Cognitive | Executive Function

Trail Making Test

Connect the circles in the correct sequence. Part A tests visual scanning; Part B tests cognitive flexibility by alternating numbers and letters.

~29s

Normal Part A

~75s

Normal Part B

B/A ratio

Flexibility index

980K+

Scores recorded

Part: —

Next: —

Errors: 0

Time: 0.0s

The Trail Making Test

The Trail Making Test was first developed in 1944 by John Partington and Raymond Leiter as the "Divided Attention Test," later incorporated into the Halstead-Reitan Neuropsychological Battery in the 1950s. It remains one of the most widely used neuropsychological instruments in clinical practice, appearing in evaluations of traumatic brain injury, dementia, ADHD, and post-surgical recovery.

The test's elegance lies in its simplicity: two sheets of paper, circles with numbers or letters, and a pencil. Despite the minimal materials, it yields remarkably rich information about neural processing. Today it is included in major assessment batteries including the WAIS, Delis-Kaplan Executive Function System (D-KEFS), and the Neuropsychological Assessment Battery (NAB).

For a broader look at cognitive flexibility and reflective thinking, our Cognitive Reflection Test measures a complementary dimension of executive function.

Part A vs Part B: What Each Measures

Part A — Visual Scanning Speed

Connect numbers 1 through 25 in ascending order. Measures basic visual-motor processing speed and the ability to scan a visual field systematically. Primary neural correlates include the occipito-parietal visual search network and dorsal attention stream.

Normal range: 20–40 seconds (ages 20–49)

Part B — Cognitive Flexibility

Alternate between numbers and letters (1→A→2→B...). Requires simultaneous task-switching and set-shifting — a core executive function. Engages the dorsolateral prefrontal cortex and anterior cingulate cortex. Part B is sensitive to frontal lobe damage and aging.

Normal range: 55–105 seconds (ages 20–49)

The B minus A difference isolates the cognitive flexibility cost by controlling for basic motor and scanning speed. A large B–A difference suggests executive function impairment even when Part A speed is normal. This is also why the Mini IQ Test includes a separate executive function sub-score.

Score Distribution

Part A Completion Time (seconds)

Age Group	Part A (Normal)	Part B (Normal)	B/A Ratio
20–29	21–36s	45–80s	~2.2
30–39	23–40s	50–90s	~2.3
40–49	25–45s	60–100s	~2.4
50–59	30–55s	70–120s	~2.6
60–69	38–70s	90–160s	~2.8
70+	45–100s	120–240s	~3.0+

B/A Ratio and Executive Function

The B/A ratio is calculated by dividing Part B time by Part A time. Because Part A and Part B share the same visual search component, the ratio isolates the additional cognitive cost of task-switching. A ratio below 3.0 is generally considered within the normal range across adult age groups.

1.5–2.5 Excellent executive function. Fast task-switching, minimal cognitive cost of alternating sequences.

2.5–3.5 Normal range. Typical cognitive flexibility for most adults. Age-related increases expected.

>4.0 Elevated ratio. May indicate executive dysfunction, frontal lobe involvement, or significant test anxiety. Requires clinical context.

This ratio is relevant to the broader family of processing speed tests on this platform — elevated B/A ratios often co-occur with slower processing speed scores.

How to Improve Processing Speed

Aerobic exercise (150 min/week)

Aerobic exercise consistently improves processing speed across all ages, with effect sizes of 0.3–0.5 in meta-analyses. The mechanism involves increased cerebral blood flow, BDNF-driven hippocampal neurogenesis, and enhanced white matter integrity — the same white matter tracts that support rapid trail-making performance.

Dual-task and task-switching practice

Practicing tasks that require switching between two rules — like playing a musical instrument, bilingual language use, or specific cognitive training games — directly trains the prefrontal circuits that mediate Part B performance. Regular practice in task-switching reduces switch costs by 15–25%.

Optimize sleep architecture

Processing speed is disproportionately impaired by sleep deprivation. Even a single night of less than 6 hours increases Trail Making B times by 20–35%. Sleep spindles during stage 2 NREM sleep consolidate procedural and executive memories — protecting both the speed and flexibility components of TMT performance.

Learn a new complex skill

Learning novel complex skills — a new language, a musical instrument, coding — drives white matter myelination in the corpus callosum and frontal projection fibers that support rapid information processing. Studies show 6 months of skill learning measurably improves processing speed test performance in adults up to age 70.