Rewiring Visual Systems
Noe appeals to an animal experiment by Sur et al. (1999) on newborn ferrets. They systematically lesioned specific connections and visual areas of the ferrets to induce partial rerouting of retinal projections to the medial geniculate nucleus. Signaling over these rerouted projections then drove neural activity in the auditory cortex.
Several studies confirmed that the rewired pathway is used for vision (Von Melchner et al. 2000; Newton et al. 2004, 2006; Sur and Rubenstein 2005). So, as Noe puts it, the ferrets see with their auditory brains. The brain in the newborn ferret demonstrates neural plasticity, allowing integration of auditory cells into the visual system. Noe believes that this neural plasticity supports his enactive view of the of Biological Autonomy: “If one says that there is a machine M in which there is a feedback loop through the environment, so that the effects of its output affect its input, one is in fact talking about a larger machine M' which includes the environment and the feedback loop in its defining organization.” Hurley (2002, p. 404) includes this passage to illustrate how to think about cognitive states spreading across the external environment. Noe, in turn, gives Varela’s (1979) Principles of Biological Autonomy as the earliest work from which the enactive approach emerged that he allies himself with. See Noe and Thompson (2002, p. 5). Varela, in turn, confirms that it was in his Principles of Biological Autonomy that the enactive approach was originally proposed (Noe and Thompson 2002, p. 352).
mind and consciousness; what determines cell function in vision is not intrinsic to cells, since auditory cells become functionally integrated in vision. Cells function in vision because of how they become part of skillful visual activity. Consequently, the development of vision in terms of neural processes needs to be understood contextually by looking at what the animal does in an environment. Noe notes:
The fact that it is possible in this way to vary consciousness in relation to its neural underpinnings teaches that there isn’t anything special about the cells in the so-called visual cortex that makes them visual. Cells in the auditory cortex can be visual just as well. (Noe 2009, p. 54)
Cells are potentially multipurpose. Noe goes on:
And this finding in turn means that if we want to understand why certain cells or certain brain areas are participating in seeing and not hearing, or in hearing and not seeing, we need to look beyond the immediate neural activity itself. (Noe 2009, p. 5)
It is reasonable to look beyond cells to understand how vision developed. But Noe then concludes:
It follows, then, that what determines and controls the character of conscious experience is not the associated neural activity. (Noe 2009, p. 5)
But why should this follow? From the fact that cells of perception can take on different perceptual roles, depending on how they are connected and their developmental history, it hardly follows that no neural activity determines experience. Think of an analogous case. Suppose I go to a neurologist, who finds that I am seeing with my auditory cortex. The neurologist tells me it can happen through spontaneous rerouting of nerve fibers during brain development. I would be surprised, but with enough evidence, I would accept that my brain, as a system, sees that way. That some cells in my brain have odd jobs, however, would not be good evidence for externalism of consciousness.