Handedness, measures of hemispheric asymmetry, and lateralised lexical decision

The goals of the present study were to evaluate the differences between measures of lateralisation in the human brain derived from a dichotic listening (DL) task and from a task involving identification of visually presented consonant-vowel-consonant (CVC) nonwords, and to correlate these lateralisation indices with performance on a lexical decision task involving visually presented words and nonwords. Visual stimuli were presented either in a central position, or to the left or right of fixation. Left-handed and right-handed participants completed each of the three tasks. Lateralisation indices were derived from performance on the DL and CVC tasks, and latency and accuracy measures of lexical decision performance were obtained for targets presented centrally and parafoveally. Lateralisation indices for left-handed and right-handed participants differed significantly for both tasks, and the two lateralisation indices had different pattern of correlation with lexical decision performance for left- and right-handers. For left-handers, lateralisation indices derived from the (visual) CVC task were correlated with lexical decision response latency for targets in central and left visual field. For right-handers, lateralisation indices derived from the (auditory) DL task were correlated with lexical decision response latency for targets in central and right visual field. A possible explanation for this finding is that the two laterality measures reflect specialisation for different types of linguistic processing in the human brain.