Individual differences in hemispheric asymmetry for global-local processing in young and older adults

The two hemispheres of the brain demonstrate functional asymmetry for global-local processing, with global processing specialised in the right hemisphere and local processing specialised in the left hemisphere. Previous research indicates that hemispheric asymmetry remains intact with age, despite older adults demonstrating worse overall performance for global processing. Participants (127 young, 58 older) completed a hierarchical-figures task using a divided visual field design - stimuli presented briefly to the left or right visual field, such that information was initially processed by the contralateral hemisphere. At the group level: (1) young and older participants demonstrated better performance for global hierarchical figures presented to the left visual field (right-hemisphere global specialisation) and for local hierarchical figures presented to the right visual field (left-hemisphere local specialisation); (2) older participants demonstrated worse overall performance only for global hierarchical figures when compared to young participants. At the individual level, while approximately half the participants demonstrated the predicted pattern of hemispheric asymmetry (right-hemisphere global specialisation; left-hemisphere local specialisation), there were subgroups of participants who demonstrated different patterns. Our findings indicate individual differences in hemispheric asymmetry exist for global-local processing in right-handed participants, and that this may explain the inconsistent findings in group-level studies with small sample sizes.