Functional asymmetry and effective connectivity of the auditory system during speech perception is modulated by the place of articulation of the consonant- A 7T fMRI study

Abstract

To differentiate between stop-consonants, the auditory system has to detect subtle place of articulation (PoA) and voice-onset time (VOT) differences between stop-consonants. How this differential processing is represented on the cortical level remains unclear. The present functional magnetic resonance (fMRI) study takes advantage of the superior spatial resolution and high sensitivity of ultra-high-field 7 T MRI. Subjects were attentively listening to consonant–vowel (CV) syllables with an alveolar or bilabial stop-consonant and either a short or long VOT. The results showed an overall bilateral activation pattern in the posterior temporal lobe during the processing of the CV syllables. This was however modulated strongest by PoA such that syllables with an alveolar stop-consonant showed stronger left lateralized activation. In addition, analysis of underlying functional and effective connectivity revealed an inhibitory effect of the left planum temporale (PT) onto the right auditory cortex (AC) during the processing of alveolar CV syllables. Furthermore, the connectivity result indicated also a directed information flow from the right to the left AC, and further to the left PT for all syllables. These results indicate that auditory speech perception relies on an interplay between the left and right ACs, with the left PT as modulator. Furthermore, the degree of functional asymmetry is determined by the acoustic properties of the CV syllables.

Vowels and Consonants in the Brain: Evidence from Magnetoencephalographic Studies on the N1m in Normal-Hearing Listeners

“…Specifically, stops are preferentially computed on the left and non-stops on the right auditory cortex (Gage et al, 1998 ), especially when attention is required by listeners (Poeppel et al, 1996 ). This is in line with a recent 7T fMRI study that found stronger left lateralized activation for alveolar stops than labials (Specht et al, 2014 ). Crucially, none of the N1m studies was successful in proving different hemispheric processing for the different VOTs in voiced and voiceless consonants.…”

“…The auditory areas are characterized by a layout that is highly specialized in analyzing different aspects of the signal: the primary auditory cortex (A1) seems engaged in the acoustic processing of the signal, while the superior temporal gyrus (STG) and the superior temporal sulcus (STS) work smoothly for encoding the acoustic patterns onto phonological features (Scott and Johnsrude, 2003 ; Santoro et al, 2014 ; for the speech perception and production link see Hickok and Poeppel, 2007 ; Rauschecker and Scott, 2009 ; Cheung et al, 2016 ). However, the localization and the lateralization of the structures engaged in the phonological encoding remain subjects of debate (McGettigan and Scott, 2012 ; Scott and McGettigan, 2013 ; Specht, 2013 ; Specht et al, 2014 ; Talavage et al, 2014 ; see also Cogan et al, 2014 ). Most importantly for the purpose of this work, the processing that leads speech sounds to be computed and represented within the auditory cortex is yet not fully understood.…”

The noise-resilient brain: Resting-state oscillatory activity predicts words-in-noise recognition

“…This proposal is consistent with a number of lines of evidence. The locus of the LH high-β peak is consistent with the region in which categorical phoneme perception has been demonstrated in fMRI (e.g., Specht, Baumgartner, Stadler, Hugdahl, & Pollmann, 2014; see Turkeltaub & Branch Coslett, 2010 for a review).…”

Lateralization and cognitive systems

“…The relation of structural and functional asymmetries was also the topic of review article that investigated the cortical microstructural basis of lateralized cognition (Chance, 2014 ). Moreover, several authors investigated auditory lateralization (e.g., Specht et al, 2014 ). For example, Hirnstein et al ( 2014a ; Erratum in Hirnstein et al, 2014b ) investigated how language lateralization measured with the Dichotic Listening Task relates to cognitive performance.…”