A series of experiments is proposed to investigate the perceptual processes underlying speech communication in normal human adults. These experiments will attempt to clarify the interaction of auditory sensitivity and knowledge of vocal articulation in perceiving speech signals, with respect specifically to the perceptual processes that establish the speech context for interpreting the acoustic cues. Several prior investigations have called attention to the fact that acoustic cues evoke phonetic percepts only when they occur in a speech context. Despite this well established dependence of acoustic cue on speech context, the current descriptions of the distinctive characteristics of speech signals are inadequate. Our experiments will examine three aspects of the perceptual criteria for maintaining speech contexts: the criterion of short-time spectrum; the perceptual continuity principle for integrating discontinuous elements in the speech signal over time; and, the time-varying criteria that permit the perception of phonetic segments from nonspeech stimulation. These studies will contribute to our understanding of the fundamental perceptual processes that preserve the unitariness of the speech signal over discontinuous acoustic change. Because our work describes the perceptual differentiation of speech and nonspeech, we will also be able to observe the relationship between speech perception and the more general auditory processes from which speech communication has emerged.