ABSTRACT
Apraxia has repeatedly been considered a pathology of the learned gesture, but there are not many studies that document a defective capacity of motor learning in apraxic patients. The functions of encoding, retrieval, and storage have seldom been separately studied, and the evidence for their failure collected up to now is scarce and only indirect.
Our purpose was to identify whether and which of these functions are impaired in apraxic patients. We used a two-stage learning model. The parameters of the learning function were estimated by the method of maximum likelihood in a Markov chain where the learning process is viewed as a series of changes of state governed by transition probabilities, from a state of complete ignorance to that of complete memorization.
Three experimental groups were studied: control subject without damage to the central nervous system, right-hemisphere-damaged patients, and left-hemisphere-damaged patients, subdivided for presence/absence of apraxia. Subjects had to learn an 8-item list of gestures (4 symbolic and 4 nonsymbolic), and a list of 4 paired-associate gestures (2 symbolic and 2 nonsymbolic). The selective reminding technique of Buschke-Fuld was used. Results indicate that: (a) Right-hemisphere-damaged patients do not perform dif838ferently from normal controls; (b) symbolic and nonsymbolic gestures are not differentially learned; (c) failure of apraxic patients in learning gestures is specifically related to failure in encoding and storage of the engram of the gesture.
