Abstract
The relationship between stimulus-dependent and task-dependent activations in human auditory cortex (AC) during pitch and location processing is not well understood. In the present functional magnetic resonance imaging study, we investigated the processing of task-irrelevant and task-relevant pitch and location during discrimination, n-back, and visual tasks. We tested three hypotheses: (1) According to prevailing auditory models, stimulus-dependent processing of pitch and location should be associated with enhanced activations in distinct areas of the anterior and posterior superior temporal gyrus (STG), respectively. (2) Based on our previous studies, task-dependent activation patterns during discrimination and n-back tasks should be similar when these tasks are performed on sounds varying in pitch or location. (3) Previous studies in humans and animals suggest that pitch and location tasks should enhance activations especially in those areas that also show activation enhancements associated with stimulus-dependent pitch and location processing, respectively. Consistent with our hypotheses, we found stimulus-dependent sensitivity to pitch and location in anterolateral STG and anterior planum temporale (PT), respectively, in line with the view that these features are processed in separate parallel pathways. Further, task-dependent activations during discrimination and n-back tasks were associated with enhanced activations in anterior/posterior STG and posterior STG/inferior parietal lobule (IPL) irrespective of stimulus features. However, direct comparisons between pitch and location tasks performed on identical sounds revealed no significant activation differences. These results suggest that activations during pitch and location tasks are not strongly affected by enhanced stimulus-dependent activations to pitch or location. We also found that activations in PT were strongly modulated by task requirements and that areas in the inferior parietal lobule (IPL) showed task-dependent activation modulations, but no systematic activations to pitch or location. Based on these results, we argue that activations during pitch and location tasks cannot be explained by enhanced stimulus-specific processing alone, but rather that activations in human AC depend in a complex manner on the requirements of the task at hand.
Highlights
Prevailing auditory models suggest that human auditory cortex (AC) consists of anatomically and functionally separate fields that are organized into two or more segregated hierarchical processing streams (Rauschecker and Scott, 2009; McLachlan and Wilson, 2010; Recanzone and Cohen, 2010; Hackett, 2011; Hickok and Saberi, 2012)
Some previous studies have reported activations associated with spatial tasks in areas of the anterior superior temporal gyrus (STG; i.e., within the putative ‘what’ pathway) and activations associated with pitch tasks in posterior STG and in the inferior parietal lobule (IPL; i.e., within the putative ‘where’ pathway; Griffiths and Warren, 2002; Arnott et al, 2004; Hall and Plack, 2009; Rinne et al, 2009, 2012; Hill and Miller, 2010; Schadwinkel and Gutschalk, 2010)
Our previous studies have shown that activations in AC depend on the task so that activations in areas of anterior STG are enhanced during discrimination but not during n-back memory task, whereas activations in posterior STG and IPL are enhanced during n-back but not during discrimination
Summary
Prevailing auditory models suggest that human auditory cortex (AC) consists of anatomically and functionally separate fields that are organized into two or more segregated hierarchical processing streams (Rauschecker and Scott, 2009; McLachlan and Wilson, 2010; Recanzone and Cohen, 2010; Hackett, 2011; Hickok and Saberi, 2012) In these models, a posterior (dorsal) stream via posterior temporal lobe to inferior parietal cortex is involved in the processing of spatial aspects of sounds or information needed in auditory–motor integration (‘where’ or ‘how’ pathway), and an anterior (ventral) pathway through anterior temporal areas to inferior frontal cortex, in turn, is involved in the analysis of auditory objects and meaning of speech (‘what’ pathway). In the present functional magnetic resonance imaging (fMRI) study, we compared activations in conditions in which the pitch and location of the sounds as well as the task were systematically varied
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