Role of Object-based Attention inLeft-lateralization of Print-specific ERP

Abstract

Implicit and rapid conversion of letters into sounds by skilled readers might be reflected in the left lateralization of print-tuned N170 event-related potential. A recent study suggests that the leftward asymmetry of the N170 depends on the attentional selection of letters as perceptual objects (Okumura et al., 2015, Neuropsychologia).The present study tested this possibility by using an experimental paradigm of object-based attention. Stimuli were letters (words, nonwords) or symbol strings that spatially overlapped with random-dot fields. Participants were asked to discriminate the color of either the letter/symbol strings or the dots. Left-lateralized negativity for print was elicited at 200–300 ms post-stimulus only when participants attended to the strings. However, this effect occurred later than the typical N170 latency, which might reflect the time required to resolve competition between overlapping stimuli or perceptual completion of letters. The current study is the first to demonstrate that the leftward asymmetry of print-specific ERP requires selective attention to letter strings.