Psychoneural isomorphism: neural codes and the structure of perception
Department of Philosophy, Boston University
Friday, January 21, 6-9 PM
STH 525, 745 Commonwealth Ave

Abstract

Our working hypothesis is that every sensation, thought, and feeling that we have has a neural basis, and further, that the structure of our experience mirrors the organization of neural activity in our brain. Organizational conceptions of mind, brain, consciousness fit naturally into a hylomorphic view in which the functional organization that constitutes a mind is inseparably embedded in the material substrate that constitutes a brain. Unfortunately, despite impressive masses of neural data and neural network theory, we still have a very dim understanding of the specific nature of that functional organization . In lieu of some understanding of how the brain works, it is difficult to determine if neural activity by itself is sufficient for conscious awareness, or whether such activity must be organized in a particular , coherent way.

In order to begin as concretely as possible in the discussion of these more general issues, we will consider the nature of neural codes and neural processing architectures that bear on the structure of perceptual experience. For the last decade I have been investigating the coding of pitch and timbre in the auditory system, and have found pervasive and robust correspondences between temporal discharge patterns (interspike interval distributions) in auditory populations and the pitches that are heard by human listeners. We will discuss the structure of these temporally-coded neural representations and how they may explain various properties of auditory perception, such as the (emergent) pitch of the missing fundamental, pitch metamery, octave similarity and harmonic relations, the relative independence of pitch, location, loudness, and duration. In particular, different, largely independent aspects of neural population activity may give rise to different dimensions of perceptual quality. Thus, it is possible that much of the structure of auditory perception, such as our ability to perceive harmonic structure in music, is inherent in the structure of underlying neural codes rather than being formed as an end-product of associative processes.

As time and interest permit, we can discuss in a more speculative mode some possibilities for neural integration that temporal coding and neural timing nets may afford: multiplexing of signals, increasing signal elaboration/dimensionality, formation of new temporal-pattern primitives, as well as broadcast-based coordinative strategies that do not require highly specific interneural connectivities. A high level process-coherence model of neural integration based on these operations would involve recurrent, buildup loops that form stable, switchable self-regenerating dynamic organizations of neural signals. Global self-production processes might then account for the unity and continuity of awareness without recourse to explicit self-description (“self-reference”). Relations of neural signals to circular-causal self-production loops (e.g. self-generated vs. externally-evoked) might then give rise to phenomenal divisions between perception, thought, and action, while relations to internal goal-states (drives, desires) as mediated through frontal and limbic circuits would confer pragmatic meaning on otherwise irrelevant sensory signals.

Suggested reading

I will try to make this discussion as self-contained as possible.

Psychoneural isomorphism
• Boring, Edwin G. 1933. The Physical Dimensions of Consciousness. New York: Dover.
• Boring, Edwin G. 1942. Sensation and Perception in the History of Experimental Psychology. New York: Appleton-Century-Crofts. • Troland, Leonard T. 1929. The Principles of Psychophysiology, Vols I-III. New York: D. Van Nostrand.

The hylomorphic perspective
• Graham, Daniel W. 1987. Aristotle's Two Systems. New York: Oxford University Press.
• Modrak, Deborah K. 1987. Aristotle: The Power of Perception. Chicago: University of Chicago

Temporal codes
• Cariani, P. 1995. As if time really mattered: temporal strategies for neural coding of sensory information. Communication and Cognition - Artificial Intelligence (CC-AI) 12(1-2):161-229. Reprinted in: K Pribram, ed. Origins: Brain and Self-Organization, Hillsdale, NJ: Lawrence Erlbaum, 1994; 208-252.
• Cariani, P. 1999. Temporal coding of periodicity pitch in the auditory system: an overview. Neural Plasticity 6(4):147-172.
• Cariani, Peter A., and Bertrand Delgutte. 1996. Neural correlates of the pitch of complex tones. I. Pitch and pitch salience. J. Neurophysiol. 76(3):1698-1716.

Regenerative process
• Organizational requisites of conscious awareness Cariani, Peter. in press. Regenerative process in life and mind. In Closure in
Complex Systems. Edited by G. Van de Vijver and J. Chandler. 8. New York: New York Academy of Sciences.