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Book Review - How to Solve the Mind-Body Problem
How to Solve the Mind-Body Problem
by Nicholas Humphrey
Imprint Academic, 2000
Review by Gregg Caruso
Nov 18th 2001

In this short but intriguing book, Nicholas Humphrey presents and defends a novel proposal for solving the mind-body problem. Readers familiar with his earlier book, A History of the Mind (1992), will find that many aspects of his current proposal were already discussed in that earlier work, and at much greater length. But unfamiliar readers will not be at a loss for Humphrey presents his theory here in a coherent, easy to follow, self-contained way. The book begins with a target paper by Humphrey and is followed by a lively discussion of his proposal by several prominent commentators. There are contributions by Andy Clark, Daniel Dennett, Naomi Eilan, Ralph Ellis, Valerie Gray Hardcastle, Steven Harnad, Natika Newton, Christian de Quincey, Carol Rovane, and Robert Van Gulick. The book concludes with Humphrey's reply to the commentators. Although Humphrey's theory needs to be developed further before a judgment can be made on whether it can "solve" the mind-body problem, I do think it sets out some interesting new avenues of investigation.

Humphrey's ambitiously titled paper, which shares the title of the book, falls into two main parts. In the first, he offers a diagnosis of the current state of the mind-body debate and a general prescription for how to go about seeking its solution. In the second, he aims to fill that prescription with a specific proposal that he believes will bring us closer to a resolution of the underlying problem. Humphrey defends a mind-brain identity theory, claiming that "each and every instance of a human mental state is identical to a brain state" (p.5). To his credit, he defends such an identity claim without shying away from the hard problem of phenomenal consciousness. Humphrey offers an analysis of qualitative mental states that purportedly renders them commensurate with brain states, allowing them to be described in terms of the same dimensions. If his attempt is successful, the conceptual gap between mind and body could be closed. Of course that's a big if!

In evaluating the current state of the mind-body debate, Humphrey points out that the incommensurate ways we describe both our mental states and our brain states has prevented us from seeing why it is they are identical. If any proposed identity is to have any chance of being valid, both sides must represent the same kind of thing. As Humphrey puts it, "both sides must have the same conceptual dimensions, which is to say they must belong to the same generic class" (p.8). When the proposal is that a certain mental state is identical to a certain brain state, mental state, m = brain state, b, the question should be: do the dimensions of the two sides match? Humphrey believes that they can be made to match. "Provided cognitive science delivers on its promise, it should soon be possible to characterize many mental states in computational or functional terms, i.e. in terms of rules connecting inputs and outputs" (p.8). He claims that most of the states of interest to psychologists-states of remembering, perceiving, wanting, talking, thinking, and so on-are in fact likely to be amenable to this kind of functional analysis. He is quick to point out, however, that there is another class of states that appear to resist functional analysis. The so-called 'hard' cases are those that involve phenomenal consciousness: the subjective sensation of redness, the taste of cheese, the pain of a headache, and so on. These are the states that Humphrey focuses on.

Borrowing a phrase from Isaac Newton, Humphrey dubs these states sensory 'phantasms'. Focusing then on identity claims like, phantasm, p = brain state, b, Humphrey insists the problem still remains getting the conceptual dimensions of the two sides to match. He warns us that we must not be too radical in redefining just one side of the identity, for we run the risk of redefining away the essential point. For example, we don't want to redefine these phantasms in a way that will define away their essential nature. Humphrey points out that, "Daniel Dennett's sallies in this direction can be a warning to us (1991)" (p.10). Roger Penrose, perhaps, can be seen as an offender in the opposite direction (The Emperor's New Mind, 1989). Humphrey's main insight is that we need to work on both sides of the identity: "So, this, I suppose, is how to solve the mind-brain problem. We shall need to work on both sides to define the relevant mental states and brain states in terms of concepts that really do have dual currency-being equally applicable to the mental and the material…And now all that remains, for this paper, is to do it" (p.10).

Humphrey's proposal for providing the required dual currency concepts has three main parts. The first deals with separating out two distinct parts to experience: sensation and perception. Quoting Thomas Reid, Humphrey argues that sensation, taken by itself, implies neither the conception nor belief of any external object, whereas perception implies a conviction and belief of something external. For Humphrey, sensation is a "subject-centered affect-laden representation of what's happening to me" (p.12). Perception, on the other hand, is "an objective, affectively neutral representation of what's happening out there" (p.12). Humphrey argues that when we try to distinguish and define the realm of sensory phantasms we are after the first of these. And it's easy, according to him, to muddle the two up. Sensation, as it is understood by Humphrey, has to do with the self, with bodily stimulation, with feelings about what's happening now to me and how I feel about it. Perception, by contrast, has to do with judgments about the objective facts of the external world. The first step, then, in Humphrey's account is to mark off the phenomenon that interests us-sensation-and get the boundary in the right place. Although some commentators, most notably Naomi Eilan, question whether such a strong distinction between these two representations can be defended, I agree with Daniel Dennett that "something like [Humphrey's] distinction between visual sensation and visual perception needs to be drawn" (p.25).

Also central to Humphrey's account of sensation is the denial of an act-object distinction; i.e., there is no real distinction between the act of sensing and the object sensed. Here again I like Humphrey's proposal. Sensory awareness, for Humphrey, is an activity. We do not have pains we get to be pained. Or more accurately speaking, we are in a state of "paining". "That is to say, sensing is not a passive state at all, but rather a form of active engagement with the stimulus occurring at the body surface" (p.13). Whenever we have a sensation, according to Humphrey, we are not sitting there passively absorbing what comes in from the body surface, we are reflexly reaching out to the body surface with an evaluative response-a response appropriate to the stimulus and body part affected. Furthermore, it is this efferent activity that we are aware of. "So that what I actually experience as the feeling-the sensation of what is happening to me-is my reading of my own response to it" (p.13). Hence the quality of the experience, the way it feels, instead of revealing the way something is being done to me, reveals the very way something is being done by me. This, the viewing of sensation as efferent activity, is the second major move in his positive proposal. Along with this move, Humphrey also argues that sensory activity has evolved from responses that in the past did carry through into actual behavior. And the result is that even today the experience of sensation retains many of the original characteristics of true bodily action.

Explaining sensory activity in terms of bodily activity allows Humphrey to correlate it with brain activity. Sensation, like bodily action, is characterized by five defining properties: ownership, bodily location, presentness, qualitative modality, and phenomenal immediacy. Each of these can be understood in terms of dual currency concepts, neither purely mental nor purely physical. Using an example of sensation, feeling a pain in my hand, and an example of bodily action, performing a hand wave, Humphrey compares the two and shows that the five defining properties can be applied equally well to both. Thus, the positive analogies between sensation and bodily activities add up. Yet Humphrey also acknowledges that there is an obvious disanalogy: namely, it is 'like something' to have sensations, but not like much to engage in most other bodily activities. Ultimately the key to an experience being 'like something', for Humphrey, lies in the experience "being like itself in time." That is, it lies in the experience "being about itself, or taking itself as its own intentional object" (p.15). This is achieved, in the special case of sensory responses, through a kind of self-resonance that effectively stretches out the present moment to create what Humphrey calls the "thick moment of consciousness" (p.15).

It is this part of Humphrey's theory that requires the most work. Much more needs to be said about how this so-called "thick moment of consciousness" comes about. Christian de Quincey goes so far as to call it Humphrey's "Achilles' heel" (p.79). In my opinion, the success or failure of Humphrey's theory rests on his ability to better explain this "thickness". That said, if this notion can be successfully fleshed out, then Humphrey has brought us a good deal closer to seeing how these phantasms can be identical to brain states. He has provided us with a way to redescribe the left hand side of the identity equation in progressively more concrete terms. "The phantasm of pain becomes the sensation of pain, the sensation of pain becomes the experience of actively paining, the activity of paining becomes the activity of reaching out to the body surface in a painy way, and this activity becomes self-resonant and thick"(p.15). With each step Humphrey has come a little closer to specifying something of a kind that we can get a handle on.

Humphrey concludes with a plausible evolutionary scenario that would connect the two sides of the mind-body problem. This is his third and final move. If the mind term involves a state of actively doing something about something, namely issuing commands for an evaluative response addressed to the body surface, then the brain term must also be a state of actively doing something about something, presumably doing the corresponding thing. If the mind term involves self-resonance, then the brain state must also involve self-resonance. The main stages in his evolutionary just-so story for how sensation developed goes like this. In the first stage, the animal or organism has a defining edge to it, a structural boundary. In the second stage, the animal acquires the ability to sort stimulus. "If it is to survive it must evolve the ability to sort out the good from the bad and to respond differently to them" (p.16). In the third stage, the animal develops a reflex arc, "there develops something like a reflex arc passing via a central ganglion or proto-brain: information arrives from the skin, it gets assessed, and appropriate adaptive action is taken" (p.16). In the forth stage, the time comes when it is advantageous for the animal to have some kind of inner knowledge of what is affecting it, which is can begin to use as a basis for making more sophisticated planning and decision making. In this stage the animal acquires "the capacity to form mental representations of the sensory stimulation at the surface of its body and how it feels about it" (p.16). To do this, according to Humphrey, all the animal needs to do is to pick up on the already-occurring command signals that it was issuing in the previous stage of development. "For, the fact is that all the requisite details about the stimulation-where the stimulus is occurring, what kind of stimulus it is, and how it should be dealt with-are already encoded in the command signals the animal is issuing when it makes the appropriate sensory response" (p.16).

In the next stage, as the animal becomes more independent of its immediate environment, there is no longer any adaptive value in the representations being tied to action. Even though the animal may no longer want to respond directly to the stimulation at its body surface as such, it still wants to be able to keep up to date mentally with what's occurring. At this stage, argues Humphrey, the animal remains dependent on the secondary representational functions that these responses have acquired. On his just-so story, the animal continues to issue commands such as would produce an appropriate response at the right place on the body if they were to carry through into bodily behavior. "But, given that the behavior is no longer wanted, it may be better if these commands remain virtual or as-if commands" (p.17). In the final two stages, the whole process becomes closed off from the outside world in an internal loop within the brain. Then the 'thickness factor', which we found to exist on the mind side of the equation, is accounted for by the progressive shortening of the sensory response pathway. In the early days feedback effects existed by modifying the very stimulation to which they are a response, but this feedback circuit was too round-about and slow to have any interesting consequences according to Humphrey. But, he argues, when the process becomes internalized and the circuit so much shortened, the conditions are there for a significant degree of recursive interaction to come into play. "The command signals for sensory responses begin to loop back upon themselves, becoming in the process partly self-creating and self-sustaining" (p.19). On this note, Humphrey concludes by saying that we now have the required set of features on the brain side of the equation to see how a solution to the mind-body problem is possible.

"We needed a certain set of features on the brain side. We could have invented them if we were brave enough. But now, I submit, we actually have them handed to us on a plate by an evolutionary story that delivers on every important point" (p.19).
Although I think much more work needs to be done, I do find Humphrey's proposal promising. I do not think, however, that Humphrey's account will ever persuade those who hold an inflated notion of what phenomenal consciousness is. For example, people who are truly troubled by the possibility of "zombies", or robots that can implement functional states, will most likely continue to feel that something important has been left unexplained. Robert Van Gulick and de Quincey seem to have just such a concern. Although it may not appear that way at first, Humphrey's account of sensations is a functional one through and through. Being a functional account, one can raise all the traditional functional objections to it. Dennett tries to preempt some of these objections on Humphrey's behalf. And Humphrey, himself, does a pretty good job replying to them. But I think that there will always be those who find any functionalist account, no matter how developed, unsatisfying. To these people, Humphrey's proposal, like many past functionalist proposals, will never be able to "solve" the mind-body problem. On the other hand, those who are still open to the functionalist project will, I think, find some promise in Humphrey's pivotal idea that sensation is itself a species of affect-laden intentional activity.

© 2001 Gregg Caruso

Gregg Caruso is currently finishing up his PhD in Philosophy at The Graduate School and University Center of the City University of New York.