2-DIMENSIONAL CANCELLATION NEGLECT - A REVIEW AND SUGGESTED METHOD OFANALYSIS

Directional bias on cancellation has thus far not been standardized. W hile cancellation tasks are primarily used to assess lateral performan ce asymmetries, they may also reveal two-dimensional (i.e., combined l ateral and radial) neglect patterns. We propose a method to evaluate a nd report cancellation neglect regardless of whether the neglect patte rn is strictly unilateral or two-dimensional. Our method establishes t he location of the geographic center of all neglected stimuli relative to the page center by averaging their Cartesian coordinates. This ''n eglect center'' is reported in polar coordinates to indicate its dista nce and direction from the page center. We apply our method to publish ed examples of two-dimensional neglect. We find that neglect centers f rom different cancellation performances may not be statistically disti nct even though they may occupy different quadrants. In addition, the net direction of neglect found by the coordinate method may differ fro m that inferred from measuring differences in quadrant omission totals . The suitability of the coordinate vs. the quadrant method will depen d on the mechanism hypothesized for visuospatial exploration under par ticular test conditions. Using both approaches may detect different at tentional biases operating during the same task. The coordinate method is appropriate for conventional cancellation testing. By incorporatin g the precise locations of all neglected stimuli and determining the n et neglect direction in two dimensions, the technique may stimulate mo re comprehensive explanations for directional bias.