- Email: [email protected]
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will?
Available online at www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Adina L Roskies This review considers recent work in neuroscience that has been thought to challenge views of free will. I argue that these experiments do little to directly undermine the belief that we have free will. However, evidence for mechanism and automatic behaviors may cause us to rethink some commonsensical notions of what is required for acting freely. Address Dartmouth College, Hanover, NH 03755, United States Corresponding author: Roskies, Adina L ([email protected])
Current Opinion in Neurobiology 2012, 22:1022–1026 This review comes from a themed issue on Decision making
[18,19,20,21]. So although the finding that neural activity precedes the reported time of conscious will appears to be robust, the standard interpretation of the timing results remains suspect [20]. Other studies that claim to predict decisions far in advance of our conscious deciding are sometimes mistakenly interpreted to show free will to be illusory: Because their prediction accuracy is only slightly greater than chance [17], they fail to show that decision precedes awareness, or that we cannot do otherwise than we do. The results merely suggest that the brain contains information relevant to, but not determinant of, future decisions. Given that the brain is a physical organ that operates on many time scales, none of these studies contradicts the expectations of physicalism or mandates revolutionary changes to commonsense notions of free will.
Edited by Kenji Doya and Michael N Shadlen For a complete overview see the Issue and the Editorial Available online 18th June 2012 0959-4388/$ – see front matter, # 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conb.2012.05.009
For centuries philosophers and theologians have worried about whether free will can be reconciled with divine foreknowledge, and deterministic and indeterministic causation [1–4]. Modern science has provided tools that begin to allow us to determine the biological causes of our behavior, and many have worried that neuroscience will reveal free will to be an illusion [5,6]. However, philosophers have developed a variety of theories that make room for free will, some with appeal to indeterministic events [3,7,8], and others in the face of determinism [9,10,11,12]. It is widely assumed that moral responsibility requires free will, although for some, it is responsibility and not free will that is the primary concept [13]. Some of the most visible challenges to free will from science have claimed to show that neural activity of decision processes precedes conscious awareness of deciding [14,15]. Since many think that awareness of intention is a requirement for free will, these studies are frequently interpreted as demonstrating that conscious will is not efficacious in initiating action or forming decisions, and thus that freedom is illusory [15–17]. However, there are significant problems with these paradigms, among them the problem of interpreting the significance of the neural signal for action initiation, and problems with identifying the moment at which one consciously decides or wills Current Opinion in Neurobiology 2012, 22:1022–1026
The work in the neuroscience of decision-making has illuminated both the general circuits involved in many types of decision [22,23,24,25,26,27–29] and the neural activity of single cells in several brain regions during simple decisions in monkeys [23,30,31,32,33–35]. Work has shown that neural activity representing evidence from sensory systems, as well as information about value, expectation of outcome, and cost, is represented by the same populations of neurons. Microstimulation studies support the causal role of these neurons in decision making [36]. Their dynamics is well described by diffusion-to-bound models [32]. With the wealth of information about the neural basis of perceptual decisions, we may ask how these results bear on our concept of free will. Some have postulated that this kind of work or other neurobiological investigations will hold an answer to the question of whether brain processes involved in decision are deterministic or indeterministic [37]. However, there is little prospect for a neurobiological resolution to the question of determinism [38]. Doing so would involve both demonstrating that at least some variable behavior seen in neural systems is a result of fundamentally indeterministic events or processes at a lower level, which would require (a) knowledge of neuronal states at a fineness of grain at the level of fundamental physics, and (b) eliminating the possibility that observed variability is because of inputs from another part of the massively complex and interconnected system that is the brain [51]. Given that the dynamics of brain activity displays the marks of complexity, the fact that chaotic activity can result from both deterministic and indeterministic processes, and the practical impossibility of reverse-engineering chaotic systems, it would seem that www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Roskies 1023
pursuing an empirical approach to the problem of free will via determinism will be in vain. The impossibility of neuroscience answering the question of determinism leaves open the possibility that at least some Libertarian accounts of free will, which posit that freedom depends on indeterminism in brain processes, are empirically adequate, or consistent with available data (e.g., [3]; see Figure 1). However, at least from this author’s perspective, Libertarian accounts suffer from the difficulty of grounding freedom and responsibility in random events over which the agent has no control. Agent causal accounts that aim to address this difficulty by positing a kind of causation that differs from ordinary physical causation and depends fundamentally on the nature of agents [7] seem unpromising on naturalistic and scientific grounds. Moreover, compatibilist accounts
(i.e., those that claim that freedom is compatible with determinism) that rely on deterministic complexity or noise [39] but are parallel in structure to some eventcausal Libertarian accounts [3] appear to be equally as good at accounting for aspects of freedom without suffering from the problems of control and responsibility introduced by randomness. Of course, neuroscience also says nothing to dissuade those who favor hard determinism (the position that determinism is true, and as such precludes freedom). It may seem that we are making little headway. But rather than addressing the problem of determinism, the neurobiological progress in understanding decision-making supports and illustrates the mechanistic nature of the mind/brain. Mechanism comes with its own challenges [9,19,38,40], but these have been less articulated and
Figure 1
Free and MR
Determinism
Indeterminism
Compatibilism
Libertarianism
No Free Will; No MR
Hard determinism
Hard Incompatibilism
Incompatibilism
Current Opinion in Neurobiology
Diagram of traditional philosophical positions that relate free will (FW) and moral responsibility (MR) to determinism. Compatibilism is the view that FW and MR are compatible with a deterministic universe. Incompatibilism is the view that they are not. Incompatibilists come in a variety of flavors: Hard determinists think that determinism is true and we are not free; Libertarians believe that determinism is false and we are free in virtue of indeterminism. Hard incompatibilists believe that FW and MR are impossible regardless of whether determinism is true, for they are not compatible with either determinism or indeterminism. There are a variety of compatibilist positions that provide different accounts of how FW and MR are possible even if determinism is true. There are also accounts that separate the conditions for FW and MR. For instance, ‘semi-compatiblism’ allows that MR is possible in a deterministic universe even if FW is not. www.sciencedirect.com
Current Opinion in Neurobiology 2012, 22:1022–1026
1024 Decision making
explored than the challenge of determinism. It seems that the main problem arising from mechanism is the sense that mechanism entails mindlessness, or that it supports a view that the psychological level is bypassed [41]. However, this inference seems unwarranted, especially given that the cognitive neurosciences aim precisely to provide an account of how mechanisms can underlie, not supplant, mindedness. Indeed, it is a fundamental assumption of most contemporary scientists and philosophers that there is no need to invoke the nonphysical to explain mind. Significant progress has already been made in explaining cognitive functions, although thus far even potential explanatory sketches of phenomena such as consciousness or qualia elude us. An examination of the models that have been developed to explain the neural data of decision-making based on single-cell recording from parietal areas [32] illustrate that psychological constructs are not eliminated by the understanding of the underlying neurobiology, but instead are central to the explanatory power of the models [51]. The neural activity is taken to realize constructs common to psychological theories: for example, hypotheses, propositions, evidence, value, costs, and reasons. In addition, neural activity in associated brain areas has been taken to represent, for example, subjective value [42] and reward [43,44]. Although it is possible that the correspondences between folk psychological constructs and neurobiological reality are only rough, there is enough correspondence evident already at this stage to allay fears of psychological bypassing. The neural systems of decision investigated thus far, and the models developed to describe them, highlight basic computations underlying simple perceptual decisions. Neural representations of aspects of the world and of internal variables constitute information that is integrated over time by decision mechanisms. In general, decisions occur when firing rates of neurons representing one of the choice options reach a certain threshold. This seems to involve fairly low-level processes. But human choice and decision-making seem to involve more active processing and modulation by the agent. How do high-level control processes such as attention, valuation, policy commitments, and so on affect the basic machinery of decision-making? That is a wide open question, begging for concerted research. For example, one of the pressing issues is how elements of the basic computation described by neurophysiological studies are set or modulated. Churchland et al. [45] found that when a monkey was given four choice options instead of two, the mechanics and threshold firing rate were unaltered, but the baseline firing rate was lowered, requiring a greater excursion before the firing rates for any one of the options reached threshold. How is this modulation accomplished and controlled? Additionally, it is thought Current Opinion in Neurobiology 2012, 22:1022–1026
that speed/accuracy tradeoffs are related to threshold levels [46], and some postulate that circuits in the basal ganglia may be involved in modulating these thresholds [33]. In order to perform tasks within the confines of certain demands and in the presence of noise that is intrinsic to these processes, the agent must make strategic or policy decisions that affect performance. How are these decisions made? Moreover, what is the relation of these kinds of decisions to questions about freedom and responsibility? One suggestion is that it is these high-level strategic decisions that should be particular objects of moral assessment [47]. This idea, prompted by consideration of the neural data, echoes familiar philosophical views that emphasize the importance to free will and responsibility of high-level executive processes involved in conscious deliberation about priorities; of the role of effort in shaping one’s own character; of the conforming of one’s desires to one’s second-order desires (desires about desires); and of rationality. The importance of high-level processes also leads us to consider the centrality of notions of capacity in accounts of freedom and responsibility. Capacities set broad outlines for domains of possibility for the engagement of certain functions important for agency and decision. Some, such as basic abilities to represent facts, make valuations, and control impulses may be necessary conditions for agency, whereas consideration of others, such as perceptual acuity, memory, attentional control and mentalizing abilities may modulate judgments of responsibility. Along these lines, a growing body of neuroscientific research is focused upon understanding the brain areas that subserve or control executive functions. Although we are a long way from understanding how neural processes realize executive function and control, the ultimate aim is surely to reach a detailed understanding of what their proper functioning is, and what sort of damage can significantly impair function. This focus on capacity dovetails nicely with some classic views in philosophy that highlight the question of an agent’s capacities, for example to engage in social practices of forming and responding to reactive attitudes [13], to bring first and second-order desires into line [11], or to feel empathy or act rationally [48,49]. Although coming from outside neuroscience, some recent work in psychology suggests that much of our decisionmaking is subconscious and/or affected by situational variables or other influences of which we are unaware. This problem of automaticity, more than any other extant research, does challenge ordinary views of free will, since commonsense notions of free will are closely tied to consciousness, and seem to entail that behavior that issues from unconscious processes is ipso facto not free [50]. Further work on automaticity and awareness may cause us to rethink the simplistic folk view that free and responsible decisions are only those we consciously make. www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Roskies 1025
It is clear even now that we need to be aware of only some aspects of decision-making, and we may need to refine or reconsider our ideas about the role of consciousness in freedom and responsibility. Because the question of determinism is neither addressable nor particularly important in neurobiology, and because neuroscience aims to describe the mechanisms underlying behavior, we are led to focus on questions of mechanism rather than classic philosophical formulations about free will in relation to determinism. Neuroscience has already illuminated to a significant extent how simple decisions are realized in neural machinery. The insights support the continued utility of psychological constructs, and draw attention to the importance of compatibilist accounts of freedom and responsibility that highlight notions of capacity. However, extant work also increasingly calls attention to the importance of determining whether and how mechanistic accounts can satisfactorily underwrite a robust conception of mindedness. Mindedness will involve understanding how high-level processes can affect and control lower-level (i.e., less complex, more automatic, and/or less flexible) circuitry, and will ultimately call for an explanation of the nature of consciousness and its role in controlling decision.
Acknowledgements Adina L. Roskies thanks the Princeton University Center for Human Values and the Big Questions in Free Will Project, funded by the John Templeton Foundation for support. The opinions expressed in this article are our own and do not necessarily reflect the views of the John Templeton Foundation.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
Pereboom D: Living Without Free Will. Cambridge: Cambridge University Press; 2001.
2.
Hume D: Enquiry Concerning Human Understanding. Oxford: Clarendon Press; 1975 [1748].
3.
Kane R: Responsibility, luck, and chance: reflections on free will and indeterminism. J Philos 1999, 96:217-240.
4.
Strawson G: The impossibility of moral responsibility. Philos Stud 1994, 75:5-24.
5.
Cashmore A: The lucretian swerve: the biological basis of human behavior and the criminal justice system. PNAS 2010.
6.
Greene J, Cohen JD: For the law, neuroscience changes nothing and everything. Phil Trans R Soc Lond B 2004, 359:1775-1785.
7. 8.
O’Connor T: Agent causation. In Free Will. Edited by Watson G. Oxford: Oxford University Press; 2003:257-284. Clarke R: Toward a credible agent-causal account of free will. Nous 1993, 27:191-203.
9. Bok H: Freedom and Responsibility. Princeton, NJ: Princeton University Press; 1998. This philosophy book presents a sophisticated compatibilist view of freedom that is sensitive to the concerns of mechanism and will be informative to those looking for a naturalistically plausible account of freedom and responsibility.
www.sciencedirect.com
10. Frankfurt H: Alternate possibilities and moral responsibility. J Philos 1969, 66. 11. Frankfurt H: Freedom of the will and the concept of a person. J Philos 1971, 68. This classic paper argues that what it is to be free is to be able to align one’s will with one’s second-order desires (i.e., desires for desires). The position has been highly influential in philosophy and is one of the several that shifts the emphasis in discussions of freedom from requirements for some metaphysically demanding property, such as the property of being an uncaused cause, to requirements for certain kinds of naturalistic properties, such as having mental states with a certain kind of coherence or having an ability to respond to reasons. 12. Vihvelin K: Causes, Laws, and Free Will: An Essay on the Determinism Problem. Oxford University Press; 2013. 13. Strawson PF: Freedom and resentment. In Free Will. Edited by Watson G. Oxford: Oxford University Press; 1982:59-80. This groundbreaking paper changed the philosophical debate on free will. Strawson argues that freedom and responsibility are grounded in and justified by normal interpersonal relationships and the kinds of emotional responses and expectations of good will that we have for others and for ourselves, and that there is no need to resort to contentious metaphysics to account for our moral practices. 14. Libet B, Gleason CA, Wright EW, Pearl DK: Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential): the unconscious initation of a freely voluntary act. Brain 1983, 106:623-642. 15. Libet B: Unconscious cerebral initiative and the role of conscious will in volutary action. Behav Brain Sci 1985, 8:529-566. 16. Wegner D: The Illusion of Conscious Will. Cambridge, MA: MIT Press; 2002. 17. Soon CS, Brass M, Heinze H-J, Haynes J-D: Unconscious determinants of free decisions in the human brain. Nat Neurosci 2008, 11:543-545. 18. Sinnott-Armstrong W, Nadel L (Eds): Conscious Will and Responsibility. New York: Oxford University Press; 2011. 19. Roskies AL: How does neuroscience affect our conception of volition? Annu Rev Neurosci 2010, 33:109-130. This review covers a large body of work in neuroscience relevant to the concept of volition and discusses its relevance to philosophical questions. It divides the general issue into five topics: the initiation of action, intention, decision, control, and phenomenology. Ultimately it is concluded that results from neuroscience put little pressure on ordinary notions of volition. 20. Roskies AL: Why libet’s studies don’t pose a threat to free will. In Conscious Will Responsibility. Edited by Sinnott-Armstrong W. Oxford University Press; 2011:11-22. 21. Mele A: Effective Intentions: The Power of Conscious Will. New York: Oxford University Press; 2009. 22. Barraclough D, Conroy M, Lee D: Prefrontal cortex and decision making in a mixed-strategy game. Nat Neurosci 2004, 7:404-410. 23. Glimcher PW: Foundations of Neuroeconomic Analysis. New York: Oxford University Press; 2010. This recent book by a leading neuroeconomist provides an introduction to neuroeconomics from both theoretical and experimental perspectives. Topics covered include classical theory, behavioral economic challenges to it, and neurobiological mechanisms of choice and valuation. 24. Daw ND, O’Doherty JP, Dayan P, Seymour B, Dolan RJ: Cortical substrates for exploratory decisions in humans. Nature 2006, 441:876-879. 25. Brass M, Haggard P: To do or not to do: the neural signature of self-control. J Neurosci 2007, 27:9141-9145. 26. Haggard P: Human volition: towards a neuroscience of will. Nat Rev Neurosci 2008, 9:934-946. This review paper offers an accessible discussion of much recent work on the will. It includes descriptions of classic experiments, a description of brain networks involved in voluntary action, an operationalization of will in terms of a series of decisions, and a discussion of computational principles and the role of consciousness. It also includes an extensive bibliography of important work.
Current Opinion in Neurobiology 2012, 22:1022–1026
1026 Decision making
27. Pesaran B, Nelson MJ, Andersen RA: Free choice activates a decision circuit between frontal and parietal cortex. Nature 2008, 453:406-409.
39. Usher M: Control, choice, and the convergence/divergence dynamics: a compatibilistic probabilistic theory of free will. J Philos 2006, 103:188-213.
28. Heekeren HR, Marrett S, Ungerleider LG: The neural systems that mediate human perceptual decision making. Nat Rev Neurosci 2008, 9:467-479.
40. Craver CF: Explaining the Brain. New York: Oxford University Press; 2007.
29. Hare TA, Camerer CF, Rangel A: Self-control in decision-making involves modulation of the vmpfc valuation system. Science 2009, 324:646-648. 30. Andersen RA, Cui H: Intention, action planning, and decision making in parietal-frontal circuits. Neuron 2009, 63:568-583. 31. Dorris MC, Glimcher PW: Activity in posterior parietal cortex is correlated with the relative subjective desirability of action. Neuron 2004, 44:365-378. 32. Gold JI, Shadlen MN: The neural basis of decision making. Annu Rev Neurosci 2007, 30:535-574. A comprehensive and accessible review of work on the neural basis of decision-making. The review begins with a theoretical framework from statistical decision theory, and then applies this framework to a variety of model systems studied by neurobiology which include perceptual decisions, motor decisions, and value-based decisions. 33. Lo C-C, Wang X-J: Cortico-basal ganglia circuit mechanism for a decision threshold in reaction time tasks. Nat Neurosci 2006, 9:956-963. 34. Platt ML, Huettel SA: Risky business: the neuroeconomics of decision making under uncertainty. Nat Neurosci 2008, 11:398-403. 35. Kennerley SW, Behrens TEJ, Wallis JD: Double dissociation of value computations in orbitofrontal and anterior cingulate neurons. Nat Neurosci 2011, 14:1581-1589. 36. Hanks TD, Ditterich J, Shadlen MN: Microstimulation of macaque area lip affects decision-making in a motion discrimination task. Nat Neurosci 2006, 9:682-689. 37. Balaguer M: A coherent, naturalistic, and plausible formulation of libertarian free will. Nous 2004, 38:379-406. 38. Roskies AL: Neuroscientific challenges to free will and responsibility. Trends Cognit Sci 2006, 10:419-423.
Current Opinion in Neurobiology 2012, 22:1022–1026
41. Nahmias E, Coates DJ, Kvaran T: Free will, moral responsibility, and mechanism: experiments on folk intuitions. Midwest Stud Philos 2007, 31:215-242. 42. Padoa-Schioppa C, Assad J: Neurons in the orbitofrontal cortex encode economic value. Nature 2006, 441:223-226. 43. Schultz W: Dopamine neurons and their role in reward mechanisms. Curr Opin Neurobiol 1997, 7:191-197. 44. Schultz W, Tremblay L, Hollerman J: Reward processing in primate orbitofrontal cortex and basal ganglia. Cereb Cortex 2000, 10:272-283. 45. Churchland AK, Kiani R, Shadlen MN: Decision-making with multiple alternatives. Nat Neurosci 2008, 11:693-702. 46. Hanks TD, Mazurek ME, Kiani R, Hopp E, Shadlen MN: Elapsed decision time affects the weighting of prior probability in a perceptual decision task. J Neurosci 2011, 31:6339-6352. 47. Shadlen MN, Roskies AL: The neurobiology of decision-making and responsibility: reconciling mechanism and mindedness. Front Decis Sci 2012, 6:1-12. 48. Fine C, Kennett J: Mental impairment, moral understanding and criminal responsibility: psychopathy and the purposes of punishment. Int J Law Psychiatry 2004, 27:425-443. 49. Morse S: Psychopathy and criminal responsibility. Neuroethics 2008, 1:205-212. 50. Sie M, Wouters A: The real challenge to free will and responsibility. Trend Cognit Sci 2008, 12:3-4. 51. Roskies AL: Can Neuroscience resolve issues about free will? In Moral Psychology: Volume 4, Free Will and Moral Responsibility. Edited by Sinnott-Armstrong W. Cambridge, Mass: MIT Press; 2013.
www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Adina L Roskies This review considers recent work in neuroscience that has been thought to challenge views of free will. I argue that these experiments do little to directly undermine the belief that we have free will. However, evidence for mechanism and automatic behaviors may cause us to rethink some commonsensical notions of what is required for acting freely. Address Dartmouth College, Hanover, NH 03755, United States Corresponding author: Roskies, Adina L ([email protected])
Current Opinion in Neurobiology 2012, 22:1022–1026 This review comes from a themed issue on Decision making
[18,19,20,21]. So although the finding that neural activity precedes the reported time of conscious will appears to be robust, the standard interpretation of the timing results remains suspect [20]. Other studies that claim to predict decisions far in advance of our conscious deciding are sometimes mistakenly interpreted to show free will to be illusory: Because their prediction accuracy is only slightly greater than chance [17], they fail to show that decision precedes awareness, or that we cannot do otherwise than we do. The results merely suggest that the brain contains information relevant to, but not determinant of, future decisions. Given that the brain is a physical organ that operates on many time scales, none of these studies contradicts the expectations of physicalism or mandates revolutionary changes to commonsense notions of free will.
Edited by Kenji Doya and Michael N Shadlen For a complete overview see the Issue and the Editorial Available online 18th June 2012 0959-4388/$ – see front matter, # 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conb.2012.05.009
For centuries philosophers and theologians have worried about whether free will can be reconciled with divine foreknowledge, and deterministic and indeterministic causation [1–4]. Modern science has provided tools that begin to allow us to determine the biological causes of our behavior, and many have worried that neuroscience will reveal free will to be an illusion [5,6]. However, philosophers have developed a variety of theories that make room for free will, some with appeal to indeterministic events [3,7,8], and others in the face of determinism [9,10,11,12]. It is widely assumed that moral responsibility requires free will, although for some, it is responsibility and not free will that is the primary concept [13]. Some of the most visible challenges to free will from science have claimed to show that neural activity of decision processes precedes conscious awareness of deciding [14,15]. Since many think that awareness of intention is a requirement for free will, these studies are frequently interpreted as demonstrating that conscious will is not efficacious in initiating action or forming decisions, and thus that freedom is illusory [15–17]. However, there are significant problems with these paradigms, among them the problem of interpreting the significance of the neural signal for action initiation, and problems with identifying the moment at which one consciously decides or wills Current Opinion in Neurobiology 2012, 22:1022–1026
The work in the neuroscience of decision-making has illuminated both the general circuits involved in many types of decision [22,23,24,25,26,27–29] and the neural activity of single cells in several brain regions during simple decisions in monkeys [23,30,31,32,33–35]. Work has shown that neural activity representing evidence from sensory systems, as well as information about value, expectation of outcome, and cost, is represented by the same populations of neurons. Microstimulation studies support the causal role of these neurons in decision making [36]. Their dynamics is well described by diffusion-to-bound models [32]. With the wealth of information about the neural basis of perceptual decisions, we may ask how these results bear on our concept of free will. Some have postulated that this kind of work or other neurobiological investigations will hold an answer to the question of whether brain processes involved in decision are deterministic or indeterministic [37]. However, there is little prospect for a neurobiological resolution to the question of determinism [38]. Doing so would involve both demonstrating that at least some variable behavior seen in neural systems is a result of fundamentally indeterministic events or processes at a lower level, which would require (a) knowledge of neuronal states at a fineness of grain at the level of fundamental physics, and (b) eliminating the possibility that observed variability is because of inputs from another part of the massively complex and interconnected system that is the brain [51]. Given that the dynamics of brain activity displays the marks of complexity, the fact that chaotic activity can result from both deterministic and indeterministic processes, and the practical impossibility of reverse-engineering chaotic systems, it would seem that www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Roskies 1023
pursuing an empirical approach to the problem of free will via determinism will be in vain. The impossibility of neuroscience answering the question of determinism leaves open the possibility that at least some Libertarian accounts of free will, which posit that freedom depends on indeterminism in brain processes, are empirically adequate, or consistent with available data (e.g., [3]; see Figure 1). However, at least from this author’s perspective, Libertarian accounts suffer from the difficulty of grounding freedom and responsibility in random events over which the agent has no control. Agent causal accounts that aim to address this difficulty by positing a kind of causation that differs from ordinary physical causation and depends fundamentally on the nature of agents [7] seem unpromising on naturalistic and scientific grounds. Moreover, compatibilist accounts
(i.e., those that claim that freedom is compatible with determinism) that rely on deterministic complexity or noise [39] but are parallel in structure to some eventcausal Libertarian accounts [3] appear to be equally as good at accounting for aspects of freedom without suffering from the problems of control and responsibility introduced by randomness. Of course, neuroscience also says nothing to dissuade those who favor hard determinism (the position that determinism is true, and as such precludes freedom). It may seem that we are making little headway. But rather than addressing the problem of determinism, the neurobiological progress in understanding decision-making supports and illustrates the mechanistic nature of the mind/brain. Mechanism comes with its own challenges [9,19,38,40], but these have been less articulated and
Figure 1
Free and MR
Determinism
Indeterminism
Compatibilism
Libertarianism
No Free Will; No MR
Hard determinism
Hard Incompatibilism
Incompatibilism
Current Opinion in Neurobiology
Diagram of traditional philosophical positions that relate free will (FW) and moral responsibility (MR) to determinism. Compatibilism is the view that FW and MR are compatible with a deterministic universe. Incompatibilism is the view that they are not. Incompatibilists come in a variety of flavors: Hard determinists think that determinism is true and we are not free; Libertarians believe that determinism is false and we are free in virtue of indeterminism. Hard incompatibilists believe that FW and MR are impossible regardless of whether determinism is true, for they are not compatible with either determinism or indeterminism. There are a variety of compatibilist positions that provide different accounts of how FW and MR are possible even if determinism is true. There are also accounts that separate the conditions for FW and MR. For instance, ‘semi-compatiblism’ allows that MR is possible in a deterministic universe even if FW is not. www.sciencedirect.com
Current Opinion in Neurobiology 2012, 22:1022–1026
1024 Decision making
explored than the challenge of determinism. It seems that the main problem arising from mechanism is the sense that mechanism entails mindlessness, or that it supports a view that the psychological level is bypassed [41]. However, this inference seems unwarranted, especially given that the cognitive neurosciences aim precisely to provide an account of how mechanisms can underlie, not supplant, mindedness. Indeed, it is a fundamental assumption of most contemporary scientists and philosophers that there is no need to invoke the nonphysical to explain mind. Significant progress has already been made in explaining cognitive functions, although thus far even potential explanatory sketches of phenomena such as consciousness or qualia elude us. An examination of the models that have been developed to explain the neural data of decision-making based on single-cell recording from parietal areas [32] illustrate that psychological constructs are not eliminated by the understanding of the underlying neurobiology, but instead are central to the explanatory power of the models [51]. The neural activity is taken to realize constructs common to psychological theories: for example, hypotheses, propositions, evidence, value, costs, and reasons. In addition, neural activity in associated brain areas has been taken to represent, for example, subjective value [42] and reward [43,44]. Although it is possible that the correspondences between folk psychological constructs and neurobiological reality are only rough, there is enough correspondence evident already at this stage to allay fears of psychological bypassing. The neural systems of decision investigated thus far, and the models developed to describe them, highlight basic computations underlying simple perceptual decisions. Neural representations of aspects of the world and of internal variables constitute information that is integrated over time by decision mechanisms. In general, decisions occur when firing rates of neurons representing one of the choice options reach a certain threshold. This seems to involve fairly low-level processes. But human choice and decision-making seem to involve more active processing and modulation by the agent. How do high-level control processes such as attention, valuation, policy commitments, and so on affect the basic machinery of decision-making? That is a wide open question, begging for concerted research. For example, one of the pressing issues is how elements of the basic computation described by neurophysiological studies are set or modulated. Churchland et al. [45] found that when a monkey was given four choice options instead of two, the mechanics and threshold firing rate were unaltered, but the baseline firing rate was lowered, requiring a greater excursion before the firing rates for any one of the options reached threshold. How is this modulation accomplished and controlled? Additionally, it is thought Current Opinion in Neurobiology 2012, 22:1022–1026
that speed/accuracy tradeoffs are related to threshold levels [46], and some postulate that circuits in the basal ganglia may be involved in modulating these thresholds [33]. In order to perform tasks within the confines of certain demands and in the presence of noise that is intrinsic to these processes, the agent must make strategic or policy decisions that affect performance. How are these decisions made? Moreover, what is the relation of these kinds of decisions to questions about freedom and responsibility? One suggestion is that it is these high-level strategic decisions that should be particular objects of moral assessment [47]. This idea, prompted by consideration of the neural data, echoes familiar philosophical views that emphasize the importance to free will and responsibility of high-level executive processes involved in conscious deliberation about priorities; of the role of effort in shaping one’s own character; of the conforming of one’s desires to one’s second-order desires (desires about desires); and of rationality. The importance of high-level processes also leads us to consider the centrality of notions of capacity in accounts of freedom and responsibility. Capacities set broad outlines for domains of possibility for the engagement of certain functions important for agency and decision. Some, such as basic abilities to represent facts, make valuations, and control impulses may be necessary conditions for agency, whereas consideration of others, such as perceptual acuity, memory, attentional control and mentalizing abilities may modulate judgments of responsibility. Along these lines, a growing body of neuroscientific research is focused upon understanding the brain areas that subserve or control executive functions. Although we are a long way from understanding how neural processes realize executive function and control, the ultimate aim is surely to reach a detailed understanding of what their proper functioning is, and what sort of damage can significantly impair function. This focus on capacity dovetails nicely with some classic views in philosophy that highlight the question of an agent’s capacities, for example to engage in social practices of forming and responding to reactive attitudes [13], to bring first and second-order desires into line [11], or to feel empathy or act rationally [48,49]. Although coming from outside neuroscience, some recent work in psychology suggests that much of our decisionmaking is subconscious and/or affected by situational variables or other influences of which we are unaware. This problem of automaticity, more than any other extant research, does challenge ordinary views of free will, since commonsense notions of free will are closely tied to consciousness, and seem to entail that behavior that issues from unconscious processes is ipso facto not free [50]. Further work on automaticity and awareness may cause us to rethink the simplistic folk view that free and responsible decisions are only those we consciously make. www.sciencedirect.com
How does the neuroscience of decision making bear on our understanding of moral responsibility and free will? Roskies 1025
It is clear even now that we need to be aware of only some aspects of decision-making, and we may need to refine or reconsider our ideas about the role of consciousness in freedom and responsibility. Because the question of determinism is neither addressable nor particularly important in neurobiology, and because neuroscience aims to describe the mechanisms underlying behavior, we are led to focus on questions of mechanism rather than classic philosophical formulations about free will in relation to determinism. Neuroscience has already illuminated to a significant extent how simple decisions are realized in neural machinery. The insights support the continued utility of psychological constructs, and draw attention to the importance of compatibilist accounts of freedom and responsibility that highlight notions of capacity. However, extant work also increasingly calls attention to the importance of determining whether and how mechanistic accounts can satisfactorily underwrite a robust conception of mindedness. Mindedness will involve understanding how high-level processes can affect and control lower-level (i.e., less complex, more automatic, and/or less flexible) circuitry, and will ultimately call for an explanation of the nature of consciousness and its role in controlling decision.
Acknowledgements Adina L. Roskies thanks the Princeton University Center for Human Values and the Big Questions in Free Will Project, funded by the John Templeton Foundation for support. The opinions expressed in this article are our own and do not necessarily reflect the views of the John Templeton Foundation.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest 1.
Pereboom D: Living Without Free Will. Cambridge: Cambridge University Press; 2001.
2.
Hume D: Enquiry Concerning Human Understanding. Oxford: Clarendon Press; 1975 [1748].
3.
Kane R: Responsibility, luck, and chance: reflections on free will and indeterminism. J Philos 1999, 96:217-240.
4.
Strawson G: The impossibility of moral responsibility. Philos Stud 1994, 75:5-24.
5.
Cashmore A: The lucretian swerve: the biological basis of human behavior and the criminal justice system. PNAS 2010.
6.
Greene J, Cohen JD: For the law, neuroscience changes nothing and everything. Phil Trans R Soc Lond B 2004, 359:1775-1785.
7. 8.
O’Connor T: Agent causation. In Free Will. Edited by Watson G. Oxford: Oxford University Press; 2003:257-284. Clarke R: Toward a credible agent-causal account of free will. Nous 1993, 27:191-203.
9. Bok H: Freedom and Responsibility. Princeton, NJ: Princeton University Press; 1998. This philosophy book presents a sophisticated compatibilist view of freedom that is sensitive to the concerns of mechanism and will be informative to those looking for a naturalistically plausible account of freedom and responsibility.
www.sciencedirect.com
10. Frankfurt H: Alternate possibilities and moral responsibility. J Philos 1969, 66. 11. Frankfurt H: Freedom of the will and the concept of a person. J Philos 1971, 68. This classic paper argues that what it is to be free is to be able to align one’s will with one’s second-order desires (i.e., desires for desires). The position has been highly influential in philosophy and is one of the several that shifts the emphasis in discussions of freedom from requirements for some metaphysically demanding property, such as the property of being an uncaused cause, to requirements for certain kinds of naturalistic properties, such as having mental states with a certain kind of coherence or having an ability to respond to reasons. 12. Vihvelin K: Causes, Laws, and Free Will: An Essay on the Determinism Problem. Oxford University Press; 2013. 13. Strawson PF: Freedom and resentment. In Free Will. Edited by Watson G. Oxford: Oxford University Press; 1982:59-80. This groundbreaking paper changed the philosophical debate on free will. Strawson argues that freedom and responsibility are grounded in and justified by normal interpersonal relationships and the kinds of emotional responses and expectations of good will that we have for others and for ourselves, and that there is no need to resort to contentious metaphysics to account for our moral practices. 14. Libet B, Gleason CA, Wright EW, Pearl DK: Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential): the unconscious initation of a freely voluntary act. Brain 1983, 106:623-642. 15. Libet B: Unconscious cerebral initiative and the role of conscious will in volutary action. Behav Brain Sci 1985, 8:529-566. 16. Wegner D: The Illusion of Conscious Will. Cambridge, MA: MIT Press; 2002. 17. Soon CS, Brass M, Heinze H-J, Haynes J-D: Unconscious determinants of free decisions in the human brain. Nat Neurosci 2008, 11:543-545. 18. Sinnott-Armstrong W, Nadel L (Eds): Conscious Will and Responsibility. New York: Oxford University Press; 2011. 19. Roskies AL: How does neuroscience affect our conception of volition? Annu Rev Neurosci 2010, 33:109-130. This review covers a large body of work in neuroscience relevant to the concept of volition and discusses its relevance to philosophical questions. It divides the general issue into five topics: the initiation of action, intention, decision, control, and phenomenology. Ultimately it is concluded that results from neuroscience put little pressure on ordinary notions of volition. 20. Roskies AL: Why libet’s studies don’t pose a threat to free will. In Conscious Will Responsibility. Edited by Sinnott-Armstrong W. Oxford University Press; 2011:11-22. 21. Mele A: Effective Intentions: The Power of Conscious Will. New York: Oxford University Press; 2009. 22. Barraclough D, Conroy M, Lee D: Prefrontal cortex and decision making in a mixed-strategy game. Nat Neurosci 2004, 7:404-410. 23. Glimcher PW: Foundations of Neuroeconomic Analysis. New York: Oxford University Press; 2010. This recent book by a leading neuroeconomist provides an introduction to neuroeconomics from both theoretical and experimental perspectives. Topics covered include classical theory, behavioral economic challenges to it, and neurobiological mechanisms of choice and valuation. 24. Daw ND, O’Doherty JP, Dayan P, Seymour B, Dolan RJ: Cortical substrates for exploratory decisions in humans. Nature 2006, 441:876-879. 25. Brass M, Haggard P: To do or not to do: the neural signature of self-control. J Neurosci 2007, 27:9141-9145. 26. Haggard P: Human volition: towards a neuroscience of will. Nat Rev Neurosci 2008, 9:934-946. This review paper offers an accessible discussion of much recent work on the will. It includes descriptions of classic experiments, a description of brain networks involved in voluntary action, an operationalization of will in terms of a series of decisions, and a discussion of computational principles and the role of consciousness. It also includes an extensive bibliography of important work.
Current Opinion in Neurobiology 2012, 22:1022–1026
1026 Decision making
27. Pesaran B, Nelson MJ, Andersen RA: Free choice activates a decision circuit between frontal and parietal cortex. Nature 2008, 453:406-409.
39. Usher M: Control, choice, and the convergence/divergence dynamics: a compatibilistic probabilistic theory of free will. J Philos 2006, 103:188-213.
28. Heekeren HR, Marrett S, Ungerleider LG: The neural systems that mediate human perceptual decision making. Nat Rev Neurosci 2008, 9:467-479.
40. Craver CF: Explaining the Brain. New York: Oxford University Press; 2007.
29. Hare TA, Camerer CF, Rangel A: Self-control in decision-making involves modulation of the vmpfc valuation system. Science 2009, 324:646-648. 30. Andersen RA, Cui H: Intention, action planning, and decision making in parietal-frontal circuits. Neuron 2009, 63:568-583. 31. Dorris MC, Glimcher PW: Activity in posterior parietal cortex is correlated with the relative subjective desirability of action. Neuron 2004, 44:365-378. 32. Gold JI, Shadlen MN: The neural basis of decision making. Annu Rev Neurosci 2007, 30:535-574. A comprehensive and accessible review of work on the neural basis of decision-making. The review begins with a theoretical framework from statistical decision theory, and then applies this framework to a variety of model systems studied by neurobiology which include perceptual decisions, motor decisions, and value-based decisions. 33. Lo C-C, Wang X-J: Cortico-basal ganglia circuit mechanism for a decision threshold in reaction time tasks. Nat Neurosci 2006, 9:956-963. 34. Platt ML, Huettel SA: Risky business: the neuroeconomics of decision making under uncertainty. Nat Neurosci 2008, 11:398-403. 35. Kennerley SW, Behrens TEJ, Wallis JD: Double dissociation of value computations in orbitofrontal and anterior cingulate neurons. Nat Neurosci 2011, 14:1581-1589. 36. Hanks TD, Ditterich J, Shadlen MN: Microstimulation of macaque area lip affects decision-making in a motion discrimination task. Nat Neurosci 2006, 9:682-689. 37. Balaguer M: A coherent, naturalistic, and plausible formulation of libertarian free will. Nous 2004, 38:379-406. 38. Roskies AL: Neuroscientific challenges to free will and responsibility. Trends Cognit Sci 2006, 10:419-423.
Current Opinion in Neurobiology 2012, 22:1022–1026
41. Nahmias E, Coates DJ, Kvaran T: Free will, moral responsibility, and mechanism: experiments on folk intuitions. Midwest Stud Philos 2007, 31:215-242. 42. Padoa-Schioppa C, Assad J: Neurons in the orbitofrontal cortex encode economic value. Nature 2006, 441:223-226. 43. Schultz W: Dopamine neurons and their role in reward mechanisms. Curr Opin Neurobiol 1997, 7:191-197. 44. Schultz W, Tremblay L, Hollerman J: Reward processing in primate orbitofrontal cortex and basal ganglia. Cereb Cortex 2000, 10:272-283. 45. Churchland AK, Kiani R, Shadlen MN: Decision-making with multiple alternatives. Nat Neurosci 2008, 11:693-702. 46. Hanks TD, Mazurek ME, Kiani R, Hopp E, Shadlen MN: Elapsed decision time affects the weighting of prior probability in a perceptual decision task. J Neurosci 2011, 31:6339-6352. 47. Shadlen MN, Roskies AL: The neurobiology of decision-making and responsibility: reconciling mechanism and mindedness. Front Decis Sci 2012, 6:1-12. 48. Fine C, Kennett J: Mental impairment, moral understanding and criminal responsibility: psychopathy and the purposes of punishment. Int J Law Psychiatry 2004, 27:425-443. 49. Morse S: Psychopathy and criminal responsibility. Neuroethics 2008, 1:205-212. 50. Sie M, Wouters A: The real challenge to free will and responsibility. Trend Cognit Sci 2008, 12:3-4. 51. Roskies AL: Can Neuroscience resolve issues about free will? In Moral Psychology: Volume 4, Free Will and Moral Responsibility. Edited by Sinnott-Armstrong W. Cambridge, Mass: MIT Press; 2013.
www.sciencedirect.com