PSYCHOPHYSICAL CONSTRAINTS ON BEHAVIOR IN UNILATERAL SPATIAL NEGLECT

The relationship between subjective sensations and objective measures of stimuli producing these sensations is normally systematic and described by a power function, psi = Kphi(beta), in which psi represents the psychological value and phi the physical value. The effect of damage to the central nervous system on this psychophysical power function is not known. Sixteen unselected patients with right brain damage and 16 age and gender-matched normal control subjects were tested on horizontal line bisection tasks to determine the relationship between awareness of linear extent and the length of line presented. The performance of all of these subjects conformed to power functions. Normal subjects had an exponent close to 1, whereas right brain damaged patients had decreased (average: 0.8) exponents. These results indicate that despite dramatic alterations in sensory awareness associated with right brain damage behavior continues to be constrained by psychophysical principles in specific ways. Describing line bisection performance as a power function provides a method to quantify the deficit in neglect with precision, and places neglect behavior on a scale that is continuous with but deviates from normal psychophysical processing.