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PubMed2000

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.

Agnosia↗
PubMed1995

Psychoacoustical deficits related to bilateral subcortical hemorrhages. A case with apperceptive auditory agnosia.

We report a case of acute deafness secondary to bilateral hemorrhages involving the external capsule and extending to both temporal isthmi. The lesions probably disrupted both auditory radiations. Deafness disappeared within 2 weeks leading to a transient auditory agnosia for environmental and verbal sounds. Performance on audiological and neurolinguistic tests were consistent with the hypothesis of a deficit of non-specific auditory processes. Psychoacoustical deficits related to subcortical lesions are very rare and might differ from those due to cortical lesions by the lack of aphasia. The present case and both previous cases with subcortical lesions might suffer from auditory agnosia of apperceptive type. Its characteristics and the role of non-specific auditory processes are discussed using the data obtained from this third case.

Agnosia↗
PubMed1993

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.

Adult↗
PubMed1992

Visual agnosia: a case of reduced attentional "spotlight"?

A case study is presented of a patient with presenile dementia, for whom the dominant clinical feature from onset was a visual agnosia. The characteristics of the patient's visual agnosia were investigated in light of her apparent use of a "feature-by-feature" strategy to identify objects. Results from various tasks showed that the patient was unable to use global shape information or other grossly defined property cues characteristic of a "wide angle" attentional processing stage (Treisman, 1988) in object recognition. The patient appeared instead to rely on 'parts' or identifying features of the objects for object recognition. The patient showed significant improvement when the size of the drawing was reduced in size, thus suggesting that the disorder may be functionally localized to a reduction of the patient's attentional "spotlight".

Agnosia↗
PubMed1994

Integrative agnosia following progressive multifocal leukoencephalopathy.

A 43 year-old man with presumed progressive multifocal leukoencephalopathy developed difficulty recognizing objects and faces in the presence of adequate visual acuity and visual fields. His copying and matching of line drawings was intact, suggesting that his agnosia was associative. However, he had difficulty perceiving overlapping forms and drawings of single objects as integrated wholes. Unlike control subjects, he made fewer errors identifying silhouettes compared to line drawings with internal details. These alterations, together with his feature-by-feature descriptions of objects and copying, suggest that his agnosia was due to a disturbance in integrating local form features, as described by Riddoch and Humphreys (1987). This interpretation is supported by the findings that his tactile recognition and semantic and structural knowledge of the objects he could not identify visually were intact. Furthermore, his deficient performance in categorical matching of photographs to objects was dependent upon the perceptual complexity of the photographs. Similar deficits in early form processing described by other investigators are discussed.

AIDS Dementia Complex↗
PubMed1994

Visual agnosia and optic aphasia: are they anatomically distinct?

A patient with left infero-medial occipital-temporal infarct suffered a visual agnosia that, by a minor change of the task, could be manipulated to optic aphasia. Tools in actual use and pantomimes of tool use were better named than stationary tools, a dissociation that suggests differences in the ability of stimuli to evoke associations over multiple modalities. Based on this case and analysis of previous reports we suggest that optic aphasia differs from visual agnosia primarily in the degree of callosal disconnection and that the preserved demonstration of tools use and semantic classification of optic aphasia reflect right hemisphere contribution to visual processing.

Aged↗
PubMed1990

Auditory sound agnosia without aphasia following a right temporal lobe lesion.

A 55-year-old right-handed man showed inability to recognize the meaning of non-verbal sounds without impairment of language comprehension after a cerebrovascular accident. His auditory acuity was intact and no other sign of agnosia, apraxia or aphasia was detectable. His errors on a test of sound recognition were acoustic rather than semantic. Brain CT scan showed a small lesion in the posterior part of the right temporal lobe. This case suggests that auditory sound agnosia without language disorder can ensure a lesion confined to the right hemisphere, and that the deficit is discriminative rather than associative in nature.

Agnosia↗
PubMed1984

Associative visual agnosia: a case study.

This report describes a case of associative visual agnosia caused by a left sided, cortico-subcortical, inferior temporo-occipital infarction. Performance on visual perceptual tests was normal, while it was defective on visual classification tasks. Visual agnosia was interpreted as a visuo-verbal disconnection plus a categorization deficit for visual meaningful common stimuli. The left occipito-temporal lesion disrupted the visual classification process and prevented access of visual information to language areas and limbic system. The absence of right hemispheric lesion accounted for the normal recognition of familiar faces and other unique individual stimuli such as familiar places, whose recognition occurs through contextual evocation.

Agnosia↗
PubMed1985

A case of visual agnosia showing a disorder of pre-semantic visual classification.

A case (J.R.) of associative visual agnosia (loss of meaning for visually presented objects without any serious sensory disorder) is reported. When asked to match a given name to sample the patient made both visual and semantic errors. Whereas semantic errors were reduced by priming, visual errors were intractable. It is argued that there is a disorder at the stage of pre-semantic abstraction, similar to that postulated elsewhere for some cases of deep dyslexia, contributing to the agnosia.

Adult↗
PubMed1988

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.

Aged↗
PubMed1997

Associative agnosia and optic aphasia: qualitative or quantitative difference?

We report a patient who, following the partial removal of a tentorial meningioma, suffered a hematoma in the left occipital lobe, which was resected. He showed severe anomia for visually presented stimuli, while naming was normal when they were presented in the tactile, auditory and verbal modality. His performance on visuo-perceptual tests, not requiring meaning identification, provided evidence that he was able to access the stored representations of stimuli. When recognition was assessed with non-verbal tasks, a mixed pattern of findings emerged and the patient showed features of both associative agnosia and optic aphasia. He was severely impaired in producing pantomimes in response to pictures, but only marginally impaired in sorting figures from the same superordinate category into fine-grained subcategories. He performed within the normal range on an associative task, in which the distractors bore no semantic relation to the target, but made many errors when the distractors and the target were semantically related. We propose that the interpretation advanced by Coslett and Saffran (Brain, 1989) for optic aphasia also holds for associative agnosia and argue that both syndromes reflect the impaired access of structured representations to left hemisphere semantics, but differ in terms of the degree of compensation provided by the semantic resources of the right hemisphere. Since the anatomical basis of the two syndromes may be very similar, we submit that what makes the difference is the semantic potential of the patient's right hemisphere.

Aged↗
PubMed1999

Category specificity in object agnosia: preservation of sensorimotor experiences related to objects.

We report a case of semantic agnosia, characterized by category specificity. Object recognition, mainly involving visual representation, was severely impaired, whereas object recognition involving both visual and sensorimotor representations, was relatively well preserved. His ability to recognize gestures and produce appropriate gestural responses to objects was remarkable. These two factors lead the authors to form a hypothesis, in an attempt to explain the mechanisms involved in object recognition. It has been argued that manipulation of an object may give access to a certain amount of knowledge about it, and that preservation of sensorimotor experiences of objects might be important in recognizing some of them. This could account for the category specificity, described in object agnosia.

Agnosia↗
PubMed2003

Category-specific visual agnosia: lesion to semantic memory versus extra-lesional variables in a case study and a connectionist model.

There is a current debate on the causes of category-specific agnosia. The aim of this study was to examine the effects of lesional and extra-lesional variables on object recognition. Extra-lesional variables, such as visual complexity or familiarity, are factors that influence recognition. Using a connectionist model based on study, we provide evidence that extra-lesional variables can yield dissociations in the recognition rate of different categories. Furthermore, it is shown that lesional and extra-lesional variables can interact (p < .01) when both are simultaneously modeled. Category-specific agnosia might thus result from complex interactions.

Adult↗
PubMed1995

Verbal auditory agnosia with focal EEG abnormality: an unusual case of a child presenting to an ENT surgeon with "deafness".

Verbal auditory agnosia implies the failure to recognize sounds in a patient who is nevertheless not deaf. We present a child referred to the ENT outpatients for suspected hearing loss investigation. At one point she had grommets inserted on the basis of a flat tympanogram but with no effect. All hearing tests, including electrocochleography and distraction tests, revealed normal hearing thresholds. At the age of three years and three months, and on direct questioning of the parents, we discovered that the child responded remarkably well to music. Paediatric neurologists made the diagnosis of verbal auditory agnosia. The condition is very similar to another acquired language disorder called Landau-Kleffner syndrome. It is unusual for such a case to present primarily to an ENT surgeon.

Agnosia↗
PubMed2006

Independent representation of parts and the relations between them: evidence from integrative agnosia.

Whether objects are represented as a collection of parts whose relations are coded independently remains a topic of ongoing discussion among theorists in the domain of shape perception. S. M., an individual with integrative agnosia, and neurologically intact ("normal") individuals learned initially to identify 4 target objects constructed of 2 simple volumetric parts. At test, the targets were mixed with distractors, some of which could be discriminated from the targets on the basis of a mismatching part, whereas the rest could be discriminated only on the basis of the altered spatial arrangements of parts. S. M. learned to identify the target objects, although at a rate slower than that of the normal participants. At test, he correctly rejected distractors on the basis of mismatching parts but was profoundly impaired at rejecting distractors made of the same local components but with mismatching spatial arrangements. These results suggest that encoding the spatial arrangements of parts of an object requires a mechanism that is different from that required for encoding the shape of individual parts, with the former selectively compromised in integrative agnosia.

Adult↗
PubMed2002

A longitudinal study of category-specific agnosia.

We report a 12-year longitudinal case study on a 60-year-old male patient (DW) with category-specific agnosia. The extent to which DW's impairment has changed over time was evaluated using identical tests at time 1 (1988) and time 2 (2000). In particular, we assessed his ability to identify pictures and real objects, to draw from memory, and to access stored semantic information about living and non-living things. The principal findings were: (i). DW was significantly better at identifying real objects in comparison with line drawings. (ii). DW presented with a category-specific impairment for living things that remained consistent over the 12-year period. (iii). He significantly improved in his ability to identify real non-living objects over the 12-year period but real living objects remained at floor. (iv). His ability to access stored visual knowledge declined over time. On the basis of these data, we suggest that visual perception is required to maintain intact visual memories over a period of time. We also suggest that integrative visual agnosia co-occurs with a category-specific impairment for living things because the recognition of these items requires more global processing than for non-living things. In addition, we suggest that degradation to stored visual knowledge can cause category-specific naming impairments for living compared with non-living things because naming living things requires access to more detailed visual knowledge.

Agnosia↗
PubMed2004

Differential impact of parvocellular and magnocellular pathways on visual impairment in apperceptive agnosia?

The term "visual form agnosia" describes a disorder characterized by problems recognizing objects, poor copying,and distinguishing between simple geometric shapes despite normal intellectual abilities. Visual agnosia has been interpreted as a disorder of the magnocellular visual system, caused by an inability to separate figure from ground by sampling information from extended regions of space and to integrate it with fine-grain local information. However,this interpretation has hardly been tested with neuropsychological or functional brain imaging methods, mainly because the magnocellular and parvocellular structures are highly interconnected in the visual system. We studied a patient (AM) who had suffered a sudden heart arrest, causing hypoxic brain damage. He was/is severely agnosic, as apparent in both the Birmingham Object Recognition Battery and the Visual Object and Space Battery. First- and especially second-order motion perception was also impaired, but AM experienced no problems in grasping and navigating through space. The patient revealed a normal P100 in visual evoked potentials both with colored and fine-grained achromatic checkerboards. But the amplitude of the P100 was clearly decreased if a coarse achromatic checkerboard was presented.The physiological and neuropsychological findings indicate that AM experienced problems integrating information over extended regions of space and in detecting second-order motion. This may be interpreted as a disorder of the magnocellular system, with intact parvocellular system and therefore preserved ability to detect both local features and colors.

Agnosia↗
PubMed2005

Wayfinding in familiar and unfamiliar environments in a case of progressive topographical agnosia.

A 71-year-old right-handed man (F.G.) presents with prosopagnosia and with an inability to recognize famous and familiar buildings. Despite his deficit, F.G. obtained normal scores on neuropsychological tests of executive functions, language, praxis and primary visuoperceptual skills. Brain MRI showed atrophy predominantly in the right temporal lobe, particularly in the fusiform gyrus and the parahippocampal cortex. The present study investigated F.G.'s ability to orient himself in familiar and new environments. His wayfinding abilities in a familiar environment (i.e., his hometown) were preserved despite an inability to recognize familiar and famous buildings, monuments and landmarks in this environment. Wayfinding was achieved through a heavy reliance on written indications (e.g., names of restaurants and streets), preservation of a pre-existing cognitive map of this familiar environment, and normal executive functions necessary to plan the execution of a given trajectory. In an unfamiliar environment, F.G.'s topographical agnosia resulted in severe wayfinding difficulties and in the inability to build an adequate cognitive spatial representation. F.G.'s topographical agnosia results from a high-level visuoperceptual deficit, characterized by an inability to access a global configuration of complex visual stimuli such as familiar and famous monuments, and an over-reliance on the processing of local features.

Aged↗