Is a Blind Person's Consciousness Partly Contained in Her Cane?
Karina Vold spoke interestingly last week at UC Riverside on "vehicle externalism" about consciousness. (Here's some of her published work on the topic.) According to vehicle externalism, the "vehicle" of consciousness -- that is, its actual physical basis -- is not, as many think, the brain, but rather the brain plus some of the world beyond the body. Central to Vold's presentation was the classic example of the blind person and her cane.
Before discussing that example, I want to start (as Vold did) with a well-known argument fom Andy Clark and David Chalmers. Otto is a forgetful fellow, and so he always carries a notepad with him, full of reminders. When he wants to go to the museum, he pulls out his notebook, which reminds him that the museum is on 53rd Street, and then heads that way. Without the notebook, he would be lost. Clark and Chalmers argue that Otto's retrieving information from the notebook is not relevantly functionally different from a less forgetful person's retrieving the same information from memory. Because of this, they argue, it's correct to say that as long as the notebook is reliably in his pocket (even before he consults its contents), Otto knows that the museum is on 53rd Street. Otto's memory, and thus his mind, is not entirely confined within his skull. It extends to the notepad in his pocket.
Vold and some other defenders vehicle externalism (but not Clark and Chalmers) want to say something similar about consciousness. To explain how and why, Vold invokes a blind person with a cane -- let's call her Genesis [name randomly selected].
Genesis skillfully uses her cane to help her move about, swinging and tapping it to detect obstacles, objects, slopes, textures, and materials. A skilled cane user can learn a lot from a tap or two! Her cane is always with her when she walks, and in some sense it feels almost as if it were a part of her body. (You might experience a lesser version of this if you take a pen in your hand and use it to stroke and tap things. Many people report that it feels almost as though they are directly feeling objects via the pen, as opposed to feeling the pen in their fingers and inferring from those sensations what the objects beyond must be like.) Genesis experiences the world via a sensorimotor loop that travels from brain through arm and hand, through cane, then both into the ears and back up through the arm into the brain.
If a brain-based view of consciousness is correct, it is from her brain alone that Genesis's sensory experience arises, with signals up the arm serving only as input to the brain processes supporting consciousness. In contrast, according to vehicle externalism, the cane and arm do not merely provide inputs. Rather, consciousness arises from cane and arm and brain jointly operating as an integrated system. Consciousness does not depend only causally on the input Genesis receives from the stick. Rather the stick itself is a constituent of an extended system that as a whole constitutes or gives rise to consciousness.
The difference between the internalist input view and the vehicle externalist view can be a little hard to fathom. Here, I think the philosophical concept of supervenience can help. But before I get to supervenience, let me stave off one possible error. The vehicle externalist is not merely saying that consciousness feels as though it is located in the cane. Everyone agrees that consciousness can feel as though it's somewhere other than the location of the system that gives rise to the experience. Pain can feel as though it's in your toe even though the material process that directly gives rise to it, on an internalist view, is in the brain rather than the toe. This seems especially clear in the case of phantom limb pain.
A set of properties, properties of Type A, supervenes on another set of properties, properties of Type B, if and only if there is no possible difference in the As without a difference in the Bs. For example, the score of a baseball game supervenes on the number of times each individual player has officially crossed home plate. There is no possible difference in score without some difference in the number of times at least one individual player has crossed home. (The converse is not the case: It is possible for the score to be the same even if some individual runners had scored a different number of runs.)
The core question of vehicle externalism, as I see it, can be expressed in terms of supervenience: Does consciousness supervene on the brain, as the internalist would say? Or is it possible to have different conscious experiences despite having exactly the same brain states? (Not all vehicle externalists need actually be committed to denying the supervenience of consciousness on the brain, but then I worry that their view might collapse into a notational variant of the internalist input view.)
Consider Otto. If you accept vehicle externalism about Otto's memory, then it should be possible to change Otto's memory state without changing his brain state at all. Otto-1 has the notepad in his pocket. Otto-2 has been pickpocketed, though he hasn't noticed it. Assume that Otto-1 and Otto-2 have exactly the same brain states. On Clark and Chalmers's vehicle externalism, Otto-2 no longer remembers where the museum is (and many other things), although Otto-1 does remember. Despite this difference in memory, on Clark and Chalmers's internalist view about consciousness, Otto-1 and Otto-2 will differ not at all in their conscious experiences. Their conscious experiences will only start to diverge when Otto-2 reaches for his missing notebook. Otto's consciousness, but not his memory, supervenes on his brain state.
Now consider Genesis. If a substantive form of vehicle externalism about consciousness is correct, we should be able to concoct a case in which Genesis-1 and Genesis-2 have identical brain states but non-identical conscious experiences. To claim that such a case is possible is just what it is to deny that consciousness supervenes on the brain.
In other words, we want to imagine changing the cane in some important way, without changing the brain. The vehicle externalist ought to say that the conscious experiences will be different. If consciousness is literally partly contained in or constituted by the cane, Genesis-1 and Genesis-2, with identical brains but different canes, ought to have different conscious experiences.
Let's consider a small slice of time -- a third of a second -- when Genesis's cane is swinging through the air between things. Suppose, hypothetically, that a friend were able to undetectably change the tip of the cane just before that third of a second. Genesis is swinging her cane and touches a passerby who "accidentally" jostles the cane a bit. In Genesis-1, the cane is unchanged after the jostling. In Genesis-2, the long tip of her cane has been covertly swapped for a shorter tip of the right weight (slightly heavier, to compensate for the difference in leverage). The swap is so perfect that for the entire third of a second after the bump and before her cane strikes the next object, the signals into their brains are identical. For this brief duration, Genesis-1 and Genesis-2 have identical brain states but different cane states.
[Update: Instead of a clever prankster, it could be a friend who arranges the swap, with Genesis's prior consent but without her knowledge of the time or method of the swap. See the comments section for discussion.]
Shortly, the brain states of Genesis-1 and Genesis-2 will diverge: Genesis-2 will think the next object is closer than it is, and after the strike she might notice some difference in the sound and tactile dynamics of her cane. The question concerns what happens before that next tap of the cane. The canes are different. The sensorimotor contingencies are different (though that difference has not yet resulted in divergent input signal). Will the conscious experiences, already, be different?
It seems unintuitive that they would be. Most of the vehicle externalists about consciousness I have pressed on this question either hesitate to answer, or try to wiggle out in some way. Also, if introspection is something that happens in the brain, and if consciousness is always immediately available for introspection, the case seems to present trouble. Some philosophers might think that if the view implies a not-immediately-introspectible difference in conscious experience, that would be a fatal flaw. But I disagree. Intuitions about consciousness aren't always correct, and simple, immediate-access models of introspection may not be correct. That Genesis-1 and Genesis-2 have different conscious experiences already in that first third of a second is an interesting possibility, worth considering, and it seems to flow naturally from vehicle externalism. If this is a "bullet", I think the vehicle externalist should bite it.