Pitch processing of dynamic lexical tones in the auditory cortex is influenced by sensory and extrasensory processes

Abstract

The aim is to evaluate how language experience (Chinese, English) shapes processing of pitch contours as reflected in the amplitude of cortical pitch response components. Responses were elicited from three dynamic, curvilinear, nonspeech stimuli varying in pitch direction and location of peak acceleration: Mandarin lexical Tone2 (rising) and Tone4 (falling); and a flipped variant of Tone2, Tone2′ (nonnative). At temporal sites (T7/T8), Chinese Na-Pb response amplitude to Tones 2 & 4 was greater than English in the right hemisphere only; a rightward asymmetry for Tones 2 & 4 was restricted to the Chinese group. In common to both Fz-to-linked T7/T8 and T7/T8 electrode sites, the stimulus pattern (Tones 2 & 4 > Tone2′) was found in the Chinese group only. As reflected by Pb-Nb at Fz, Chinese amplitude was larger than English in response to Tones 2 & 4; and Tones 2 & 4 were larger than Tone2′; whereas for English, Tone2 was larger than Tone2′ and Tone4. At frontal electrode sites (F3/F4), regardless of component or hemisphere, Chinese responses were larger in amplitude than English across stimuli. For either group, responses to Tones 2 & 4 were larger than Tone2′. No hemispheric asymmetry was observed at the frontal electrode sites. These findings highlight that cortical pitch response components are differentially modulated by experience-dependent, temporally distinct but functionally overlapping weighting of sensory and extrasensory effects on pitch processing of lexical tones in the right temporal lobe and, more broadly, are consistent with a distributed hierarchical predictive coding process.

Experience-dependent enhancement of pitch-specific responses in the auditory cortex is limited to acceleration rates in normal voice range

“…Over the temporal sites, Chinese exhibit a rightward asymmetry; they also have larger amplitude than English. Our failure to observe language-dependent, asymmetry at the F3/F4 electrode sites is consistent with our previous findings (Krishnan et al, 2015a, Krishnan et al, 2015b). This suggests that the temporal electrodes proximal to and located over the auditory cortices, the putative regions for pitch processing, are better situated to capture the experience-dependent, preferential recruitment of the right auditory cortex for pitch processing.…”

“…Given the poor spatial resolution of EEG even using multiple electrodes, the focus here is not to localize the source of the CPRs with just two electrodes, but to characterize the relative difference in the pitch-related neural activity over the widely separated right and left temporal electrode sites. We are quite confident that robust differences in CPR-related neural activity over the T7 and T8 electrode sites do represent a functional, experience-dependent rightward asymmetry that we have consistently observed across our crosslanguage CPR studies (Krishnan et al, 2014b, Krishnan et al, 2015a, Krishnan et al, 2015b). The re-referenced electrode site, Fz-linked(T7/T8), was used to characterize the transient pitch response components.…”

“…This finding agrees with previous observations of amplitude reduction for these components at higher pitch acceleration rates regardless of language group (Krishnan et al, 2014a, 2015a). We infer that reduced sensitivity to pitch acceleration rates that exceed the normal speech range is a language-universal property of early sensory level processing of dynamic pitch in the auditory cortex, similar to these components’ differential sensitivity to location of the acceleration peak (early vs. late) (Krishnan et al, 2015b). …”

“…For example, Na’s sensitivity is indicated by its longer latency for stimuli (i) with weaker, relative to stronger, pitch salience (Gutschalk et al, 2002, Krumbholz et al, 2003, Gutschalk et al, 2004, Krishnan et al, 2012a); (ii) with a rapidly rising portion of the pitch contour that occurs early, relative to late, after stimulus onset (Krishnan et al, 2015b); (iii) with a falling compared to rising pitch contour (Krishnan et al, 2015b); and (iv) with linear ramps or steady-state pitch compared to curvilinear T2 (Krishnan et al, 2014b). In this study, a similar pattern of Na latency change is observed with increasing pitch acceleration in both groups.…”

“…The re-referenced electrode site, Fz-linked(T7/T8), was used to characterize the transient pitch response components. The Fz electrode site was chosen because both the MEG and EEG derived pitch responses are prominent at the fronto-central sites (Krumbholz et al, 2003, Bidelman and Grall, 2014, Krishnan et al, 2014b, Krishnan et al, 2015a, Krishnan et al, 2015b). It also allows us to compare our CPR data with the Fz-derived POR data (Gutschalk et al, 2002, Krumbholz et al, 2003, Gutschalk et al, 2004).…”