The effect of ipsilesional cues on line-bisection errors: the importance of predictive value.

Patients with unilateral neglect were tested on a line-bisection task in which vertical lines were added to the ipsilesional or contralesional end. During some blocks, these vertical lines accurately predicted the horizontal length of the line, while on other blocks the vertical lines had little predictive value. We found that much of the improvement for ipsilesional vertical bars can be explained by their ability to predict the extent of the horizontal line. These results suggest that the predictive value of a ipsilesional cue is responsible for the reduction in line-bisection errors noted by Halligan and Marshall [Neuropsychologia 32 (1994) 13]. This effect of the predictive ipsilesional cue may work in combination with the expanded attentional effects posited by the ipsilesional contraction model that they proposed.