In speech perception, a functional hierarchy has been proposed by recent functional neuroimaging studies: Core auditory\r\nareas on the dorsal plane of superior temporal gyrus (STG) are sensitive to basic acoustic characteristics, whereas\r\ndownstream regions, specifically the left superior temporal sulcus (STS) and middle temporal gyrus (MTG) ventral to Heschl�s\r\ngyrus (HG) are responsive to abstract phonological features. What is unclear so far is the relationship between the dorsal\r\nand ventral processes, especially with regard to whether low-level acoustic processing is modulated by high-level\r\nphonological processing. To address the issue, we assessed sensitivity of core auditory and downstream regions to acoustic\r\nand phonological variations by using within- and across-category lexical tonal continua with equal physical intervals. We\r\nfound that relative to within-category variation, across-category variation elicited stronger activation in the left middle MTG\r\n(mMTG), apparently reflecting the abstract phonological representations. At the same time, activation in the core auditory\r\nregion decreased, resulting from the top-down influences of phonological processing. These results support a hierarchical\r\norganization of the ventral acoustic-phonological processing stream, which originates in the right HG/STG and projects to\r\nthe left mMTG. Furthermore, our study provides direct evidence that low-level acoustic analysis is modulated by high-level\r\nphonological representations, revealing the cortical dynamics of acoustic and phonological processing in speech\r\nperception. Our findings confirm the existence of reciprocal progression projections in the auditory pathways and the roles\r\nof both feed-forward and feedback mechanisms in speech perception.
Loading....