Effect of stimulus number, target-to-distractor ratio, and motor speed on visual spatial search quality following traumatic brain injury

The object of this study was to investigate stimulus effects and motor limitations on visuospatial performance after traumatic brain injury (TBI). Previous findings have not fully explained the basis of attentional impairments after TBI. There has been little study of the spatial aspects of attention and information processing in this group. We studied 20 patients after severe TBI and 21 healthy controls. Four random-array letter cancellation tasks, varying in number of stimuli (50 and 100) and target-to-distractor ratio (1:4 and 1:9) were employed. Performance was calculated from the number and proportion of cancelled targets, as well as time to completion. TBI subjects were slower on finger tapping and achieved lower cancellation performance scores. Both TBI subjects and controls performed better on tasks with target-to-distractor (T/D) ratios of 1:4 than on those with 1:9. There was no effect of stimulus number. We conclude that there are both quantitative (speed) and qualitative contributors to impaired visuospatial ability following TBI. Motor impairments may slow the overall cancellation performance, but the differential effect of T/D ratio in the two populations suggests that TBI impairs quality of research. Accounting for both speed and accuracy suggests increased utility for the cancellation paradigm in clinical and research assessment of visuospatial attention.