The Trail Making Test: How Neuropsychologists Measure Executive Function

The Trail Making Test (TMT) originated in the Army Individual Test Battery in 1944 and was adapted into civilian neuropsychology by Ralph Reitan in the 1950s. It remains one of the most commonly administered neuropsychological tests worldwide, despite its simplicity — connecting circles on a page with a pencil.

Part A asks the participant to connect numbered circles (1→2→3…25) as quickly as possible. Part B asks them to alternate between numbers and letters (1→A→2→B→3→C…). Both parts are timed. The test is used to screen for cognitive impairment, assess recovery from traumatic brain injury, and monitor the cognitive effects of medications.

Part A primarily measures visual scanning speed and psychomotor processing speed — how quickly you can locate the next target in a spatially disordered array and draw a line to it. Part B additionally requires cognitive set-shifting: mentally alternating between two sequences (numbers and letters) while maintaining the position in each independently.

The B-minus-A difference score is the key clinical metric. It represents the cognitive cost of set-shifting over and above basic visual scanning. Elevated B-A times are associated with frontal lobe damage, attention deficit disorders, and early dementia, even when Part A performance is normal.

Set-shifting — the cognitive operation uniquely taxed by Part B — is a component of executive function, the family of higher-level cognitive processes that manage and coordinate other mental operations. It's the same ability engaged when you stop one task and begin another, when you update a plan in response to new information, or when you suppress a habitual response in favour of a new one.

Executive function is among the strongest predictors of academic achievement, occupational success, and physical health across the lifespan — stronger than IQ in some longitudinal studies. Trail Making B performance correlates substantially with real-world measures of executive function and daily living competence.

Visual scanning efficiency improves with practice through two mechanisms: faster target recognition (distinguishing a '7' from a 'T' at a glance) and better spatial memory for already-visited locations (reducing re-scanning of completed areas). Both improve with repetition.

Set-shifting speed improves through tasks that require frequent, deliberate switching between competing response sets. Task-switching paradigms, dual-task practice, and activities requiring attention alternation (sport, musical improvisation, debate) all appear to produce modest set-shifting gains.