Attenuated hemispheric asymmetry in metaphor processing among adults with ADHD

Objective: To characterize the hemispheric processing of metaphors in adults with ADHD compared to controls. Method: We investigated the hemispheric processing of metaphors in 24 adult participants diagnosed with ADHD and 24 control participants. The hemispheric processing was examined using a divided visual field paradigm, in which different kinds of metaphors as well as literal word pairs and unrelated word pairs were presented either to the right visual field/left hemisphere (RVF/LH) or to the left visual field/right hemisphere (LVF/RH). Results: Control participants processed metaphors more efficiently when presented in the LVF/RH than when presented in the RVF/LH, whereas participants with ADHD demonstrated attenuated asymmetry of hemispheric processing. Furthermore, asymmetry of hemispheric processing, together with sustained attention, contributed significantly to the prediction of self-report of ADHD symptoms. Conclusion: Our results suggest that the hemispheric processing of adults with ADHD is less lateralized than the hemispheric processing of control participants. Moreover, the diminished lateralization of metaphor processing along with deficient sustained attention may reflect distinct cognitive mechanisms underlying ADHD and as such our results support multiple pathway models of ADHD.