Le phénomène de la continuité auditive et la répartition de la sonie entre flux auditifs

Abstract
A pure tone whose amplitude alternates between two levels can give rise to a perception not of alternation, but of an intermittent sound superimposed on a continuous sound. The more intense part is segregated into two simultaneous parts, one assigned to the continuous sound and the other to the intermittent sound. According to the theory of auditory scene analysis, the loudness of the intermittent part is computed from what is left over after having subtracted the energy assigned to the continuous part. To test this hypothesis, we presented subjects with sequences composed of a 1 kHz pure tone alternating between two levels 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 continuous or intermittent comparison sequence to have the same loudness as the corresponding part of the alternating sequence. The theory predicts zero difference between the lower level and the adjusted continuous sound, but differences of -3.3, -6.0 and -13.7 dB between the higher level segments and the adjusted intermittent sound. Results conform qualitatively to the theory though the adjusted level of the intermittent sound is higher than expected. Adjustments errors can be partly explained by errors in partitioning the stimulus energy and partly by the weakness of the phenomenon at small level differences.