Ipsilateral neglect: Reversal of bias or exaggerated cross-over phenomenon?

When right brain injury produces contralesional neglect (CN), patients typically misbisect lines to the right. However, others demonstrate so-called "ipsilateral neglect" (IN) with misbisection to the left of midpoint. Paradoxically, most patients with CN also demonstrate a "cross-over" phenomenon whereby they misbisect short lines to the left. It is not known whether patients with IN actually have a contralesional bias opposite the ipsilesional bias observed with CN, or if their performance reflects an exaggerated crossover. These alternatives can be distinguished by power function analysis which evaluates the relationship between magnitude of perception and stimulus magnitude. Using line bisection tasks to derive a power function, an IN patient showed a reduced exponent (beta=0.841), falling outside 95% confidence intervals (CI) for controls but within the CI for CN patients. The IN patient showed a greatly increased constant (K=7.82), extending outside the CI for both controls and CN patients. The results suggest that the anomalous leftward misbisection with IN is associated with an exaggerated cross-over point and not simply reversal of spatial bias.