Event-related EEG suggests modality rather than material specific memory lateralisation

Material-specific memory impairment can be observed in patients with unilateral temporal lobe dysfunction. Measures of verbal memory appear to predict memory loss with left temporal lobe damage, but nonverbal measures are poor predictors of memory impairment with right temporal lobe damage. Typically, cognitive neuroscience models of right hemisphere processing have not informed test development. Putatively "nonverbal" tasks are also frequently verbalisable, confounding their specificity to the right hemisphere. We measured event-related EEG during recognition memory in 24 healthy subjects. These measures were taken during learning of visually presented nonwords, auditorily presented (different) nonwords, and then cross-modal paired associations of the two. Similarly, measures were taken during learning of dot patterns, novel melodies, and then pairings. It was found that learning dot patterns was related to greater event-related desynchronisation in the right hemisphere, while auditory nonwords demonstrated a left hemisphere bias. Surprisingly, hemispheric biases to the right were shown by visual nonwords and to the left by melodies, suggesting that the modality (visual or auditory) of novel materials has a stronger effect on hemispheric lateralisation than the material (verbal or nonverbal). Consistent with this view, crossmodal tasks lacked lateralisation. Findings from this study will guide development of clinical test materials.