Multidimensional scaling analyses of two construction-related tasks.

Representations involved in two construction-related tasks were analyzed by multidimensional scaling (MDS), a statistical technique that allows the dimensions of internal representations to be derived from empirically obtained judgment data. The tasks involved judgments of how similar two objects were and how well they fitted together; these judgments are related to copying and assembly abilities that are impaired in constructional apraxia. Analyses of numerical subjective ratings and response times for these judgments showed that within the same set of geometric objects, different shape-related properties were emphasized under different task conditions. The similarity judgment depended most on a representational dimension related to enclosure of space, while the fit judgment depended to a greater extent on a dimension related to the objects' symmetry properties. This pattern of results was found in both subjective ratings and response times, as analyzed by MDS and by confirmatory classical statistics. The findings suggest that construction-related tasks depend on representations that are context-dependent, and that MDS may be useful in a variety of settings as an intermediate-level tool for analyzing representations related to context-specific abilities.