Summary: Researchers report the brain is not only able to anticipate the conclusion of sentences, it can also anticipate an auditory stimulus and determine the phonemes or specific words a speaker is going to pronounce.
Prediction is one of the main neuro-cognitive mechanisms of our brain. Every millisecond, the most complex organ of the human being constantly tries to actively anticipate what will happen next depending on the knowledge it has of its environment.
In recent years, many research studies have been launched to understand the phenomenon of prediction in depth, but little was known until now about the role played by this phenomenon in the understanding of language.
Now, a study carried out by the Basque Center on Cognition, Brain and Language (BCBL), goes a step further in its knowledge. The results have recently been published in the journal Scientific Reports.
So far, multiple experiments have shown that the brain is able to anticipate the information it will hear and know exactly what the speaker is going to talk about.
However, this work describes for the first time that the complex machinery of the brain is able to estimate even what specific words it will hear before they are spoken.
The main target was to check how the auditory system acts in the phenomenon of prediction. Thus, the brain can estimate when a word is going to start, which phonemes will be the first ones to be heard and pre-activate the auditory system to actively anticipate the stimulus that will impact the ear.
The researchers from the centre in San Sebastian used magnetoencephalography (MEG) studies – a non-invasive method for recording brain activity – to detail what mechanisms the brain uses and what neural networks it activates in order to predict what it is going to hear.
“The perspective on how our brain works is changing; we are beginning to give much more weight to the predictive component. The brain is always trying to estimate what the future will be like, when the future has not yet arrived,” explains Nicola Molinaro, researcher at the BCBL.
Predicting the word before it appears
The experts were helped by the participation of 47 volunteers who had to see different images on a screen and then listen to the word associated with that photograph.
Before the appearance of the auditory stimulus, the researchers identified brain activity in the primary auditory cortex, the region of the brain responsible for the processing of auditory information.
“This is more than clear evidence that the auditory regions do not passively respond to the stimulus that impacts on our ear, but actually predict something in advance,” Molinaro adds.
The experts could see how a second after seeing the image, the auditory regions began to work and to show brain activity in a different way depending on the physical properties of the words they were going to hear next.
According to the authors, the brain knows exactly what the physical form of the word it is going to hear will be like, even before it is pronounced. In the case of the occlusive phonemes, the brain oscillations began to work with much more energy approximately one second before listening to the auditory stimulus.
“We have found clear evidence that the neuronal system can predict the form of a word before it appears,” says the expert.
The brain´s great secret
Knowing better how the brain works in this sense could help, in the future, to develop more effective treatments for certain disorders that are related to brain prediction.
“Many disorders have to do with failures of the predictive system, such as autism, in which children have problems predicting the future and, therefore, fail to extract regularities about how the environment is working,” claims Molinaro.
“In the case of linguistic disorders such as dyslexia, if the brain could synchronize better with the sound waves it hears, the phonological problem they suffer from could be alleviated,” he concludes.
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Original Research: Open access research for “Avoiding sedentary behaviors requires more cortical resources than avoiding physical activity: An EEG study” by Irene F. Monsalve, Mathieu Bourguignon & Nicola Molinaro in Scientific Reports. Published June 22 2018.
Theta oscillations mediate pre-activation of highly expected word initial phonemes
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.