While seeking new functional methods to reassess the concept of hemisphericity, a two-hand line-bisection task was investigated because of reports of large, stable differences among the general population. These were found to be due to hemispheric differences in judgment of the midpoint of horizontal lines, made visible due to the unilateral brain control of each hand. By use of a two-hand line-bisection test (Best-Hand Test), university workers (n=412) were readily sorted into theoretical response categories, resulting in the production of two large groups. These two groups correlated well with those produced by four independent hemisphericity assessments, two physiological and two psychological. This is the third biophysical method whose performance-based group separations significantly correlated with those produced by preference-based hemisphericity-type questionnaires. It is rapid and avoids language, education, or cultural bias.