Attentional load and visual neglect.

Ten subjects suffering from left unilateral neglect carried out a letter cancellation task under normal conditions, while counting forward, and when generating random numbers, respectively. The index of neglect increased with each of these conditions, though only the normal-random difference was statistically significant. In a second study, four left unilateral neglect subjects and four right brain-damaged controls carried out a simple reaction time task, with stimuli appearing randomly to the left and right, with and without the simultaneous performance of a secondary task (counting backward in threes from 100). The discrepancy between left versus right latencies increased significantly in the secondary task condition for two patients in the neglect group but not for the other two. None of the control group showed this effect. Theoretical implications of these findings for understanding neglect are discussed.