Sensitivity to (sub)lexical cues as a function of cognitive profile and language abilities
To achieve efficient language comprehension, multiple linguistic cues have to be integrated rapidly by readers and listeners when they encounter morphologically simple and complex words. However, there is no compelling evidence to suggest that this process is identical for everyone. The aim of this thesis is to explore systematic inter-individual differences in the integration of form-based cues (i.e. phonological and orthographic) with morphological, semantic, and lexico-semantic cues during written and spoken word processing, as evidenced by behavioural and MEG data.
The first part of the thesis shows that the processing of visual words and pseudowords in English varies considerably between individuals. Study 1 reveals that individual differences in vocabulary and spelling not only modulate overall processing speed and precision, but also readers’ processing strategy as evidenced by variable sensitivity to orthographic, morphological, and lexico-semantic information during lexical decision. Building on this, study 2 shows that processing speed and accuracy (as indicators of cognitive differences) also affect readers’ sensitivity to morphological information in visual priming.
The second part of the thesis extends these findings to the auditory modality. Study 3 demonstrates for the first time that individual differences in processing speed also affect cue sensitivity in spoken word processing as seen in listeners’ strategic use of morpho-phonological and semantic information during an auditory judgment task. Study 4 expands the findings from language-unimpaired English speakers to Spanish speakers with a common language difficulty (dyslexia). Combined behavioural and MEG data show that phonological deficits impact the neural encoding not only of phonological information, but also lexico-semantic information.
The findings from this thesis provide comprehensive evidence that the extent to which individuals rely on form-based information compared to other linguistic cues systematically varies as a function of cognitive profile and language abilities, with important implications for both theoretical accounts and language remediation practices.