Online research in philosophy

The explanatory gap . Consciousness is a mystery. No one has ever given an account, even a highly speculative, hypothetical, and incomplete account of how a physical thing could have phenomenal states. (Nagel, 1974, Levine, 1983) Suppose that consciousness is identical to a property of the brain, say activity in the pyramidal cells of layer 5 of the cortex involving reverberatory circuits from cortical layer 6 to the thalamus and back to layers 4 and 6,as Crick and Koch have suggested for visual consciousness. (See Crick (1994).) Still, that identity itself calls out for explanation! Proponents of an explanatory gap disagree about whether the gap is permanent. Some (e.g. Nagel, 1974) say that we are like the scientifically naive person who is told that matter = energy, but does not have the concepts required to make sense of the idea. If we can acquire these concepts, the gap is closable. Others say the gap is uncloseable because of our cognitive limitations. (McGinn, 1991) Still others say that the gap is a consequence of the fundamental nature of consciousness.

Various neurophysiological experiments have revealed remarkable correlations between cortical neuronal activity and subjective experiences. However, the mere presence of neuronal electrical activity does not appear to be sufficient to produce these experiences. It has been suggested that the explanation for the neural basis of consciousness might lie in understanding the reason that some types of neuronal activity possess subjective correlates and others do not. Here I propose and develop the idea that this difference may be caused by the existence of an elementary nonarbitrary linkage between temporal or spatiotemporal patterns of neuronal activity and their subjective attributes. I also show how cortical neural circuits capable of generating experience-coding patterns could emerge during evolution and brain development, due to the presence of spontaneous stochastic neuronal activity and activity-dependent synaptic plasticity. This hypothesis leads to several testable predictions, principal among which is the idea that the neural correlates of consciousness are essentially innate and universal.

J. G. Taylor advances an empirically testable local neural network model to understand the neural correlates of phenomenal experience. Taylor's model is better able to explain the presence (i.e., persistence, latency, and seamlessness) and unity of phenomenal consciousness which support the idea that consciousness is coherent, undivided, and centered. However, Taylor fails to offer a satisfactory explanation of the nonlinear relationship between local and global neural systems. In addition, the ontological assumptions that PE is immediate, intrinsic, and incorrigible limit an understanding of the different experiential forms consciousness takes during neurobehavioral development. Recent studies suggest that neurobehavioral development is discontinuous and that judgment emerges under conditions of uncertainty to render feeling and perception in equivalent terms of energy and behavior. Approaching the problem of phenomenal experience from a developmental perspective may help resolve the paradox of feeling infinitely close as well as distant from one's self.

Why is neural activity in a particular area expressed as experience of red rather than green, or as visual experience rather than auditory? Indeed, why does it have any conscious expression at all? These familiar questions indicate the explanatory gap between neural activity and ‘what it’s like’-- qualities of conscious experience. The comparative explanatory gaps, intermodal and intramodal, can be separated from the absolute explanatory gap and associated zombie issues--why does neural activity have any conscious expression at all?. Here I focus on comparative gaps: why is neural activity in a given area expressed as this type of experience rather than that type of experience?

and apply it to various examples of neural plasticity in which input is rerouted intermodally or intramodally to nonstandard cortical targets. In some cases but not others, cortical activity ‘defers’ to the nonstandard sources of input. We ask why, consider some possible explanations, and propose a dynamic sensorimotor hypothesis. We believe that this distinction is important and worthy of further study, both philosophical and empirical, whether or not our hypothesis turns out to be correct. In particular, the question of how the distinction should be explained is linked to explanatory gap issues for consciousness. Comparative and absolute explanatory gaps should be distinguished: why does neural activity in a particular area of cortex have this qualitative expression rather than that, and why does it have any qualitative expression at all? We use the dominance/deference distinction to address the comparative gaps, both intermodal and intramodal (not the absolute gap). We do so not by inward scrutiny but rather by expanding our gaze to include relations between brain, body and environment.