Abstract
SummaryThe size of a resonant source can be estimated by the acoustic-scale information in the sound [1–3]. Previous studies revealed that posterior superior temporal gyrus (STG) responds to acoustic scale in human speech when it is controlled for spectral-envelope change (unpublished data). Here we investigate whether the STG activity is specific to the processing of acoustic scale in human voice or whether it reflects a generic mechanism for the analysis of acoustic scale in resonant sources. In two functional magnetic resonance imaging (fMRI) experiments, we measured brain activity in response to changes in acoustic scale in different categories of resonant sound (human voice, animal call, and musical instrument). We show that STG is activated bilaterally for spectral-envelope changes in general; it responds to changes in category as well as acoustic scale. Activity in left posterior STG is specific to acoustic scale in human voices and not responsive to acoustic scale in other resonant sources. In contrast, the anterior temporal lobe and intraparietal sulcus are activated by changes in acoustic scale across categories. The results imply that the human voice requires special processing of acoustic scale, whereas the anterior temporal lobe and intraparietal sulcus process auditory size information independent of source category.
Highlights
The perception of acoustic scale does not appear to depend on learned associations based on audio-visual co-occurrence; listeners can extract size information from speech that has been resynthesized to simulate unnatural speaker sizes [3]
This suggests that there is a generic mechanism for the analysis of acoustic scale—a mechanism that supports size perception across a range of natural categories and possibly even in novel categories
Previous studies revealed that the neural activity associated with the acoustic-scale information in speech sounds is located in posterior superior temporal gyrus (STG)
Summary
The effects of a change in size on a human vowel, a French horn note, and a bullfrog call are illustrated, which presents auditory images of the sounds [6, 10], and in Figure S1 (in the Supplemental Data available online), which presents spectrograms. Previous studies revealed that the neural activity associated with the acoustic-scale information in speech sounds is located in posterior superior temporal gyrus (STG) (unpublished data, [11]).
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