THE CROSS-OVER EFFECT IN UNILATERAL NEGLECT - MODELING DETAILED DATA IN THE LINE-BISECTION TASK

The line-bisection task is the standard assessment of unilateral visua l neglect. It supplies one effect, the crossover effect, that challeng es models of neglect: in left neglect, the rightward displacement of t he midpoint of the line becomes a left displacement for small lines. W e review the various attempts to account for the crossover effect, bef ore describing a computational model of performance in the line-bisect ion task that produces a cross-over effect quite naturally in its dama ged state. The model trades on aspects of several current theories of neglect, including independent attentional processing in the two hemis pheres, each of which possesses an attentional gradient in which the c ontralateral field is accentuated. We assume a small residual noise, a long the same gradient, in the damaged hemisphere. When lesioned to si mulate right hemisphere damage, the model produces line bisections sim ilar to human performance, in terms of the relationship with line leng th, a variable crossover point for the smaller lines, and an ameliorat ion of performance with leftside, but not rightside cueing.