Rough primes and rough conversations: evidence for a modality-specific basis to mental metaphors.

How does our brain organize knowledge? Traditional theories assume that our knowledge is represented abstractly in an amodal conceptual network of formal logic symbols. The theory of embodied cognition challenges this view and argues that conceptual representations that constitute our knowledge are grounded in sensory and motor experiences. We tested this hypothesis by examining how the concept of social coordination is grounded metaphorically in the tactile sensation of roughness. Participants experienced rough or smooth touch before being asked to judge an ambiguous social interaction. Results revealed that rough touch made social interactions appear more difficult and adversarial, consistent with the rough metaphor. This impact of tactile cues on social impressions was accompanied by a network including primary and secondary somatosensory cortices, amygdala, hippocampus and inferior prefrontal cortex. Thus, the roughness of tactile stimulation affected metaphor-relevant (but not metaphor-irrelevant) behavioral and neural responses. Receiving touch from a rough object seems to trigger the application of associated ontological concepts (or scaffolds) even for unrelated people and situations (but not to unrelated or more general feelings). Since this priming was based on somatosensory brain areas, our results provide support for the theory that sensorimotor grounding is intrinsic to cognitive processes.