Perception of self-generated movement following left parietal lesion.
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Three apraxic patients with lesions in the left parietal cortex were required to execute finger movements with either hand, while the visual feedback they received about the movement was manipulated systematically. We used a device which allowed us to present on a video monitor either the patient's hand or the examiner's hand simultaneously performing an identical or a different movement. In each trial, patients were required to decide whether the hand shown on the screen was their own or not. Hand movements produced in response to verbal command included simple (single-finger extension) and complex gestures (multi-finger extension). Ownership judgements were analysed and compared with those produced by six normal controls and two non-apraxic neurological patients. Apraxic patients and controls accurately recognized their own hand on the screen (own movement condition) and correctly identified the viewed hand as the examiner's when it performed a movement different from their own movement (incongruent movement condition). However, when the viewed hand was the examiner's hand executing their own movement (congruent movement condition), apraxic patients were significantly more impaired than controls. When the results were analysed as a function of gesture type, the number of correct responses was significantly lower for apraxic patients with respect to controls only for complex gestures. Interestingly, when patients executed the finger gestures inaccurately, they still failed to recognize the examiner's hand as alien, and claimed that the correct movement presented on the screen was their own. These results confirm that parietal lesions alter the representational aspects of gestures, and suggest a failure in evaluating and comparing internal and external feedback about movement. We conclude that the parietal cortex plays an important role in generating and maintaining a kinaesthetic model of ongoing movements. (+info)
The whole-hand point: the structure and function of pointing from a comparative perspective.
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Pointing by monkeys, apes, and human infants is reviewed and compared. Pointing with the index finger is a species-typical human gesture, although human infants exhibit more whole-hand pointing than is commonly appreciated. Captive monkeys and feral apes have been reported to only rarely "spontaneously" point, although apes in captivity frequently acquire pointing, both with the index finger and with the whole hand, without explicit training. Captive apes exhibit relatively more gaze alternation while pointing than do human infants about 1 year old. Human infants are relatively more vocal while pointing than are captive apes, consistent with paralinguistic use of pointing. (+info)
Cortical and subcortical contributions to ideomotor apraxia: analysis of task demands and error types.
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Ideomotor apraxia (IMA) is often associated with damage of the dominant parietal cortex, but many other lesion sites have been implicated suggesting that the praxis system is mediated by a distributed modular network. Although IMA has been reported with subcortical lesions, the role of subcortical structures in the praxis neural network has not been fully addressed. To ascertain the role of subcortical structures in praxis, we compared praxis performance on a variety of tasks in patients with left hemisphere cortical and subcortical lesions. The cortical patients presented with deficits in the production of transitive and intransitive gestures-to-verbal command and imitation, as well as impaired gesture discrimination. In contrast, the subcortical group demonstrated mild production-execution deficits for transitive pantomimes, but normal imitation and discrimination. Qualitative error analysis of production deficits, revealed that both patient groups produced timing errors and the full range of spatial errors. Whereas the subcortical group made more postural errors than the cortical group, sequencing, unrecognizable and no-response errors were only produced by the cortical group. The different profiles of praxis deficits associated with cortical and subcortical lesions, suggests that these structures may have different roles in praxis. (+info)
Differential use of vocal and gestural communication by chimpanzees (Pan troglodytes) in response to the attentional status of a human (Homo sapiens).
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This study examined the communicative behavior of 49 captive chimpanzees (Pan troglodytes), particularly their use of vocalizations, manual gestures, and other auditory- or tactile-based behaviors as a means of gaining an inattentive audience's attention. A human (Homo sapiens) experimenter held a banana while oriented either toward or away from the chimpanzee. The chimpanzees' behavior was recorded for 60 s. Chimpanzees emitted vocalizations faster and were more likely to produce vocalizations as their 1st communicative behavior when a human was oriented away from them. Chimpanzees used manual gestures more frequently and faster when the human was oriented toward them. These results replicate the findings of earlier studies on chimpanzee gestural communication and provide new information about the intentional and functional use of their vocalizations. (+info)
Pantomime to visual presentation of objects: left hand dyspraxia in patients with complete callosotomy.
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Investigations of left hand praxis in imitation and object use in patients with callosal disconnection have yielded divergent results, inducing a debate between two theoretical positions. Whereas Liepmann suggested that the left hemisphere is motor dominant, others maintain that both hemispheres have equal motor competences and propose that left hand apraxia in patients with callosal disconnection is secondary to left hemispheric specialization for language or other task modalities. The present study aims to gain further insight into the motor competence of the right hemisphere by investigating pantomime of object use in split-brain patients. Three patients with complete callosotomy and, as control groups, five patients with partial callosotomy and nine healthy subjects were examined for their ability to pantomime object use to visual object presentation and demonstrate object manipulation. In each condition, 11 objects were presented to the subjects who pantomimed or demonstrated the object use with either hand. In addition, six object pairs were presented to test bimanual coordination. Two independent raters evaluated the videotaped movement demonstrations. While object use demonstrations were perfect in all three groups, the split-brain patients displayed apraxic errors only with their left hands in the pantomime condition. The movement analysis of concept and execution errors included the examination of ipsilateral versus contralateral motor control. As the right hand/left hemisphere performances demonstrated retrieval of the correct movement concepts, concept errors by the left hand were taken as evidence for right hemisphere control. Several types of execution errors reflected a lack of distal motor control indicating the use of ipsilateral pathways. While one split-brain patient controlled his left hand predominantly by ipsilateral pathways in the pantomime condition, the error profile in the other two split-brain patients suggested that the right hemisphere controlled their left hands. In the object use condition, in all three split-brain patients fine-graded distal movements in the left hand indicated right hemispheric control. Our data show left hand apraxia in split-brain patients is not limited to verbal commands, but also occurs in pantomime to visual presentation of objects. As the demonstration with object in hand was unimpaired in either hand, both hemispheres must contain movement concepts for object use. However, the disconnected right hemisphere is impaired in retrieving the movement concept in response to visual object presentation, presumably because of a deficit in associating perceptual object representation with the movement concepts. (+info)
Interlocking finger test: a bedside screen for parietal lobe dysfunction.
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This study sought to determine the utility of an interlocking finger task in screening for parietal lobe dysfunction. The ability of 69 patients to imitate a standardised set of four interlocking finger figures was compared with concurrent performance on formal neurocognitive tests. Poor interlocking finger test scores correlated most highly with standard measures of parietal lobe dysfunction. In addition, an analytical model of parietal dysfunction indicated the interlocking finger test was similar to, if not better than, standard tests of parietal lobe dysfunction. Attempts to imitate these figures should serve as a fast and simple screen of parietal lobe dysfunction. (+info)
Assessing choice making among children with multiple disabilities.
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Some learners with multiple disabilities display idiosyncratic gestures that are interpreted as a means of making choices. In the present study, we assessed the validity of idiosyncratic choice-making behaviors of 3 children with multiple disabilities. Opportunities for each child to choose between food and drink were provided under two conditions. In one condition, the children were given the food or drink item corresponding to their prior choice. In the other condition, the teacher delivered the item opposite to that chosen. It was reasoned that valid choice-making behaviors would be reflected in a greater tendency to accept the chosen item and refuse the unchosen item. Direct observations revealed all children consistently indicated choices during both conditions. Choices of both the food and drink items were made by all 3 children. A reversal design demonstrated that acts of refusal were more frequent when choices were followed by delivery of the item opposite to that chosen. Similar assessment procedures may be effective in determining the function of idiosyncratic gestures exhibited by persons with multiple disabilities. For children lacking such skills, intervention to teach valid choice-making behaviors may be needed to complement assessment procedures. (+info)
Children creating core properties of language: evidence from an emerging sign language in Nicaragua.
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A new sign language has been created by deaf Nicaraguans over the past 25 years, providing an opportunity to observe the inception of universal hallmarks of language. We found that in their initial creation of the language, children analyzed complex events into basic elements and sequenced these elements into hierarchically structured expressions according to principles not observed in gestures accompanying speech in the surrounding language. Successive cohorts of learners extended this procedure, transforming Nicaraguan signing from its early gestural form into a linguistic system. We propose that this early segmentation and recombination reflect mechanisms with which children learn, and thereby perpetuate, language. Thus, children naturally possess learning abilities capable of giving language its fundamental structure. (+info)