predictability of behavior.doc

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Predictability of behavior

Empirical and theoretical issues in the predictability ofhuman behavior

Introduction

No curious person still lingers on the mystery of our bodiesorigins. Where once our best explanation of the human form drewa line between the natural and the divine, we now see acontinuum of evolved creatures. But few of us, even many whoaccept our natural origins, are ready to abandon all forms ofthe lan vital and see a human being as nothing more than abundle of mechanisms. Most still cling to a dualistic view in which,through means unspecified, we somehow remain metaphysicallyautonomous agents. Galen Strawson put it this way:

Almost all human beings believe that they are free to choosewhat to do in such a way that they can be truly, genuinelyresponsible for their actions in the strongest possible sense;responsible period; responsible without any qualification;responsible sans phrase, responsible tout court, absolutely,radically, buck-stoppingly responsible; ultimately responsible, in aword and so ultimately morally responsible when moral matters

are at issue.

If human beings are notfree in that wayif our brains are thepurely biological machines they give every evidence of being,built by genes, sculpted by development and life historythenwhat are we doing when we assess a persons status as a rationalagent, grade their competence to make important decisions, orhold them responsible for their actions? How does ourunderstanding of the brain bear on how we treat people and dealwith each other socially? Neuroscience is more than on its way to

resolving the conditional: it has arrived. We are not free agents. Inthis article, we will review some of the evidence leading to thatconclusion and begin to address some of the questions it raises.

Philosophical perspectives


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The sort of freedom Strawson describes is called libertarian freewill. Most people probably find it so intuitively obvious that theywould flatly reject any alternative as preposterous. This proveshasty, because even without leaning on neuroscience, problems

emerge rather quickly. For one thing, your apparent freedom isnot absolute: do not think about zebras for the next fifteenseconds. That you cannot help from doing so shows thatenvironmental stimuli (or an authors perversity) can overridewhat you take to be absolute control over your own thoughts.

Second, consider David Humes (1739) Treatise of HumanNature, in which he argued that free choices are not uncaused.Such choicesfree here meaning unforced, not coerced byother agents or circumstancesare not usually capricious, but

rather careful deliberations based on desires, intentions, goals,prior experience, and so on. But this is equivalent to saying that ifa third party knew your desires, intentions, etc. and also knewthat you were acting according to them, then your actions wouldbe, to the same degree as the perfection of the third partysknowledge, predictable. The alternative to predictability israndomness, but an overriding commitment to random acts is notthe kind of free will we think we have. If, in order to be free, onemust make only those choices that have absolutely no correlation

with anything we want, know, or believe, then freedom, it seems,has been relegated to the basest form of chaos. The moreschizophrenically one behaved, the more free one would be.Indeed, the mere fact ofwanting somethingconstrains ourfreedom, not only because it biases our behavior in predictabledirections, but also because we do not seem to be freeto choose what we find pleasing. As Schopenhauer said, you maybe free to do what you want, but you are not free to want whatyou want.

As a corollary to Humes argument, one can see quite clearly afirst cause problem: if we were ultimately responsible in thisway, then we would stand, as it were, at the beginning ofcausality. We would be causeless causes (causa sui), origins untoourselves, or to philosophers, agents oforiginativeresponsibility. An axiom of methodological naturalismof scienceitselfis that every phenomenon, every effect in the universe has


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a cause. Every one, that is, except for the wayward decisions of aparticular Earth-bound primate. Either the presumptuousness orthe illogic of that position alone ought to constitute sufficientgrounds for skepticism.

However reasonable these rebuttals may be, philosophers have aspecial talent for squeezing the maximum possible confusion fromany given problem. Is there any scientific problem with free will?Are there any data?

Neurophysiology of motor intentions

Benjamin Libet (1983) conducted the seminal experiment. Humansubjects outfitted with an EEG cap were asked to watch a rapidlymoving clock hand and move a finger whenever they wished.Once they moved, they indicated where the clock hand had beenwhen they first became aware of their intention to move. Thismoment turned out to average about 200 msec before motiononset. Libets EEG recordings, however, showed that a readinesspotentiala discernible electrical signal in the cortexhadbegun about 1400 msec before the movementthus more than asecond before the subject reported a conscious intention to move.While the length of that duration depends on experimentalparticulars, the basic ordering of unconscious preparation first,

followed by intention, has been replicated many times. Thisclearly suggests that conscious intention is not the proximalcause of behavior.

Lau et al. (2004) extended Libets results by upgrading from EEGto fMRI. In the time leading up to movement, neurons in the pre-supplementary motor area (pre-SMA), dorsal prefrontal cortex(DPFC), and intraparietal sulcus became active. The precisefunctional role of these areas has not been firmly established (seeRoskies, 2010 for a review), but it appears that the pre-SMA maybe more closely linked to actual execution, while the other twoareas collaborate in generating forecasts of motor plans. More onthis below.

It is well known that brain injury can impair our ability to executea wide variety of cognitive tasks. Motor and speech problems, forexample, are usually evident to the patient, memory loss and


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cognitive impairment perhaps only to others. Discoveries of braincorrelates of volitional movement, such as those described by Lauand others, raise the possibility that lesions to those areas couldalter the phenomenology of volition and free will itself. To that

end, Sirigu (2004) found that patients with parietal lobe lesionscould accurately assess the time at which a movement hadbegun, but had impaired awareness of their own intention tomove. Rather than the 200 msec warning, their intention tomove entered consciousness only 50 msec prior to movement.Desmurget et al. (2009) showed an even subtler functionaldissociation. Human patients undergoing awake brain surgery hadelectrodes inserted into their inferior parietal lobes and frontalpremotor cortex. Weak stimulation of the parietal lobeactually induced feelings of intending to move; stronger

stimulation enhanced this feeling to the point that patientsclaimed that they actually had moved, when in fact they had not.Stimulation of the premotor cortex did the reverse: induced anactual movement but without the patients awareness. In relatedstudies of healthy subjects (no surgical intervention), Ammon &Gandevia (1990) and Brasil-Neto at al. (1992) successfully alteredfree choice of which hand to move by interfering with thesupplementary motor area via transcranial magnetic stimulation(TMS). Subjects choices were strongly influenced but the subjects

themselves disavowed any such influence.

Roskies (2010) reviews a number of primate studies in anexperimental paradigm first described by Newsome et al. (1989).A monkey views a field of moving dots and moves a joystick inthe direction the majority of the dots are moving. Correct answersare rewarded. Neurons in the lateral interparietal area (LIP) play akey role in this task. When active, they signal the subjects choiceof an action plan (e.g. move the joystick to the right) and theexpected hedonic value of that action (e.g. how much of a reward

the subject anticipates as a consequence of the behavior). Bystimulating LIP, experimenters can bias the response and causesubjects to (for example) select a rightward joystick movementwhen in fact the visual stimulus was not coherently to the right.Roskies notes that LIP is probably not unique in this regard andmay be but one example of a whole class of modality-specific (inthis case, visuomotor) decision-making circuits. There may be


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modality-independent circuits as well: neurons in dorsolateralprefrontal cortex (DLPFC) can also be used to predict behavior,and also have firing rates that vary with expected reward value.

A general though admittedly not universal pattern begins to

emerge from these and related studies. With respect to bodilymovement, neural ensembles in the dorsal prefrontal cortex (andperhaps parts of the parietal cortex) compete with each other todetermine the action plan that will maximize expected hedonicreturn. During this phase, subjects are not aware of havingformed an actual intention to take action. Once this competition iscomplete, the winning motor program is sent both to thesupplementary motor area and to inferior parietal cortex. Themotor area activation produces the movement but no awareness

of intention. The parietal activation generates a prediction aboutwhat the body position (and perhaps too a broader representationof the spatial arrangement of the world around us) will be oncethe motor program is complete.This prediction of the way theworld will be, once the action is complete, is identical with thephenomenology of intention to move.

On one hand, this seems, in hindsight, not altogetherunsatisfying. The parietal lobes in general provide a variety ofspatial processing services. Inasmuch as an intention to move is a

forward-looking model, an envisioning of a goal state, andinasmuch as we are talking about physical movement, it seemsreasonable that a clear spatial picture of that goal state could becloser to intention than, say, the means by which we will achieveit. Iintend to exit the room. I dont intend to lift my left knee, flexmy quadriceps, etc. The intention is the goal state, and the goalstate is an updated spatial arrangement of body- and world-state.Since such representations are the business of the parietal lobes,the model seems at least plausible.

Psychological mechanisms: Why do we feel free?

As disconcerting as it may be to confront the possibility that wemay not be as in charge of ourselves as we thought, there seemsto be no getting around the fact that even if we arenotin charge,we feel as if we are. Under normal conditions, we do not feel like


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passive observers of our own behavior (as we do with, forinstance, the patellar reflex), coerced by external forces, orcompelled to move on pain of internal discomfort. Rather, we feelthat we are in the drivers seat of our bodies. At each moment we

can turn or accelerate in whichever direction we like. Havingchosen, we feel in retrospect that we could just as easily havedone otherwise. As the results above reveal, however, at leastsome of these impressions are mistaken. Perhaps we might havedone otherwise, but if so, it wouldnt have been conscious choicethat made the difference. Our intention to move is not theproximal cause of our movement. So why do we feel that it is?

One answer may follow from the competing neural ensemblesmodel described above. In that model, discrete populations of

neurons in the frontal cortex simulate alternative behaviors. Theensembles then compete, one motor program wins, and is actedon. Haggard (2005) suggests that the brain, in the interests ofcomputational efficiency, allows the representations of all losingmotor programs to dissipate. From an attentional perspective, itwould be overwhelming to be aware of all those things that wemight have done but didnt. While the neural ensemblesrepresenting unused programs shut down and therefore lost toconscious awareness, the winning program can beand

possiblymust

bekept active so as to compare the predictedmotion with the actual motion and thereby generate an errorsignal used in learning and online behavioral correction. Theoutcome of this programmatic pruning is a reliable sequence:a single motor program followed by movement. We interpret suchconsistent temporal correspondences as causal chains.

In a related model, Wegner (2005) asks us to imagine a magicalprocess by which we could always know when a particular treebranch was going to move, and in which direction. Further

assume that by the same magic, we would always happen to bethinking about the tree branchs motion just before the event.Observing the reliable sequence of eventsour thought, followedsoon after by the real motion of the branchwe could scarcely failto conclude that our thinking of it was the cause of the motion.And yet, the setup can stipulate from the beginning that no suchcausal connection exists. Wegner proposes thatattending to ones


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model of oneself before a behavior gives rise to the sense ofcausal agency. To unpack the metaphor, we need a source ofmagic, which could spring from the brains representation oftime. We know from other examples that the brain plays tricks in

this way. Given neuronal conduction velocity, for example, weshould see our foot touch the ground before we feel it, but wedont. The events seem simultaneous. This could be because ourbrain takes the sensory signal and, as it were, spoofs thetimestamp.

Inferences of causal agency can be affected through interventionsmuch simpler than the neural-level ones mentioned above.Gibbons (1990) asked subjects to imagine you are rushing downa narrow hotel hallway and bump into a housekeeper who is

backing out of a room. If subjects were asked this question whilefacing a mirror or hearing their own voices on tape, they becamemore likely to say that they were the cause of the collision. This isprobably not trivial, because judgments of agency imply a worldmodel and chains of causes and effects. What Gibbons showedwas that models of ones own agency could be changed viaseemingly minor cognitive manipulations.

The moments in which we are attending to ourselves as agents inthe world are of special importance in evolutionary terms,

because they are moments when the process of learning aboutour ability to influence our surroundings is in full force. Ourattention is more engaged in these moments than it is when weexecute a well-worn routine. This attentional asymmetry producesa textbook example ofconfirmation bias: the moments when weare most alert and therefore most likely to remember are exactlythose moments in which we are most likely to experience theillusion of causing our own behavior. In hindsight, our own causalagency stands out as a key feature of conscious existence.

Implications and applications

Surely most audiences outside the particular psychological andneurophysiological subfields discussed here are unaware of thesefindings, so it should not surprise us that they continue to seethemselves as buck-stoppingly free. Suppose, however, that they


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were aware of these findings. What would be the result? Onemight expect lukewarm reactions, not least because weakeningthe causal role of intention seems to have disturbing implicationsfor the law, criminal law in particular, and other areas of applied

ethics. As we will see, however, some of these concerns aredispatched by reference to de factocurrent practice. Moreover,the intuition that libertarian free will is necessary for attribution ofresponsibility stands, on deeper reflection, in direct conflict withreasonable definitions of a functioning system of justice. -But letus start with a summary of current practice.

Philosophers of criminal justice make a distinction betweenconsequentialist and retributivist motivations for punishment.Consequentialist motivations include deterrence (dissuading

would-be criminals), incapacitation (preventing future bad actsfrom a criminal already caught), rehabilitation (turning a criminalinto a productive citizen), and restoration (restoring something tothe victim(s) of a crime). These are all practical concernsmotivated by the desire to create a functioning society, and itdoes not take a great imagination to conceive of such efforts asfinding harmony with even strongly mechanistic views of theindividual. Deterrence, for example, requires nothing more or lessthan a careful study of behavioral conditioning. Understanding the

principles involved and being able to apply them to a desiredeffect is, to be sure, an exceedingly complex problem, not leastbecause the governments of free societies cannot control most ofthe influences on a given person. But this is a practical concern.

The conceptualization of a person as a bundle of mechanisms iswell suited, as far as it goes, to a science and technology ofdeterrence. The other three consequentialist motivations can besimilarly grounded.

Retributivist motivations for punishment, in contrast, are based

on the idea of moral redress. In that sense, they look backward intime and dispense punishments proportional to the infraction.Greene & Cohen (2004) summarize the retributive philosophy asone under which we legitimately punish to give people what theydeserve based on their past actions in proportion to theirinternal wickedness, to use Kants (2002) phraseand not,primarily, to promote social welfare in the future. Despite its


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seemingly metaphysical basis, retributive justice is the dominantphilosophy in many, if not most countries, including the UnitedStates, partially because rehabilitation in practice has proven sodifficult.

Unlike consequentialism, retributivism seems less easilyreconciled with the picture of man as a bundle of mechanisms,lacking in originative responsibility. This appearance, however,loses some significance when put into context with the waycriminal prosecution actually operates. As summarized by Morse(2007):

The law does not treat people as non-intentional creatures ormechanical forces of nature. The law treats persons, including

people with mental disorders, as intentional creatures, agentswho form intentions based on their desires and beliefs. Mentalhealth laws treat crazy people specially not because thebehaviors of crazy people are mechanisms, but because peoplewith mental disorder may lack sufficient rational capacity in thecontext at issue. In other words, they were or are not responsiblefor their legally relevant conduct.

The central question, in other words, is not whether a person isbuck-stoppingly free, but whether they have a general rational

capacity sufficient to determine the likely consequences of theiractions. So although Morse explicitly disavows the mechanisticview of a person, the role he assigns to intentionality entails nocommitment to originative responsibility. Indeed, the descriptionof intentions as things based on desires and beliefs suggests aview in which intentions constitute plans that will plausibly bringabout the realization of whatever goals the person may have. If aperson lacks the capacity to accurately forecast the likely resultsof their actions, or to understand that those results are illegal,

they become candidates for exclusion from legal responsibility. Inthe United States, many insanity defenses, including the widelyused MNaghten Rules, express logic of this form. The sameargument can be applied to cases in which the defendant is tooyoung to have developed the requisite cognitive capacities(Roper v. Simmons).


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In this light, the neurophysiological understanding of behavioralflow becomes not only not inimical to the assignment of legalresponsibility, but downright friendly. One can imagine, forinstance, using our understanding of the neurophysiological

processes described above to probe a defendants actual abilityto forecast consequences, rather than relying on measures asindirect as holistic psychological assessments obtained viainterview.

One final point. Suppose you endorse retributive justice becauseyou believe a criminal possesses originative responsibility for hisactions. You cannot admit into that picture the notion that he didwhat he did because he lived in oppressive poverty, was abusedas a child, etc. The word because indicates that one is about to

supply a set of causes that sufficiently explains an effect. Underoriginative responsibility, there are no antecedent causes, or atleast not sufficient ones: choice stands as the ultimate go/no-goarbiter of behavior. Presumably you, like the criminal, possessoriginative responsibility, in the sense that external events do notdeterministically cause you to think in any particular way. What,then, is your responsibility in wishing that punishment be metedout to the criminal? It seems obvious that your desire to punishfollows from the commission of the crime. But beware: said crime

cannot be asufficient

cause for your desire for justice. If it were,then your desire would be psychologically predetermined, and asa retributivist, you deny just that kind of determinism. The crimecan push you so far, but ultimately,your decision to punish or not

punish has no sufficient cause. Its ultimate origin is your own free-floating will. For your punishment to be justified, it must not bearbitrary. But if it is not arbitrary, it is determined. Retributivistsare caught in a Humean trap. They must choose eitherarbitrariness or causal determination as the master of humanbehavior.

Consider a hypothetical: An active, healthy 35-year-old man isinjured in a car accident, paralyzed at C1, and dependent on afeeding tube. He becomes severely depressed and expresses hiswish that the feeding tube be removed and he be allowed to die.


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One assessment of this patients condition might regard suchfeelings as acute and understandable, perhaps even predictableconsequences of the injury. On that view, the patients suicidalideation is not under his volitional control, but rather, is the result

of psychological and neurological causes which we understand atleast in part. Being able to explain things in this way seems tostrip from the patient some sort of metaphysical ownership of hisown thoughts. These are not his feelings, but organicconsequences of external events. When he says he wants to die,therefore, our instinct may be to hear the depression talking,

judge the man as temporarily not in possession of sufficientrational capacity, and on that basis deny his request to be left todie.

In medicine, both competence and informed consent rest uponthe same sort of rational capacity as that required by law whendetermining responsibility. One widely used standard is Gillickcompetence: a person is judged competent when they havesufficient comprehension and intelligence to understand fullywhat is proposed. This test may be applied to minors, adults withmental illness or brain injury, or those making decisions underconditions (e.g. extreme stress) that compromise their mentalcapacities. It is no coincidence that these are the same

populations and conditions treated as special cases in law moregenerally.

Under the provisional model of decision-making described earlier,neural populations in the dorsolateral prefrontal cortex (andelsewhere anatomical details are not essential here) wereidentified as likely candidates for computing the consequences ofa behavioral plan. In the hypothetical case we are nowconsidering, the mans DLPFC is still computingsomething: it isnot as if he cannot make any forecasts whatever. Indeed he can

make them, has made them, and has chosen a plan that to himseems maximally rewarding. Our problem with his decision seemsat least partially due to the fact that we find it sopredictable: hehas revealed himself not only as a bundle of mechanisms, but asone whose structure is disappointingly transparent. This offendsour intuitions about ourselves and the amount of computationalcomplexity we expect for normal rational processes. If we are to


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be mechanismssomething barely tolerable anywaywe shouldat least be complicated mechanisms. Only if this mans motiveswere more obscure would we become comfortable that he wasindeed himself. Whether this sort of thought process really does

play or ought to be allowed to play a role in clinicaldeterminations of competence is a question beyond the scope ofthis paper.

There is a curious connection here to a rather different body ofliterature, but one rich enough to warrant mention. The field ofcomplexity science studies, among other things, the conditionsunder which systems can compute. A system composed ofinterconnected elements that remain utterly static, no matterwhat inputs are provided, is clearly not capable of computing, no

matter how those elements may be wired together. Contrarily, asystem composed of elements with internal states so chaotic thatthey maintain no correlation with the past is also incapable ofdoing interesting calculations. Langton (1990) applied to suchsystems the language of statistical mechanics in general, phasetransitions in particular. The first system is seen as frozen, asolid. Such systems are perfect for storing memories, since theinternal states are so non-volatile. The latter system is seen,metaphorically, as a hot gas. In between are liquids:

thermodynamically loose enough to allow changes to oneelements state to propagate to other elements: information flow.In the hot gas, information flows so easily that smallperturbations, even those caused by noise, propagate quickly andthreaten the elemental stability required for long-term memory.

The upshot of this metaphor is that interesting computationalsystems seem to exist at some kind of computational phasetransition, balanced between the needs of stable memories onethe one hand, and information transmission on the other.

Kauffman (1993) suggests that life itself exists at such a phasetransition, and that evolution is tuned to maintain the balance.Living things too computationally frozene.g. those with nomutationcannot evolve, while those too liquid cannot maintainstable identities or store adaptive solutions they discover. Itseems just possible that our intuitions about the definingcharacteristics of consciousness obey some of these same rules:


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solid enough to be lawful, rational engines, liquid enough to reactto changing stimuli and defy predictability. Minds that sway toofar to either side are treated specially.

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