PERCEPTUAL ATTENUATION OF NONFOCUSED AUDITORY STREAMS

The aim of this study was to measure the perceptual attenuation, measu red in decibels, resulting from the focusing of attention on one strea m within a multistream auditory sequence. The intensity of a nonfocuse d stream was increased until the accuracy of detecting a temporal irre gularity in this stream was the same as in a focused stream. Eight sub jects were required to detect a temporal irregularity created by delay ing or advancing one tone which could be situated in one of three temp orally regular streams played simultaneously to create a multistream s equence. The three streams differed in tempo and frequency. Subjects' attention was focused on one of the streams by preceding the multistre am sequence with one of the single streams (a cue). We first establish ed the size of temporal irregularity detected at a 90% level in cued s treams, confirming that subjects were able to focus on one particular stream. Second, an irregularity of this size was not detected above ch ance level in noncued streams, demonstrating that listeners focus only on the cued stream. Third, for 5 subjects, a 15-dB increase in the le vel of one of the noncued streams was necessary to bring detection up to that found in the cued streams. This gain provides an equivalent me asure of the perceptual attenuation of nonfocused streams. For 3 other subjects, detection in the noncued stream remained at chance performa nce whatever the level. For all subjects, detection in the cued stream decreased slightly as the level of the noncued stream increased. We c onclude that the attenuation of nonfocused auditory streams can attain as much as 15 dB, at least for some subjects.