A computational theory of consciousness in cognition

Issues of awareness and consciousness are becoming increasingly important in studies of psychological phenomena such as perceptual priming, implicit memory, automatization, and the disorders resulting from brain damage, yet the role of consciousness in these phenomena remains unclear. This thesis develops a computational theory of the processes underlying consciousness, which accounts for these data under a single unifying framework. Simulation models of five experiments are described showing that the theory is consistent with data across several domains. Motivated by findings in cognitive psychology, neuropsychology and neuroscience, the theory consists of three basic claims. (1) The human cognitive architecture consists of a set of functionally specialized modules, each of which functions as an associative memory in its domain. Each module computes an output that represents the most appropriate interpretation of its inputs that is consistent with a set of domain constraints. (2) Each module computes its output in a two-stage process consisting of a fast, input-output mapping step, followed by a slower, incremental relaxation search step. The mapping step produces and output quickly, but which may not satisfy domain constraints. The relaxation step then gradually transforms the initial output into one that maximally satisfies domain constraints. (3) Stable states in the outputs of modules correspond to the contents of consciousness. Unlike most theories, consciousness in our theory is fully distributed: stable states in any module may reach consciousness without requiring the involvement of a special brain area or consciousness system. A connectionist implementation of the theory is used to model data from five cognitive psychology experiments. These experiments cover a range of phenomena, including basic subliminal perceptual priming, unconscious processing of ambiguous words, visual metacontrast masking, speeded response effects in perception, and the effects of conscious decisions on cognition. Our theory offers accounts for this set of experiments within a single, unified framework. The question of the computational utility of consciousness in cognition is addressed, and it is shown through simulations that the mechanisms underlying consciousness in the theory serve an important computational function within the system, boosting performance in cognitive tasks.