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 oi derived measures from the TMT with a view to ascertaini ng the nature of the contribution of each tc the performance. Performa nce on the TMT(A) was uniquely contributed to by visual search and mot or speed measures, whereas the performance on TMT(B) was uniquely cont ributed to by the visual search and cognitive alternation measures. Af ter controlling for the effects oi TMT(A) on TMT(B), further variance in the score on TMT(B) was contributed to, in order of effect, by lowe red reading level. poor skill in visual search, poor ability to mental ly maintain two simultaneous sequences, as well as decrease in attenti on and working memory functions. The analysis indicates that, in a non clinical sample, the TMT measures a number oi different functions and the observation of impaired performance must be further investigated t o ascertain the specific nature of these deficits in order to guide re habilitation and management planning. (C) 1998 John Wiley & Sons, Inc.