| dc.description.abstract | Objective: To determine and graphically represent the ways that language bilaterality is defined in Wada studies, and to estimate the prevalence of language bilaterality according to those definitions.
Methods: A systematic analysis of 33 Wada studies was conducted. All Wada studies were published in English, did not use children as participants, were primarily or substantially concerned with language laterality, and included at least 100 participants who underwent the Wada procedure. Definitions for language laterality categories and language laterality distributions were collected from each article. This information was used to generate lateralization matrices. In the lateralization matrices, the vertical axis represents the independent functioning of the right brain hemisphere and the horizontal axis represents the independent functioning of the left brain hemisphere. The matrices provide a visual representation of the behavior that the researchers attributed to different categories, and include the number of patients assigned to each category.
Results: The definitions of language bilaterality from the 33 studies fell into four broad categories and were represented graphically with 26 matrices. There were seven articles for which a matrix could not be constructed. The prevalence of language bilaterality was estimated as 9.8% with an SD of 4.3%, the prevalence of left-hemisphere dominance was estimated as 78.0% with an SD of 6.6%, and the prevalence of right-hemisphere dominance was estimated as 8.5% with an SD of 4.4%. The mean proportions of patients with bilaterality (9.8%) and patients with right-hemisphere lateralization (8.5%) were similar, so the articles were organized into the following groups: (1) right-hemisphere lateralization proportion > bilaterality proportion; (2) bilaterality proportion > right-hemisphere lateralization proportion; and (3) right-hemisphere proportion within 0.2% of bilaterality proportion. The set of matrices in each group were then examined to investigate whether there is a relationship between the way these two proportions vary with respect to one another and the articles’ definitions of the categories. No pattern was found among these sets of matrices that could account for the variance.
Conclusion: This collection of Wada studies suggests that the prevalence of language bilaterality is approximately 9.8% in the populations they investigated. While the analysis of the matrices generated in this study did not yield a clear pattern in matrix configuration and the variance of right-hemisphere lateralization and bilaterality with respect to one another, laterality matrices may still be useful for future research, as they provide a means of graphically comparing disparate definitions of laterality categories. | en_US |
