"Embodied" language processing: Mental motor imagery aptitude predicts word-definition skill for high but not for low imageable words in adolescents

Our study was designed to test a recent proposal by Cayol and Nazir (2020), according to which language processing takes advantage of motor system "emulators". An emulator is a brain mechanism that learns the causal relationship between an action and its sensory consequences. Emulators predict the outcome of a motor command in terms of its sensory reafference and serve monitoring ongoing movements. For the purpose of motor planning/learning, emulators can "run offline", decoupled from sensory input and motor output. Such offline simulations are equivalent to mental imagery (Grush, 2004). If language processing can profit from the associative-memory network of emulators, mental-imagery-aptitude should predict language skills. However, this should hold only for language content that is imageable. We tested this assumption in typically developing adolescents using two motor-imagery paradigms. One that measured participant's error in estimating their motor ability, and another that measured the time to perform a mental simulation. When the time to perform a mental simulation is taken as measure, mental-imagery-aptitude does indeed selectively predict word-definition performance for high imageable words. These results provide an alternative position relative to the question of why language processes recruit modality-specific brain regions and support the often-hypothesized link between language and motor skills.