Orthographic Neighborhood Effects During Lateralized Lexical Decision Are Abolished With Bilateral Presentation

Words presented to the right visual field (RVF) are processed more rapidly than those in the left visual field (LVF), presumably because of more direct links to the language dominant left cerebral hemisphere. This effect is moderated by a word's orthographic neighborhood size (N), with LVF facilitation and RVF inhibition for words with a large N. Across two experiments, we sought to further examine lateralized N effects. Experiment 1 examined how hemispheric dominance for language influenced lateralized N effects, in 140 left-handers using a visual half-field task with bilateral presentation. Neither participants with a right ear advantage on a dichotic listening task nor participants with no right ear advantage showed the expected N effect, making the results ambiguous: it could be that left-handers fail to show N effects, or the effect could be abolished by some procedural aspect. Experiment 2 looked to test these options by testing 56 right-handers who responded to the same stimulus set under the original bilateral presentation condition and under unilateral presentation. N effects were found under unilateral but not bilateral presentation. We had adopted bilateral presentation because it had been recommended as better than unilateral presentation for controlling fixation and visual stimulation; our results indicate that this is not a minor methodological modification: it can dramatically affect lateralized N effects. Public Significance Statement Words presented in the right visual field are initially projected to the left cerebral hemisphere. Conversely, words presented in the left visual field are initially projected to the right hemisphere. Word-level properties, such as orthographic neighborhood size, differentially affect word identification across each cerebral hemisphere. In particular, having many neighbors facilities word identification in the right hemisphere whereas it inhibits word identification in the left hemisphere. We explored these asymmetries further across two studies where words were displayed in isolation or accompanied by a distractor. The data is conclusive in showing that presentation mode has nontrivial consequences for lateralized orthographic neighborhood effects: neighborhood effects are only detectable under unilateral presentation where words are displayed in isolation