Effects of syntactic complexity, semantic reversibility, and explicitness on discourse comprehension in persons with aphasia and in healthy controls

Understanding, facilitating and predicting aphasia recovery after rehabilitation

Purpose: This paper reviews several studies whose aim was to understand the nature of language recovery in chronic aphasia and identify predictors of how people may recover their language functions after a brain injury.Method: Several studies that mostly draw from data collected within the Centre for Neurobiology of Language Recovery were reviewed and categorised in four aspects of language impairment and recovery in aphasia: (a) neural markers for language impairment and recovery, (b) language and cognitive markers for language impairment and recovery, (c) effective treatments and (d) predictive modelling of treatment-induced rehabilitation.Result: Language impairment and recovery in stroke-induced aphasia is multi-factorial, including patient-specific and treatment-specific factors. A combination of these factors may help us predict treatment responsiveness even before treatment begins.Conclusion: Continued work on this topic will lead to a better understanding of the mechanisms that underly language impairment and treatment-induced recovery in aphasia, and, consequently, use this information to predict each person's recovery profile trajectory and provide optimal prescriptions regarding the type and dosage of treatment.

Reading for Meaning: What Influences Paragraph Understanding in Aphasia?

PURPOSE

The current study investigated the effect of text variables including length, readability, propositional content, and type of information on the reading comprehension of people with aphasia.

METHOD

The performance of 75 people with aphasia was compared with 87 healthy, age-matched control participants. Reading comprehension was considered in terms of both accuracy in responding to questions tapping comprehension and reading time. Participants with aphasia (PWA) were divided into 2 groups (no reading impairment [PWA:NRI] and reading impairment [PWA:RI]) depending on whether their performance fell within the 5th percentile of control participants.

RESULTS

As groups, both PWA:NRI and PWA:RI differed significantly from control participants in terms of reading time and comprehension accuracy. PWA:NRI and PWA:RI differed from each other in terms of accuracy but not reading time. There was no significant effect of readability or propositional density on comprehension accuracy or reading time for any of the groups. There was a significant effect of length on reading time but not on comprehension accuracy. All groups found main ideas easier than details, stated information easier than inferred, and had particular difficulty with questions that required integration of information across paragraphs (gist).

CONCLUSIONS

Both accuracy of comprehension and reading speed need to be considered when characterizing reading difficulties in people with aphasia.

The effect of a sentence comprehension treatment on discourse comprehension in aphasia

BACKGROUND

While it is well understood that individuals with aphasia have difficulty with discourse comprehension, very few studies have examined the nature of discourse comprehension deficits in aphasia and the potential for improvement in discourse comprehension after rehabilitation. To address the first goal, we previously developed the Test of Syntactic Effects on Discourse Comprehension (TSEDC), which provides a measure of the extent to which a participant's sentence comprehension ability aids in comprehending passages (Levy et al., 2012).

AIMS

The goal of this study was to examine the effect of a sentence comprehension treatment on the TSEDC to assess if training participants to understand sentences of different syntactic complexity would improve their ability to understand passages that vary by their level of syntactic complexity.

METHODS & PROCEDURES

Forty participants with aphasia received sentence comprehension treatment using one of two syntactic comprehension tasks: object manipulation (OM) or sentence to picture matching (SPM). The dependent measure was improved sentence comprehension of one sentence type in one task-related protocol, with the order of task and structure counterbalanced across participants. Before and after treatment, participants also completed a self-paced auditory story comprehension task which involved 9 passages that contained either semantically reversible canonical sentences (simple passages) or semantically reversible noncanonical sentences (complex passages). At the end of each passage, participants were asked explicit or implicit questions about the story. Accuracy and reaction times were measured for each patient for each story before and after treatment.

OUTCOMES & RESULTS

Analysis of the treatment data revealed that participants improved in their ability to understand trained sentences (both in terms of effect size and percent change on trained structure), irrespective of whether the trained task was SPM or OM. There was no significant relationship between treatment improvements on the SPM/OM treatment (even when the task targeted in treatment was controlled for) and changes in performance on the TSEDC. Also, there was no significant improvement in TSEDC accuracy after treatment, even when various aspects of the narrative passages, including passage complexity (simple/complex), the nature of sentence type (semantically constrained/semantically reversible) and the nature of questions asked (explicit or implicit) were accounted for.

CONCLUSIONS

Inherent differences between the sentence comprehension treatment and the TSEDC may have precluded generalization.

Adaptive significance of right hemisphere activation in aphasic language comprehension

Aphasic patients often exhibit increased right hemisphere activity during language tasks. This may represent takeover of function by regions homologous to the left-hemisphere language networks, maladaptive interference, or adaptation of alternate compensatory strategies. To distinguish between these accounts, we tested language comprehension in 25 aphasic patients using an online sentence-picture matching paradigm while measuring brain activation with MEG. Linguistic conditions included semantically irreversible ("The boy is eating the apple") and reversible ("The boy is pushing the girl") sentences at three levels of syntactic complexity. As expected, patients performed well above chance on irreversible sentences, and at chance on reversible sentences of high complexity. Comprehension of reversible non-complex sentences ranged from nearly perfect to chance, and was highly correlated with offline measures of language comprehension. Lesion analysis revealed that comprehension deficits for reversible sentences were predicted by damage to the left temporal lobe. Although aphasic patients activated homologous areas in the right temporal lobe, such activation was not correlated with comprehension performance. Rather, patients with better comprehension exhibited increased activity in dorsal fronto-parietal regions. Correlations between performance and dorsal network activity occurred bilaterally during perception of sentences, and in the right hemisphere during a post-sentence memory delay. These results suggest that effortful reprocessing of perceived sentences in short-term memory can support improved comprehension in aphasia, and that strategic recruitment of alternative networks, rather than homologous takeover, may account for some findings of right hemisphere language activation in aphasia.