The present experiment required subjects to judge the stream organization of patterns consisting of the elements of an ascending sequence of tones presented in rapid alternation with the elements of a descending sequence. The principle of grouping tones by their frequency proximity was found to dominate over the principle of grouping tones that follow a smooth trajectory. Therefore, subjects could not follow a sequence through its intersection in frequency with another sequence in a number of

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... fferent tonal patterns. Differences of harmonic structure among the members of ascending and descending sequences allowed listeners to hear the sequences as crossing. The effects of rhythmic regularity and the slope and length of the tones themselves (when presented as short glides) were much less important. Several researchers (Bregman & Campbell, 1971; Dowling, 1973; Miller & Heise, 1950; and van Noorden, 1975) have encountered an interesting phenomenon in the course of investigating organizational processes in the perception of rapid acoustic sequences. It has been found that a rapidly presented sequence of alternating high and low tones tends to split perceptually into two sequences: one restricted to the high tones and the other to the low tones. Each of these can be called an auditory stream (Bregman, 1978c) . Both the frequency separation of the tones and the speed of the sequence contribute to splitting, so that as the presentation speed is increased, the streams become restricted to narrower ranges of frequencies. The tendency for tones to group with others that are close to it in frequency can be called the frequency-proximity principle. This splitting of acoustic events into auditory streams on the basis of frequency proximity appears to affect pattern recognition. Apparently, one can perform detailed sequential analyses on only one stream at a time, and it is difficult to hear patterns that include elements of different streams. It has been shown, for example, that in repeating cycles of tones, judgments about the relative order of tones seems to be possible only within a stream, not across streams (Bregman & Campbell, 1971 ). Requests for reprints should be sent to Albert S. Bregman,