Orthographic neighbourhood effects during lateralised lexical decision are abolished with bilateral presentation
Mills R., Woodhead ZVJ., Parker AJ.
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 neighbourhood size (N), with LVF facilitation and RVF inhibition for words with large N. Across two experiments, we sought to further examine lateralised N effects. Experiment 1 examined how hemispheric dominance for language influenced lateralised N effects, in 140 left-handers using a visual half-field task with bilateral presentation. Neither typically nor atypically lateralized participants 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 effects.