Implicit learning of structure occurs in parallel with lexically-mediated syntactic priming effects in sentence comprehension

- Decreases in fixation times across study sessions indicated learning of structure.
- Lexically-mediated priming effects were also observed at the target sentences.
- Lexically-mediated priming was found to be independent from the learning effects.
- Consistent with a dual mechanism account of syntactic priming in comprehension.

The aim of this study was to determine whether cumulative structural priming effects and trial-to-trial lexically-mediated priming effects are produced by the same mechanism in comprehension. Participants took part in a five-session eye tracking study where they read reduced-relative prime-target pairs with the same initial verb. Half of the verbs in these sentences were repeated across the five sessions and half were novel to each session. Total fixation times on the syntactically challenging parts of prime sentences decreased across sessions, suggesting participants implicitly learned the structure. Additional priming was also observed at the critical regions of the target sentences, and the magnitude of this effect did not change over the five sessions. These finding suggests long-lived adaptation to structure and short-lived lexically-mediated priming effects are caused by separate mechanisms in comprehension. A dual mechanism account of syntactic priming effects can best reconcile these results.