Lexical Processing Drives Motor Simulation

While growing evidence suggests that sentence understanding engages perceptual and motor systems for the purpose of mentally imagining or simulating the content of utterances (Barsalou 1999) it is not known whether processing words alone does the same. We investigated whether making a decision about the form of a word would lead to activation of motor mechanisms, using a modified version of the Action-sentence Compatibility Effect (Glenberg and Kaschak 2002). Fluent signers of American Sign Language (ASL) were shown pairs of ASL signs which were either identical or not. Critical signs involved hand motion forward or backward, relative to the body. Subjects indicated whether the two signs were the same or different with a manual response requiring their hand to move either forward or backward- thus in a direction either compatible or incompatible with the direction of motion denoted by the sign. Results demonstrated a compatibility effect- literal and metaphorical motion signs facilitated response motion in the same direction, suggesting that mere phonological processing of a lexical item with motion meaning engages the motor system. The same experiment, performed with non-signers yielded no such effect, demonstrating that the effect was not simply the result of perceptual processing of the form of the sign. These results support an embodied view of linguistic processing where the content of language about motor actions is simulated using parts of the cognitive system responsible for actually performing the described actions