Line bisection and neglect severity

The relationship between (horizontal) line length and bisection accuracy continues to be of theoretical interest in the study of visuospatial neglect. In a recent paper, Koyama, Ishiai, Seki and Nakayama (1997) claim that line bisection performance by patients with severe neglect is "not only quantitatively but also qualitatively different" from that of patients with moderate or mild neglect. In particular, they argue that line length does not control bisection displacements in severe neglect. Contrary to that position, I first demonstrate that the conclusion of Koyama et al. (1997) does not follow from their own data; second, I describe empirical results showing that bisection displacement in severe neglect is exquisitely sensitive to line length. The standard psychophysical models of line bisection in visuospatial neglect are not falsified by the results of Koyama et al.