What kinds of conscious experiences accompany (and perhaps assist) the exercise of control over bodily and mental action?
For answers on this and related questions, one might turn to the rapidly growing literature on the so-called ‘sense of agency.’ The sense of agency is supposed to be something experiential and related to action, but I think it is fair to say that there is little unity in the ways scientists deploy the term. Andreas Kalckert (2014) writes that the sense of agency is ‘the experience of being able to voluntarily control limb movement.’ Hauser et al. (2011) write that the sense of agency is ‘the experience of controlling one’s own actions and their consequences.’ Damen et al. (2015) write that ‘The sense of agency refers to the ability to recognize oneself as the controller of one’s own actions and to distinguish these from actions caused or controlled by other sources.’ Chambon et al. (2013) write ‘sense of agency’ refers to the feeling of controlling an external event through one’s own action.’ David et al. (2008) write ‘The sense of agency is a central aspect of human self-consciousness and refers to the experience of oneself as the agent of one’s own actions.’ These glosses variously emphasize voluntary control of limb movement, controlling actions and consequences, controlling consequences through action, abilities of recognition and discrimination, and an experience of oneself as agent. While these glosses might share a neighborhood, they differ in details that are, arguably, quite important if one wants to understand the kinds of experience at issue in bodily (and mental) action control.
In my own work, then, I have eschewed use of the term sense of agency, preferring instead to start with a more detailed account of the phenomenology. Consider, for example, what I have called the experience of trying.
To get a grip on this kind of experience, consider lifting a heavy weight with one’s arm. Doing so, one will often experience tension in the elbow, strain or effort in the muscles, heaviness or pull on the wrist, and so on. In addition, there is an aspect of this experience that is not to be identified with any of these haptic elements, or with any conjunction of them. When lifting the heavy weight, one has an experience of trying to do so. Put generally, then, we might say that the experience of trying is an experience as of directing activity towards the satisfaction of an intention (this is not to say that possessing a concept of intention or of an intention’s satisfaction is necessary for the capacity to have such experiences). In the example at hand, it is a phenomenal character as of directing the movements of the arm.
With this much, many appear to agree. David Hume speaks of the ‘internal impression’ of ‘knowingly giving rise to’ some motion of the body or perception of the mind. His language suggests that he regards the ‘giving rise to’ as fundamentally directive.
It may be said, that we are every moment conscious of internal power; while we feel, that, by the simple command of our will, we can move the organs of our body, or direct the faculties of our mind. An act of volition produces motion in our limbs, or raises a new idea in our imagination. This influence of the will we know by consciousness. (2000, 52)
Further evidence for this point is that Hume thought of this experience-type as whatever is shared in both successful and failed actions:
A man, suddenly struck with palsy in the leg or arm, or who had newly lost those members, frequently endeavours, at first to move them, and employ them in their usual offices. Here he is as much conscious of power to command such limbs, as a man in perfect health is conscious of power to actuate any member which remains in its natural state and condition. (53)
More recently Carl Ginet has asserted a very similar view.
It could seem to me that I voluntarily exert a force forward with my arm without at the same time its seeming to me that I feel the exertion happening: the arm feels kinesthetically anesthetized. (Sometimes, after an injection of anesthetic at the dentist’s office, my tongue seems to me thus kinesthetically dead as I voluntarily exercise it: I then have an illusion that my will fails to engage my tongue.) (1990, 28)
Are these philosophers right? In a recent paper (Shepherd 2015) I argue for a position that seems (to me) to indicate the answer is yes. This is the view:
Constitutive view. The neural activity that realizes an experience of trying is just a part of the neural activity that directs real-time action control.
My argument – very briefly – is this. There is no good empirical reason to deny this view. And there is some empirical reason to adopt it. In what follows I’ll offer a shortened version of the first part of this argument.
Why do I say there is no good empirical reason to deny the view? The best empirical reason would stem from application of a certain kind of theory of the ‘sense of agency’ to experiences of trying. This theory seeks to establish that some version of a comparator model of the sense of agency is correct. According to the comparator model:
an intention produces overt action by interacting with a tangled series of modeling mechanisms that take the intention’s relatively abstract specification of a goal-state and transform it into various fine-grained, functionally specific commands and predictions. An inverse model (or ‘controller’) takes the goal state as input and outputs a motor command designed to drive the agent towards the goal-state. A forward model receives a copy of the motor command as input and outputs a prediction concerning its likely sensory consequences. Throughout action production, the inverse model receives updates from various comparator mechanisms. On standard expositions of the model (e.g., Synofzik et al. 2008), three types of comparator mechanism are posited. One compares the goal-state with feedback from the environment, and informs the inverse model of any errors; a second compares the goal-state with the forward model’s predictions, and informs the inverse model of any errors; a third compares the forward model’s prediction with feedback from the environment, and informs the forward model (so as to develop a more accurate forward model). (Shepherd 2015, 5)
On a comparator account of agentive experience, when predicted and desired (or, at slower time scales, predicted and actual) states match, the given comparator ‘codes’ the activity as self-generated. This code is then sent to a system hypothesized to use it in generating the sense of agency. Proponents of the comparator account recognize that this is not a complete explanation of agentive experience, but they maintain that this matching process “lies at the heart of the phenomenon” (Bayne 2011, 357).
Notice that according to the comparator account, the neural activities that realize agentive experience are not directly involved with action generation and control. If a comparator model can account for the experience of trying, then the constitutive view is likely false. Of course, this account was not designed to explain experiences of trying, but rather the sense of agency. Can a comparator account be extended to experiences of trying?
I argue from self-paralysis studies that the answer is no. In these studies, experimenters paralyzed themselves with neuromuscular blocks that left them conscious, and then attempted to perform various actions. Regarding the resultant experiences, here is what Simon Gandevia and colleagues report.
All reported strong sensations of effort accompanying attempted movement of the limb, as if trying to move an object of immense weight. Subjective difficulty in sustaining a steady level of effort for more than a few seconds was experienced, partly because there was no visual or auditory feedback that the effort was appropriate, and because all subjects experienced unexpected illusions of movement. As examples, attempted flexion of the fingers produced a feeling of slight but distinct extension which subsided in spite of continued effort, and attempted dorsiflexion of the ankle led to the sensation of slow plantar flexion. Further increases in effort repeatedly caused the same illusory movements. (Gandevia et al. 1993, 97)
As I note in (Shepherd 2015):
[P]articipants had experiences of trying to move a finger or ankle in a certain direction. And participants had experiences of the relevant finger or ankle moving in the other direction. This indicates that the experience of trying is both causally linked with and distinct from the experience of the body moving. (7)
This also looks like confirmation of the claims made by Hume and Ginet, and indication that a comparator model does not work for experiences of trying. Nothing like a matching process appears to underlie these experiences.
This leaves open a number of interesting questions. Do we have positive empirical reason to adopt the constitutive view? How do experiences of trying relate to other agentive experiences – experiences of action, perceptual experiences in action, experiences of control or of error in action, and so on? I deal with some of these questions in my (2015). I deal with others in work in progress. Dealing with all of them is more than enough work for much more than one person.
Bayne, T. (2011). The sense of agency. In F. Macpherson (ed.), The Senses. Oxford: Oxford University Press: 355–374.
Chambon, V., Wenke, D., Fleming, S. M., Prinz, W., & Haggard, P. (2013). An online neural substrate for sense of agency. Cerebral Cortex, 23(5), 1031-1037.
Damen, T. G., Müller, B. C., van Baaren, R. B., & Dijksterhuis, A. (2015). Re-Examining the Agentic Shift: The Sense of Agency Influences the Effectiveness of (Self) Persuasion. PloS one, 10(6), e0128635.
Ginet, C. 1990. On Action. Cambridge University Press.
Hauser, M., Moore, J. W., de Millas, W., Gallinat, J., Heinz, A., Haggard, P., & Voss, M. (2011). Sense of agency is altered in patients with a putative psychotic prodrome. Schizophrenia research, 126(1), 20-27.
Hume, D. (2000). An Enquiry Concerning Human Understanding: A Critical Edition, (ed.) T. L. Beauchamp. Oxford University Press.
Kalckert, A. (2014). Moving a rubber hand: the sense of ownership and agency in bodily self-recognition.
Shepherd, J. (2015). Conscious action/Zombie action. Noûs.
Synofzik, M., Vosgerau, G. and Newen, A. (2008). Beyond the comparator model: A multifactorial two-step account of agency. Consciousness and Cognition 17(1): 219–239.