EXPRESS: Coexisting leftward asymmetry for single-letter flankers and symmetry for bigram flankers in the flanker lexical decision task

The study of parafoveal effects on word recognition has been a central topic in psycholinguistics for decades. Recently, the flanker lexical decision task (Dare & Shillcock, 2013) has become a key paradigm for investigating how parafoveal letter strings affect the processing of a foveally presented target word. A key unresolved question is whether the right and left flankers exert a similar influence or whether one hemifield plays a stronger role. Previous research has yielded inconsistent results (i.e., no asymmetry in some experiments, rightward asymmetry in others, and, more recently, leftward asymmetry), with these differences potentially attributable to methodological differences. The present experiment employed a within-subjects design in which single-letter and bigram flankers were intermixed within the same trial blocks. Results showed symmetrical effects for bigram flankers, but a sizable leftward asymmetry (greater facilitation from left than from right flankers) for single-letter flankers. This dissociation suggests length-dependent differences in parafoveal orthographic processing, with the privileged status of word-initial letters becoming most visible when the relevant letter is extracted under conditions of reduced crowding. More generally, these findings indicate that flanker asymmetries are not reducible to a fixed directional bias but reflect the interaction between attentional allocation and the grain size of the orthographic information available in the parafovea.