The Yin and the Yang of visuo-spatial neglect: a case study.

We report a patient (R.B.) who has shown gross left visuo-spatial neglect over the 3 years since he sustained a right parietal infarct. Although his neglect is severe on such tasks as line bisection, cancellation, and drawing, there are some domains of preserved perceptual performance: he can perceive subjective contours, he can use lateral symmetry as a cue to figure-ground segregation, and he benefits from some forms of global cueing. In a series of five experiments, we show that R.B. has a selective inability to analyse and copy accurately the left contours of geometric nonsense-figures. These results hold even when there is a single vertical contour (to be copied) that divides a rectangle or a circle into two sub-figures; this physically-identical boundary is copied more accurately when it is cued as the right edge of the left sub-figure than when it is cued as the left edge of the right sub-figure. These effects are not influenced by a manipulation in which R.B. is required to trace the outline of the relevant sub-figure with his finger immediately prior to drawing his copy. The results are interpreted in terms of classical Gestalt theories of figure-ground assignment. Pre-attentive (global) figure-ground parsing is basically intact; but when focal attention is demanded, only the right side of an object is coded as figure.