Article
Understanding discourse-linked processes in agrammatic and fluent aphasia: a threefold study in Russian
Agrammatic speakers have problems with grammatical encoding and decoding. However, not all syntactic processing are equally problematic: present- time –reference /who-questions/ reflexives can be processed by narrow syntax alone and are relatively spared compared to past - time –reference / which-questions/ that need additional access to discourse and information structures to link to their referent outside the clause (Avrutin , 2006). Agrammatic aphasic speakers find it more difficult to produce and comprehend verb forms that refer to the past than verb forms that refer to the non-past (Bastiaanse, 2011). The same holds for which-questions compared to who-questions and for pronouns compared to reflexives (Avrutin , 2006).
The present study employed the visual-world paradigm with eyetracking to discriminate between two versions of the reordered access model - namely, whether meaning frequency and context affect (a) speed of lexical access or (b) the relative weight of simultaneously accessed meanings. The time course of lexical access and meaning integration were studied in 3 groups of Russian speaking participants: 36 individuals in control group as well as 16 individuals with non-fluent and 8 with fluent aphasia. The results allow to confirm psychological reality of the first version, since in balanced ambiguous words contextual bias influences the speed of lexical access. In addition, it was found that healthy population and participants with non-fluent aphasia are affected by the contextual bias even after processing information that resolves ambiguity.
Aphasia, a language impairment following stroke or brain trauma, is normally manifested behaviorally. Patients with the so-called non-fluent aphasia experience major difficulties at the level of morphosyntax (that is, producing and comprehending complex morphology and syntax). In contrast, patients with fluent aphasia predominantly show problems at the lexical-semantic level (that is, accessing word forms and lexical semantics). However, a few studies have proven that the language deficit in patients with aphasia is expressed not only in their linguistic performance, but also in specific electrophysiological responses.
In healthy individuals, incongruencies at different linguistic levels cause distinct event-related brain potentials (ERPs) registrated at the scalp. Syntactic incongruency elicits the ELAN and the P600 potentials, lexical-semantic incongruency elicits the N400 potential. Critically, in standard for those potentials linguistic contexts the lack of N400 was reported for fluent patients, while the lack of the ELAN and a reduced and delayed P600 – for non-fluent patients (Friederici et al. 1998, Wassenaar and Hagoort 2005). These findings support the idea of electrophysiological brain mapping on specific linguistic problems observed in different aphasia types.
The study was aimed at further investigating electrophysiological evidence for the suggestion that spoken sentence comprehension problems in individuals with fluent and non-fluent aphasia are caused, at least partly, by breakdowns at different levels of language processing – lexical-semantic and morphosyntactic respectively. To test this, we performed a study in healthy and aphasic Russian individuals using the method of event-related potentials (ERPs) that has become a powerful tool in addressing temporal aspects of language processing.
51st Academy of Aphasia Proceedings
The distractive effects on attentional task performance in different paradigms are analyzed in this paper. I demonstrate how distractors may negatively affect (interference effect), positively (redundancy effect) or neutrally (null effect). Distractor effects described in literature are classified in accordance with their hypothetical source. The general rule of the theory is also introduced. It contains the formal prediction of the particular distractor effect, based on entropy and redundancy measures from the mathematical theory of communication (Shannon, 1948). Single- vs dual-process frameworks are considered for hypothetical mechanisms which underpin the distractor effects. Distractor profiles (DPs) are also introduced for the formalization and simple visualization of experimental data concerning the distractor effects. Typical shapes of DPs and their interpretations are discussed with examples from three frequently cited experiments. Finally, the paper introduces hierarchical hypothesis that states the level-fashion modulating interrelations between distractor effects of different classes.
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