Visual Search for Letters in the Right Versus Left Visual Hemifields

The current study investigated the relationships between attention, word processing, and visual field asymmetries. There is a discussion on whether each brain hemisphere possesses its own attentional resources and on how attention allocation depends on hemispheric lateralization of functions. We used stimuli with lateralized processing in an attentional task presented across the two visual hemifields. Three experiments investigated the visual search for a prespecified letter in displays containing words or nonwords, placed left and right to fixation, with a variable target letter position within the strings. In Experiment 1, two letter strings of the same type (words or nonwords) were presented to both visual hemifields. In Experiment 2, there was only one letter string presented right or left to fixation. In Experiment 3, two letter strings of different type were presented to both hemifields. Response times and accuracy data were collected. The results of Experiment 1 provide evidence for letter-by-letter search within a word in the left visual field (LVF), within a nonword in the right visual field (RVF), and for position-independent access to letters within a nonword in LVF and within a word in RVF. Experiment 3 produced similar results except for letter-by-letter search within words in RVF. In Experiment 2, for all types of letter strings in both hemifields, we observed the same letter-by-letter search. These results demonstrate that presence of stimuli in both one or two hemifields and the readiness to process a certain string type might contribute to the search for a letter within a letter string.