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Comparing parasitic infection among individuals of wildlife populations can provide insight into factors that influence wildlife disease ecology. Strongylids are parasitic worms that infect the intestinal tract of vertebrates, and infection with strongylids can be approximated by counting strongylid eggs in dung samples. Here we tested for correlations between strongylid egg counts and 18 different individual characteristics, environmental and social factors in individually known wild African elephants. We counted more eggs in the dung samples of younger elephants and females relative to mature elephants and males. We also found that elephants spending more time outside reserves shed more strongylid eggs than elephants that were more often within reserves. Elephants that were less socially integrated, as measured by how much aggression they received from other elephants, shed fewer strongylid eggs; relatedly, socially isolated orphan elephants that had left their family shed fewer strongylid eggs than elephants that remained with their family. Our results suggest that landscapes altered by livestock grazing and social disruption caused by humans may impact parasitic infection in wildlife.
Objectives: Exploring the nature of defective pantomime in apraxia. Methods: Critical review of behavioral associations and dissociations between defective pantomime, imitation of gestures, and real tool use. Analysis of congruencies between crucial lesions for pantomime, imitation, and tool use. Results: There are behavioral double dissociations between pantomime and imitation, and their cerebral substrates show very little overlap. Whereas defective pantomime is bound to temporal and inferior frontal lesions, imitation is mainly affected by parietal lesions. Pantomime usually replicates the motor actions of real use but on scrutiny there are important differences between the movements of real use and of pantomime that cast doubt on the assumption that pantomime is produced by the same motor programs as actual use. A more plausible proposal posits that pantomime is a communicative gesture that uses manual actions for conveying information about objects and their use. The manual actions are constructed by selection and combination of distinctive features of tools and actions. They frequently include replications of characteristic motor actions of real use, but the main criterion for selection and modification of features is the comprehensibility of the gestures rather than the accurate replication of the motor actions of real use. Conclusions: Pantomime of tool use is a communicative gesture rather than a replication of the motor actions of real use. (JINS, 2017, 23, 121–127)
For seeing persons vision is the major source of object recognition. Although agnosia can affect recognition by other sensory channels (see Chapter 18) the majority of research and clinical interest in object agnosia concerns visual agnosia, which is also the topic of this chapter.
The term agnosia characterizes absent recognition in spite of preserved perception. Clinical diagnosis of visual agnosia is based on a model of visual recognition which was developed at the turning from the nineteenth to the twentieth century (Liepmann, 1908; Lissauer, 1890) but still serves as the starting point for cognitive analyses of visual recognition (Humphreys and Riddoch, 1987; Marr, 1982). This model distinguishes two stages leading from visual perception to recognition. At the “apperceptive” stage, elements of primary visual perceptions, like contours, brightness, texture, and color, are integrated into a coherent structural representation of the object. At the following “associative” stage, the structural representation gains access to semantic memory where knowledge about non-visual properties of the object is stored. Activation of knowledge about the object is equivalent to recognition and a necessary prerequisite for retrieving its name. Agnosia is classified as apperceptive or associative according to which of these stages is affected. Although modern neurophysiology casts doubts on the clean distinction between subsequent stages of visual recognition, the syndromes of “apperceptive agnosia” and “associative agnosia” have proven to correspond to salient and distinguishable clinical syndromes.
Based on neuropsychological evidence of nonverbal impairment accompanying aphasia, I propose that the neural prerequisites for language acquisition are shared with a range of nonverbal capacities. Their commonality concerns the ability to recognize a limited number of finite elements in manifold perceptual entities and to combine them for constructing manifold entities.
Observations on patients who lost visual imagery after brain damage call into question the notion that the knowledge subserving visual imagery is “tacit.” Dissociations between deficient imagery and preserved recognition of objects suggest that imagery is exclusively based on explicit knowledge, whereas retrieval of “tacit” visual knowledge is bound to the presence of the object and the task of recognizing it.
Neuropsychological research on imitation has a history of nearly a hundred years. Liepmann (1908) investigated performance of meaningful gestures on command, like giving a military salute or showing how to turn a key, in patients with damage to the right or left hemisphere and normal controls. He found that only patients with left-brain damage (LBD) committed errors even when they performed the gestures with the nonparetic left hand. As most LBD patients were aphasic they might have had difficulties understanding the verbal instructions. However, they also committed errors when imitating the same gestures. Liepmann ascribed defective gesturing in LBD patients to “apraxia.” He emphasized that, in contrast to other motor sequels of unilateral brain damage, apraxia affects not only the contralesional but also the ipsilesional limbs, and concluded that it interferes with motor actions at a level beyond “elementary” motor control. He conceived of two possibilities for a higher level of disturbances of motor control: apraxia might stem from an inability to conjure up a mental representation of the required action, or from an inability to convert the mental representation into appropriate motor commands. Errors on imitation testified to Liepmann that “there is not only an inexactness of the spatial-temporal image of the movement, but a difficulty or inability to direct the leftsided members according to certain spatial conceptions” (Liepmann, 1908).
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