Effect of rhythmic grouping on stream segregation.

Three experiments investigated the role of temporal grouping on auditory stream segregation. For sounds that formed frequency streams (e.g., 400 Hz, 500 Hz, 1600 Hz, and 2000 Hz), the effect of rhythm was minimal. Temporal grouping did not affect judgments of stream segregation and did not affect difficulty of sequence identification. In contrast, for sounds that tended to form one coherent sequence (e.g., 750 Hz, 1500 Hz, 3000 Hz, and 6000 Hz), temporal grouping affected judgments of stream segregation as well as difficulty of identification. The temporal grouping could space the three lower or three higher pitch tones equally in time and this induced isochronous stream segregation. Subjects could not interleave the resulting streams, and identification became far more difficult. The role of rhythmic grouping is therefore contextual, depending on the relationships between the elements as well as the order of the elements.