1/7. Number processing and calculation in a case of visual agnosia.We describe the performance of a brain-damaged subject who suffered from visual agnosia leading to major difficulties in generating and exploiting visual representations from long-term memory. His performance in a physical judgement task in which he was required to answer questions about the visual shapes of Arabic numerals reflected his agnosic problems. However, he showed no impairment in usual number processing and calculation tasks. This case shows that, despite some commonalities in number and object processing, actual numerical processes are not affected by visual agnosia and can be preserved even when fine visual processes are impaired.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
2/7. Covert processing of visual form in the absence of area LO.The patient D.F., who suffers from severe visual form agnosia, has been found to have a bilateral lesion of area LO, an area known to be intimately involved in the perception of object shape. Despite her perceptual impairment, however, D.F. retains residual form processing abilities that can provide distal visuomotor control, for example in the configuration of her grasp when reaching to pick up objects of different shapes and sizes. This dissociation has been interpreted as reflecting the sparing of a dedicated system for processing the physical properties of objects solely for purposes of guiding action. Here we test this hypothesis in two studies designed to examine whether or not spared shape processing capacities might be revealed under other kinds of indirect test conditions. First, we exploited the fact that a redundant shape cue will speed search for a coloured stimulus within an array, and vice versa. Unlike our control subjects, D.F. showed no facilitation effect of either kind. Second, we used two Stroop tasks in which single coloured uppercase letters were presented. Our intention was to determine (a) whether naming the colour would be influenced by whether the letter was the initial letter of the correct or incorrect colour name (e.g. 'R' or 'G'); and (b) whether the reverse might be true, that is that D.F.'s guesses at letter identity might be influenced by their colour. We found no evidence for a Stroop effect of the former (standard) kind in D.F., but we did find evidence for reverse-Stroop effects. This result may reflect a partial sparing of ventral stream areas specialised for letter-form processing.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
3/7. Unawareness of impaired face recognition.We report investigations of the face processing abilities of SP, a right-handed woman who had suffered a subarachnoid haemorrhage from a right middle cerebral artery aneurysm. Although she could correctly assign visual stimuli to the 'face' category without difficulty, SP performed poorly on all other face processing, tasks, including 'closure' (Mooney faces), perception of facial expression, unfamiliar face matching, and identification of familiar faces. Identification of familiar people from nonfacial cues (names) remained relatively well-preserved, but severe impairments were evident on all face recognition tasks. Her errors mostly involved either failures to find a face familiar at all, or misidentification as another familiar person. In face-name learning tasks, there was evidence of 'covert' recognition of faces she failed to recognize overtly. SP's face processing impairment remained stable across a 20-month period of investigation, yet throughout this period she did not think that she had any problems in face recognition, and continued to show lack of insight into this impairment even when directly confronted with its consequences on formal testing. In contrast, SP showed adequate insight into other physical and cognitive impairments produced by her illness, including poor memory, hemiplegia, and hemianopia. We propose that her lack of insight into her face recognition problems involves a deficit-specific anosognosia, resulting from impairment of domain-specific monitoring abilities.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
4/7. 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.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
5/7. A case of associative visual agnosia: neuropsychological findings and theoretical considerations.A 61-year-old right-handed man fell downstairs and was found unconscious. There was no abnormality in the general physical examinations. Neurological examinations revealed a quadrantanopia. Neuropsychological examination revealed an impairment in recent verbal memory, alexia, agraphia, object agnosia, color naming difficulty, prosopagnosia, and visuospatial constructional disability. CT scan demonstrated subcortical hematomas in the temporo-occipital regions of both hemispheres. MRI demonstrated extensive low-intensity lesions in the lingual, fusiform and posterior inferior temporal gyri on both hemispheres. Both inferior longitudinal fasciculi were also affected. His neuropsychological deficits seem best described as a typical form of associative visual agnosia. From the results of neuroradiological findings, the authors emphasize that associative visual agnosia might be produced by an intrahemispheric disconnection between the visual cortices and the temporal lobes which are supposed to be the storage site of the engrams of visual memories. Moreover, the neuropsychological findings suggest that the visuo-constructional ability to convert the two-dimensional input to the three-dimensional construction and the capacity of three-dimensional imagination were severely impaired in our patient. It was considered that these neuropsychological features play an important role in the recognition difficulties of associative visual agnosia.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
6/7. Visual apperceptive agnosia: a clinico-anatomical study of three cases.The visuo-perceptual abilities of three cases with unilateral lesions of the right hemisphere selected on the basis of the co-occurrence of impaired performance on a test of visual object perception and normal performance on a test of shape discrimination are reported. Their performance was also impaired on other tests of visual object recognition in which the perceptual difficulty of the task was manipulated by obscuring the salient features of the representation. At the same time it was found that on a variety of other tests of visual-sensory processing their performance was entirely normal, as was their performance on tests of visual semantic knowledge, tests that were failed by a patient with a visual associative agnosia. It is argued that this syndrome has all the hallmarks of an apperceptive agnosia, a failure of perceptual categorisation in which the physical identity of the object is specified. The two discontinuities between visual-sensory processing, perceptual categorisation and visual-semantic processing are discussed in terms of a 2 categorical stage model of object recognition.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |
7/7. The fuzzy boundaries of apperceptive agnosia.Following a trauma that mainly involved the right hemisphere, a 21-year-old girl showed a profound impairment in visual object recognition, without language and intellectual deficit. Her elementary sensory functions were preserved and she performed in the normal range on visual matching tasks, on taks requiring to detect small differences between similar complex shapes and in copying drawings, without any evidence of a line by line approach. Her deficit emerged with tests that, though not implying identification of meaning, demanded to disentangle a form from a confused background and to achieve a highly structured description of the stimulus. In addition to this high-level perceptual processing disorder, there was a deficit in recovering from the visual store the shape of an object, also when the performance did not involve perceptual discrimination, e.g., in drawing from memory or telling the physical difference between two named stimuli. knowledge of the semantic and contextual attributes of objects was intact. The case is taken as evidence that the borders of apperceptive agnosia may be ampler than usually thought and its distinction from associative agnosia less rigid, with some patients laying in-between the two syndromes.- - - - - - - - - - ranking = 1keywords = physical (Clic here for more details about this article) |