD measuring choice preference. Choice
preference, when compared to behavior inhibition , is suggested to reflect
a higher-order cognitive process involving the subjective evaluation of a
number of contingency factors. Comparatively, behavior inhibition is a
less cognitive, less evaluative, and a less learning-mediated process. In
the present argument, behavior inhibition (Le., DG) is put forward as the
more basic underlying process that ultimately becomes incorporated into
one's more subjective processes involving value and choice preference
(Le., DD).
452
REYNOLDS AND SCHIFFBAUER
Figure 3 represents a conceptual framework for the relation between
the processes measured by OG and 00. From left to right , Figure 3
shows the temporal progression of what might be the most typical
ecologically valid situation involving both choice and delayed rewards.
We contend that the vast majority of realistic, delay-related situations
relevant to impulsive behavior involve both a component of choice and a
component involving the sustaining of that choice. To illustrate, the far left of
Figure 3 is the initial choice between an immediate or short-delay option
Feedback Model of Delay-Related Impulsive Behavior
Feedback Processes
(Learning)
Processes of Delay Discounting (DO)
(Decision/Choice)
Processes of Delay of Gratification (DG)
Immedi:lte or Short Del:!.)' (ISO)
Y
Long Delay (LO)
L
Deliv.'l' of ISO
(Sustain Decision/Choice)
ISO
A ______De_liv.'l' of LD Y
y---~
Time
LO
T ____.IL__
- _
)
Figure 3. Feedback Model of DG and DO. From left to right, there are three main
components to this depicted Feedback Model: DO processes, DG processes, and feedback
learning processes. In this depicted relation between DO and DG , these two processes are
considered discrete; however, they are still related (and should be correlated) through
individual experiences in DG types of situations becoming incorporated through learning
processes into one's choice behaviors measu red by DO.
(ISO) and a long-delay option (LO). Choice in this conceptualization would
be what is characterized by 00 procedures. Actual choice preference for, or
subjective value for, either the ISO or LO options would be influenced by a
number of personal factors. Among these would be the perceived magnitude
or quality difference between the choice options, perception of delay length,
perceived differential probabilities of actually receiving the ISO or LO options
and, as suggested above, personal history with ability to sustain choices for
LO options.
As diagramed in Figure 3, if a choice is made for the LO option , the
situation then likely becomes one involving ability to sustain that LD
choice, because most choices involving delayed benefits also will involve
regular opportunities for defection. From a discounting perspective it
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
453
could also be argued that ability to sustain a choice during this period
might instead simply be a succession of choices for the delayed option.
However, we would argue that an initial choice for a LD option is
qualitatively different in at least two ways from any continued choices that
might occur during a delay-to-reward period. The initial choice is
essentially a statement of commitment on the part of the chooser to wait
for the LD option, which is then taken to reflect greater subjective value
for that option over the ISD option. Any continued choices during the
delay-to-reward period would be different in that (a) the choice question
itself would necessarily change to a choice about maintaining the original
commitment, and (b) some delay would have elapsed. Unless something
happens to specifically reduce the value of a LD option (e.g., it becomes
uncertain), it would generally be maladaptive in terms of optimization to
choose an ISD option (which had been continually available) after having
invested in a LD option by waiting through a portion of its delay. However,
such choices, or defections, clearly do occur as evinced from much DG
research. In interpreting this failure to optimize, the question then
becomes one of what would motivate such a choice under these
conditions? Rachlin (2000) suggests that it might be a perception of
increasing delay length to delivery of the LD option. However, for reasons
already discussed, we would contend that ability to delay gratification
also plays a determining role in any such choices during delay-to-reward
periods. For example, willfully delaying gratification is consistent with
observations of reduced DG times when the actual primary reinforcer is
present (see above). Conversely, we would not expect having the
reinforcer present to affect perception of remaining delay.
The feedback component of Figure 3 represents the learning
involved in incorporating one's personal history with sustaining LD
choices into future choice preferences when choosing between ISD and
LD options. If an individual has a history of being unable to stick with or
sustain choices for delayed rewards, then due to time- and energyexpenditure issues it would be highly disadvantageous to continue to
value and choose delayed options as though sustaining such choices
were not a problem. This type of personal history with delayed options
should impact subsequent choice preferences for ISD and LD options,
which, in turn, should also be reflected in choice performance on DD task
procedures. This model does not directly address learning that may occu r
as a result of initial choices for ISD options. However, learning from such
choices may serve to establish a frame of reference for determining the
relative subjective value of LD options.
From Figure 3, a number of predictions and research questions arise.
From a developmental perspective, correlations between DG and DD
should be weaker for younger children than for older children. Such an
age-related pattern would likely reflect the development and experiencerelated refinement of the feedback component of Figure 3. Research is
needed to improve measures of DG and DD in both children and adults
to allow developmental research questions to be more fully explored.
454
REYNOLDS AND SCHIFFBAUER
In addition to developmental changes, however, the feedback aspect
of Figure 3 leads to a somewhat counterintuitive prediction regarding an
individual's choice preference and his or her ability to sustain choices for
certain commodities. For commodities in which an individual finds it
especially difficult to sustain LD choices, choice preference should be
less for LD options involving that commodity. Put another way, for
commodities that a person would have a particularly difficult time
sustaining choices involving delay, that person should discount the value
of that commodity more as a function of delay than commodities for which
he or she does not find it as difficult to sustain choices. For example,
given the characteristic nature of addiction, a person who smokes
cigarettes chronically or who is addicted to heroin might be expected to
have a more difficult time delaying gratification for cigarettes or heroin in
real-world settings than for other commodities, like money. If this were
true, the feedback loop of Figure 3 leads to the prediction that such
individuals should discount the value of cigarettes or heroin more by
delay than other "less intense" commodities not involving addiction. In
keeping with this prediction, several researchers have shown that chronic
cigarette smokers discount the value of cigarettes more by delay than
comparable monetary rewards (Bickel et aI., 1999), crack/cocainedependent participants discount crack/cocaine rewards more than
comparable monetary rewards (Coffey, Gudleski, Saladin, & Brady,
2003), and individuals addicted to heroin discount the value of heroin
more than monetary rewards (e.g., Madden, Bickel, & Jacobs, 1999).
Odum and Rainaud (2003) also found that healthy non-addicted
participants who reported liking beer and pizza discounted the value of
these reinforcers (Le., hypothetical beer and pizza) more than they did
monetary reinforcers, suggesting this differential discounting tendency is
not restricted to just drugs of abuse.
These findings with specific substances of addiction, and
consumable reinforcers more generally, are somewhat counterintuitive in
that DO research with only monetary rewards has shown that people
discount the value of larger amounts of money less than smaller amounts
of money (e.g., Ostaszewski & Karzel, 2002). This means the general
tendency is to discount higher value commodities less than lower value
commodities. Therefore, these findings involving commodities of
addiction and food cannot logically be attributed to the participants
valuing these commodities more than they valued the monetary rewards.
Conversely, one could argue that these commodities may be valued less
than the comparable amounts of money; however, this notion would be
inconsistent with the nature of addiction and subjective value for the drug
of addiction. A central aspect of the pathology surrounding addictive
behavior is the apparent greater value the addicted person holds for a
drug and its effects relative to almost anything else in his or her life.
Rather, as illustrated in Figure 3, such DO findings are more consistent
with the notion that these commodities are difficult to resist over time,
which is then reflected in the observed differential rates of discounting.
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
455
Similarly, the finding of higher rates of discounting for beer and pizza
compared to money might reflect commodity-related differences in ability
to sustain choices for primary versus secondary reinforcers. Delay-ofgratification research showing shorter DG times when a primary
reinforcer is present compared to having a symbolic representation of the
re inforcer (see above) suggests this possibility, especially if hypothetical
money can be considered more symbolic as a reinforcer than
hypothetical beer or pizza.
Other research questions from Figure 3 primarily involve the extent of
correlation between choice preferences and ability to sustain choices
involving delay. A lack of correlation may lead individuals to make choices
involving delayed consequences in a manner that is unrealistic, thus
setting these individuals up for failure in terms of being able to follow
through on decisions involving delayed benefits. In addition to age, a
number of other factors may contribute to a lack of concordance between
choice preference and ability to sustain choices. For example, IQ might
be a determining factor involved in the relation between choice
preference and ability to sustain choices, with greater intelligence
expected to be associated with more correspondence between choice
preferences and sustaining choices.
Another factor possibly influencing this relation might be certain
pharmacological influences on ability to sustain choices that do not also
influence actual choice preference. It stands to reason that if the
contingency-evaluative processes measured by DD are partly the product
learning history (as illustrated in Figure 3) that such processes should be
more resistant to acute-type changes than the ability to sustain choices.
From Figure 3, changes in choice preference based on Feedback
Processes would require historical experience with ability to sustain choices.
For example, ethanol should be expected to influence performance on DG
types of tasks in that ethanol has been shown to interfere with behavioral
inhibition (e.g., Vogel-Sprott, Easdon, Fillmore, Finn, & Justus, 2001), which
is similar to resisting the temptation of immedia.te rewards for the DG
procedure. However, in two studies examining the effects of ethanol on
performance of a DO type of task there was no significant ethanol effect
(Ortner, MacDonald, & Olmstead, 2003; Richards, Zhang, Mitchell, & de Wit,
1999). Therefore, it can be expected that while under the influence of
ethanol, the degree of correspondence between choice preference and
ability to sustain choices for an individual may be reduced, thus leading such
an individual to make choices that are unrealistic for him or her to sustain
while under the influence. But, as would be predicted from Figure 3, if the
individual were to somehow remain under the influence of ethanol for an
extended period, and during that time have experiences with a decreased
ability to sustain choices involving delay, choice preference should
eventually change in a manner to be consistent with his or her reduced
ability to sustain choices.
As diagrammed in Figure 3, individual differences in the extent of
relatedness between choice preference and ability to sustain choices
456
REYNOLDS AND SCHIFFBAUER
may be an important feature of impulsive behavior to consider, which is
not possible when DG and DD are conceptualized as reflecting the same
underlying processes. A lack of relatedness between these two aspects
of impulsive behavior could lead to problems in choices being made
which are ultimately untenable. For example, an individual might decide
to lose weight or stop smoking cigarettes by drastically reducing caloric
intake or quitting smoking cold turkey. In these instances, these decisions
do not represent impulsive choice as defined by DD; however, as too
often turns out to be the case, if the person is unable to sustain such a
choice, then the choice is still problematic (and arguably impulsive) in that
the person is less likely to lose weight or stop smoking than if a more
individually realistic decision had been made. We contend that individual
differences in the extent of relation between the processes measured by
DG and DD is an aspect of behavior that warrants further attention in
delay-related impulsivity research.
Concluding Comments
In the current paper, we discussed the DG and DD measurement
procedures and what the underlying psychological processes are
believed to be for each. Also, we put forth an argument for the position
that DG and DD are not measures of the same or equivalent aspects of
impulsive behavior. Rather, it is more consistent with what is known about
DG and DD to view these procedures as measures of discrete, yet
related, dimensions of impulsive behavior, that is, ability to sustain or stick
with choices involving delay and choice preference, respectively. Further,
a conceptual model was presented for the specific relation between the
processes measured by DG and DD (Figure 3). This model represents
the processes of DG as more foundational and basic when compared to
the processes of DD, which are comparatively more cognitive and
learning mediated. This conceptualization of the relation between DG and
DD is almost exactly opposite of what has been proposed in the one other
published conceptualization of the relation between these two indices of
impulsive behavior (Rachlin, 2000) .
From the presented model (Figure 3), it becomes apparent that
certain predictions and research questions emerge that would otherwise
be lost without the current two-dimensional conceptualization of DG and
DD, such as a lack of correspondence between choice preference and
ability to sustain choices that may lead to problematic choice behavior.
We believe that the research questions posed from the presented
conceptualization warrant future attention in an effort to more fully
understand delay-related impulsive behavior as it may pertain to choice
behavior and ability to sustain choices.
DELAY OF GRATIFICATION AND DELAY DISCOUNTING
457
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