Error analysis at the level of single moves in Block Design.

The method of error analysis has been fruitfully applied to the performance of brain-damaged patients in a number of different domains. This approach has also been used for investigating the visuo-constructional abilities of neurological patients, but only in a limited fashion. In the present work we applied error analysis to the performance of three patients, each showing a different pattern of errors, and 12 controls on a modified version of the WAIS Block Design task. Data were collected about the single moves made by the subjects to arrive at a copy of the model, and errors were classified using 14 categories. The error patterns of the three patients were found to be reliably different and so putatively suggest different processing impairments. Patient BV showed errors possibly reflecting the lack, or absence, of a plan during the reproduction attempt. Patient GP mainly showed errors reflecting impairment in the processing of metric spatial relations, while patient VQ's errors were those predicted by impaired mental rotation ability. Overall, we showed that Block Design performance can be used productively in the investigation of spatial processing by means of the single-case approach.