When we search for explanatory unity in the study of consciousness, we should first consult philosophy of science to clarify the notions of “unity” and “explanation”.
Theoretical unity could be achieved in the form of a coherent,progressive research program. Such a program should be committed to empirically plausible philosophical background assumptions about consciousness that could be shared by most empirical scientists working in the field (Revonsuo 2000). My proposal for such background assumptions would be to regard consciousness as a real biological phenomenon residing within the confines of the brain, or biological realism. This background assumption is in harmony with empirical cognitive neuroscience. Furthermore, biological realism implies that the framework of multilevel mechanistic explanation, widely applied in the biological sciences (Bechtel & Richardson 1993; Machamer et al. 2000), should also apply to the explanation of consciousness. In this framework, the explanation of consciousness is the task of constructing a multilevel mechanistic model with a detailed phenomenal-level description, and a causal-mechanical network surrounding the phenomenal level.
The multilevel model makes explicit the relationship of consciousness to the lower and higher levels of organization as well as to events causally modulating consciousness. This multilevel explanatory framework might bring significant unity to the empirical research on consciousness because it allows all the different sources of empirical evidence to be integrated under one framework. We could ask, concerning any particular empirical approach: (1) Does it tell us about the internal quality and organization and the temporal dynamics of consciousness, on phenomenological terms? If yes, then it contributes to the phenomenal-level description. (2) Does it describe, at an abstract computational level, what kind of input-output transformations the phenomenal level is capable of performing? If yes, then it contributes to the input-output description of consciousness. (3) Does it contribute to our understanding of where in the brain the underlying constitutive mechanisms of consciousness might be located, or what kind of neurophysiological activity might be involved (Revonsuo 2001)? If yes, then the data contributes to the downward-looking explanation of consciousness. (4) Does the data reveal how conscious information, in interaction with sensory and motor mechanisms, causally contributes to organism-environment interaction and behavior? If yes, then it contributes to the upward-looking, contextual explanation of consciousness. (5) Does it tell us about the preceding events (say, the early processing of sensory input) that causally modulate consciousness? Then it is a contribution to the etiological explanation of consciousness. Doesn¹t the empirical data tell us anything that could be fitted into the multilevel explanatory framework? Then that particular approach is not useful to the description and explanation of consciousness, and should perhaps be abandoned.
The framework of mechanistic biological explanation could show the contribution and the relative importance of different sources of empirical evidence to the overall explanation of consciousness. The overall goal would be to add new pieces to the multilevel and multidimensional causal-mechanical model of consciousness, which would be not unlike many other mechanistic models of complex biological phenomena. The model would also indicate the areas where we still lack empirical data, and which parts of the description and explanation are already approaching completion.
In this paper, I will first describe the mechanistic explanatory framework at a more general level, and then show how various sources of evidence concerning visual consciousness could be fitted into this framework.