1/202. 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 = visual (Clic here for more details about this article) |
2/202. Memories are made of this: the effects of time on stored visual knowledge in a case of visual agnosia.We report the effects of the passage of time on the longterm visual knowledge for objects in a patient with visual agnosia (H.J.A.). The naming of real objects was found to have improved, although this was not associated with any change in H.J.A.'s basic perceptual abilities which were stable over a 16-year period. The improvement in object naming was attributed to better use of non-contour-based visual information (such as surface detail and depth cues). In addition, we demonstrate a deterioration in H.J.A.'s long-term memory for the visual properties of objects, and argue that this has occurred as a result of his having impaired perceptual input. The deterioration was only apparent in drawing from memory and in the verbal descriptions of items; with forced-choice testing, H.J.A. operated at ceiling; we propose that current tests of visual imagery may not be sufficiently sensitive to detect subtle impairments of visual memory. Our findings can be taken to indicate that perceptual and memorial processes are not functionally independent, but are linked in an interactive manner.- - - - - - - - - - ranking = 14keywords = visual (Clic here for more details about this article) |
3/202. Tactile morphagnosia secondary to spatial deficits.A 73-year old man showed visual and tactile agnosia following bilateral haemorrhagic stroke. Tactile agnosia was present in both hands, as shown by his impaired recognition of objects, geometrical shapes, letters and nonsense shapes. Basic somatosensory functions and the appreciation of substance qualities (hylognosis) were preserved. The patient's inability to identify the stimulus shape (morphagnosia) was associated with a striking impairment in detecting the orientation of a line or a rod in two- and three-dimensional space. This spatial deficit was thought to underlie morphagnosia, since in the tactile modality form recognition is built upon the integration of the successive changes of orientation in space made by the hand as it explores the stimulus. Indirect support for this hypothesis was provided by the location of the lesions, which could not account for the severe impairment of both hands. Only those located in the right hemisphere encroached upon the posterior parietal cortex, which is the region assumed to be specialised in shape recognition. The left hemisphere damage spared the corresponding area and could not, therefore, be held responsible for the right hand tactile agnosia. We submit that tactile agnosia can result from the disruption of two discrete mechanisms and has different features. It may arise from a parietal lesion damaging the high level processing of somatosensory information that culminates in the structured description of the object. In this case, tactile recognition is impaired in the hand contralateral to the side of the lesion. Alternatively, it may be caused by a profound derangement of spatial skills, particularly those involved in detecting the orientation in space of lines, segments and complex patterns. This deficit results in morphagnosia, which affects both hands to the same degree.- - - - - - - - - - ranking = 1keywords = visual (Clic here for more details about this article) |
4/202. 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 = 0.037148891915245keywords = sensitivity (Clic here for more details about this article) |
5/202. 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 = 10keywords = visual (Clic here for more details about this article) |
6/202. axis-based grouping reduces visual extinction.We examined the effects on extinction of grouping by collinearity of edges and grouping by alignment of internal axes of shapes, in a patient (GK) with simultanagnosia following bilateral parietal brain damage. GK's visual extinction was reduced when items (equilateral triangles and angles) could be grouped by base alignment (i.e., collinearity) or by axis alignment, relative to a condition in which items were ungrouped. These grouping effects disappeared when inter-item spacing was increased, though factors such as display symmetry remained constant. overall, the results suggest that, under some conditions, grouping by alignment of axes of symmetry can have an equal beneficial effect on visual extinction as edge-based grouping; thus, in the extinguished field, there is derivation of axis-based representations from the contours present.- - - - - - - - - - ranking = 6keywords = visual (Clic here for more details about this article) |
7/202. 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 = 1keywords = visual (Clic here for more details about this article) |
8/202. A componential analysis of visual object recognition deficits in patients with herpes simplex virus encephalitis.Five patients with a diagnosis of herpes simplex Virus encephalitis (HSVE) underwent neuropsychological assessment to explore the integrity of their visual perceptual abilities. Selective deficits affecting different levels of the recognition processing were found; impaired recognition abilities were also influenced by selective task requirements, which resulted either in facilitatory or constraining effects on patients' performance. A theoretical model of object recognition (Humphreys & Riddoch, 1987) was taken into account to explain patients' performance. Further, the role of specific components of visual processing was evidenced in explaining the performance of patients affected by HSVE.- - - - - - - - - - ranking = 6keywords = visual (Clic here for more details about this article) |
9/202. 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 = 0.046449337373526keywords = contrast (Clic here for more details about this article) |
10/202. 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 = 6keywords = visual (Clic here for more details about this article) |
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