1/117. Prosodic preservation in landau-kleffner syndrome: a case report.landau-kleffner syndrome (LKS) is a rare acquired condition of auditory verbal agnosia and convulsive disorder in children. It has been proposed that there is a functional relationship between electrical disturbance and the speech defect. Prosody or the melody of language, as described by Monrad-Krohn (1947), is one aspect of non-verbal communication which is distributed bilaterally in the brain. Prosodic parameters of expression and perception in one 7.5-year-old child were tested to see if they were preserved as a means of communication. The child was observed during video-electroencephalogram (EEG) monitoring over a 48-hour period. All utterances were recorded and subject to analysis for the salience and variation of acoustic correlates of prosody. Prosodic comprehension was measured using specific perceptual tasks previously presented to normal children between the ages of 5.5 and 8.5. Despite being unable to meaningfully use or perceive phonemes, the child was able to use variations in fundamental frequency, duration and intensity of utterances, to convey both emotional and propositional intent. Similarly, the child was able to discriminate prosodic contours of a male adult voice to an age equivalent to 5.5 to 6.5 years. This argues in favour of the notion for educating such children not only through the visual channel but also through the auditory channel.- - - - - - - - - - ranking = 1keywords = perception, speech (Clic here for more details about this article) |
2/117. Can face recognition really be dissociated from object recognition?We argue that the current literature on prosopagnosia fails to demonstrate unequivocal evidence for a disproportionate impairment for faces as compared to nonface objects. Two prosopagnosic subjects were tested for the discrimination of objects from several categories (face as well as nonface) at different levels of categorization (basic, subordinate, and exemplar levels). Several dependent measures were obtained including accuracy, signal detection measures, and response times. The results from Experiments 1 to 4 demonstrate that, in simultaneous-matching tasks, response times may reveal impairments with nonface objects in subjects whose error rates only indicate a face deficit. The results from Experiments 5 and 6 show that, given limited stimulus presentation times for face and nonface objects, the same subjects may demonstrate a deficit for both stimulus categories in sensitivity. In Experiments 7, 8 and 9, a match-to-sample task that places greater demands on memory led to comparable recognition sensitivity with both face and nonface objects. Regardless of object category, the prosopagnosic subjects were more affected by manipulations of the level of categorization than normal controls. This result raises questions regarding neuropsychological evidence for the modularity of face recognition, as well as its theoretical and methodological foundations.- - - - - - - - - - ranking = 1.2616897670264keywords = discrimination (Clic here for more details about this article) |
3/117. Unconscious letter discrimination is enhanced by association with conscious color perception in visual form agnosia.Adaptive behavior guided by unconscious visual cues occurs in patients with various kinds of brain damage as well as in normal observers, all of whom can process visual information of which they are fully unaware [1] [2] [3] [4] [5] [6] [7] [8]. Little is known on the possibility that unconscious vision is influenced by visual cues that have access to consciousness [9]. Here we report a 'blind' letter discrimination induced through a semantic interaction with conscious color processing in a patient who is agnosic for visual shapes, but has normal color vision and visual imagery. In seeing the initial letters of color names printed in different colors, it is normally easier to name the print color when it is congruent with the initial letter of the color name than when it is not [10]. The patient could discriminate the initial letters of the words 'red' and 'green' printed in the corresponding colors significantly above chance but without any conscious accompaniment, whereas he performed at chance with the reverse color-letter mapping as well as in standard tests of letter reading. We suggest that the consciously perceived colors activated a representation of the corresponding word names and their component letters, which in turn brought out a partially successful, unconscious processing of visual inputs corresponding to the activated letter representations.- - - - - - - - - - ranking = 10.203389480134keywords = discrimination, perception (Clic here for more details about this article) |
4/117. Coding space within but not between objects: evidence from Balint's syndrome.The ability to make spatial judgements was examined in a patient demonstrating poor perception of multiple objects following bilateral parietal lesions, under conditions in which the presence of the stimuli to which judgements were made could be detected. The tasks required judgements of spatial length or the position of coloured parts of stimuli. We manipulated the degree to which two uprights in a display could be encoded into a single perceptual object using either stored knowledge or bottom-up cues based on 2D or 3D image relations. Performance was dependent on the presence of both bottom-up grouping and familiarity. However, connectedness in the image was not sufficient to benefit performance, when stimuli were separate objects in 3D space. This deficit in spatial judgements, arising following detection of the relevant stimulus elements, is attributed to an impairment in coding the spatial relations between separate perceptual objects. This deficit could be overcome if stimuli could be grouped in 3D, using bottom-up cues and top-down knowledge.- - - - - - - - - - ranking = 0.97373516125034keywords = perception (Clic here for more details about this article) |
5/117. Auditory agnosia and auditory spatial deficits following left hemispheric lesions: evidence for distinct processing pathways.Auditory recognition and auditory spatial functions were studied in four patients with circumscribed left hemispheric lesions. Patient FD was severely deficient in recognition of environmental sounds but normal in auditory localisation and auditory motion perception. The lesion included the left superior, middle and inferior temporal gyri and lateral auditory areas (as identified in previous anatomical studies), but spared Heschl's gyrus, the acoustic radiation and the thalamus. Patient SD had the same profile as FD, with deficient recognition of environmental sounds but normal auditory localisation and motion perception. The lesion comprised the postero-inferior part of the frontal convexity and the anterior third of the temporal lobe; data from non-human primates indicate that the latter are interconnected with lateral auditory areas. Patient MA was deficient in recognition of environmental sounds, auditory localisation and auditory motion perception, confirming that auditory spatial functions can be disturbed by left unilateral damage; the lesion involved the supratemporal region as well as the temporal, postero-inferior frontal and antero-inferior parietal convexities. Patient CZ was severely deficient in auditory motion perception and partially deficient in auditory localisation, but normal in recognition of environmental sounds; the lesion involved large parts of the parieto-frontal convexity and the supratemporal region. We propose that auditory information is processed in the human auditory cortex along two distinct pathways, one lateral devoted to auditory recognition and one medial and posterior devoted to auditory spatial functions.- - - - - - - - - - ranking = 3.8949406450014keywords = perception (Clic here for more details about this article) |
6/117. Hemianopic colour blindness.A man developed cortical blindness after cerebral infarction in the distribution of both posterior cerebral arteries. When he recovered from this condition, he was found to be colour blind in the left visual field, but not in the right. This unusual situation resulted in apparently contradictory performances on hemifield and free-field tasks of colour discrimination, naming, and recognition. The contradictions may be explained by interhemispheric competition between a hemisphere which could discriminate colours and a hemisphere which was colour blind.- - - - - - - - - - ranking = 1.2616897670264keywords = discrimination (Clic here for more details about this article) |
7/117. Perception of dynamic acoustic patterns by an individual with unilateral verbal auditory agnosia.Previous studies have found that subjects diagnosed with verbal auditory agnosia (VAA) from bilateral brain lesions may experience difficulties at the prephonemic level of acoustic processing. In this case study, we administered a series of speech and nonspeech discrimination tests to an individual with unilateral VAA as a result of left-temporal-lobe damage. The results indicated that the subject's ability to perceive steady-state acoustic stimuli was relatively intact but his ability to perceive dynamic stimuli was drastically reduced. We conclude that this particular aspect of acoustic processing may be a major contributing factor that disables speech perception in subjects with unilateral VAA.- - - - - - - - - - ranking = 2.3142194445258keywords = discrimination, perception, speech (Clic here for more details about this article) |
8/117. Neuronal representation of object orientation.The dissociation between object identity and object orientation observed in six patients with brain damage, has been taken as evidence for a view-invariant model of object recognition. However, there was also some indication that these patients were not generally agnosic for object orientation but were able to gain access to at least some information about objects' canonical upright. We studied a new case (KB) with spared knowledge of object identity and impaired perception of object orientation using a forced choice paradigm to contrast directly the patient's ability to perceive objects' canonical upright vs non-upright orientations. We presented 2D-pictures of objects with unambiguous canonical upright orientations in four different orientations (0 degrees, -90 degrees, 90 degrees, 180 degrees ). KB showed no impairment in identifying letters, objects, animals, or faces irrespective of their given orientation. Also, her knowledge of upright orientation of stimuli was perfectly preserved. In sharp contrast, KB was not able to judge the orientation when the stimuli were presented in a non-upright orientation. The findings give further support for a distributed view-based representation of objects in which neurons become tuned to the features present in certain views of an object. Since we see more upright than inverted animals and familiar objects, the statistics of these images leads to a larger number of neurons tuned for objects in an upright orientation. We suppose that probably for this reason KB's knowledge of upright orientation was found to be more robust against neuronal damage than knowledge of other orientations.- - - - - - - - - - ranking = 0.97373516125034keywords = perception (Clic here for more details about this article) |
9/117. Implicit semantic evaluation of object symmetry and contralesional visual denial in a case of left unilateral neglect with damage of the dorsal paraventricular white matter.It is well documented that right brain damaged patients with left unilateral neglect may show unconscious processing of contralesional stimuli. However, the anatomical correlates of this phenomenon are still not well defined. Here we report the case of a neglect patient with a circumscribed lesion of the dorsal parietal-occipital white matter showing clear implicit processing of the contralesional side of line drawings and object based neglect. The patient was able to perform correct semantic analysis of the symmetry (or asymmetry) of the drawings. Additional testing disclosed denial of the existence of the contralesional side of asymmetrical geometrical shapes with correct perception of symmetrical ones and of shapes without the left side. These findings provide direct evidence supporting a critical role of the dorsal visual system in the activation of conscious representations of visual stimuli.- - - - - - - - - - ranking = 0.97373516125034keywords = perception (Clic here for more details about this article) |
10/117. Perceiving left and imagining right: dissociation in neglect.Signor Piazza, a patient with a left parieto-occipital haemorrhage and a right thalamic stroke, showed severe right personal neglect (e.g. touching own body parts) and right perceptual neglect in tasks with (e.g. cancelling tasks) or without (e.g. description of a complex picture) motor response. He had also right-sided neglect dyslexia (including single words), without language impairments. However, the patient also presented with a clear left-sided deficit in the representational domain (e.g. imagery tasks). Signor Piazza's pattern of performance suggests dissociation between imagery and perception within the neglect syndrome.- - - - - - - - - - ranking = 0.97373516125034keywords = perception (Clic here for more details about this article) |
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