Narrowing the Explanatory Gap with Bridge Metaphors

Narrowing the Explanatory Gap with Bridge Metaphors Jeff Yoshimi (jyoshimi@ucmerced.edu) Cognitive and Information Sciences, UC Merced Merced, CA, 95343 USA Abstract 2. The relationship between consciousness and neural activity cannot be made intelligible. A central problem in philosophy of mind concerns the rela- tionship between subjective experiences and the physical pro- cesses that subserve them. There seems to be an unbridgeable “explanatory gap” between the two. Whereas other scientific explanations (e.g. the explanation of temperature in terms of kinetic energy) involve determinate relationships between two kinds of phenomena, correlations between patterns of neural activity and conscious experiences seem to be arbitrary. I argue that by developing computer models of embodied agents, and interpreting them using the tools of philosophical phenomenol- ogy, the relationship between neural and conscious processes can be seen to be systematic, and non-arbitrary. Visualiza- tions of these models serve as “bridge metaphors” that further emphasize how systematic neuro-phenomenological relations are. By showing that links between brain states and conscious states are non-arbitrary, the explanatory gap is narrowed. 3. The relationship between consciousness and neural activity cannot be explained. Keywords: Explanatory Gap; Hard Problem of Conscious- ness, Dynamical Systems Theory; Neural Networks; Phe- nomenology; Reinforcement Learning; Husserl The Explanatory Gap The familiar mind-body problem is rooted in the difficulty we have understanding how subjective feelings could be re- ducible to (or identical with) objective physical facts. How could my rush of excitement at the birth of a child “just be” a distributed pattern of spiking neurons? This problem is asso- ciated with a kind of explanatory challenge. When it comes to consciousness, there seems to be an explanatory gap (Levine, 1983), or a “hard problem” (Chalmers, 1995), that does not arise when inter-theoretic reductions are pursued in other ar- eas of science. The problem is a matter of ongoing discussion, and there is a fairly well-developed taxonomy of responses to it; for review see (Tye, 2013). 1 The explanatory gap argument can be presented as a modus tollens: Let us consider the two premises and conclusion of this argu- ment in more detail. The first premise describes an intelligibility condition on explanation. 2 According to Levine, when something is made intelligible, “There doesn’t seem to be anything ‘left out”’ (Levine, 1983, p. 358). In the explanatory gap literature this has also been characterized as a feeling of necessity or non- arbitrariness. If an explanation makes a phenomenon intelli- gible, we feel that the explanandum is necessitated by the ex- planans. To use Levine’s example, that water boils at 100 de- grees Celsius at sea level, seems necessary, given the laws of chemistry. Or, to use an example from Tye, “Once one learns that in solid things, the molecules are not free to move around as they are in liquids, one immediately grasps that solid things do not pour easily, that they tend to retain their shape and vol- ume. Having been told the physical story, to ask: ‘Yes, but why are things with molecules that are fixed in place solid? Why shouldn’t such things not be solid?’ is to show a concep- tual confusion” (Tye, 1999, p. 705). In these cases it does not seem like the phenomenon explained (boiling water, solidity) could be any other way, given the explanation. We could not just change the mapping from low level physical states of a thing to temperatures, or to states of matter (solid, liquid, gas, etc.) in any arbitrary way. The intelligibility condition can be summarized as follows: If an explanation of some phenomenon p in terms of phys- ical state s and laws L is intelligible, then the relationship between s and p is felt to be necessary, rather than arbitrary. 1. To explain a phenomenon x requires making x intelligible. 1 The relationship between the explanatory gap argument and the mind-body problem is subtle. The explanatory gap argument is epis- temological: it concerns our ability to understand how brain states are related to conscious states. The mind-body problem is a meta- physical problem: it concerns how brain states and mental states are actually related to each other (in particular: are they identical or sep- arate?). So they are distinct issues. Some have used the explanatory gap argument as a metaphysical argument against materialism (and in support of dualism), by adding a premise to the effect that what cannot be explained in terms of physics is not itself physical. Others defend the view that physicalism is true, and that the explanatory gap is just a problem we human cognizers have with understanding how physicalism is true. For an overview see (Chalmers, 2003). I am officially neutral on these issues. I argue that there is less of an explanatory gap than the authors of the original arguments sup- pose. This naturally supports physicalism, but is nonetheless strictly speaking compatible with dualism and even other forms of monism. More formally, if we describe the relationship between phys- ical states s and higher level phenomena p using a function f , then if an explanation using f is intelligible, we must feel that f is fixed by the relevant laws, and is not just arbitrarily stipu- lated. 3 For example, the mapping between low-level physical 2 I refer to explanations, the phenomena explained in an expla- nation, and the theoretical relationships involved in an explanation, as being “intelligible.” These usages are related as follows: if a re- lationship is intelligible it is determinate and non-arbitrary (details are in the main text); if a phenomenon is made intelligible it is de- scribed in terms of an intelligible relationship; if an explanation is intelligible, it makes the phenomenon it explains intelligible. 3 Notice the reference to “feeling”: intelligibility is, at least in part, a phenomenological concept. Indeed, the phrase “felt contin- gency” occurs five times in Levine’s paper.