Distilling the neural correlates of consciousness
Talis Bachmann2011, Neuroscience & Biobehavioral …
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Abstract
Solving the problem of consciousness remains one of the biggest challenges in modern science. One key step towards understanding consciousness is to empirically narrow down neural processes associated with the subjective experience of a particular content. To unravel these neural correlates of consciousness (NCC) a common scientific strategy is to compare perceptual conditions in which consciousness of a particular content is present with those in which it is absent, and to determine differences in measures of brain activity (the so called "contrastive analysis"). However, this comparison appears not to reveal exclusively the NCC, as the NCC proper can be confounded with prerequisites for and consequences of conscious processing of the particular content. This implies that previous results cannot be unequivocally interpreted as reflecting the neural correlates of conscious experience. Here we review evidence supporting this conjecture and suggest experimental strategies to untangle the NCC from the prerequisites and consequences of conscious experience in order to further develop the otherwise valid and valuable contrastive methodology.
Key takeaways
- These contradictory results can be understood when considering a severe methodological pitfall: the result of the contrast between trials with and without conscious perception of a target is not only the NCC proper but could also reflect processes that in a particular experiment paradigm, regularly and lawfully, precede and/or follow conscious perception without directly corresponding to the subjective experience (Bachmann, 2009;de Graaf et al., 2012;Melloni and Singer, 2010).
- NCC is the "minimal set of neural events jointly sufficient for a specific conscious experience (given the appropriate enabling conditions)" (Koch, 2004).
- Therefore, if we want to proceed in understanding consciousness, the NCC has to be experimentally distilled from the prerequisites for and the consequences of conscious perception.
- Empirical and theoretical arguments in the mid-1990s suggested that V1 might not be necessary for visual conscious experience (Barbur et al., 1993;Crick and Koch, 1995) but further research and theoretical positions generally favored the idea that cortical feedback to V1 is indeed necessary for visual conscious perception and therefore part of the NCC (Lamme, 2001;Pascual-Leone and Walsh, 2001;Tong, 2003).
- Despite its original simplicity and appeal, the traditional method, contrasting trials with and without conscious perception of a particular target, by itself does not appear to have the necessary specificity to reveal the NCC.
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