Tower of London Task (ToL)

Background

The Tower of London Task (ToL) was developed in 1982 by Tim Shallice at University College London to investigate planning deficits in patients with frontal lobe lesions. The ToL is a "look-ahead" task that requires a problem to be decomposed into a series of subgoals, some of which may seem to take one further from the final goal.

The ToL is an adaptation of the classic Tower of Hanoi (ToH) puzzle invented in 1883 by French mathematician Édouard Lucas. The task requires respondents to rearrange 3 objects of different colors from their current positions on 3 pegs to a different configuration. The ToL differs from the ToH in two ways. Whereas the ToH uses disks of different sizes with the rule that larger disks can not be placed above smaller disks, the ToL uses balls of the same size. Whereas each peg in the ToH can hold 3 disks, the ToL uses different sized pegs that can hold at most 1, 2, or 3 balls, respectively.

Task Procedure

The participant is presented with gameboard featuring a red, green, and blue ball positioned on 3 pegs along with an image of the balls in different positions (the goal). Participants must re-arrange the balls into the goal positions using as few moves as possible. Only the topmost balls on each peg can be moved.

The participant is presented 1 practice problem and 12 test problems of increasing difficulty. For each problem, a running tally of executed moves is displayed along with the maxium number of moves allowed (the ideal solution for each problem). If the participant uses up the allowed moves without solving the problem, the problem is reset and the participant starts over. After success or 3 failed attempts, the task moves on to the next problem. Participants can also skip a problem by pressing the Next button.

What it Measures

The ToL is not diagnostic of any single condition, but rather a general assessment of executive functioning.

Psychological domains

• Executive Functioning
• Planning: Requires generating and maintaining a plan while looking ahead multiple steps
• Problem-Solving, Strategic Thinking: Identifying the most efficient solution ahead of time rather than through trial-and-error
• Working Memory: Holding and manipulating the current configuration, goal state, and intermediate steps online
• Cognitive Flexibility: Adjusting plans when initial strategies fail
• Inhibitory Control / Response Inhibition: Avoiding moves that seem intuitively correct but violate rules or increase total moves

Main Performance Metrics

• Total Score: Planning efficiency (3 points per problem less the number of failed attempts)
• Mean Planning Time: Speed of planning (latency before the first move)
• Mean Execution Time: Speed of plan implementation (latency between first move and solution)
• Mean Solution Time: Planning and execution time
• Rule Violations: Inhibitory control

Psychiatric Conditions

Performance tends to be impaired in patients with the following conditions.

• Schizophrenia
• Traumatic Brain Injury (TBI)
• Parkinson’s Disease
• Eating Disorders
• Dementia
• Attention Deficit Hyperactivity Disorder (ADHD)
• Autism Spectrum Disorder

Available Test Variations

References

Search Google Scholar for peer-reviewed, published research using the Inquisit Tower of London Task (ToL).

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Shallice, T. (1982). Specific impairments of planning. Philosophical Transcripts of the Royal Society of London, B298, 199–209.

Krikorian, R., Bartok, J. & Gay, N. (1994) Tower of London procedure: a standard method and developmental data. Journal of Clinical Experimental Neuropsychology, 16, 840–850.

Anderson, P., Anderson, V., & Lajoie, G. (1996). The Tower of London test: Validation and standardization for pediatric populations. The Clinical Neuropsychologist, 10, 55 - 65.

Schnirman, G.M., Welsh, M.C., Retzlaff, P.D. (1998). Development of the Tower of London-Revised. Assessment, 5, 355–360.

Delis, D. C., Kaplan, E., & Kramer, J. H. (2001). Delis- Kaplan executive function system: Technical manual. San Antonio, TX: Psychological Corporation.

Berg, W. K. & Byrd, D. L. (2002) The Tower of London Spatial Problem Solving Task: Enhancing Clinical and Research Implementation. Journal of Experimental and Clinical Neuropsychology, 25, 586-604.