Theta oscillations mediate pre-activation of highly expected word initial phonemes

Abstract

Prediction has been proposed to be a fundamental neurocognitive mechanism. However, its role in language comprehension is currently under debate. In this magnetoencephalography study we aimed to find evidence of word-form phonological pre-activation and to characterize the oscillatory mechanisms supporting this. Participants were presented firstly with a picture of an object, and then, after a delay (fixed or variable), they heard the corresponding word. Target words could contain a phoneme substitution, and participants’ task was to detect mispronunciations. Word-initial phonemes were either fricatives or plosives, generating two experimental conditions (expect-fricative and expect-plosive). In the pre-word interval, significant differences (α = 0.05) emerged between conditions both for fixed and variable delays. Source reconstruction of this effect showed a brain-wide network involving several frequency bands, including bilateral superior temporal areas commonly associated with phonological processing, in a theta range. These results show that phonological representations supported by the theta band may be active before word onset, even under temporal uncertainty. However, in the evoked response just prior to the word, differences between conditions were apparent under variable- but not fixed-delays. This suggests that additional top-down mechanisms sensitive to phonological form may be recruited when there is uncertainty in the signal.

Oscillatory dynamics underlying noun and verb production in highly proficient bilinguals

“…Nevertheless, we find this unlikely for several reasons. First, previous studies have used a similar methodological approach leading in all cases to adequate estimates of brain non-contaminated activity 30 , 32 , 67 , 68 . Second, the beamformer technique used here to reconstruct underlying brain sources is known to attenuate myogenic artifacts by suppressing signals whose spatial scalp distribution cannot be explained by a dipolar source in the brain (please see 30 for a further discussion of this aspect).…”

After-effects of 10 Hz tACS over the prefrontal cortex on phonological word decisions

“…The observed increase in the post-stimulus theta power might indicate increased working memory efficiency that facilitated phonological decisions. Indeed, increased theta power was previously associated with successful performance in visual working memory tasks [83] and during phonological processing [84,85]. Initially, we expected a strong tACS-induced modulation in the alpha band.…”

Evidence and implications of abnormal predictive coding in dementia

“…Healthy language comprehension shows remarkable speed and resistance to noise, which is supported by predictive coding mechanisms at multiple levels of linguistic representation: phonological (Gagnepain et al, 2012;Ettinger et al, 2014;Monsalve et al, 2018), semantic (DeLong et al, 2005;Lau et al, 2013;Lau and Nguyen, 2015;Maess et al, 2016;Wang et al, 2018;Klimovich-Gray et al, 2019), syntactic (Fonteneau, 2013;Wlotko and Federmeier, 2015;Henderson et al, 2016) and discourse context (Otten and Van Berkum, 2008). In neurodegenerative aphasias, many of the deficits of frontotemporal and temporo-parietal networks can be understood in terms of impairments of predictive coding.…”