Hemisphere asymmetry in schizophrenia as revealed through line bisection, line trisection, and letter cancellation.

Individuals with schizophrenia are known to demonstrate reduced or reversed brain asymmetry. While much is known regarding anatomical brain asymmetry, little is known about how this affects the individual at the functional level. Based on the known leftward bias in normal individuals, the aim of this study was to explore whether any difference in this function would be noted in schizophrenia. This study therefore investigated the phenomenon of functional asymmetry in schizophrenia patients by means of the following tasks: line bisection, line trisection (assessing hemifield spatial neglect) and letter cancellation (assessing contralateral visuospatial exploration). Forty-five schizophrenia inpatients maintained on antipsychotic medication were evaluated. Transections were measured for accuracy, lateralization, and directional bias. In the line bisection task subjects indicated no pseudo-neglect, thus differing from a normal, leftward bias. In the line trisection there was a significant preference to perform the ambiguous instruction on the right side, with no consistent bias in accuracy. Irrespective of conditions, in the letter cancellation task there was always a significant tendency to succeed on the left third compared to the right third. Results may support findings in schizophrenia indicating decreased or altered function of the left hemisphere.