Modality-specific and supramodal mechanisms of apraxia

This study investigated the relation of apraxia to the nature of the stimulus which is given to elicit the gesture. Patients were required to perform a movement imitation test and to demonstrate the use of the same ten objects, once on verbal command, once with the object shown but not handled, and once with the object handled but not seen. One set of comparisons concerned the performance on two tasks involving the visual modality, movement imitation and use of objects presented visually. Although the majority of left brain-damaged patients either failed or passed both tests, there were at least 13 patients who showed an exceedingly poor performance on demonstration of use as compared to imitation. We infer that the distinction between ideational and ideomotor apraxia is warranted. Another set of comparisons concerned the performance on the use of objects presented in the verbal, visual and tactile modalities. A greater percentage of patients failed on the verbal or visual modalities than on the tactile modality. Out of 64 left brain-damaged patients who were diagnosed as apraxic in at least one modality, 23 had an exceedingly poor score on one test as compared to their score on either or both other tests. Fourteen patients selectively failed on verbal presentation, 14 on visual presentation and 2 on tactile presentation. These findings are viewed as supporting the hypothesis that apraxia results from the disconnection between the areas where information is processed and the areas where the movement is programmed.