An Argument Against Dual Valuation System Competition: Cognitive Capacities Supporting Future Orientation Mediate Rather Than Compete With Visceral Motivations.

Abstract

The dynamic inconsistency of preference is well documented in behavioral research, but its basis remains controversial. In this article, we summarize recent functional magnetic resonance imaging (fMRI) work in the domain of intertemporal choice, specifically considering evidence bearing on the hypothesis that delay discounting in humans is determined by competition between an evolutionarily older system that discounts precipitously with delay (System 1), and a newer system that exhibits very little discounting (System 2). We argue that neuroimaging evidence does not support the hypothesized separate and competing value systems. While it is clear that the sophisticated cognitive capacities that lead to greater valuation of larger later alternatives (e.g., selective attention and self-signaling) depend critically on neocortical structures, these capacities affect intertemporal choice through mediation of (rather than competition with) older cortical and subcortical structures central to reward and motivation. Taken together, neuroimaging evidence supports the alternative hypothesis that intertemporal choice is guided by a single valuation system.

Full text

Page 1

An Argument Against Dual Valuation System Competition:
Cognitive Capacities Supporting Future Orientation Mediate
Rather Than Compete With Visceral Motivations
John R. Monterosso and Shan Luo
University of Southern California
The dynamic inconsistency of preference is well documented in behavioral re-
search, but its basis remains controversial. In this article, the authors summarize
recent functional MRI (fMRI) work in the domain of intertemporal choice, specif-
ically considering evidence bearing on the hypothesis that delay discounting in
humans is determined by competition between an evolutionarily older system that
discounts precipitously with delay (System 1) and a newer system that exhibits very
little discounting (System 2). The authors argue that neuroimaging evidence does
not support the hypothesized separate and competing value systems. While it is
clear that the sophisticated cognitive capacities that lead to greater valuation of
larger later alternatives (e.g., selective attention and self-signaling) depend criti-
cally on neocortical structures, these capacities affect intertemporal choice through
mediation of (rather than competition with) older cortical and subcortical structures
central to reward and motivation. Taken together, neuroimaging evidence supports
the alternative hypothesis that intertemporal choice is guided by a single valuation
system.
Keywords: self-control, delay discounting, self-signaling, neuroeconomics
Rational Choice Theory (RCT) dominated
the behavioral sciences throughout most of the
20th century (Arrow, 1951). RCT models the
individual as maximizing his or her utility based
on a stable set of preferences (Becker, 1976).
From the perspective of neuroscience, it is as-
tonishing that this model holds as well as it
does; somehow the immeasurable complexity
of the living human brain achieves functionality
that is not all that far from the rational pursuit of
a stable set preferences. That said, systematic
irrationality in intertemporal choice and other
domains has been well documented and there is
growing dissatisfaction with RCT. Of course,
demonstration of systematic irrationality is in-
sufficient basis for abandoning RCT; as econo-
mist Milton Friedman noted, “Complete realism
is clearly unattainable, and the question whether
a theory is “realistic enough” can be settled only
be seeing whether it yields predictions that are
good enough for the purpose in hand or that are
better than predictions from alternative theo-
ries” (Friedman, 1971, p. 51).
Attempts to find an alternative that makes
better predictions than RCT have generally tried
in one way or another to increase the psycho-
logical realism of choice models (Edwards,
1953; Kahneman & Tvesky, 1979; Simon,
1967). These efforts incorporate functional con-
structs intermediate to the contingencies in the
environment and the individual’s choice (e.g.,
emotions and cognitions) that serve as psycho-
logical gears within the human decision-making
apparatus. The trend has been toward increased
collective confidence that the payback in mod-
eling accuracy justifies this massive complica-
tion. The rapid emergence of “neuroeconomics”
reflects the possibility that we are on the cusp of
a new development in this program, grounding
behavioral theories in neural realism. Perhaps
John R. Monterosso and Shan Luo, Department of Psy-
chology, Brain and Creativity Institute, University of South-
ern California.
This work was supported by the National Institute of
Health R01DA021754 (J. M.) and R01DA023176 (J. M.).
The authors thank Antonio Damasio for helpful suggestions
made on a prior draft of this work.
Correspondence concerning this article should be ad-
dressed to John R. Monterosso, Department of Psychology,
University of Southern California, SGM 501, 3620 South
McClintock Ave., Los Angeles, CA 90089-1061. E-mail:
johnrmon@usc.edu
Journal of Neuroscience, Psychology, and Economics
2010, Vol. 3, No. 1, 1–14
© 2010 American Psychological Association
1937-321X/10/$12.00DOI: 10.1037/a0016827
1

Page 2

consideration of the physical gears within the
human decision-making apparatus will lead to
better behavioral science, at least in those areas
in which RCT is most faulty. In this article, we
look specifically at this issue with respect to
intertemporal choice, giving special consider-
ation to the widely discussed idea of dual value
systems (Loewenstein, 1996; McClure, Ericson,
Laibson, Loewenstein, & Cohen, 2007;
McClure, Laibson, Loewenstein, & Cohen,
2004). Whether or not the dual valuation sys-
tems hypothesis is correct, we think it is illus-
trative of how the neural systems perspective
could, in principle, contribute something impor-
tant to behavioral science.
Intertemporal Choice and RCT
There has been intense investigation of the
relationship between immediacy of conse-
quences and motivation (the term intertemporal
choice is primarily used in neuroscience; delay
discounting is primarily used in behavioral psy-
chology; and time preference is primarily used
in economics.) Research on intertemporal
choice generally requires participants to express
preference between a narrow set of alternatives
(generally two alternatives) that form a conspic-
uous “sooner smaller” versus “later larger” con-
trast (e.g., $5 today or $10 in a month.) Ratio-
nality with respect to delay has been conceived
in two ways; the first, which we think is in line
with common sense, conceives the perfectly
rational agent as unaffected by delay per se
(though of course opportunity costs and any
associated uncertainty are rational consider-
ations by any reasonable standard.) As Jevons
put it, while characterizing the rational ideal,
“all future pleasures or pains should act upon us
with the same force as if they were present”
(Jevons, 1871, p. 76). The second conception
allows that the rational actor devalue delayed
outcomes (a preference for immediacy of good
outcomes and delay of bad outcomes), provided
that the devaluation occurs at a fixed rate per
unit of time (Friedman, 1963). Although such
“exponential discounting” can be of any rate
and is thus, we think, inconsistent with the
common sense idea of a rational orientation to
delay, it is attractive to Rational Choice theo-
rists because it allows delay to affect motiva-
tion, while arguably introducing no violation of
RCT’s axioms. Present value for a stream of
consumptions (c1, c2, . . . ) discounted expo-
nentially can be represented as:
V ??
t?0
?
?tu?ct?
(l)
where u is the utility function, with lower values
of the discount parameter ? indicating steeper
exponential discounting.
Exponential discounting introduces no dy-
namic inconsistency in preferences. The expo-
nential discounter can make a plan with the
expectation that she will follow it unless the
circumstances upon which she based her plan
shift in an unanticipated way. Her past and
future selves harmoniously pursue preferences
in an unbroken chain, their success limited only
by imperfect information or power. But human
and nonhuman decision making does not con-
form to this standard. On the contrary, there are
conditions under which most subjects reverse
their initial preference for larger later rewards
when smaller sooner alternatives are near at
hand. Furthermore, when given the opportunity,
subjects choose to lock in their larger later pref-
erence while it is still the most appealing option
in order to protect against an anticipated future
self with alternate preferences (Ainslie, 1974;
Schelling, 1978; Shefrin & Thaler, 1992; Strotz,
1956). In this way, behavioral discounting data
look systematically nonexponential, although
opinions differ as to the precise alternative func-
tional form that best fits behavioral data (Green
& Myerson, 2004). One widely considered al-
ternatives is hyperbolic discounting (discount-
ing that is proportional to delay; Ainslie, 1975,
1992, 2001; Strotz, 1956). Present value for a
stream of consumptions (c1, c2, . . . ) dis-
counted hyperbolically can be represented as:
V ??
t?0
?
u?ct?
K?t ? 1
(2)
where u is the utility function, with higher val-
ues of the discount parameter k indicating
steeperhyperbolicdiscounting.Asecondproposal
to account for preference reversals is quasi-
hyperbolic discounting. In quasi-hyperbolic dis-
counting, a ballistic devaluation occurs in the
presence of any delay, but the effect of addi-
2 MONTEROSSO AND LUO

Page 3

tional delay is modeled exponentially (Laibson,
1997). Present value for a stream of consump-
tions (c1, c2, . . . ) discounted quasi-hyperboli-
cally can be represented as
V ? u?c0? ? ??
t?1
?
?tu?ct?
(3)
where u is the utility function, with parameters
? and ? both serving as discount parameters.
Note that ? does not affect the immediate
period in the stream of consumption; lower
values of ? indicate a greater devaluation of
all outcomes that are not immediate. The ad-
ditional effect of delay beyond this disconti-
nuity (?) is exponential.
In both hyperbolic and quasi-hyperbolic dis-
counting, the difference in value between im-
mediacy and some delay, d, is proportionally
greater than the difference between some posi-
tive delay, X, and X ? d. As a result, both
introduce time inconsistency, though for quasi-
hyperbolic discounting, this inconsistency is re-
stricted to situations involving immediacy rela-
tive to situations without immediacy. As we
will consider below, the discontinuity inherent
in quasi-hyperbolic discounting lends itself well
to a dual-process account of the neural basis of
temporal discounting.
The lack of resolution regarding modeling
alternatives is related to the enormous variabil-
ity in discounting observed within individuals
across contexts (Chapman, 2000), between in-
dividuals in the same context (Ainslie &
Monterosso, 2003a), and across different re-
search studies (Frederick, 2002). As a result,
there is now considerable skepticism that any
model of delay discounting will be consistently
adequate. As Roelofsma and Read (2000) put it,
The study of intertemporal choice is currently un-
dergoing a change in emphasis, as has already oc-
curred in the study of decision making under risk
and uncertainty. Rather than searching for the holy
grail of a single utility function, researchers now
take the more pragmatic view that preferences are
constructed based on the circumstances of their ex-
pression. (p. 172)
We will return later to the issue of endemic
variability in intertemporal choice behavior.
What Does Intertemporal Choice Have To
Do With Impulsivity and Self-Control?
Synchronic Multiple Selves Models
We think that much of the interest in delay
discounting relates to the underlying expecta-
tion that it bears importantly on self-control
problems, including overspending, overeating,
underexercising, and addiction. But given the
emotionally “cool” nature of the typical inter-
temporal choice assessment (would you prefer
$5 today or $10 in a month?), it is not self-
evident that they would be associated with real
self-control phenomena. The hypothesized as-
sociation between intertemporal choice mea-
sures and self-control turns on the researcher’s
conceptualization of the nature of self-control
struggle. With rare exception (Becker & Mur-
phy, 1988), behavioral scientists that model
self-control problems either a) drop the RCT
modeling assumption that the relevant agent is a
whole unified person and instead model her as
the product of conflicting subperson agents
(e.g., Shefrin & Thaler, 1992) or b) drop the
modeling assumption that the agent is unified
over time (Ainslie, 1992, 2001; Ross, 2005;
Schelling, 1978, 1980, 1984; Strotz, 1956) and
instead model her as the product of a temporal
series of agents, sometimes engaged in strategic
opposition to each other. Following Ross (in
press), we refer in turn to these two classes of
self-control models as “synchronic multiple
selves” and “diachronic multiple selves” mod-
els. We presently focus on synchronic multiple-
self models and will return later to diachronic
models.
Purely “synchronic” models conceptualize
self-control struggle as occurring between dis-
tinct “subagents” within the person that differ-
entially value the same outcome. Although
there is no reason why synchronic multiself
models are restricted to two subperson agents,
most, in fact, do include just two, sometimes
referring to a “System 1” that is evolutionarily
older, that is instantiated largely in limbic and
paralimbic brain structures, that works faster
and without requiring attention, and that is more
stimulus bound and present focused; and a
“System 2” that is evolutionarily recent, that is
instantiated in the neocortex, that is generally
slow and demanding of attention, and that uti-
lizes more abstract representations of the envi-
3SPECIAL ISSUE: ARGUMENT AGAINST DUAL VALUATION SYSTEM COMPETITION

Page 4

ronment and so is capable of future-oriented
behavior (Evans, 2008).
Freud’s “ego” and “id” were so conceived,
with each operating by its own principles and
often at odds. Thaler and Shefrin proposed to
capture self-control phenomena with a model of
the individual as including “two sets of coexist-
ing and mutually inconsistent preferences: one
concerned with the long run, and the other with
the short run.” (Shefrin & Thaler, 1992, p.
291).1Loewenstein’s “visceral motivations”
model is also in this spirit, since visceral moti-
vations sit apart from nonvisceral motivations
and so imply synchronic multiple selves (Loe-
wenstein, 1996). Metcalf and Mischel’s analy-
sis of the “dynamics of willpower” posits mul-
tiple agents: one the manifestation of a cool,
cognitive “know” system, the other a hot emo-
tional “go” system (Metcalfe & Mischel, 1999).
The strength-model of self-control (Baumeister,
Vohs, & Tice, 2007) implies a dual system as
well, since there is a presumed set of motiva-
tions that the “willpower muscle” preferences
and an alternative set that it does not.
From the perspective of these synchronic
multiagent models, delay discounting is gener-
ally viewed as one relevant factor, but neither as
the primary source of impulsivity, nor as the
key to understanding mechanisms of self-
control. Instead, in purely synchronic models,
time inconsistency is one manifestation of the
underlying competition between subperson
agents with competing preferences and self-
control maps directly as the outcome of that
competition. In a purely synchronic model of
self-control an act entails that a certain subagent
or subagents prevails over others. (Freud’s
“ego” prevailing over “id,” Thaler’s “planner”
over “doer,” Loewenstein’s “nonvisceral” over
“visceral” motivations, Metcalf and Mischel’s
“know-system” over “go-system,” and the
strength model’s “ideals” over “passions.”)
From the standpoint of neuroeconomics, the
possibility that there are two separate valuation
systems within the brain is attractive. In addi-
tion to creating clear intervention targets (e.g.,
intervening to shift the balance between the
systems to treat self-control problems), it sug-
gests that models of individual behavior could
be dramatically improved by finding a way to
develop two sets of utility functions for the
individual. This would not, we think, be mere
“neuro-fication” of the timeless rational versus
emotional self model, since it would suggest
incorporating neuroscience methodologies to
efficiently solve for the set of parameters in
whatever underlying dual-system utility func-
tion was used. For instance, if the dual-system
discounting function included a weighting pa-
rameter to capture the strength of the contribu-
tion of each system, the weighting parameter
might be informed by gross neural markers like
metabolism, connectivity, gray matter density,
tonic and phasic striatal dopamine, receptor
availability, and so forth.
Neuroimaging Research on Intertemporal
Choice: The Case for Dual Valuation
There have been a series of reports combin-
ing an intertemporal decision-making task with
functional MRI. Thus far, the highest impact
papers among them (Kable & Glimcher, 2007;
McClure et al., 2007; McClure et al., 2004)
have focused on assessing the validity of a
synchronic multiple self perspective, and we
will discuss these in some detail. McClure et al.
(2004) conducted the first study pairing the typ-
ical methodology of intertemporal choice inves-
tigation with functional MRI (fMRI). In their
study (which had already been cited 450 times
at present, according to Google Scholar) the
rewards at stake for participants were gift cer-
tificates for Amazon.com, ranging from $5 to
$40. The smaller sooner option varied in delay
between the same day (“today”) and 4-week
delay; the larger later option was always either 2
or 4 weeks after the smaller sooner option.
Subjects received one of their certificates at the
specified delay chosen but did not find out
which one until after the end of the test. The
analytic approach taken was directed at assess-
ingwhetherthe modeling
quasi-hyperbolic discounting (eq. 3) might cor-
respond to an underlying duality in neural sub-
strates of valuation. Recall that quasi-hyper-
bolic discounting models behavior with two fit
duality of
1Indeed they argued that their theory was, “roughly con-
sistent with the scientific literature on brain function. The
planner in our model represents the prefrontal cortex. The
prefrontal cortex continually interfaces with the limbic sys-
tem, which is responsible for the generation of emotions.
The doer in our model represents the limbic system. It is
well known that self-control phenomena center on the in-
teraction between the prefrontal cortex and the limbic sys-
tem (Restak, 1984)” (Shefrin & Thaler, 1992, p. 291).
4MONTEROSSO AND LUO

Page 5

parameters: ?, which represents a ballistic de-
valuation with any delay, and ? (delta), which
represents additional exponential discounting
that is continuous over delay. The authors’ were
interested in the possibility that these two pa-
rameters relate to two separate valuation sys-
tems: “Our key hypothesis is that the pattern of
behavior that these two parameters summa-
rize-?, which reflects the special weight placed
on outcomes that are immediate, and ?, which
reflects a more consistent weighting of time
periods-stems from the joint influence of distinct
neural processes, with ? mediated by limbic
structures and ? by the lateral prefrontal cortex
and associated structures supporting higher cog-
nitive functions” (McClure et al., 2004, p. 504).
Rather than seeking to identify regions that re-
flected value at the time of choice, the analytic
approach taken sought to identify regions that
were preferentially recruited during choices that
included an immediate alternative. Consistent
with their hypothesis, this pattern was observed
in a set of regions that included parts of limbic
and paralimbic systems (“beta regions”). In
contrast, lateral prefrontal cortex and posterior
parietal cortex were active while subjects were
making choices irrespective of delay (and so
labeled “delta regions”). They also observed
greater activity in limbic/paralimbic regions
was associated with choosing smaller sooner
rewards, whereas greater activity in fronto-
parietal regions was associated with choice of
larger later rewards. Thus, the authors viewed
their results as suggesting not only the neural
basis of delay discounting’s functional form but
also a more general synchronic multiple-selves
account of self-control, arguing that behavior is
“. . . governed by a competition between lower
level, automatic processes that may reflect evo-
lutionary adaptations to particular environ-
ments, and the more recently evolved, uniquely
human capacity for abstract, domain-general
reasoning and future planning” (McClure et al.,
2004, p. 506).
There is something on its face odd, however,
about the idea of a valuation system only con-
cerned with immediate reward that is recruited
by the prospect of an immediate gift certificate
to Amazon.com. The participant’s stream of
consumption was not likely to change any time
soon by obtaining an immediate gift certificate.
And the idea that the nonexponential compo-
nent of discounting is a function of a categorical
devaluation of anything that is not immediate is
inconsistent with behavioral data (Green &
Myerson, 2004) and conceptually problematic
since all goal-directed behavior, by definition,
entails delayed reward. The fact that the shortest
delay used in the study was 2 weeks makes it
difficult to discern a continuous effect of delay
if discounting is relatively steep (Ainslie &
Monterosso, 2004).
In order to address these concerns, McClure
et al. conducted a follow-up study (McClure et
al., 2007) that used primary rewards with clear
points of consumption; thirsty subjects were
asked to decide between receiving smaller
sooner and larger later amounts of fruit juice (or
water), with delays ranging from 0 to 25 min. In
addition to quasi-hyperbolic discounting, the
researchers considered a “continuous-time gen-
eralization” variant of quasi-hyperbolic dis-
counting in which value in the beta system was
exponentially related to delay but at a steeper
rate than the delta system. Present value for a
stream of consumptions (c1, c2, . . . ) dis-
counted accordingly can be represented as the
double-exponential discount function:
V ? w?
t?0
?
?tu?ct? ? ?1 ? w??
t?0
?
?tu?ct?
where u is the utility function, and discount
parameter ? and ? are bounded between 0
and 1, with lower values indicating steeper ex-
ponential discounting for each of the hypothe-
sized systems, and a weighting parameter, w,
also bounded between 0 and 1, that serves to
parameterize the relative contribution of beta
and delta systems. Although discounting is ex-
ponential within each system, the aggregated
result is nonexponential, since the differential
rates of the two systems means the net effect of
a unit of delay is not uniform across delays.
Again they reported frontoparietal activation
that was present during decision making regard-
less of immediacy and limbic and paralimbic
activation when an immediate or near immedi-
ate reward was possible. However there was
little voxel-level overlap in the identified beta-
regions across the studies, which may be related
to different reward types used or alternatively
could relate to timing differences across the
studies (Lamy, 2007). Their analysis indicated
that the identified beta system did not respond to
5SPECIAL ISSUE: ARGUMENT AGAINST DUAL VALUATION SYSTEM COMPETITION