Proceedings of the Annual Meeting of the Cognitive Science Society

n processing systems face a continual challenge of extracting only the most important information from the environment, resulting in awareness of some but not all of the available Information. The? current study investigates the psychophysical determinants of awareness. It examines the hypothesis that relative energy level of a stimulus is the critical factor in determining what comes to consciousness. In Experiments 1 and 3 two conceptually incompatible stimuli (one lexical, one pictorial) are presented successively in the same position of a tachistoscope for only 1 msec each, with a zero interstimulus interval. Observers report seeing one or the other, or nothing at all, at a more-or-less chance level when the stimulus durations are equal. As soon as one stimulus is given as little as onequarter to one-half a millisecond more duration than the other, the longer stimulus is reported on 68% to 84% of the test trials. In Experiment 2 an advantage for word perception at these low energy levels was investigated and measured. The results of these experiments indicate that extremely small differences in duration (about .25 or .50 msec) were sufficient to bring one concept to the consciousness of the observer at the expense of the other. Small stimulus intensity differences were investigated in Experiment 4, yielding similar results. The results can be accounted for by contemporary parallel-distributed-processing, connectionist network models of perception and cognition which use a winner-take-all decision rule.