Dynamic and Task-Dependent Encoding of Speech and Voice by Phase Reorganization of Cortical Oscillations

Abstract

Speech and vocal sounds are at the core of human communication. Cortical processing of these sounds critically depends on behavioral demands. However, the neurocomputational mechanisms enabling this adaptive processing remain elusive. Here we examine the taskdependent reorganization of electroencephalographic responses to natural speech sounds (vowels /a/, /i/, /u/) spoken by three speakers (two female, one male) while listeners perform a one-back task on either vowel or speaker identity. We show that dynamic changes of sound-evoked responses and phase patterns of cortical oscillations in the alpha band (8 -12 Hz) closely reflect the abstraction and analysis of the sounds along the task-relevant dimension. Vowel categorization leads to a significant temporal realignment of responses to the same vowel, e.g., /a/, independent of who pronounced this vowel, whereas speaker categorization leads to a significant temporal realignment of responses to the same speaker, e.g., speaker 1, independent of which vowel she/he pronounced. This transient and goal-dependent realignment of neuronal responses to physically different external events provides a robust cortical coding mechanism for forming and processing abstract representations of auditory (speech) input.

Auditory Evoked Responses in Musicians during Passive Vowel Listening Are Modulated by Functional Connectivity between Bilateral Auditory-related Brain Regions

“…This previous work extends the findings on the functional contribution of alpha oscillations to inhibitory control (Klimesch, Sauseng, & Hanslmayr, 2007) and shows that the precise timing of alpha oscillations promotes sensory speech processing as well. On the basis of the work of Bonte et al (2009), the increased connectivity in the alpha band we revealed in musicians is interpreted as reflecting a training-related tuning of bilateral auditory-related brain regions during speech processing.…”

“…Finally, previous work has elucidated that alpha oscillations have the faculty to temporal realign their phase while processing vowels in a task-dependent manner (Bonte, Valente, & Formisano, 2009). This previous work extends the findings on the functional contribution of alpha oscillations to inhibitory control (Klimesch, Sauseng, & Hanslmayr, 2007) and shows that the precise timing of alpha oscillations promotes sensory speech processing as well.…”

Role of Neuronal Synchrony in the Generation of Evoked EEG/MEG Responses

“…In the case of a phase-reset mechanism, changes in evoked responses might indicate adaptive fine-tuning of neuronal oscillations for current processing demands (Bonte et al 2009;Hanslmayr et al 2006). On the other hand, ER changes consistent with added-energy mechanism would reflect either the number of neurons being recruited for the current processing demands or their mean activity (Jones et al 2007).…”

Multiple brain signatures of integration in the comprehension of degraded speech

“…In an early time range (approximately 100 ms after sound onset), effects of the degree of speech degradation are expected on the N100 component which has been shown to index early abstraction and percept-formation stages (Krumbholz et al, 2003;Naatanen, 2001;Obleser et al, 2006), especially in the context of an active comprehension task (for task effects on the N100/N100m see Bonte et al, 2009;Obleser et al, 2004a;Poeppel et al, 1996). Also based on a recent study finding enhanced N100 amplitudes in response to degraded sound (Miettinen et al, 2010), we expect the following: the more thorough the degradation of the signal, the more neural effort is likely be allocated to encoding the acoustic signal and mapping it onto known phonological and lexical categories, leading to an enhanced N100 amplitude measured on the scalp.…”