Trail Making Test

Version: v1 (current)

A neuropsychological assessment of visual attention, processing speed, task switching, and executive function through number and letter sequencing.

Overview

The Trail Making Test (TMT) is one of the most widely used neuropsychological instruments worldwide. It consists of two parts: Part A requires connecting numbered circles in ascending order (1-2-3...), measuring processing speed and visual scanning. Part B requires alternating between numbers and letters in sequence (1-A-2-B-3-C...), adding a cognitive switching component that taps executive function.

The difference between Part B and Part A completion times (B-A) provides a relatively pure measure of executive function (task switching and mental flexibility) while controlling for processing speed. The TMT is sensitive to brain injury, dementia, ADHD, and normal aging, making it valuable for clinical assessment and cognitive screening.

Originally developed for military personnel assessment, the TMT has been validated across countless studies and is included in virtually all comprehensive neuropsychological batteries.

Scientific Background

Classic Findings:

Part A (Numbers Only): Mean completion time ~25-30 seconds in healthy adults
Part B (Number-Letter Switching): Mean completion time ~60-75 seconds in healthy adults
B-A Difference: Mean ~40 seconds; represents executive function "cost"
Error Rate: Healthy adults make 0-1 errors; increased errors suggest executive dysfunction
Age Effects: Strong age gradient; older adults significantly slower, especially on Part B
Brain Sensitivity: Sensitive to frontal lobe damage, diffuse injury, white matter disease

Key Mechanisms:

Processing Speed: Visual scanning and motor speed (Part A)
Task Switching: Alternating between number and letter sequences (Part B)
Working Memory: Maintaining two sequences simultaneously
Cognitive Flexibility: Shifting between mental sets
Visual Search: Locating next target among distractors

Seminal Papers:

Reitan (1958): Validity of the Trail Making Test
Lezak, Howieson, Bigler, & Tranel (2012): Neuropsychological Assessment (comprehensive review)
Sánchez-Cubillo et al. (2009): Construct validity of Trail Making Test: Role of task-switching

Why Researchers Use This Task

Neuropsychological Assessment: Screen for cognitive impairment across disorders
Dementia Screening: Sensitive to early Alzheimer's disease and MCI
Executive Function: Measure task-switching and mental flexibility
Traumatic Brain Injury: Assess recovery and persistent deficits
ADHD Assessment: Evaluate attention and executive control
Aging Research: Track cognitive decline across lifespan
Clinical Trials: Outcome measure for cognitive interventions

Current Implementation Status

Fully Implemented:

✅ Part A (numbers 1-25)
✅ Part B (alternating numbers 1-13 and letters A-L)
✅ Completion time measurement
✅ Error detection and correction tracking
✅ Touch/mouse drawing of paths
✅ Practice trials

Partially Implemented:

⚠️ Digital format (not pen-and-paper; may affect norms)
⚠️ Fixed layouts (not multiple equivalent forms)

Not Yet Implemented:

❌ Automatic path validation (currently relies on participant honesty)
❌ Pressure/stylus sensitivity for motor analysis
❌ Multiple equivalent forms for repeat testing

Configuration Parameters

Part A Parameters

Parameter	Type	Default	Description
Part A Max Number	number	25	Highest number in sequence (standard = 25)
Part A Layout	string	'random'	Node position layout ('random', 'fixed')
Canvas Width (px)	number	800	Width of drawing area
Canvas Height (px)	number	800	Height of drawing area

Part B Parameters

Parameter	Type	Default	Description
Part B Max Number	number	13	Highest number in alternating sequence
Part B Max Letter	string	'L'	Highest letter (13 numbers + 12 letters = 25 total)
Part B Layout	string	'random'	Node position layout

Timing and Feedback

Parameter	Type	Default	Description
Show Timer	boolean	true	Display elapsed time during task
Immediate Error Feedback	boolean	true	Alert participant immediately on error
Auto Correct Errors	boolean	true	Allow correction by returning to previous node
Max Time Seconds	number	300	Maximum time before timeout (5 minutes)

Practice Configuration

Parameter	Type	Default	Description
Practice Mode	string	'mandatory'	Practice availability
Practice Part A Max	number	8	Practice: connect 1-8
Practice Part B Max	number	4	Practice: connect 1-A-2-B-3-C-4-D

Data Output

Markers

{
  "type": "part_start",
  "ts": "2024-01-01T00:00:01.000Z",
  "hr": 1234.56,
  "data": {
    "part": "A",
    "max_number": 25,
    "node_positions": [
      {"id": 1, "x": 120, "y": 450},
      {"id": 2, "x": 680, "y": 230},
      {"id": 3, "x": 240, "y": 680}
    ]
  }
}

Response Data

Node connected:

{
  "part": "A",
  "from_node": 5,
  "to_node": 6,
  "correct_next": true,
  "elapsed_ms": 12450,
  "total_errors": 0,
  "ts": "2024-01-01T00:00:13.450Z",
  "hr": 13684.56
}

Error:

{
  "part": "B",
  "current_node": 7,
  "attempted_node": "F",
  "correct_next": "D",
  "elapsed_ms": 45200,
  "error_count": 1,
  "ts": "2024-01-01T00:00:46.200Z",
  "hr": 46434.56
}

Summary Artifact

{
  "task_kind": "trail_making",
  "part_a": {
    "completion_time_seconds": 28.4,
    "errors": 0,
    "self_corrections": 1,
    "completed": true,
    "percentile": 50,
    "interpretation": "Average for age"
  },
  "part_b": {
    "completion_time_seconds": 72.1,
    "errors": 1,
    "self_corrections": 2,
    "completed": true,
    "percentile": 45,
    "interpretation": "Average for age"
  },
  "derived_scores": {
    "b_minus_a_seconds": 43.7,
    "b_divided_by_a": 2.54,
    "executive_function_interpretation": "Normal task-switching ability"
  },
  "path_data": [...]
}

Example Research Configurations

Standard Clinical Administration (Reitan Version)

Part A: Connect 1-25 in order
Part B: Alternate 1-A-2-B-3-C through 13-L
Layout: Randomly positioned nodes (different for each participant)
Timing: Record to nearest second
Errors: Immediate feedback, allow correction
Scoring: Time in seconds, number of errors

Dementia Screening Battery

Part A: Standard 1-25
Part B: Standard alternating
Administration: Part A first, brief rest, then Part B
Analysis: Compare to age-adjusted norms; B-A > 75s suggests impairment
Include: Error rate (>2 errors raises concern)

Longitudinal Study (Repeat Testing)

Baseline: Standard TMT
Follow-ups: Use equivalent forms with different layouts
Interval: Minimum 6 months between administrations
Analysis: Track change over time; increases >10 seconds = meaningful decline

Research Protocol (Computerized)

Version: Digital with touch/mouse input
Advantage: Precise millisecond timing, automated error detection
Caution: May not align with pen-and-paper norms
Analysis: Use computerized norms or compare within-subjects

Participant Experience

Instructions - Part A: "You will see numbered circles on the screen. Using your mouse/finger, draw a line connecting them in order: 1 to 2, 2 to 3, and so on. Work as quickly and accurately as you can."
Practice - Part A:
- See circles numbered 1-8 scattered on screen
- Click/touch 1, drag to 2, drag to 3... up to 8
- If error: "Oops! That's not the next number. Go back to [X]."
- Complete practice successfully
Main Task - Part A:
- See circles numbered 1-25
- Timer starts automatically
- Connect all numbers in sequence as fast as possible
- Timer stops when reaching 25
Instructions - Part B: "Now you'll see both numbers and letters. Connect them in alternating order: 1 to A, A to 2, 2 to B, B to 3, and so on."
Practice - Part B:
- See circles with 1, A, 2, B, 3, C, 4, D
- Connect in alternating order: 1-A-2-B-3-C-4-D
- Practice until correct
Main Task - Part B:
- See circles with 1-13 (numbers) and A-L (letters)
- Connect in alternating sequence: 1-A-2-B-3-C... 12-L-13
- Timer records completion time
Completion: "Task complete. Part A: [X] seconds. Part B: [Y] seconds."

Design Recommendations

General Guidelines

Order: Always administer Part A before Part B (standardization)
Practice: Mandatory for valid results; ensure understanding
Environment: Minimize distractions; quiet testing space
Equipment: Touch screen or mouse with precision
Instructions: Clear, consistent across participants

Scoring and Interpretation

Normative Data (Approximate, Healthy Adults 20-50 years):

Part A: Mean ~25-30 sec, SD ~8-10 sec
Part B: Mean ~60-75 sec, SD ~20-25 sec
B-A Difference: Mean ~40 sec, SD ~15 sec
Errors: 0-1 typical; 2+ suggests concern

Age-Adjusted Norms (critical for interpretation):

Ages 20-39: A ~22 sec, B ~52 sec
Ages 40-59: A ~28 sec, B ~72 sec
Ages 60-79: A ~40 sec, B ~110 sec
Ages 80+: A ~55 sec, B ~165 sec

Impairment Cutoffs (vary by source):

Mild Impairment: A >40 sec or B >110 sec (for ages 20-59)
Moderate Impairment: A >60 sec or B >180 sec
Severe Impairment: A >90 sec or B >300 sec (timeout)
Executive Dysfunction: B-A >75 sec or errors >2

Population-Specific Adaptations

Children (Ages 8-15):

Part A: 1-15 (fewer nodes)
Part B: 1-A through 8-H
Slower expected times; use pediatric norms
More practice trials tolerated

Older Adults (75+):

Standard version appropriate
Allow generous time limit (no pressure)
Very sensitive to white matter disease
Expect 2-3x longer than young adults

Low Education/Literacy:

Part A less affected by education
Part B may be more challenging
Ensure familiarity with alphabet sequencing
Use education-adjusted norms

Clinical Populations:

Alzheimer's: Dramatically slowed, especially Part B; many errors
Frontal Lobe Damage: Severe Part B deficit; B-A often >100 sec
ADHD: Moderately slowed; more errors on B
Depression: Slowed but fewer errors; improves with treatment
Parkinson's: Slowed motor speed; B-A ratio often normal

Common Issues and Solutions

Issue	Solution
Participant lifts pen/finger	Instruct to maintain continuous path; doesn't invalidate if rare
Many errors on Part B	Repeat instructions; ensure understanding of alternation
Very slow but accurate	Normal strategy; record time; don't pressure for speed
Fast but errors ignored	Emphasize accuracy as well as speed in instructions
Digital vs. paper norms	Use digital-specific norms or compare within-subjects
Learning effects (retest)	Use alternate forms; wait 6+ months between administrations

Data Analysis

Primary Outcomes:

Time to Completion: Part A, Part B (in seconds)
Error Count: Total errors on each part
B-A Difference: Executive function index
B/A Ratio: Alternative executive measure (less age-sensitive)

Secondary Measures:

Self-Corrections: Errors caught and fixed by participant
Path Efficiency: Total path length (if tracking X-Y coordinates)
Segment Times: Time between each node pair
Velocity Changes: Speed-up or slow-down patterns

Statistical Considerations:

Age Adjustment: Critical; use age-stratified norms
Education Adjustment: Some norms adjust for education level
Outliers: Ceiling at 300 seconds (timeout) for statistical analysis
Skewness: Times are positively skewed; consider log transformation

References

Reitan, R. M. (1958). Validity of the Trail Making Test as an indicator of organic brain damage. Perceptual and Motor Skills, 8(3), 271-276.
Lezak, M. D., Howieson, D. B., Bigler, E. D., & Tranel, D. (2012). Neuropsychological Assessment (5th ed.). Oxford University Press.
Tombaugh, T. N. (2004). Trail Making Test A and B: Normative data stratified by age and education. Archives of Clinical Neuropsychology, 19(2), 203-214.
Sánchez-Cubillo, I., Periáñez, J. A., Adrover-Roig, D., Rodríguez-Sánchez, J. M., Ríos-Lago, M., Tirapu, J., & Barceló, F. (2009). Construct validity of the Trail Making Test: Role of task-switching, working memory, inhibition/interference control, and visuomotor abilities. Journal of the International Neuropsychological Society, 15(3), 438-450.
Arbuthnott, K., & Frank, J. (2000). Trail Making Test, Part B as a measure of executive control: Validation using a set-switching paradigm. Journal of Clinical and Experimental Neuropsychology, 22(4), 518-528.

Overview​

Scientific Background​

Why Researchers Use This Task​

Current Implementation Status​

Configuration Parameters​

Part A Parameters​

Part B Parameters​

Timing and Feedback​

Practice Configuration​

Data Output​

Markers​

Response Data​

Summary Artifact​

Example Research Configurations​

Standard Clinical Administration (Reitan Version)​

Dementia Screening Battery​

Longitudinal Study (Repeat Testing)​

Research Protocol (Computerized)​

Participant Experience​

Design Recommendations​

General Guidelines​

Scoring and Interpretation​

Population-Specific Adaptations​

Common Issues and Solutions​

Data Analysis​

References​

See Also​