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 Human research

 Neural correlates of auditory stream segregation in human auditory cortex Voice processing

Selective listening to an instrument in an orchestra or a human voice in a cocktail party relies on the separation of acoustic components of that instrument/voice from overlapping acoustic objects. We found that an auditory area on the planum polare (anterior to Heschl’s gyrus) is specifically activated in tasks in which a prominent or loud background sound complicates the detection of target sounds in the foreground (Scheich et al. 1998, Brechmann et al. 2002). Besides such a foreground-background decomposition, creating a Gestalt of melodies or syllable strings also requires the sequential grouping of sound events that are similar to one another in preference to events that follow one another (sequential stream segregation). This can be studied by using the classical ABAB design of alternating tones (Fig.1.). The representation of sequential stream segregation in human auditory cortex was studied with two approaches (SFB Transregio 31 „Das aktive Gehör“).


1. Active sequential stream segregation

Susann Deike, André Brechmann, Henning Scheich

We showed that the left auditory cortex is selectively involved in sequential stream segregation of sounds independent of the acoustic cue, i.e. pitch or timbre differences (Fig.2.). This finding is consistent with views on left hemispheric specialization for sequential aspects of information processing especially important for speech perception. Nevertheless the activation of particular territories depends on the cue used for sequential stream segregation. An enhancement of activation in left secondary territories T2 and T3 was shown in both, sequential stream segregation relying on pitch and on timbre. Sequential stream segregation relying on pitch additionally involves the left territory TA anterior to Heschl’s gyrus on planum polare and the left territory T1 on Heschl’s gyrus covering the primary auditory cortex.


Fig. 1. A sequence of high and low pitch tones (ABAB) presented at slow presentation rate can be perceived as one integrated stream alternating in pitch or as two separated streams, one consisting of high and the other of low pitch tones. Please listen to the example and attempt to integrate the high and low pitch tones into one stream or to segregate the high and low pitch tones into separate streams and follow the high or the low pitch stream. (download example)

Fig. 2. Activation pattern of a single subject showing enhanced activation in left auditory cortex during sequential stream segregation on timbre (B) compared to the perception of one inseparable stream (A). In contrast activation in the right auditory cortex is nearly unchanged.


References:

  • Deike, S., Gaschler-Markefski, B., Brechmann, A., Scheich, H., 2004. Auditory stream segregation relying on timbre involves left auditory cortex. NeuroReport 15, 1511-1514.
  • Deike, S., et al., 2010. Active stream segregation specifically involves the left human auditory cortex. Hear Res. 265, 30-7.

 

2. Cross-modal influence of visual stimulation on the perception of a perceptually ambiguous ton sequence

Torsten Rahne, Susann Deike, Elena Selezneva, Michael Brosch, Reinhard König, Henning Scheich, Martin Böckmann, André Brechmann

We report first results of a multilevel, cross-modal study on the neuronal mechanisms underlying auditory sequential stream segregation, with the focus on the impact of visual sequences on perceptually ambiguous tone sequences which can either be perceived as two separate streams or one alternating stream. We combined two psychophysical experiments performed on humans and monkeys with two human brain imaging experiments which allow to obtain complementary information on brain activation with high spatial (fMRI) and high temporal (MEG) resolution. Our multilevel approach provides experimental evidence that the pairing of auditory and visual stimuli can reliably introduce a bias towards either an integrated or a segregated perception of ambiguous sequences. Thus, comparable to an explicit instruction, this approach can be used to control the subject’s perceptual organization of an ambiguous sound sequence without the need for the subject to directly report it.

 

References:

  • Rahne, T., Böckmann, M., von Specht, H., Sussman, E., 2007. Visual cues can modulate integration and segregation of objects in auditory scene analysis. Brain Res 1144:127-135.
  • Rahne, T., Deike, S., Selezneva, E., Brosch, M., Konig, R., Scheich, H., Bockmann, M., Brechmann, A., 2007b. A multilevel and cross-modal approach towards neuronal mechanisms of auditory streaming. Brain Res 1220:118-131.

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