PHENOMENON OF CONTINUOUS SOUND AND DISTRI BUTION OF SOUND INTENSITY BETWEEN AUDITORY STREAMS

A pure tone whose amplitude alternates between two levels can give ris e to a perception not of alternation, but of an intermittent sound sup erimposed on a continuous sound. The more intense part is segregated i nto two simultaneous parts, one assigned to the continuous sound and t he other to the intermittent sound. According to the theory of auditor y scene analysis, the loudness of the intermittent part is computed fr om what is left over after having subtracted the energy assigned to th e continuous part. To test this hypothesis, we presented subjects with sequences composed of a 1 kHz pure tone alternating between two level s every 200 ms. The difference in levels was 2, 6 or 10 dB, the lower one roving randomly around 60 dB. Subjects were asked to adjust a cont inuous or intermittent comparison sequence to have the same loudness a s the corresponding part of the alternating sequence. The theory predi cts zero difference between the lower level and the adjusted continuou s sound, but differences of -3.3, -6.0 and - 13.7 dB between the highe r level segments and the adjusted intermittent sound. Results conform qualitatively to the theory though the adjusted level of the intermitt ent sound is higher than expected. Adjustments errors can be partly ex plained by errors in partitioning the stimulus energy and partly by th e weakness of the phenomenon at small level differences.