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The notion that human perceptual decisions are based on discrete processing cycles rather than a continuous accumulation of information was examined experimentally. Significant periodicities were found in human response times (RT) to feature and conjunction discrimination tasks in the visual and auditory modalities. Individual RT histograms were multimodal, with regularly spaced peaks and troughs, indicating that responses were emitted more frequently at regularly recurring time intervals following stimulus presentation. On average, responses were initiated after four to seven discrete processing steps whose "quantum" duration was proportional to task difficulty.
Psychological Science © 1993 Association for Psychological Science