Abstract
Behavioral and event-related potential (ERP) studies on aphasia patients showed that lexical information is not lost but rather its integration into the working context is hampered. Studies have been conducted on the processing of sentence-level information (meaningful versus meaningless) and of word-level information (related versus unrelated) in aphasia patients, but we are not aware of any study that assesses the relationship between the two. In healthy subjects the processing of a single word in a sentence context has been studied using the N400 ERP. It was shown that, even when there is only a weak expectation of a final word in a sentence, this expectation will dominate word relatedness. In order to study the effect of semantic relatedness between words in sentence processing in aphasia patients, we conducted a crossed-design ERP study, crossing the factors of word relatedness and sentence congruity. We tested aphasia patients with mild to minimum comprehension deficit and healthy young and older (age-matched with our patients) controls on a semantic anomaly judgment task when simultaneously recording EEG. Our results show that our aphasia patient’s N400 amplitudes in response to the sentences of our crossed-design study were similar to those of our age-matched healthy subjects. However, we detected an increase in the N400 ERP latency in those patients, indicating a delay in the integration of the new word into the working context. Additionally, we observed a positive correlation between comprehension level of those patients and N400 effect in response to meaningful sentences without word relatedness contrasted to meaningless sentences without word relatedness.
Highlights
Aphasia is one of the most common neurological syndromes as up to 35% of post-stroke patients suffer from it Wade et al (1986), Kauhanen et al (2000)
If the significance of this effect was consistent over a 50 ms time interval (13 consecutively significant analysis of variance (ANOVA)), we considered this instance as the onset latency of the N400 potential
Mixed design ANOVA with sentence congruity (Con., two levels), association (AS, two levels), subject group (SubG, three levels) and their interactions as independent factors showed a significant effects of Con [F(1,178) = 8.16, p = 0.0048], AS [F(1,178) = 4.77, p = 0.03], SubG [F(2,178) = 23.47, p < < 0.00001] and some of their interactions: Con × AS (p = 0.0013), and Con × SubG (p = 0.017)
Summary
Aphasia is one of the most common neurological syndromes as up to 35% of post-stroke patients suffer from it Wade et al (1986), Kauhanen et al (2000). Based on the Lynch et al (2013) study on reading strategies and the one of Coulson et al (2005) with lateralized presentation of lexico-semantic stimuli, we hypothesize that in aphasic patients word association might play a more significant role in comprehension of sentence level information than in healthy subjects. This might even be evident in patients with mild comprehension deficit (our target patient group). The N400 potential should not be different for sentences with or without associations as it was shown to be the case with healthy subjects (Van Petten et al, 1999)
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