Body-specific representations of action verbs: Evidence from fMRI in right-and left-handers

Body-specific representations of action verbs: Evidence from fMRI in right- and left-handers Daniel Casasanto 1 Roel Willems 2 Peter Hagoort 1,2 (daniel.casasanto@mpi.nl) (roel.willems@donders.ru.nl) (peter.hagoort@donders.ru.nl) Max Planck Institute for Psycholinguistics Wundtlaan 1, 6525 XD Nijmegen, The Netherlands Donders Institute for Brain, Cognition and Behaviour, Radboud University, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands Abstract neurocognitive representations should differ for people who perceive and act upon the environment in systematically different ways. We investigated whether activity in motor cortex during action verb processing reflects the way an individual language user typically performs the action that the verb refers to. Across neuroimaging studies, activity in cortical motor areas associated with manual action verbs has been left- lateralized (Aziz-Zadeh et al., 2006; Hauk et al., 2004; Ruschemeyer, Brass, & Friederici, 2007; Tettamanti et al., 2005). This lateralization could be due to the general left- hemisphere dominance for language. Alternatively, it could be a consequence of testing only right-handed participants. We propose that if word meanings are implicit simulations, then understanding words for actions that people typically perform with their dominant hand should involve simulating these actions in contralateral premotor areas (i.e., areas that subserve planning of actions with the dominant hand). To test this proposal, we used fMRI to compare premotor activation in right- and left-handers during a lexical decision task on manual action verbs (e.g., grasp, throw) and non- manual action verbs (e.g., kneel, giggle). If the motor component of an action verb’s meaning is a body-specific simulation of the action it refers to as the particular language user would be likely to perform it, then activity in premotor cortex during manual action verb processing should be differently lateralized in right- and left-handers. Each group should preferentially activate premotor areas contralateral to their dominant hand. 1 The non-manual action words served as a control. Finding the predicted difference between right- and left-handers for manual action words, alone, could be evidence for implicit body-specific simulation of manual actions during word reading. Alternatively, it could be an artifact of differences in language laterality between right- and left-handers, more generally. However, this alternative is ruled out by testing for the predicted interaction of Hemisphere (right premotor, left premotor) and Handedness (right-handed, left-handed) in voxels that are significantly more active during manual compared to non-manual action verbs (i.e., essentially, by testing for a particular three-way interaction of Hemisphere, Handedness, and Verb Type). According to theories of embodied cognition, understanding a verb like throw involves unconsciously simulating the action throwing, using areas of the brain that support motor planning. If understanding action words involves mentally simulating our own actions, then the neurocognitive representation of word meanings should differ for people with different kinds of bodies, who perform actions in systematically different ways. In a test of the body-specificity hypothesis (Casasanto, 2009), we used fMRI to compare premotor activity correlated with action verb understanding in right- and left-handers. Right-handers preferentially activated left premotor cortex during lexical decision on manual action verbs (compared with non-manual action verbs), whereas left- handers preferentially activated right premotor areas. This finding helps refine theories of embodied semantics, suggesting that implicit mental simulation during language processing is body-specific: Right and left-handers, who perform actions differently, use correspondingly different areas of the brain for representing action verb meanings. Keywords: Action; Body-specificity; Embodied cognition; fMRI; Handedness; Semantics Introduction Theories of embodied cognition propose an intimate link between language and bodily experience. In this framework, to understand a word is to create an implicit mental simulation of its referent, using regions of the brain that support perception and action (e.g. Anderson, 2003; Barsalou, 2008; Zwaan, 2004). Consistent with this view, studies show that when participants read action-related verbs like ‘kick’, ‘pick’ and ‘lick’ they activate effector- specific regions of premotor cortex, as when they move the effector most associated with these verbs (i.e. their foot, hand, or tongue) (Aziz-Zadeh, Wilson, Rizzolatti, & Iacoboni, 2006; Hauk, Johnsrude, & Pulvermuller, 2004; Tettamanti et al., 2005). The goal of the present study was to refine the notion of implicit mental simulation during language processing, by framing experimental predictions in terms of the body- specificity hypothesis (Casasanto, 2009): If concepts and word meanings are constituted, in part, by implicit simulations of our own perceptions and actions, then their