Attentional control and slowness of information processing after severe traumatic brain injury.

Attention is a basic cognitive function and a prerequisite for other cognitive processes and is frequently impaired after traumatic brain injury. In the present study, 29 severe traumatic brain injury patients and 30 control subjects completed a battery of three neuropsychological tests of attention (WCST, TMT, Stroop). The aim was to clarify the attentional mechanisms underlying tests performance and to explore the types of attentional impairment after severe traumatic brain injury. Significant differences were found between the control and clinical groups in almost all measures. However, some of these differences disappeared when the speed of information processing was controlled using covariance analysis. In addition, a factor analysis revealed a four-factor solution explaining 89.6% of the variance in the data, i.e. cognitive flexibility, speed of processing, interference and working memory. This result supports the view of at least four different subprocesses of attentional control underlie test performance and allows one to differentiate between high- and low-level processes. The implications for neuropsychological assessment and rehabilitation are discussed.