An ERP study of the global precedence effect: the role of spatial frequency.

OBJECTIVE This study investigated the neural mechanisms underlying the effects of removal of low spatial frequency (SF) contents from stimulus displays on the processing of global and local properties of compound stimuli. METHODS Event-related brain potentials (ERPs) were recorded from 16 subjects who selectively attended to the global or local features of compound letters, which were either white on a gray background containing broadband SFs or were contrast-balanced (CB) to eliminate low SFs, and were randomly presented in the left or right visual fields. ERPs were analyzed to examine how global/local attention modulations of neural substrates were influenced by SF manipulations. RESULTS We found that an early process of global recognition was indexed by a negativity peaking at 190 ms over contralateral occipito-temporal cortex and was eliminated by contrast balancing. The late stage of global recognition was reflected in a late negativity peaking at 300 ms and was only retarded by contrast balancing. Global-to-local interference was characterized by enhanced occipito-temporal negativities and was evident for both broadband and CB stimuli. CONCLUSIONS The results clarify distinct cognitive and neural mechanisms underlying the global precedence and interference effects, which were different in terms of the independence of low SFs in compound stimuli.