Hierarchical Processing in Spoken Language Comprehension

Abstract

Understanding spoken language requires a complex series of processing stages to translate speech sounds into meaning. In this study, we use functional magnetic resonance imaging to explore the brain regions that are involved in spoken language comprehension, fractionating this system into sound-based and more abstract higher-level processes. We distorted English sentences in three acoustically different ways, applying each distortion to varying degrees to produce a range of intelligibility (quantified as the number of words that could be reported) and collected whole-brain echo-planar imaging data from 12 listeners using sparse imaging. The blood oxygenation level-dependent signal correlated with intelligibility along the superior and middle temporal gyri in the left hemisphere and in a less-extensive homologous area on the right, the left inferior frontal gyrus (LIFG), and the left hippocampus. Regions surrounding auditory cortex, bilaterally, were sensitive to intelligibility but also showed a differential response to the three forms of distortion, consistent with sound-form-based processes. More distant intelligibility-sensitive regions within the superior and middle temporal gyri, hippocampus, and LIFG were insensitive to the acoustic form of sentences, suggesting more abstract nonacoustic processes. The hierarchical organization suggested by these results is consistent with cognitive models and auditory processing in nonhuman primates. Areas that were particularly active for distorted speech conditions and, thus, might be involved in compensating for distortion, were found exclusively in the left hemisphere and partially overlapped with areas sensitive to intelligibility, perhaps reflecting attentional modulation of auditory and linguistic processes.

Behavioral and fMRI evidence that cognitive ability modulates the effect of semantic context on speech intelligibility

“…Compared to noise alone, speech in noise and speech in quiet together evoked statistically significant activity in the STG bilaterally and in the left MTG (see Figure 5a). This has been observed in other studies as well (e.g., Binder et al, 2004;Davis & Johnsrude, 2003;Obleser et al, 2007;Zekveld et al, 2006). Figure 5a.…”

Interaction between auditory and motor systems in speech perception

“…The Hickok and Poeppel study showed that when the task load is high, requiring both speech identification and speech categorization, the activated frontal region extends to the premotor cortex [17] . Also, when speech signals are distorted, the motor cortex is markedly activated [45,46] . Interestingly, non-verbal signals can activate motor areas [31,47] , and there is no difference in activation magnitude in the motor cortex between perceiving speech and perceiving nonverbal sounds [31] .…”

“…Interestingly, non-verbal signals can activate motor areas [31,47] , and there is no difference in activation magnitude in the motor cortex between perceiving speech and perceiving nonverbal sounds [31] . Some studies have further shown that blurred speech causes even stronger activation in the bilateral premotor cortex, compared to clear speech [45] and perceiving a foreign language causes larger activation in the motor cortex than the native language [25] . Also, lowfrequency words induce higher activation in the motor cortex than high-frequency words [48] .…”

Spectral and temporal degradation of speech as a simulation of morphosyntactic deficits in English and German

“…Converging evidence from several methodologies, such as ERP (Aydelott, Dick, & Mills, 2002), fMRI (Davis & Johnsrude, 2002;Poldrack et al, 2001), and neuropsychology (Aydelott Utman, Blumstein, & Sullivan, 2001;Moineau, Dronkers, Ludy, & Bates, 2002) suggest that the brain regions and processes affected by such degradations overlap to a large extent with those affected in biologically based language breakdown.…”