The background tones were spaced evenly on either a harmonic scale (H) or on a logarithmic scale (L), or they were “shifted” (S) complexes which were produced by shifting all harmonics (upward for four subjects, downward for the four others) by 25% of the F0 (as in Micheyl et al., 2010 8. The background tones were 100 ms in duration each and they were presented either synchronously with 100-ms targets (“Sync”), or 40 ms before each 60-ms target (“Async,” for “asynchronous”) in all cases the offsets of the targets and background tones were synchronous. The target tones were accompanied by background tones. Moreover, the strong TCT predicts that harmonic relationships-or lack thereof-between the target and background tones would have either no effect, or a small effect compared to that of temporal coherence between targets and maskers.
Thus, the strong TCT predicts good performance in all conditions in which the target and background tones (up to the penultimate burst) were temporally incoherent, and poor performance in all conditions in which the target and background tones were temporally coherent. We therefore reasoned that listeners would show good performance only in conditions in which they were able to hear the target tones as a separate stream.
“ Hearing out repeating elements in randomly varying multitone sequences: a case of streaming?,” in Hearing-From Basic Research to Applications., edited by B. “ Multiple bursts, multiple looks, and stream coherence in the release from informational masking,” J. “ Reducing informational masking by sound segregation,” J. In general, repeating target tones can be “heard out” from a multi-tone background when the targets form a separate stream (e.g., Kidd et al., 1994 5. Depending on the condition tested, the background tones were either temporally coherent or incoherent with the targets, and they were either harmonically related to the targets or not-with the exception of the final burst in each sequence, for which the frequencies of the masker tones were always randomly jittered. Listeners were given a task that required “hearing out” a sequence of target tones embedded in a multi-tone background, and judging the direction of a frequency change at the end of the sequence.
This study sought to provide a test of these two predictions, using psychophysical performance measures. In this context, the notion of temporal coherence extends that of synchrony, and refers specifically to the repeated synchronous activation of auditory “channels” (or neural populations) tuned to different sound parameters, e.g., different frequencies, or different sound features, e.g., pitch and spatial location. “ Temporal coherence and attention in auditory scene analysis,” Trends Neurosci. for a review, see Shamma et al., 2010 15. “ Temporal coherence in the perceptual organization and cortical representation of auditory scenes,” Neuron 61, 317– 329. Elhilali, M., Ma, L., Micheyl, C., Oxenham, A. “ A cocktail party with a cortical twist: How cortical mechanisms contribute to sound segregation,” J. ), recent work has emphasized the role of temporal coherence ( Elhilali and Shamma, 2008 3. “ Behind the scenes of auditory perception,” Curr. for a review, see Shamma and Micheyl, 2010 16. “ Stream segregation and peripheral channeling,” Mus. In particular, while several psychophysical, neurophysiological, and modeling studies of auditory streaming performed during the last thirty years have focused on the importance of spectral-or tonotopic-contrasts for stream segregation (e.g., Hartmann and Johnson, 1991 4. However, the relative importance of these factors is still a matter of debate. Auditory Scene Analysis: The Perceptual Organisation of Sound ( MIT Press, Cambridge, MA). Research on auditory scene analysis has identified various factors that govern the perceptual organization of sounds into “streams” ( Bregman, 1990 1.
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