Abstract
Planning on the 4-disk version of the Tower of London (TOL4) was examined in stroke patients and unimpaired controls. Overall TOL4 solution scores indicated impaired planning in the frontal stroke but not non-frontal stroke patients. Consistent with the claim that processing the relations between current states, intermediate states, and goal states is a key process in planning, the domain-general relational complexity metric was a good indicator of the experienced difficulty of TOL4 problems. The relational complexity metric shared variance with task-specific metrics of moves to solution and search depth. Frontal stroke patients showed impaired planning compared to controls on problems at all three complexity levels, but at only two of the three levels of moves to solution, search depth and goal ambiguity. Non-frontal stroke patients showed impaired planning only on the most difficult quaternary-relational and high search depth problems. An independent measure of relational processing (viz., Latin square task) predicted TOL4 solution scores after controlling for stroke status and location, and executive processing (Trail Making Test). The findings suggest that planning involves a domain-general capacity for relational processing that depends on the frontal brain regions.
Highlights
Planning is important in many areas of life and impairments in this capacity have adverse implications for independent living (Jefferson et al, 2006)
The research investigated the claim that processing the relations between current states, intermediate states, and goal states is a key process in planning (Halford et al, 1998) and that the complexity of these relations is a good indicator of the experienced difficulty of the Tower of London (TOL) problems
The overall solution scores provided evidence of impairment but only in those whose strokes resulted in damage to frontal regions of the brain
Summary
Planning is important in many areas of life and impairments in this capacity have adverse implications for independent living (Jefferson et al, 2006). The goal is to transform the initial configuration (Figure 1A) into the target configuration (Figure 1B) in which yellow and white are on pole 1 and black and blue disks are on www.frontiersin.org disk to pole 3, shift(Y, 3), which is binary-relational, as in the previous example. In a more complex problem, the goal is to transform the initial configuration (Figure 1A) into the target configuration (Figure 1C) in which all four disks are on pole 3 in the top-down order yellow, white, blue, and black. If the LST accounts for variance in TOL4 performance over and above the TMT this would further support the view that TOL4 involves complex relational processing
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