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Recent research in comparative psychology suggests that similarities between the behaviour of two individuals may not be the consequence of imitation only, but also of nonimitative social-learning processes. In the present study we aimed to investigate whether these alternative learning processes can take place in human adults, specifically in patients whose ability to imitate has been reduced by brain damage. Left (LBD) and right (RBD) brain-damaged patients were asked to perform four tool use tasks in three experimental conditions: exposure to the apparatus (N); demonstration of the correct solution (C); and demonstration of a failed attempt followed by the correct solution to the problem (I + C). Results suggest that the left hemisphere is indeed critical for action and that selective neuropsychological deficits can affect action imitation and selection of goal-directed movements, independently from each other. Findings also indicate that when the ability to imitate actions is lowered emulation may become available. [ABSTRACT FROM AUTHOR]

We propose STIMA, a short test for ideo-motor apraxia, allowing us to quantify the apraxic deficit according to action meaning and affected body segment. STIMA is based on a neurocognitive model holding that there are two processes involved in action imitation (i.e., a semantic route for recognizing and imitating known gestures, and a direct route for reproducing new gestures). The test allows to identify which imitative process has been selectively impaired by brain damage (direct vs. semantic route) and possible deficits depending on the body segment involved (hand/limb vs. hand/fingers). N = 111 healthy participants were administered with an imitation task in two separated blocks of known and new gestures. In each block, half of the gestures were performed mainly with the proximal part of the upper limb and the remaining half with the distal one. It resulted in 18 known gestures (nine proximal and nine distal) and 18 new gestures (nine proximal and nine distal) for a total of 36. Each gesture was presented up to a maximum of two times. Detailed criteria are used to assign the final imitation score. Cut offs, equivalent scores and main percentile scores were computed for each subscale. Participants imitated better known than new gestures, and proximal better than distal gestures. Age influenced performance on all subscales, while education only affected one subscale. STIMA is easy and quick to administer, and compared to previous tests, it offers important information for planning adequate rehabilitation programs based on the functional locus of the deficit. [ABSTRACT FROM AUTHOR]

Normally we can perform a variety of goal-directed movements effortlessly. However, damage to the parietal cortex may dramatically reduce this ability, giving rise to optic ataxia and limb apraxia. Patients with optic ataxia show clear misreaches towards targets when presented in the peripheral visual field, whereas limb apraxia refers to the inability to use common tools or to imitate simple gestures. In the present paper we describe the case of a left-brain damaged patient, who presented both symptoms. We systematically investigated both spatial and temporal parameters of his movements, when asked to reach and grasp common objects to move (Experiment 1) or to use them (Experiment 2), presented either in the central or peripheral visual field. Different movement parameters changed in relation to the goal of the task (grasp to move vs. grasp to use), reflecting a normal modulation of the movement to accomplish tasks with different goals. On the other hand, grip aperture appeared to be more affected from both task goal and viewing condition, with a specific decrement observed when CF was asked to use objects presented peripherally. On the contrary, a neat effect of the viewing condition was observed in the spatial distribution of the end-points of the movements, and of the horizontal end point in particular, which were shifted towards the fixation point when reaching towards peripheral targets. We hypothesized that optic ataxia and limb apraxia have a differential effect on the patient’s performance. The specific presence of optic ataxia would have an effect on the movement trajectory, but both symptoms might interact and influence the grasping component of the movement. As a ‘cognitive side of motor control impairment’, the presence of limb apraxia may have increased the task demands in grasping to use the objects thus exacerbating optic ataxia. [ABSTRACT FROM AUTHOR]