In sum, dichotic listening tasks are appropriate for testing whether perception requires attention. The separate issue of the possible presence of perception that can never be brought under the spotlight of awareness should indeed be investigated by paradigms such as masking. However, the ultimate criterion for availability to awareness must be phenomenal experience. The discrepancy between thresholds of different perceptual indices is an important empirical finding, but its theoretical interpretation is not straightforward. In addition, it is suggested that we worry about the possibility that so-called indirect evidence reflects side effects of perceptual processing rather than the contents of its final product. In that case, what are being observed are vestiges of the processing of stimuli that do not make it to awareness. Whether those stimuli are below the threshold for overt response is an open question.

The cerebral cortex is a rich and diverse structure that is the basis of intelligent behavior. One of the deepest mysteries of the function of cortex is that neural processing times are only about one hundred times as fast as the fastest response times for complex behavior. At the very least, this would seem to indicate that the cortex does massive amounts of parallel computation.

This paper explores the hypothesis that an important part of the cortex can be modeled as a connectionist computer that is especially suited for parallel problem solving. The connectionist computer uses a special representation, termed value unit encoding, that represents small subsets of parameters in a way that allows parallel access to many different parameter values. This computer can be thought of as computing hierarchies of sensorimotor invariants. The neural substrate can be interpreted as a commitment to data structures and algorithms that compute invariants fast enough to explain the behavioral response times. A detailed consideration of this model has several implications for the underlying anatomy and physiology.