Evidence for High-Level Feature Encoding and Persistent Memory During Auditory Stream Segregation

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A test sequence of alternating low-frequency (A) and high-frequency (B) tones in a repeating “… ABAB …” pattern is more likely to be heard as 2 segregated streams of tones when it is preceded by an isofrequency inducer sequence whose frequency matches either the A- or B-tone frequency (e.g., “… BBBB …”) of the test, a phenomenon referred to as stream biasing. Low-level processes such as stimulus-selective adaptation of frequency-tuned neurons within early auditory processing stages have been thought by some to mediate stream biasing; however, the current study tested for the involvement of higher level processes. Inducers whose frequency matched neither the A- nor B-tone frequency (e.g., “… CCCC …”) sometimes facilitated stream biasing. Stream biasing was also sensitive to complex features of the inducer sequence, namely whether the rhythmic pattern of the inducer matched the rhythm of the ABAB test. Stream biasing occurred even when an 8-s silent interval separated the inducer and test sequences, a time span longer than previously recognized (Beauvois & Meddis, 1997). These results suggest the involvement of persistent activation of high-level representations that affect perception.

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