Auditory stream segregation relying on timbre involves left auditory cortex

Abstract

An important aspect of auditory scene analysis is sequential grouping of sounds that are similar to one another in preference to sounds that follow one another. This grouping problem is captured by stream segregation tasks with alternating distinct sounds. We examined human auditory cortex activity with low noise fMRI in a stream segregation experiment relying on timbre differences of alternating harmonic tones (organ-like and trumpet-like). We found that stream segregation performance in comparison to monitoring a non-separable control stream increased activation exclusively in left auditory cortex and particularly in posterior areas. Our results suggest that left auditory cortex is selectively involved in this complex sequential task although the available cue for sequential grouping was timbre, usually attributed to right hemisphere analysis.

Human Cortical Activity during Streaming without Spectral Cues Suggests a General Neural Substrate for Auditory Stream Segregation

“…Instead, the changes are likely attributable to the ⌬f 0 -related differences in the temporal properties of the A and B tones. This dependence on temporal rather than spectral differences between A and B represents a crucial difference compared with previous imaging studies of streaming, all of which have used repeating sequences of pure tones (Gutschalk et al, 2005;Snyder et al, 2006;Wilson et al, 2007) or complex tones with gross spectral differences (Deike et al, 2004).…”

“…The neural underpinnings of auditory stream segregation have been investigated with intracortical recordings in animals (Fishman et al, 2001(Fishman et al, , 2004Kanwal et al, 2003;Klump, 2004, 2005;Micheyl et al, 2005), and noninvasively in humans, using electroencephalography (EEG) (Sussman et al, 1999, Sussman, 2005Snyder et al, 2006), magnetoencephalography (MEG) (Gutschalk et al, 2005), and functional magnetic resonance imaging (fMRI) (Deike et al, 2004;Cusack, 2005;Wilson et al, 2007). All of these studies have used pairs of sounds that differed in frequency content, and were presented alternately, or in other repeating temporal patterns.…”

Global versus local processing of frequency-modulated tones in gerbils: An animal model of lateralized auditory cortex functions

“…Moreover, a matching-to-sample task with the same FM stimuli in serial comparisons generated dominant left AC activations (45). Similarly, in a ''streaming'' task, where the selective segmental comparison of stimuli is crucial, BOLD activation was lateralized to the left AC (46). This led to the hypothesis that, at least for stimuli with no primary semantic valence, their dominant representation in either right or left AC will depend on the type of task that is executed with them.…”

“…In our animal model (42), we lesioned ACs of gerbils bilaterally or unilaterally and trained them before and after lesions on various discriminations of linearly FM tone sweeps that were either continuous or segmented. Based on our previous lateralization studies in gerbils (42) and humans (44)(45)(46) and considering the related data of other authors (6, 13, 49), we used artificial stimuli that varied along spectral and temporal dimensions (see Table 1). In gerbils, a hypertrophied middle-ear cavity results in increased low-frequency hearing, a feature that seems to be important in a desert environment where it is necessary to escape from predators, e.g., owls and snakes that produce frequencies in the range of 1-2 kHz.…”

The role of auditory cortex in the formation of auditory streams

“…In all of the above-described MEG and fMRI studies, the stimuli were sequences of pure tones and stream segregation was induced by frequency differences, which produced salient tonotopic cues. A recent fMRI study by Deike et al (2004) used ABAB sequences in which the A and B sounds were harmonic complex tones that spanned the same frequency range but differed in spectral envelope -and thus timbre. The results of that study are consistent with those of Wilson et al (2005) in showing stronger activation in auditory cortex in response to such alternating sequences, which were perceived as two streams, compared to sequences consisting of identical sounds (AAAA or BBBB), which were perceived as a single stream.…”