Philosophers
should be interested in ‘common currency’ claims in the cognitive and
behavioural sciences.
David Spurrett (UKZN) for PSSA 2014
spurrett@ukzn.ac.za
Abstract
A recurring claim
made in a number of behavioural, cognitive and neuro-scientific literatures is
that there is, or must be, a unidimensional ‘common currency’ in which the
values of different available options are represented.
There is striking
variety in the quantities or properties that have been proposed as determinants
of the ordering in motivational strength. Among those seriously suggested are
pain and pleasure, biological fitness, reward and reinforcement, and utility
among economists, who have regimented the notion of utility in a variety of
ways, some of them incompatible.
This topic
deserves philosophical attention for at least the following reasons: (1)
Repeated invocation of the ‘common currency’ idiom isn’t merely terminological
coincidence because most of the claims are competing
explanations for one or the other of two putative kinds of fact. In one
case the currency represents a principle of manifest pattern in choices. In the
other, it is a functional part of the processes which produce choice. (2) We
can’t suppose that the different currency claims within each area are
compatible, because there are significant obstacles to identifying pairs of
members of either the ‘pattern’ or ‘process’ group. (3) There are, finally,
seriously opposed positions about the relationships (generally, and in specific
cases including that of humans) between the pattern facts and the process
facts.
Philosophical positions both favouring and
opposing a common currency exist. Philosophers who incline to view their
positions as at least partly empirical, should be more interested in the issues
outlined here than they are.
1. Introduction
A recurring claim
made in a number of behavioural, cognitive and neuro-scientific literatures is
that there is in fact, or must be, a unidimensional ‘common currency’ in which
the values (actual, or expected) of different available options are
represented. These currency metaphors partly succeed older, less overtly
economic, yet similarly quantitative ways of speaking of decision-making as a
kind of ‘weighing’, or of options attracting with varying ‘force’. What these images
share is doing approximate justice to the pre-theoretical notion that the value
– to the choosing agent – of two options may be equal, or unequal, and when
unequal that the relative difference between them can differ in magnitude.[1]
When all options are taken to stand
in these relations, we are on the way to a common
currency thesis.
The theses get
fleshed out in a variety of ways as the pre-theoretical notion is regimented in
specific scientific and philosophical contexts. Different kinds of argument and
evidence are appropriate to defending the more specific formulations. Here are
two fairly typical and widely cited examples:
“In natural settings, the goals competing for behavior are complex,
multidimensional objects and outcomes. Yet, for orderly choice to be possible,
the utility of all competing resources must be represented on a single, common
dimension” (Shizgal & Conover 1996).
“Any attempt to understand behavior in terms of the evolutionary
advantage that it might confer has to find a "common currency" for
comparing the costs and benefits of various alternative courses of action”
(McNamara and Houston 1986: 358).
These arguments
are at least superficially similar enough that they might be taken as variants
of a single argument, or as complementary arguments for the same thesis. Both
seem to demand a single currency, encouraging
viewing them as complementary. Indeed, the prospect that they, or combinations
of similar seeming arguments, might collectively justify multiple and
fundamentally distinct currencies (as opposed to superficially distinct ones
that turned out to be equivalent) is prima
facie perplexing. At the very least, the claim of one currency to be
‘common’ would be undermined by the existence of others.
One claim I defend
here is that this superficial appearance – that we have complementary arguments
for one claim – is misleading. Significantly different claims about common
currencies can and should be recognized. The remark by Shizgal and Conover
occurs in discussion of experiments demonstrating that behaviour allocation in rats
given choices between natural (gustatory)[2]
rewards and brain stimulation reward is sensitive to opportunity cost in the
un-chosen reward, and that combination rewards with components in both
modalities are (approximately) valued as sums
of their components. The ‘common currency’ in question is reward magnitude for
the individual rat. And Shizgal and Conover claim that this kind of pattern in
allocation – the sensitivity to opportunity cost and disposition to value
combination rewards as sums of their components that they call ‘orderly choice’
– is empirically observable and
warrants an inference to a common currency that contributes to the choice
process.
McNamara and
Houston, on the other hand, are describing the project of behavioural ecology.
They observe that this project presupposes that behaviours have determinate
fitness consequences, and seeks to determine what those consequences are. One
of their central claims is, furthermore, that the main successes of behavioural
ecology up to that time had focused on restricted currencies, such as net rate
of energy intake in optimal foraging models (e.g. Pyke et al 1977), and made
relatively little headway with interpreting more comprehensive behavioural
repertoires and life histories from the perspective of fitness. Such a
comprehensive mapping, though, would express the relative values of all
behaviours in an evolutionary common currency.
The two currency
theses (Shizgal and Conover’s on the one hand, and McNamara and Houston’s on
the other) are clearly not equivalent. Among the differences, one is centrally
concerned with fitness, the other with
something closer to subjective (expected)
utility. Only one of them seems concerned with the choice-making process.
Perhaps the repeated occurrence of ‘common currency’ talk is simply an
un-interesting coincidence of terminology: researchers talking about distinct
phenomena happen to use a superficially similar idiom. Perhaps, though, there
is a tangle worth trying to unravel.
I favour the
latter view, and in this brief paper offer a compressed survey of the terrain
in which common currency theses occur, along with a preliminary defence of the
claims that there is a tangle at all, and that the tangle is philosophically
interesting. Identifying all of the interestingly distinct claims about common
currencies, and assessing the bodies of evidence relevant to each, is far too
large a project for a single paper. My aims here are therefore more modest. In
what follows I introduce a classification of common currency theses (section
2), and explain why some of the thus classified theses should be understood as
competitors (section 3). Not all currency theses conflict, but where
combinations of them are possibly complementary, we find additional disputes
and disagreements (section 4), and this set of issues is philosophically
interesting (section 5).
2.
Common currency claims distinguished
Distinct claims
about common currencies or value scales occur in various scientific settings.
Generically, and perforce vaguely – to begin with – because different more
precise formulations pull in partly incompatible directions, a common currency
is a unidimensional quantity that different options have in varying amounts. A common
currency is a representation of what an agent maximises, or, more weakly, it is
some value ordering with which the agent’s behaviour is consistent.
The two main ways
of clarifying currency claims are, first, to specify in greater detail the
characteristics of the value scale (whether ordinal, interval, etc.), and, second,
to describe groupings within the range
of currency theses and the types of explanations in which they feature. The latter
task commands priority because the specific regimentation of the notion of
scale that is appropriate depends on what purportedly is being measured or
described and how. Here I focus mostly on classification, making only passing
remarks about scale.[3]
Claims about
common currencies are offered as explanations of one or both of two putative
facts:
The currency represents the fundamental principle in some pattern in
the choices made by some agent. OR
The currency is a characteristic of the processes by which choice is
produced.
Scientifically
interesting claims about common currencies, that is, can be divided into two groups. To mark this division I
follow, but slightly adapt, an established distinction, and refer to ‘ultimate’
and ‘proximal’ currencies. An ultimate
currency is a construct in a descriptive or explanatory theory of the behaviour
of some agent. A proximal currency,
on the other hand, is supposed to play some role in the processes by which
options are selected by an agent.
Any single ranking of options on a scale such
that behaviour can be described as – perhaps approximately – consistent with
that ordering counts as an instance of what I will call an ‘ultimate’ common
currency. An ultimate currency relates values to options, or to what selecting
those options achieves or perhaps have the function of achieving. It is easy to
imagine possible instantiations of an
ultimate currency (‘all of Jim’s actions are efficiently ordered to contribute
to the greater glory of the Flying Spaghetti Monster’) but among the
scientifically interesting forms of consistency, two families stand out. One of
these relate to fitness, and the
other to some of other form of utility.
To mark this
distinction I say that an ultimate currency can be evolutionary or subjective.
Here I’m knowingly, albeit slightly, departing from standard usage, insofar as
the usual way of distinguishing proximal from ultimate has the latter taken to
be synonymous with fitness promoting. The standard sense is partly preserved
here, because what I call an evolutionary
ultimate currency attributes values that are a function of contribution
to fitness. A guiding presumption of behavioural ecology is that behavioural
dispositions make contributions to fitness, and that to the extent that the
dispositions have a heritable basis, selection will tend to drive them towards
making (constrained) optimal contributions. The statement by McNamara and
Houston briefly discussed above is an exemplary assertion about an evolutionary
ultimate currency.
There are compelling
reasons for thinking that natural selection will operate on at least some behavioural
tendencies, and so a strong general justification for the project of
behavioural ecology. Nonetheless, the question of whether the behaviour
allocation of the individuals in any particular species does indeed tend to
optimise fitness (or would have in historical selective environments) is an
empirical one. Behavioural ecologists have studied many species and types of
behaviour and achieved striking successes in restricted domains such as
foraging and mate selection. These successes have often relied on focusing on a
simplified and more empirically tractable currency such as net rate of calorie
intake (in the case of foraging), or the health of the selected mate (in mate
selection). These proxy currencies plausibly contribute to fitness. Even so, success
relating behaviour patterns to the proxies falls short of establishing
relationships between all behavioural dispositions and overall fitness in any
species. Two of the most serious shortfalls are in the area of relative
allocation between significantly different modalities (such as calorie intake
versus pursuit of mating opportunities versus predator avoidance) and variation
in allocation over extended periods of time, including the full life-history.
A subjective
ultimate currency, in contrast, attributes values that are a function of the
revealed preferences or inferred utilities of the individual agent, without
requiring any relationship to fitness. The paradigmatic sciences of subjective
ultimate currencies are microeconomics (with variously regimented notions of
utility functions revealed through consumption) and behavioural psychology (where
strength of reinforcement is defined in terms of effect on patterns of
behaviour allocation). Evolutionary ultimate currencies, then, have stronger empirical
conditions than subjective ones, because the latter require ‘mere’ consistency
in behaviour, whereas the former require consistency in contributing to fitness.
The distinction
between evolutionary and subjective ultimate currencies, as I’ve sketched it,
conceals important technical variation. There are different and competing
fitness concepts, debates over the level (especially gene or individual) at
which selection operates, and differing positions over the correct (if any)
individuation principles for genes, genomes, species and other relevant
categories. There are also different and competing utility concepts, offering
different explanations of the same empirical data. (For example, some make
randomness a feature of the utility representation itself, while others
hypothesise randomness in the form of ‘trembling hands’ in the process of
expressing the preferences.) Surveying this terrain is beyond the scope of this
brief paper, but one further complication must be noted. It concerns two
different ways of understanding ‘consistency’.
Economists tend to
favour a strict notion of consistency because they recognise that predictable inconsistency
makes agents vulnerable to systematic exploitation, so such agents would lose
an influence on markets. Perhaps the best-known specific version of this worry is the argument that an agent with
cyclical preferences[4]
could be used as a ‘money pump’ (See Ross 2005, Chapter 5). Such an agent would
freely pay for a series of trades that eventually left it with no effective money
or stock. This convinces most economists that viable agency requires acyclicity
(‘transitivity’), among other criteria for consistency. Behavioural
psychologists, on the other hand, seek phenomenological fits of functions to
empirical data, and have recognised patterns in behaviour objectionable to
micro-economists. The clearest example of this is their accepting that the
generalised Matching Law applies to delayed rewards (Chung and Herrnstein 1967).
This implies that rewards are valued in inverse proportion to delay (i.e. by a
hyperbolic function), and the relative desirability of incentives at different
times can change simply with the passage of time. Given appropriate repeated
choices, cyclical preferences follow.[5]
That should mean vulnerability to money pumping, and non-behavioural economists
have favoured delay discounting according to exponential functions largely for
this reason (again, see Ross 2005, Chapter 5). The hyperbolic delay discounter is
inconsistent insofar as she temporarily prefers
smaller rewards that are immanently available. But to the behavioural
psychologist her choices are all consistently
reward seeking, in the sense that once some empirical parameters have been
determined, relative rates of behaviour are predictable.
The other main
role for currency claims is to explain the processes
by which options are selected. Such theses assert the existence of a ‘proximal’
common currency. Here are some examples. A realist about desires who holds that
for any pair of desires there is a fact of the matter about whether they are of
equal strength or one is stronger, is committed to a common currency thesis.
Shizgal and Conover’s inference regarding a “single, common dimension” is a
scientifically motivated claim about the cognitive requirements of producing “orderly
choice”. A conventional chess-playing programme generating a tree of possible game-states,
then attaching values to them on the basis of some alogorithm, in order to
select a best move (among the options explored in the available time)
implements a common currency. Finally, the leading current scientific research
programme focused on a proximal common currency is neuroeconomics, which seeks to
determine how utilities are represented in brains, and how these
representations are processed in choosing and learning (e.g. Levy &
Glimcher 2012).
Not everyone who
thinks that behaviour is consistent, and that there is a mechanical process
explaining behaviour selection, is committed to a proximal common currency.
This is because not all views about how behaviour is caused involve
representations, including value representations. One reason is respect for
what is now sometimes known as ‘Morgan’s cannon’:
In no case may we interpret an action as the outcome of the exercise
of a higher psychical faculty, if it can be interpreted as the outcome of one
which stands lower on the psychological scale. (Morgan, 1894)
Giant sea slugs (Pleurobranchaea), for example, are
carnivorous and typically eat any animal matter they run into, “including other
sea-slugs and their eggs” (Manning and Dawkins 1998: 226). They do not, however,
eat their own eggs during egg laying. This disposition is obviously fitness
enhancing: creatures that routinely consume their own offspring leave fewer viable
descendants. The mechanism which stops sea slugs from eating their own eggs,
though, while it could be regarded as in some very broad sense ‘cognitive’ is
not one in which values are represented (e.g. Godfrey-Smith 2002).[6]
When sea slugs lay eggs, they release a hormone that inhibits movement of the
mouth (Davis et al 1977). This simple
override exemplifies the ‘subsumption’ relationship between control layers
championed by Rodney Brooks (e.g. 1991), who famously maintained that
‘intelligent’ behaviour could be achieved in the absence of representation.
A claim asserting
a proximal common currency, then, is
not any assertion about mechanisms
producing behaviour, even consistent behaviour. A proximal common currency is,
rather, a single, structured and integrated set of states that represents
values, in at least the weak sense that there is a supportable mapping between
the states and values in an ultimate currency.
There are three
generic and complementary forms of argument in favour of a proximal currency.
The first attempts an inference to best explanation for observed order in
behaviour. The second considers abstract features of a control system, and argues
that the control bottlenecks make it more likely that some unified value
representation is playing a role. This is sometimes called the ‘final common
path’ argument (e.g. McFarland & Sibley 1975). Finally, there are cases
where it is claimed that a proximal currency has effectively been observed in
action, through study of the behaviour control system at work (e.g. in
neuroeconomics). All three are, furthermore, contested.
I maintain that scientifically
interesting talk about common currencies can almost entirely be organised into
arguments (i) in favour of or against one kind of currency in this taxonomy,
and (ii) in favour of or against inferences from ultimate to proximal
currencies. I regard this as a significant payoff of the taxonomy just outlined.
Let me now argue briefly that the set of currency theses to be found in current
science warrant serious philosophical examination.
3. Competitors, not complements
I discuss attempted
inferences between distinct currency
thesis types, especially from ultimate to proximal, in the next section. Here I
consider relationships between ultimate (pattern) and proximal (process) common
currency theses. The number of at least superficially distinct common currency theses
is striking. As we’ve seen, behavioural ecologists seek to relate patterns of
behaviour to their contribution to fitness.
Early utilitarians, and some contemporary theorists about pain and analgesia
claim that pain and pleasure provide a common scale (e.g.
Bentham 1789, Cabanac 1971, Leknes & Tracey 2010). Behaviourist
psychologists refer to reward or reinforcement, while contemporary
economists are more likely to advance a currency thesis about utility. In addition some of the central
concepts which characterise the scales have been theoretically elaborated in varied
ways. This is most striking in the case of utility, both within economics,
including behavioural economics, and in neighbouring areas such as decision
theory.
This mere
proliferation is not intrinsically interesting,
of course. Perhaps the various theses are complementary. In the case of ultimate
currencies, there is, prima facie, a prospect of pluralistic harmony, because
such theses are claims about pattern. And, surely, more than one kind of
pattern can be discerned in the same data. It is, though, an observation that
is familiar to the point of banality that subjective preferences – for example
for sex with contraceptives – don’t always coincide with what is fitness
promoting. More generally, and not only in humans what is fitness promoting is
not always motivating, and what is motivating is not always fitness promoting.
The fact that animal subjects in behavioural experiments would work for
non-nutritive sweeteners, for example, was recognised decades ago as an obstacle
to identifying reward with evolutionary interest (see, e.g., Rachlin 1991,
Chapter 3).
It is not unusual,
in fact, to find biologists expressing scepticism about the chances of a
currency thesis outside biology, even while being optimistic within it. Maynard-Smith,
for example, suggested that “it has turned out that game theory […] is more
readily applied to biology than to the field of economic behavior for which it
was originally designed”. And part of his justification for this is that he
finds utility to be a “a somewhat artificial and uncomfortable concept”,
whereas in biology “Darwinian fitness provides a natural and genuinely
one-dimensional scale” (Maynard Smith 1982, quoted in Glimcher 2002, p323).
Many economists
and behaviourists dispute this, on the grounds that the utility concept is in
much better shape than Maynard-Smith allows. My point is not to endorse either
view, but to observe that the lack of consensus suggests work for applied
philosophy of science. One impediment to taking sides is, in any event, that economists
disagree with each other. There are competing formulations of utility and
disputes over which do best justice to the evidence, or best suit what
theoretical purposes. I noted above that economists’ concern with consistency
leads them to favour exponential delay discount functions, while behavioural
psychologists are more inclined to hyperbola-like functions. This is just one
instance of a wider pattern. To give one more example, defenders of prospect
theory (e.g. Kahneman & Tversky 1979) claim that their model, built to
account for phenomena including apparent violations of the independence axiom, and
asymmetries of risk sensitivity in gains and losses, does better justice to
data about real human choices. Sceptics, though, express frustration that the sheer
number of free parameters in prospect theory undermines the empirical value of
such fits (see Glimcher 2011, Chapter 5).
A further incompatibility
between the currency claims of behavioural ecologists and psychologists arises
because they seek to explain somewhat different things, even while both calling
it ‘behaviour’. We’ve noted the giant sea slug’s apparent restraint over eating
its own eggs. My point there was to explain why behavioural ecologists are often
carefully agnostic about proximal common currencies. Similar cases can also be
used to make a different point. For example, a textbook case in in behavioural
ecology is clutch sizes in oviparous species (on birds, see e.g. Lack 1966).
There’s substantial evidence that clutch sizes in many bird species are close
to what would maximise lifetime reproductive success of parent birds, whose
situation involves trade-offs between current and future clutches, and between
members of individual clutches, given that larger (better fed) young generally do
better.
Some of the
determinants of clutch size plausibly respond only to phylogenetic rewards,
where successful offspring are the payoffs in repeated games with genotypes as
the players or strategies. There is little reason to think, though, that clutch
size is modifiable by reward or punishment directed at the individual bird, any
more than one might bribe a giant sea slug into eating its own eggs. But
responsiveness to reinforcement is what would make it behaviour for a behavioural
psychologists or economist.
What about proximal
common currency theses? It seems that multiple distinct proximal theses raise the prospect of over-determination.
That is, if the mechanisms of choice include more than one structured and
integrated set of states representing values and involved in causing behaviour,
then we’d have more explanation than we needed. (‘I did it because it had to
most expected utility, and it was
pleasurable and I preferred it…’) This
worry could be dissolved if it turned out that the different proximal currency
theses expressed substantially the same claim, so that what some kind of agent
wanted (or desired) was also what it liked (or gave it pleasure) and what promoted its fitness.
The prospects for
such an outcome, though, are slim. Among other reasons, behavioural economists
have drawn attention to various examples of apparently motivated behaviour involving
considerable pain, for example mountaineering (e.g. Loewenstein 1999). Brain
scientists studying the learning, enjoying and choosing brain now mostly maintain
that ‘wanting’ and ‘liking’ (including enjoying and suffering) are neurally and
functionally dissociated and that only the former promises to provide a
perspective from which behaviour can be understood as consistent with some
value representation (e.g. Berridge 2004). These arguments conflict directly
with the claim defended by some researchers on hedonic experience that pain and
pleasure provide a common currency for behaviour selection (e.g. Leknes and
Tracey 2010). Whatever consensus eventually emerges, it seems clear that no
more than one of the current proximal common currency theses can be correct.
4. Inferences from ultimate to proximal currency
theses
Within categories
– ultimate and proximal – different common currency theses, then, are
competitors, but there are obvious ways that one thesis of each type could be complementary.
If the order in behaviour warrants attributing an ultimate common currency,
then this might justify hypothesising a proximal currency involved in producing
the pattern. Conversely, if we had grounds to suppose that some agent’s cognitive
processes implemented a proximal common currency, we might expect its behaviour
to exhibit pattern consistent with an ultimate currency. Versions of both
inferences have been defended, and contested.
The range of
options for relations between proximal and ultimate currency theses is
approximately analogous with those regarding the status of folk psychological
kinds in in the philosophy of cognitive science. (Analogous might not be the
best term, because folk psychology includes
desires and beliefs. But most of the debates over folk psychology focused on epistemic
states – like belief, perception, and memory – to the relative neglect of motivation
states, like desires.) The major options are realism (beliefs are scientifically
respectable), eliminativism (cognitive processes include nothing sufficiently
like beliefs for belief talk to pass scientific muster) and attributionism, for
example Dennett’s intentional stance (the conditions for belief attribution exclusively
concern pattern in behaviour). Approximately corresponding to this, we find the
following positions regarding proximal common currencies:
First there are
realists committed to the existence of cognitive states standing for the
motivational strength of different courses of action in humans, and at least
some other agents. Examples include typical realists such as Fodor (1983), some
scientists specialising in hedonic experience (e.g. Cabanac 1971) and
neuroeconomists identifying preferences with brain states. A paradigmatic
example of an inference from pattern to proximal representation is, of course,
the syllogism stated by Shizgal and Conover (1996) quoted above, linking
‘orderly choice’ with the requirement of ‘representation’ on a common scale.
Second, are
eliminativist positions, denying – to varying degrees – the reality or
necessity of cognitive states corresponding to desires. Brooks (1991), for
example, argues against the need for representations of any kind to produce
‘intelligence’. For him the world is ‘its own best representation’. Brooks
directs most of his fire against representations in the sense of models of the
external environment, but his arguments clearly imply rejection of
representations of values.[7]
Brooks’ work remains an inspiration to some philosophers. Clark (e.g. 1997, chapter
9) claims that pattern in human economic choices depends heavily on highly
scaffolded choice environments. Sterelny (2003), on the other hand, suggests
that the cognitive implementation of preferences in humans is “incomplete”, and
that pattern in the behaviour of most non-humans can be explained without
hypothesising preference like states as parts of their cognitive architectures.
Finally, we find
attributionists, emphasising the view that the work of those who trade in
ultimate common currencies is independent from proximal considerations. The
exemplary contemporary attributionist about folk psychology is Dennett, and
scientific attributionists share behaviourist inspiration. Micro-economists
mostly regiment their notion of utility so that it makes no psychological or
hedonic commitments, in favour of specifying different degrees of consistency
that can be empirically manifest in behaviour (e.g. Samuelson 1938, see Ross
2005). Behaviourist psychologists are similarly suspicious of – or hostile to –
claims about hedonic experience, and favour more empirically tractable notions
such as reinforcement and reward (Thorndike 1927).
The task of
assessing the strengths and weaknesses of realism, eliminativism and
attributionism in the case of the more epistemic aspects of folk psychology
(believing, perceiving, remembering, inferring…) attracted wide and deep
philosophical activity over several decades. Over this period considerably less
attention was paid to the motivational aspects of folk psychology (wanting,
desiring, choosing). In the final section of this brief survey I attempt to say
a little more about why these topics deserve more attention.
5. This is philosophically interesting
Suppose that I’ve
convinced a reader that there is a tangle of variously competing and (possibly)
complementary theses about common currencies across a number of cognitive and
behavioural sciences. Why think that this tangle is of any philosophical significance? Among the reasons I could offer, let me
single out three.
First, there’s an
image of philosophers associated with Locke as a kind of conceptual janitor for
empirical science (Locke’s image, in the Epistle to the Reader of his Essay concerning human understanding,
was of an ‘under-labourer’). Such conceptual work is more clearly indicated,
perhaps, in cases where there is conflict within and between empirical
sciences. To illustrate this, consider the different situations of behaviourism
in psychology, and economics. Behaviourist psychologists thought of themselves,
to state the obvious, as being in the psychology business, although driven by a
distinctive vision of what it meant to do that business in a methodologically
serious way. Their rejection of introspection was methodological, motivated by
the consideration that scientific evidence should be inter-subjectively
available. Consistently with that commitment, some more recent behaviourists
have argued that reports of subjective experience can be a kind of data (e.g.
Dennett’s ‘heterophenomenology’ in his 1991). Furthermore, advances in
measuring devices have made previously unobservable brain processes amenable to
empirical study, and so allowed different kinds of data to pass muster by
behaviourist lights. Neuroeconomics now promises to provide an empirical basis
for a theory of reinforcement or reward that
explains observed pattern in what behaviour can be reinforced, and to what
degree. While some individual behaviourists might reject specific theoretical
suggestions in this area, the lack of some
theory commanding wide acceptance has long been recognised.
Given the noted
inspiration behaviourism provided for contemporary formulations of the concept
of utility in economics, one might expect similar enthusiasm for neuroeconomics
among working economists. Instead, one finds lively and sometimes intensely
polarised debate. This should not be especially surprising. Unlike
behaviourists, who had a distinctive view about how psychology should be done,
economists (who used to view their discipline as at least closely linked to
psychology – e.g. Jevons 1911) view their discipline as having made progress by
getting out of the psychology business entirely. While some behavioural
economists have more recently sought to move in the opposite direction, they by
no means dominate the profession.
This helps explain
some of the response to an enthusiastic early manifesto for neuroeconomics (Camerer,
Loewenstein and Prelec 2005). Here, and in related publications around the
time, it was claimed that a new and importantly psychological research programme
held out the hope of providing new ‘foundations’ for microeconomics. While the
experimental techniques would have amazed Mill, Bentham, Jevons and their
colleagues, the generic view of the relationship between economics and
psychology probably would not. But 2005 is not the eighteenth century, and one
of the most spirited responses to neuroeconomics was called ‘The case for
mindless economics’, and argued forcefully (whether or not correctly) that
economics and psychology were separated by a ‘logical’ gulf, that they
addressed “different questions”,
used “different abstractions” and relied on “different types of empirical
evidence”, with the consequence that neuroscience could have no bearing on
economics whatsoever (Gul & Pesendorfer 2005). It
should not need pointing out that this dispute is, among other things, a
special case of a wider and older debate about the status of folk-psychology.[8]
Second, the
specific issues relating to the status of folk-psychology that arise in the
case of motivation, and with respect to the credibility of this or that common
currency thesis, are not simply ‘more of the same’ in the sense of being mere
repetitions or generalisations of arguments about beliefs or representations.
Were that the case, there would still be philosophical work to do, because
applying whatever lessons emerged from the earlier debates would depend partly
on specific details that science has revealed in the domain of preference and
decision. Brooks’ general case against representation, for example, is widely
recognised as failing in the case of belief except for very simple control
systems, and may also fail in the case of preference, but perhaps not for the
same reasons.
But there are also
important ways in which things are different
here. The ‘old’ debate over folk psychology was, as noted, disproportionately
focused on epistemic matters, and so unsurprisingly much of the traffic with
philosophy was in areas relating to epistemology and language. But those aren’t
the most obvious or promising sources of exchange in the case of desires.
There, in fact, the fruitful exchange is more likely to be in areas engaged
with thinking about practical reasoning and decision, and thinking about value.
Third, and
finally, philosophers already defend, assume or deny common currency theses or
positions implying such commitments. A common opening move among decision
theorists, for example, is to assume that values – whatever their ‘content’ –
can be represented with the real numbers (e.g. Briggs 2010). More generally
what one might call ‘empiricist’ views of motivation suppose that there is a
central economy of desires competing on the basis of their strength, however
that strength is understood. On the other hand more ‘rationalist’ views favour
the view that in at least some cases motivation is not simply a matter of
relative strength of desires, but is rather rule-based, or otherwise based on
reason in opposition to desire.
Whether or not
directly defending rationalism in this very loose sense, a number of lines of
philosophical thinking oppose, directly or by implication, the thought that all
options are valued on a single scale. Among the examples of this are: arguments
that some options or values might be incommensurable, in the sense that there
is no fact of the matter about which is more valuable, or whether they are
equal (e.g. Raz 1986, Williams 1981); positions maintaining that some values
are ranked ‘lexically’ in the sense that any amount of some – no matter how
small - is worth more than any amount of others – no matter how large (e.g.
Rawls 1971). In addition, in some recent empirical literature we find arguments
that some values are ‘protected’ or ‘sacred’ and somehow isolated from
trade-offs with others (e.g. Baron & Spranca 1997, Atran & Ginges 2012).
A number of
long-standing philosophical questions about desire, decision, preference and
practical reasoning, then, (and this survey is woefully short of comprehensive)
are partly questions about the degree
to which motivational systems are, or can be, unified, and about the kinds of
ranking and hierarchy systems of value or motivational strength can or should
have. Common currency theses – whether affirmed or denied – provide a useful
level of abstraction that permits comparison of otherwise mutually isolated
theses and theories, and a substantial and tangled scientific terrain is
debating aspects of these very questions.
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[1] Some
have an opposed hunch that there is no fact of the matter about the relative
ranking of at least some options, perhaps because they are incommensurable
(e.g. Williams 1981, Raz 1986).
[2] The
‘natural’ rewards were modified in various ways in order to manipulate their
similarities to and differences from brain stimulation reward (BSR). Shizgal
and Conover make further inferences about the neural representation of value on
the basis of how BSR and gustatory reinforcement respond differently to these
manipulations.
[3] For
a classic discussion of the formal properties of some notions of preference see
Luce and Suppes (1965), and for more general remarks on scales and measurement
see Suppes and Zinnes (1963).
[5] Nobody
has done more than George Ainslie when it comes to thinking seriously about
what it would mean for humans if we value rewards approximately in inverse
proportion to their delay. See Ainslie (1992, 2001).
[6] I
follow Godfrey-Smith’s suggested policy regarding understanding ‘cognitive’ in
a broad way to embrace the processes controlling behaviour, even in systems
(e.g. some plants and fungi) that lack central nervous systems.
[8] A striking feature of much of this
specific version is repeated invocation of the notion of a common currency
(e.g. Levy & Glimcher 2012).
Hey,
ReplyDeleteI enjoyably read parts of your common currencies blog a couple days ago - it's a fun read.
I was a little puzzled that it seemed like you don't leave much room for the idea of agents with consistent behavior, without a proximal currency but with representations. For example, in the why philosophers should be interested paper: "Not everyone who thinks that behaviour is consistent, and that there is a mechanical process explaining behaviour selection, is committed to a proximal common currency. This is because not all views about how behaviour is caused involve representations, including value representations."
Perhaps you're not really committed to this view and just expressed it this way because of space constraints or perhaps 'mechanical process' is doing some work for you here, but otherwise the 'This is because' seems wrong to me. I'd claim that the 'interesting' reasons people may hold the view in the first sentence mostly have nothing to do with denying representations but rather with models which posit processes like rule-based decision making. Another way of putting this is that it seems to me that there are interesting questions about the correctness of views which claim that process models should posit a common currency, but the opposition to these views worth grappling with isn't solely (or even mostly) views which deny representations but rather views which deny that the way all decisions are made is by assigning a value to each option and then choosing the option with the highest value.
But perhaps I'm misreading you and just missing something obvious!
John
Hey John,
ReplyDeleteThanks for the comment/question.
Space constraints did indeed force me to be rather cryptic in that paper - the conference proceedings maximum length was about half the size of my working draft. (A slightly revised version of the text above is now in press, but I'm also still tinkering on the longer version.)
That said, no, you’re not misreading me. But I agree that you’ve described a possibility that my ‘because’ elided. So here’s a longer (not exhaustive) list of options, given order/consistency in behaviour:
1. There’s a mechanism and it consumes an orderly value representation. (Inferring from ultimate to proximal, as some think we must.)
2. There’s a mechanism, but it doesn’t consume an orderly value representation:
2a. It’s some kind of architecture with no representations at all. (One class of examples would be subsumption architectures, but other distributed architectures might also be candidates.)
2b. It’s some kind of architecture with an incompletely orderly value representation. (A mix of valuations and procedures, or valuations and subsumption, or …)
2c. It’s some kind of architecture that consumes representations, but not value representations.
I reckon, by the way, that humans are instances of (2b).
I take it that (2c) is what you were driving at when you referred to “rule-based decision making”. And yes, that’s a perfectly coherent option. (One could also hypothesise a large enough lookup table, which might count as representational but for all that not involving rules in any interesting sense.)
I wonder how much consistency (with some behaviourally determined preference ordering) it would be possible to get a rule-based system to exhibit without it processing representations that stood for preferences. Do you have any thoughts about this?
Meant to reply a while ago. This'll be a little scattered. I think that's a useful list of the possibilities. I'm not sure though that your description of 2b and its gloss in parentheses match up, although I'm also not exactly sure what 'incompletely orderly' means. In particular, I'm not sure whether it means that you can assign a value to anything but these values induce, for example, transitivity violations or whether it means that there are some things you cannot/do not assign a value to. I'd like to keep as separate possibilities systems which exclusive take in values but these values do not induce consistent preferences and systems which do not exclusively take in values.
ReplyDeleteI'd guess that humans are examples of the gloss of 2b.
Something like 2c is what 'rule-based decision making' was pointing to, although my own view obviously isn't that people exclusively do this. To flesh out my thought a little, the kind of idea I had in mind was something like elimination by aspects (chosen as an example only because it's classic). People are choosing from some consideration set, they go through this procedure, and they eliminate items giving rise to some set of preferences. I initially thought of this as a case where it doesn't seem like you should necessarily posit a system which takes in values, but perhaps proponents would want to posit some kind of ordinal one.
With respect to your question re how much consistency a rule-based system might exhibit, I think that's an interesting question, but that half the work is probably making the question itself precise enough to get a handle on :) I think that could well be a useful thing to try and do. The question makes me realise that I'm not sure the extent to which you want to conflate representations which stand for preferences and representations which stand for values.
John
Thanks again, John. A partial response for now:
ReplyDeleteElimination by aspects is a useful case. It could provide an example of what I meant by an incompletely ordered value representation. Suppose that I was choosing a car, and wanted more top speed, more acceleration, more fuel economy, and more rear leg room. But I was also bad at expressing (and perhaps just didn’t have) a determinate sense of how I’d trade those off if required to. Then I might choose by eliminating aspects, but my partial valuations (of separate aspects) would be inputs to that process.
But maybe I’m choosing a novel as a gift, and I want a title less than one year old, by a writer who has won at least one prize before, where the story is set in Ireland, but also involves animals. Then my elimination by aspects process will be more procedural - I might not ever have to deal with relative valuations at all - especially if I’m happy to accept the first candidate that satisfies all the conditions.
Two things about this, though:
(1) We need to be careful to hold constant the fact that the behaviour produced is supposed to be consistent. This matters because the issue (in the rather cryptic paragraph you commented on) is competing explanations of consistency, and whether they refer to proximal mechanisms that consume representations, including representations of value.
So returning to elimination by aspects, compare the two illustrations I came up with. In the one case it seems possible that elimination by aspects could sometimes produce consistent choice (that is, consistent with a definite ‘exchange rate’ between quantities of the various aspects, which might be discoverable via something like conjoint analysis). But it’s hard to see that it would generally or always.
But in the second case, it seems far less likely that choice would be consistent. Elimination by aspects transforms intractable (or prohibitively expensively tractable) problems into more tractable ones that produce decent enough solutions often enough.
(2) I think there’s more than one way of a value representation being incompletely ordered. Here’s one: It might be ‘locally complete’ for a number of separate categories of valuation (food, mate selection, nest location) but instead of all of those having determinate exchange values, the overall ‘mode’ of activity could be determined by semi-procedural systems. (For example, ones that simply interrupt or over-ride foraging when mating prospects are identified.)
Here’s another: It could be made of a series of locally complete orderings, but which are organised into a hierarchy with discontinuities, such that no amount, no matter how large, of any good from a ‘lower’ level was worth as much as any amount, no matter how small, of one from a ‘higher’ level. (People sometimes say something like this about so-called ‘sacred’ or ‘moral’ values.)
I’ll keep on thinking about other parts of your comment.