Hemispheric asymmetry for processing unpronounceable and pronounceable letter trigrams.

In each of two experiments, observers attempted to identify three-letter strings presented briefly to the left visual field/right hemisphere (LVF/RH), to the right visual field/left hemisphere (RVF/LH), or to both visual fields (and hemispheres) simultaneously (redundant BILATERAL trials). Similar visual half-field effects were obtained for both all-consonant (CCC) strings and consonant-vowel-consonant (CVC) nonwords. For both types of strings, there were fewer errors on RVF/LH trials than on LVF/RH trials and the pattern of error types was qualitatively different for the two visual fields. The similarity of visual half-field results for CCC and CVC strings indicates that results that have been reported in earlier studies with CVC strings are not restricted to letter strings that can be coded as a single pronounceable syllable, as some have suggested. Instead, the results are consistent with hypotheses about hemispheric differences in the ability to encode and remember individual letters in a multielement display. In addition, for both CCC and CVC letter strings there were fewer errors on redundant BILATERAL trials than on either type of unilateral trial, suggesting interhemispheric collaboration in both cases. However, the qualitative error patterns obtained on redundant BILATERAL trials suggest that the precise way in which the hemispheres collaborate differs with the type of letter string.