This dissertation presents research into variation between and within participants in their metalinguistic judgments about, and processing of, multi-word sequences. It thus contributes to the development of the usage-based framework in linguistics. Individual differences in mental representations of language naturally follow from a usage-based approach. Since people differ in their linguistic experiences, they are expected to differ in the extent to which a linguistic construction is entrenched in their mental lexicons. Furthermore, a language user gains new linguistic experiences over time, and mental representations of language are hypothesized to change accordingly. There is a shortage of empirical data on these types of variation, though.
To examine inter- and intra-individual variation, two studies in this dissertation use a test-retest design: participants performed the same judgment task twice within the space of a few weeks. In another study, recruiters, job-seekers, and people not (yet) looking for a job performed a completion task, a voice onset time task, and a metalinguistic judgment task consecutively. These groups differ in their exposure to a particular register (job ads), which is expected to lead to differences in mental representations of language.
Veronique Verhagen compares participant-based measures and measures based on amalgamated data of different people (corpus-based frequencies, surprisal, cloze probabilities) as predictors of performance in psycholinguistic tasks. This provides insight into individual variation and the merits of going beyond amalgamated data. The thesis demonstrates how investigations of inter- and intra-individual variation in psycholinguistic data advance our understanding of the dynamic character of mental representations of language.