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.
Highlights
Context and prior knowledge strongly influence perception
Answering this question has been hindered by the fact that most studies of prediction in language have focused on post-target word interval, rendering both interpretations plausible
In a picture-word matching paradigm, Dikker and Pylkkanen[13] found increased magnetoencephalography (MEG) activity in the theta band (4–7 Hz) before word onset in the left mid-temporal and, successively, in visual cortex, when the previous picture represented a single object as compared to a picture of a group of objects
Summary
Context and prior knowledge strongly influence perception. Language processing is no exception to this, with decades of neuro- and psycho-linguistic research showing contextual facilitation of comprehension, both in behavioural and neural measures. One of the contended aspects is whether semantic-level contextual constraints may facilitate phonological (or orthographic) processing of predicted words through word-form pre-activation (before bottom-up information is available), or through faster selection of possible candidates once bottom-up input has arrived Answering this question has been hindered by the fact that most studies of prediction in language have focused on post-target word interval, rendering both interpretations plausible. In a picture-word matching paradigm, Dikker and Pylkkanen[13] found increased magnetoencephalography (MEG) activity in the theta band (4–7 Hz) before word onset in the left mid-temporal and, successively, in visual cortex, when the previous picture represented a single object as compared to a picture of a group of objects This finding was interpreted as evidence of lexical retrieval (given the role of the mid-temporal gyrus in lexical access14,15) and visual feature pre-activation, when the identity of the upcoming word could be predicted. Top-down influences on sensory areas have been well documented in the auditory domain[18,19], these have always focused on response to the actual word and have examined processing differences once initial sensory input is available
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