What is bilateral language? Evidence from distributions of laterality indices

In a study of patterns of language laterality in left- and right-handers, Woodhead et al. (2021) noted that several tasks showed no bias to the left-hemisphere in left-handed individuals. This might appear to suggest that these functions were mediated by the two hemispheres working together equally in left-handers. Here, I consider an alternative possibility: that individuals show lateral bias on these tasks, but the bias can occur to either left or right. Further analysis of the distributions of data from individuals in Woodhead et al is compared with simulated data. The pattern of results suggests that the impression of bilateral language processing may be an artefact of reliance on group data: even though the group mean does not differ from zero, a high proportion of individuals are biased to left or right.