Task‐free auditory EEG paradigm for probing multiple levels of speech processing in the brain

Abstract

While previous studies on language processing highlighted several ERP components in relation to specific stages of sound and speech processing, no study has yet combined them to obtain a comprehensive picture of language abilities in a single session. Here, we propose a novel task-free paradigm aimed at assessing multiple levels of speech processing by combining various speech and nonspeech sounds in an adaptation of a multifeature passive oddball design. We recorded EEG in healthy adult participants, who were presented with these sounds in the absence of sound-directed attention while being engaged in a primary visual task. This produced a range of responses indexing various levels of sound processing and language comprehension: (a) P1-N1 complex, indexing obligatory auditory processing; (b) P3-like dynamics associated with involuntary attention allocation for unusual sounds; (c) enhanced responses for native speech (as opposed to nonnative phonemes) from ∼50 ms from phoneme onset, indicating phonological processing; (d) amplitude advantage for familiar real words as opposed to meaningless pseudowords, indexing automatic lexical access; (e) topographic distribution differences in the cortical activation of action verbs versus concrete nouns, likely linked with the processing of lexical semantics. These multiple indices of speech-sound processing were acquired in a single attention-free setup that does not require any task or subject cooperation; subject to future research, the present protocol may potentially be developed into a useful tool for assessing the status of auditory and linguistic functions in uncooperative or unresponsive participants, including a range of clinical or developmental populations.

Applied potential of task-free event-related paradigms for assessing neurocognitive functions in disorders of consciousness

“…This effect is generally referred to as an automatic lexical enhancement and has been found in both repetitive oddball designs and non-oddball paradigms. Such attention-independent responses that do not depend on overt tasks may therefore be of use in situations when the subject’s cooperation cannot be obtained ( Gansonre et al , 2018 ; Hyder et al , 2020 ), and thus may be of use for assessing patients with DoC or CMD. While ELAN/syntactic MMN and lexical enhancement certainly hold a promise as potential assessment tools, they have so far not been tested in DoC, which, we suggest, should be tackled in future studies.…”

“…It, therefore, seems reasonable to suggest that future research should develop combined designs with multiple, yet controlled, acoustic, phonological, and psycholinguistic manipulations to elicit these components in a single task-free paradigm (see, e.g. Shtyrov et al , 2012 ; Gansonre et al , 2018 ) to provide a more comprehensive multidimensional test for different cognitive and linguistic processes.…”

Objective assessment of automatic language comprehension mechanisms in the brain: Novel E/MEG paradigm

“…We aligned this time frame to the point in time when all acoustic information necessary for full word identification (in lexical and semantic contrasts) and grammatical processing (in morphosyntactic contrasts) was available, that is, 400 ms after the stimulus onset. Other responses associated with basic auditory processing (such as obligatory P50 and N100 auditory responses to sound onsets) were of no particular interest here (for an investigation of these, see e.g., Gansonre et al, ).…”

“…For this purpose, we designed and tested two different auditory sequences using the same set of linguistic stimuli ( N = 16): one using a more conventional multifeature oddball approach, and one optimized even further for time by changing from an oddball approach to equiprobable presentation of all stimuli. We selected a set of spoken Danish‐language stimuli (see Figure a for an example of the stimuli used) following a previously suggested strategy (Gansonre, Højlund, Leminen, Bailey, & Shtyrov, ). The selected stimulus set consisted of spoken CV‐syllables ( N = 4; bi, mi, gi, ni ) and disyllabic stimuli ( N = 12) which differed from the CV‐syllables by their second syllables and were either meaningful words with different semantic and syntactic features (including syntactic violations) or meaningless pseudowords.…”

Left anterior temporal lobe is necessary for efficient lateralised processing of spoken word identity

“…Here we employed a spoken-word version of the auditory mismatch 6 paradigm (for a review see Näätänen et al, 2007), in which repeated 'standard' words (for example PLAY) were changed in either tense or semantic meaning by the spliced addition of the additional ending syllables d/t (to become, in this case, PLAYED or PLATE). This paradigm is a sensitive tool for measuring automatic lexico-semantic processing of spoken words in the brain (Pulvermüller et al, 2006, Shtyrov et al, 2010 and has a special benefit for patient studies as it does not require any active stimulus processing, or even attention on the auditory stream (Gansonre et al, 2018). Here, presentation was designed such that the occurrence and timing of a deviant word were predictable, but the identity and meaning of the word were unpredictable until the last tens of milliseconds of its utterance.…”