Primary auditory stream segregation and perception of order in rapid sequences of tones.

A recent finding of the inability of listeners to judge the order of three or four nonspeech sounds presented in a repetitive cycle is explained by the concept of stream segregation. Two experiments showed that at high presention rates of a short cycle of six tones (three high and three low), 5s invariably segregated the tone sequences into streams based on frequency and could perceive only those patterns relating elements of the same subjective stream. Recently, Warren, Obusek, Farmer, and Warren (1969) reported a remarkable in-ability of listeners to judge the order of three or four nonspeech sounds (e.g., high tone, hiss, low tone, buzz) presented repetitively in a loop. Warren et al. reported they had to lengthen each sound to about 700 msec, in duration before half of the 5s could judge the order of sounds correctly. The difficulty 5s encountered in their experiment may be related to another phenomenon, that of auditory stream segregation. In the course of investigating organi-zational processes in the perception of rapid sequences of sounds, we have en-countered a phenomenon in which a single rapid sequence of tones seems to break up perceptually into two or more parallel sequences, as if two or more different instruments, each restricted to a certain class of sounds or range of frequencies, were playing different but interwoven parts. We call this phenomenon primary auditory stream formation. A stream may be denned as a sequence of auditory events whose elements are related perceptually to one another, the stream being segregated perceptually from other co-occurring audi-tory events. We assume that attention cannot be paid to more than one such stream at a time, i.e., that the apparent