Hello from the other side: a behavioral account of the lexical orthographic abilities of the right hemisphere as revealed by an eye-tracking-controlled lateralized lexical decision task

Introduction The advantage of the Right Visual Field/Left Hemisphere (RVF/LH) over the Left Visual Field/Right Hemisphere (LVF/RH) for reading is a ubiquitous finding in behavioral and neuropsychological enquiry (1). A Neuropsychological account (2) suggests that such advantage could depend on “two lateralized lexical stores” in the brain, which would be differently organized with respect to different lexical variables. An alternative account, grounded on half-field studies on control subjects suggests that the left and the right brain differ in the pathways they use to access a “unique lexical store”, located in the LH (3). According to this latter view, the benchmark of such different routes would be a word length effect only appearing in the LVF/RH. When hemispheric differences in the early processing steps are ironed out, no further visual field effects should be observed. Materials & Methods In the current study, 60 young healthy right-handed volunteers were administered with an eye-tracking-controlled lateralized lexical decision task, in which either words or non-words were presented for 128ms at 3.5° left or right from central fixation. Word stimuli were manipulated by word length, frequency, imageability and orthographic neighborhood (N) size. Results In line with previous evidence, we observed a RVF/LH advantage over the LVF/RH for both accuracy and reaction times. We also detected main effects of length, imageability, and frequency, as well as a frequency-by-visual field interaction. In a subsequent analysis, we observed that whereas the performance of the LH was significantly above chance level for both high- and low-frequency words, in the RH this was only true for high-frequency words. We also report a positive effect of N size on word detection accuracy in the RVF/LH but not in the LVF/RH. Discussion The emergence of a visual field effect in spite of the absence of a different length effect in the two visual fields indicates that the two hemispheres do not employ different pathways to reach a unique LH lexicon. Rather, our data suggest that the two hemispheres employ similar processes (at least for the early visual computations that can be responsible for length effects) to access different lexical stores. In addition, a chance level performance for low-frequency words in the LVF/RH and a different sensitivity to N size suggest that lexical knowledge is differently represented in the two hemispheres, which is in line with the neuropsychological view. References 1. Lindell, A. K. (2006). In your right mind: right hemisphere contributions to language processing and production. Neuropsychology review, 16(3), 131-148. 2. Saffran, E. M., & Coslett, H. B. (1998). Implicit vs. letter-by-letter reading in pure alexia: A tale of two systems. Cognitive Neuropsychology, 15(1-2), 141-165. 3. Ellis, A. W. (2004). Length, formats, neighbors, hemispheres, and the processing of words presented laterally or at fixation. Brain and Language, 88(3), 355-366.