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1/4. Modularity of music: evidence from a case of pure amusia.

    A case of pure amusia in a 20 year old left handed non-professional musician is reported. The patient showed an impairment of music abilities in the presence of normal processing of speech and environmental sounds. Furthermore, whereas recognition and production of melodic sequences were grossly disturbed, both the recognition and production of rhythm patterns were preserved. This selective breakdown pattern was produced by a focal lesion in the left superior temporal gyrus. This case thus suggests that not only linguistic and musical skills, but also melodic and rhythmic processing are independent of each other. This functional dissociation in the musical domain supports the hypothesis that music components have a modular organisation. Furthermore, there is the suggestion that amusia may be produced by a lesion located strictly in one hemisphere and that the superior temporal gyrus plays a crucial part in melodic processing.
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keywords = dissociation
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2/4. Short-term memory impairment and unilateral dichotic listening extinction in a child with landau-kleffner syndrome: auditory or phonological disorder?

    The neuropsychological profile of a child with a landau-kleffner syndrome is presented here. The observed cognitive difficulties included verbal short-term memory and seemed partially compensated for when the experimental assessments bypassed the auditory channel. This case study is especially challenging since the child, whose phonological skills were quite efficient and who exhibited a dichotic listening unilateral extinction, had developed average reading and spelling abilities. The fact that B.E.'s performance on memory tasks was quite poor when the stimuli were presented auditorily and more efficient when the stimuli were presented visually, strongly suggests that the observed memory impairment was due to a deficit at the level of cortical auditory processing. B.E.'s phonological skills were efficient, suggesting a neuropsychological dissociation between phonological ability and auditory processing. The fact that B.E. dramatically recovered language and easily acquired reading and spelling accounts for the hypothesis that compensatory strategies allowed him to develop phonological skills from predominantly visual input.
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keywords = dissociation
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3/4. Impaired speech perception in aphasic patients: event-related potential and neuropsychological assessment.

    The mismatch negativity component (MMN) of auditory event-related potentials (ERP) was recorded in four aphasic patients and in age, gender and education matched controls. The MMN changes elicited by tone, vowel, voicing stop consonant and place-of articulation contrasts were recorded over both hemispheres. The results of MMN amplitude, latency and distribution differences between aphasics and controls were analyzed in detail. An extensive neuropsychological investigation was performed in order to highlight the assumed dissociation and possible interactions between the impaired acoustic/phonetic perception and deficient comprehension in aphasic patients. Our principal finding was that MMN elicited by pitch deviations is not enough sensitive to distinguish between patients and age-matched controls. The MMN elicited by consonant contrasts was found to be the most vulnerable in aphasic patients investigated. The MMN elicited by voicing ([ba:] vs. [pa:]) and place-of-articulation ([ba:] vs. [ga:]) could be characterized by total lack, distorted or very limited distribution and correlated with the patients' performance shown in the behavioral phoneme discrimination task. The magnitude of the deficient phoneme (vowel and consonant contrasts) processing shown by MMN anomalies was proportionally related to the non-word discrimination and did not interact with the word discrimination performance. The impact of deficient speech sound processing on higher level processes may depend on the type of aphasia, while the presence of perceptual deficits in processing acoustic/phonetic contrasts seems to be independent of the type of aphasia.
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keywords = dissociation
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4/4. Auditory agnosia with relative sparing of speech perception.

    We report a case of auditory agnosia in which the initial clinical picture began with generalized auditory agnosia for verbal and non verbal sounds, but rapidly changed to a selective auditory agnosia confined to the perception of non verbal sounds. CT scanning and MRI did not demonstrate cortical or subcortical damage, except for bilateral ventricular enlargement. The patient was submitted to audiological investigations including physical and psychoacoustic studies. Deficits were revealed during the decay and loudness discrimination test, but no temporal auditory acuity deficit was observed. The results of these studies are discussed in relation to the clinical picture. Also the dissociation between verbal perception and non verbal perception is discussed.
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ranking = 1
keywords = dissociation
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