Pre-proof From action to abstraction : The sensorimotor grounding of metaphor in Parkinson ’ s disease

Embodied cognition theories propose that the semant ic representations engaged in during language comprehension are partly supported by perc e tual and motor systems, via simulation. Activation in modality-specific regions of cortex i s associated with the comprehension of literal language that describes the analogous modalities, b ut studies addressing the grounding of nonliteral or figurative language, such as metaphors, have yielded mixed results. Differences in the psycholinguistic characteristics of sentence stimul i across studies have likely contributed to this lack of consensus. Furthermore, previous studies ha ve been largely correlational, whilst patient studies are a critical way of determining if intact sensorimotor function is necessary to understand language drawing on sensorimotor informa tion. We designed a battery of metaphorical and literal sentence stimuli using act ion and sound words, with an unprecedented level of control over critical psycholinguistic var i bles, to test hypotheses about the grounding of metaphorical language. In this Registered Report, w e assessed the comprehension of these sentences in 41 patients with Parkinson’s disease, who were predicted to be disproportionately affected by the action sentences relative to the so und sentences, and compared their performance to that of 39 healthy age-matched controls who were predicted to show no difference in performance due to sensory modality. Using preregis t red Bayesian model comparison methods, we found that PD patients’ comprehension of literal action sentences was not impaired, while there was some evidence for a slowing of responses to action metaphors. Follow up exploratory analyses suggest that this response time modality e ffect was driven by one type of metaphor (predicate) and was absent in another (nominal), de spite the fact that the action semantics were similar in both syntactic forms. These results sugg est that the conditions under which PD patients demonstrate hypothesized embodiment effects are lim ited. We offer a critical assessment of the PD action language literature and discuss implicati ons for the embodiment debate. In addition, we suggest how future studies could leverage Bayesi n statistical methods to provide more convincing evidence for or against embodied cogniti o effects.