Research Article: Early positivity signals changes in an abstract linguistic pattern

Date Published: July 5, 2017

Publisher: Public Library of Science

Author(s): Júlia Monte-Ordoño, Juan M. Toro, Etsuro Ito.

http://doi.org/10.1371/journal.pone.0180727

Abstract

The extraction of abstract structures from speech (or from gestures in the case of sign languages) has been claimed to be a fundamental mechanism for language acquisition. In the present study we registered the neural responses that are triggered when a violation of an abstract, token-independent rule is detected. We registered ERPs while presenting participants with trisyllabic CVCVCV nonsense words in an oddball paradigm. Standard stimuli followed an ABB rule (where A and B are different syllables). Importantly, to distinguish neural responses triggered by changes in surface information from responses triggered by changes in the underlying abstract structure, we used two types of deviant stimuli. Phoneme deviants differed from standards only in their phonemes. Rule deviants differed from standards in both their phonemes and their composing rule. We observed a significant positivity as early as 300 ms after the presentation of deviant stimuli that violated the abstract rule (Rule deviants). The amplitude of this neural response was correlated with participants’ performance in a behavioral rule learning test. Differences in electrophysiological responses observed between learners and non-learners suggest that individual differences in an abstract rule learning task might be related to how listeners select relevant sources of information.

Partial Text

Language proficiency involves the ability to understand and create novel sentences not encountered or produced before. Putatively, such ability depends on the acquisition of abstract rules according to which a language is organized [1]. For example, at the sentence level, affirmative sentences in English are produced following the SVO (Subject-Verb-Object) word order. Once this order has been established, its variables can take any acceptable value and produce a valid English sentence. Similarly, at the word level, affixation rules allow for the creation of words by adding morphemes to word stems (e.g. adding the affix “-ed” to a regular verb will create a past tense of it). Because combinations of stems and affixes (just as combinations of subjects, verbs and objects) can use any acceptable values to create valid words and sentences; they are considered as examples of a token-independent pattern. Processing of such abstract patterns in speech seems to recruit dedicated neural circuits (e.g. [2]). However, even though much interest has been raised by the mechanisms responsible of learning abstract structures, there is still much to be learned from how our brain discovers the relevant regularities in the signal. For instance, although it has been suggested that both infants and adults extract this kind of information incidentally [3,4] it is still an open question whether the brain can detect violations in such abstract patterns pre-attentively or whether additional attentional or prosodic cues are needed. More importantly, it would be interesting to identify neural markers that could predict successful performance in the processing of abstract linguistic regularities. In the present study we contribute to these issues by characterizing the neural responses linked to the violation of target abstract structures. We thus will explore the neural responses that are triggered when a violation of an abstract pattern is detected and contrast them with the responses triggered when a violation of surface phonetic regularities are detected.

The main goal of the present study was to explore the neural events that are triggered by the detection of an abstract rule violation. We observed a positive response around 330 ms elicited after the presentation of deviant words that followed a different abstract pattern from standards (Rule deviants), but not after deviant words that followed the same patterns (Phoneme deviants). Even more, the amplitude of the positivity was correlated with the behavioral performance of the participants in the rule learning test.

In the current study, we explored the rapid detection of rule violations in an Oddball paradigm. We used two kinds of deviant stimuli, one changing only in the phonemes (Phoneme deviant) and the other changing also in the rule (rule deviants). We observed that a P300 component was elicited only after Rule deviant stimuli and was correlated with the behavioral performance of the participants in the rule learning test. This is in line with some studies showing that P300 is related with the processing of structure information. Moreover, two marginal components were observed only in the particular study of the groups of learners and non-learners. The learner’s group elicited a frontal N400 component after the presentation of rule deviants, while the non-learner’s group elicited a parietal N400 component after the presentation of phoneme deviants. Differences in electrophysiological responses observed between learners and non-learners suggest that individual differences in an abstract rule learning task might be related to how listeners select relevant sources of information from the signal. Our results thus demonstrate early responses triggered by changes in an abstract rule and identify processes that might underlie individual differences in the detection of abstract structures.

 

Source:

http://doi.org/10.1371/journal.pone.0180727

 

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