Left-hand muscle contractions improve novel metaphor comprehension among adolescents

For people to understand metaphors that require the creation of associations between remote concepts, both the diffuse spread of activation in semantic networks in the right hemisphere (coarse semantic coding) and the tight and focused spread of activation in the left hemisphere (fine semantic coding) are required. During adolescence, the dynamic between the left and right hemispheres that enables the processing of metaphors is not yet established. Thus, the present study aimed to (1) test whether left-hand muscle contractions that activate the right hemisphere's sensory-motor regions can boost metaphor comprehension in adolescents; (2) compare conventional and novel metaphor processing (with no muscle contractions) in adolescents and adults. For the first goal, 83 adolescents between the ages of 14–16 squeezed a rubber ball with either their right hands, left hands, or not at all (control group) while presented with two-word expressions of four types: literal expressions, conventional metaphors, novel metaphors, and unrelated expressions. Results showed that left-hand muscle contractions led to more accurate processing of literal expressions and conventional and novel metaphors. However, the over-activation of the right hemisphere led to a decreased ability to process unrelated expressions. For the second goal, the adolescent control group was compared with an adult group of participants. Results revealed that despite a general disadvantage in language processing (including conventional metaphors), adolescents were more accurate in processing novel metaphors. Our findings suggest that adolescents' left lateralization for language is not yet established, resulting in over-reliance on coarse semantic coding. In addition, our results demonstrate the effectiveness of a simple, non-invasive technique for enhancing metaphor comprehension in adolescents. This technique may especially benefit adolescents who struggle with metaphor comprehension, such as adolescents with autistic spectrum disorders or with poor social skills.