Abstract
We investigated the perceptual time-course of global/local processing using event-related potentials (ERPs). Subjects discriminated the global or local level of hierarchical letters of different sizes and densities. Subjects were faster to discriminate the local level of large/sparse letters, and the global level of small/dense letters. This was mirrored in early ERP components: the N1/N2 had smaller peak amplitudes when subjects made discriminations at the level that took precedence. Only global discriminations for large/sparse letters led to amplitude enhancement of the later P3 component, suggesting that additional attention-demanding processes are involved in discriminating the global level of these stimuli. Our findings suggest a dual-locus time course for global/local processing: 1) level precedence occurs early in visual processing; 2) extra processing is required at a later stage, but only for global discriminations of large, sparse, stimuli, which may require additional attentional resources for active grouping.
NSERC, SSHRC, CIHR, MSFHR.