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 cross-over. 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.
Adair
J C
JC
Department of Neurology, University of New Mexico Health Sciences Center, USA. Adair.John@Albuquerque.VA.Gov
Chatterjee
A
A
Schwartz
R L
RL
Heilman
K M
KM
D000328:Adult; D002544:Cerebral Infarction / Q000000981:diagnostic imaging / Q000523:psychology*; D003072:Cognition Disorders / Q000000981:diagnostic imaging / Q000523:psychology*; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D009483:Neuropsychological Tests; D014057:Tomography, X-Ray Computed