Effects of word frequency and contextual predictability on sentence reading in aphasia: an eye movement analysis

Background: Mild reading difficulties are a pervasive symptom of aphasia. Whilst much research in aphasia has been devoted to the study of single word reading, little is known about the process of (silent) sentence reading. Reading research in the non-brain damaged population has benefited from the use of eye tracking methodology, allowing inferences on cognitive processing without participants making an articulatory response. This body of research identified two factors, which strongly influence reading at the sentence level: word frequency and contextual predictability (influence of context). Aims: The main aim of this study was to investigate whether word frequency and contextual predictability influence sentence reading by people with aphasia, in parallel to that of neurologically healthy individuals. A second aim was to examine whether readers with aphasia show individual differences in the effects, and whether these are related to their underlying language profile. Methods & Procedures: Seventeen people with aphasia (PWA) and associated mild reading difficulties and twenty neurologically healthy individuals (NHI) took part in this study. Individuals with aphasia completed a range of language assessments. For the eye tracking experiment, participants silently read sentences that included target words varying in word frequency and predictability whilst their eye movements were recorded. Comprehension accuracy, fixation durations and the probability of first-pass fixations and first-pass regressions were measured. Outcomes & Results: Eye movements by both groups were significantly influenced by word frequency and predictability, but the predictability effect was stronger for the people with aphasia than the neurologically healthy participants. Additionally, effects of word frequency and predictability were independent for the neurologically healthy individuals, but the individuals with aphasia showed a more interactive pattern. Correlational analyses revealed i) a significant relationship between lexical-semantic impairments and the word frequency effect score, and ii) a marginally significant association between the sentence comprehension skills and the predictability effect score. Conclusions: Consistent with compensatory processing theories, these findings indicate that decreased reading efficiency may trigger a more interactive reading strategy that aims to compensate for poorer reading by putting more emphasis on a sentence context, particularly for low frequency words. For those individuals who have difficulties applying the strategy automatically, using a sentence context could be a beneficial strategy to focus on in reading intervention.