The differential contribution of mental tracking, cognitive flexibility, visual search, and motor speed to performance on parts A and B of the Trail Making Test.

Ninety-eight undergraduate students were subjected to the TMT as well as a series of derived measures from the TMT with a view to ascertaining the nature of the contribution of each to the performance. Performance on the TMT(A) was uniquely contributed to by visual search and motor speed measures, whereas the performance on TMT(B) was uniquely contributed to by the visual search and cognitive alternation measures. After controlling for the effects of TMT(A) on TMT(B), further variance in the score on TMT(B) was contributed to, in order of effect, by lowered reading level, poor skill in visual search, poor ability to mentally maintain two simultaneous sequences, as well as decrease in attention and working memory functions. The analysis indicates that, in a nonclinical sample, the TMT measures a number of different functions and the observation of impaired performance must be further investigated to ascertain the specific nature of these deficits in order to guide rehabilitation and management planning.