The weak field specificity and the heterogeneity of neuronal filters found in any given auditory cortex field does not substantiate the view that such fields are merely descriptive maps of sound features. But field mechanisms were previously shown to support behaviourally relevant classification of sounds. Here the prediction was tested in human auditory cortex (AC) that classification-tasks rather than the stimulus class per se determine which auditory cortex area is recruited. By presenting the same set of frequency-modulations we found that categorization of their pitch direction (rising versus falling) increased functional magnetic resonance imaging activation in right posterior AC compared with stimulus exposure and in contrast to left posterior AC dominance during categorization of their duration (short versus long). Thus, top-down influences appear to select not only auditory cortex areas but also the hemisphere for specific processing.
"An auditory task is defined as an operation requiring the production of an intentional connection between sounds, other context-relevant environmental stimuli, and behavioral actions, the latter being responses executed because subjects are motivated by a reinforcer (e.g., Scheich & Brosch, 2012). Task engagement is reflected in different forms of neuronal activity in auditory cortex (Brechmann & Scheich, 2005; Alho et al., 2014), including the neuronal firing (Scheich & Brosch, 2012). Compared to passive exposure to sounds, task engagement can change spectrotemporal and spatial receptive fields (Fritz et al., 2003, 2005; Lee & Middlebrooks, 2011). "
"Currently, it is assumed that the PT samples acoustic signals by extracting spectral and temporal information (Giraud et al. 2007; Griffiths and Warren 2002; Poeppel 2003; Zatorre and Belin 2001). In fact, responses in the left PT are preferentially driven by fast changing acoustic features (Elmer et al. 2012; Jancke et al. 2002; Zaehle et al. 2004, 2008; Belin et al. 1998; Merzenich et al. 1996), whereas the right-sided counterpart is more likely responsive to slow acoustic modulations (Griffiths and Warren 2002; Kühnis et al. 2013; Meyer 2008; Meyer et al. 2012; Brechmann and Scheich 2005). A similar division of labour has previously also been shown to be true for the Heschl's gyrus (HG) (Warrier et al. 2009). "
[Show abstract][Hide abstract] ABSTRACT: Currently, there is strong evidence showing that musicianship favours functional and structural changes of the left planum temporale (PT), and that these cortical reorganizations facilitate the discrimination of temporal speech cues. Based on the proposition of a division of labour between the left and right PT, here we postulated that the musicians’ advantage in processing temporal speech cues and PT specialization origin, at least in part, from increased white matter connectivity between the two auditory-related cortices. In particular, we assume that increased transcallosal PT connectivity might promote functional specialization and asymmetry of homotopic brain regions. With this purpose in mind, we applied diffusion tensor imaging and compared axial diffusivity (AD), radial diffusivity (RD), and fractional anisotropy (FA) of the interhemispheric connection between the left and right PT in thirteen musicians and 13 nonmusicians. Furthermore, in the form of an addendum, we integrated cortical surface area values and blood oxygenation level dependent (BOLD) responses of the left PT that were collected in the context of two previous studies conducted with the same sample of subjects. Our results indicate increased connectivity between the left and right PT in musicians compared to nonmusicians, as indexed by reduced mean RD. We did not find significant between-group differences in FA and AD. Most notably, RD was related to the performance in the phonetic categorization task, musical aptitudes, as well as toBOLD responses in the left PT. Hence, we provide first evidence for a relationship between PT connectivity, musicianship, and phonetic categorization.
Brain Structure and Function 10/2014; DOI:10.1007/s00429-014-0910-x · 5.62 Impact Factor
"Corresponding to this, one might suggest that the stronger BOLD response in auditory cortex for the higher fmod A of 300 Hz also reflects the task difficulty. This notion finds support in human imaging studies providing evidences that even in sensory areas the activation can be modulated by task difficulty (Gerlach et al., 1999; Brechmann and Scheich, 2005; Reiterer et al., 2005; Harinen and Rinne, 2013). "
[Show abstract][Hide abstract] ABSTRACT: Auditory stream segregation refers to a segregated percept of signal streams with different acoustic features. Different approaches have been pursued in studies of stream segregation. In psychoacoustics, stream segregation has mostly been investigated with a subjective task asking the subjects to report their percept. Few studies have applied an objective task in which stream segregation is evaluated indirectly by determining thresholds for a percept that depends on whether auditory streams are segregated or not. Furthermore, both perceptual measures and physiological measures of brain activity have been employed but only little is known about their relation. How the results from different tasks and measures are related is evaluated in the present study using examples relying on the ABA- stimulation paradigm that apply the same stimuli. We presented A and B signals that were sinusoidally amplitude modulated (SAM) tones providing purely temporal, spectral or both types of cues to evaluate perceptual stream segregation and its physiological correlate. Which types of cues are most prominent was determined by the choice of carrier and modulation frequencies (f mod) of the signals. In the subjective task subjects reported their percept and in the objective task we measured their sensitivity for detecting time-shifts of B signals in an ABA- sequence. As a further measure of processes underlying stream segregation we employed functional magnetic resonance imaging (fMRI). SAM tone parameters were chosen to evoke an integrated (1-stream), a segregated (2-stream), or an ambiguous percept by adjusting the f mod difference between A and B tones (Δf mod). The results of both psychoacoustical tasks are significantly correlated. BOLD responses in fMRI depend on Δf mod between A and B SAM tones. The effect of Δf mod, however, differs between auditory cortex and frontal regions suggesting differences in representation related to the degree of perceptual ambiguity of the sequences.
Frontiers in Neuroscience 06/2014; 8(8):119. DOI:10.3389/fnins.2014.00119 · 3.66 Impact Factor
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