Visual associative agnosia and optic aphasia. A single case study and a review of the syndromes.

The case is presented of a patient who showed visual naming disturbances caused by a left occipital infarction. His performance on tests of visual naming, of recognition not requiring a verbal response, and of verbal-visual matching demonstrated a wide range of qualitatively different errors, including complete inability to recognize the object, access to partial semantic knowledge, and mere name finding difficulty. On the basis of the present case and of a review of the recent literature, the clinical distinction between visual associative agnosia and optic aphasia and the relation of these disorders with the anatomical site of lesion are discussed.     

Associative visual agnosia and its related deficits: The role of the minor hemisphere in assigning meaning to visual perceptions

A patient with severe associative visual agnosia for objects and pictures could identify those objects by touch and copy them; neither naming nor visual processing difficulties could account for his deficit. He was not alexic. The CAT scan revealed bilateral infarctions: a large left parietal-occipital lesion and a smaller right occipital lesion involving underlying white matter. Evidence suggests the presence of independent pathways for meaningful representation of objects and pictures, written material, familiar faces, and, perhaps, colors. Independence of these pathways at their origin indicates the right hemisphere is important in analyzing visual material beyond the perceptual level.     

Tactile agnosia and tactile aphasia: symptomatological and anatomical differences.

Two patients with tactile naming disorders are reported. Case 1 (right hand tactile agnosia due to bilateral cerebral infarction) differentiated tactile qualities of objects normally, but could neither name nor categorize the objects. Case 2 (bilateral tactile aphasia after operation of an epidural left parietal haematoma) had as severe a tactile naming disturbance as Case 1, but could categorize objects normally, demonstrating that tactile recognition was preserved. Case 1 may be the first case of tactile agnosia clearly differentiated from tactile aphasia. CT scans of Case 1 revealed lesions in the left angular gyrus, and in the right parietal, temporal, and occipital lobes. Case 2 had lesions in the left angular gyrus and of posterior callosal radiations. Our findings suggest that tactile agnosia appears when the somatosensory association cortex is disconnected by a subcortical lesion of the angular gyrus from the semantic memory store located in the inferior temporal lobe, while tactile aphasia represents a tactual-verbal disconnection.     

Visual agnosia contrasted with visual-verbal disconnection

Serial neuropsychological findings are contrasted in two cases: one with a syndrome of visual agnosia, the other with a disorder resulting from visual-verbal disconnection. Both patients were impaired in confrontation naming of objects and pictures, but the patient with visual-verbal disconnection was able to perform tasks of color-object matching and pantomime recognition, whereas the patient with visual agnosia could not do so, demonstrating a failure to establish meaningful nonverbal visual-visual association. Additionally, the performance of the patient with visual agnosia reflected an evolution from the apperceptive to associative forms of the disorder, suggesting that the various impairments of visual identification form a continuum of related disorders.     

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.     

Visual agnosia and amnesia from a left unilateral lesion

This case report describes the behavior of a patient with a visual agnosia of the associative type, developing to optic agnosia at a later stage. Language, general intelligence and right hemisphere functions were well preserved, but recognition of visually presented objects, colors, faces, words, and complex stimuli was impaired. Agnosia was accompanied by a multimodal amnestic syndrome. CT displayed a focal left hemisphere lesion. The observed pathomorphology is not consistent with a bilateral visuolimbic disconnection syndrome, as suggested from previous case studies. Significant components of visual semantic processing may be executed by the left hemisphere.     

Visual associative agnosia: a clinico-anatomical study of a single case.

A single case study of a patient with visual associative agnosia is described. The patient had well preserved language, spatial, visual, and perceptual abilities but nevertheless was impaired in recognising visually presented common objects. It is argued that his deficit cannot be accounted for in terms of a disconnection syndrome. Behavioural and anatomical (MRI scan) evidence for focal unilateral dysfunction is presented. It is concluded that the left hemisphere plays a crucial role in recognising the meaning of common objects.     

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.     

Optic Aphasia: Evidence of the Contribution of Different Neural Systems to Object and Action Naming

Visual stimulus naming was studied in a 66-year-old male patient with optic aphasia subsequent to left occipito-temporal infarction. While having difficulty in naming objects perceived visually, he was able to name objects by viewing gestures illustrating their use, and to name actions shown in pictures. These results suggest that naming performance depends on the kind of stimulus that is visually presented (object vs. action). The present findings lend support to cognitive models which postulate the existence of visual and functional semantic systems.     

Visual object agnosia: current conceptions

Visual agnosia for objects is a difficulty in recognizing objects presented visually. This difficulty can not be explained by a mental deterioration, a disorder of attention or a lack of familiarity with the object. Two criteria are essential but disputed: the absence of visual sensory difficulty necessary for adequate perception; possible recognition of the object by another sensory modality. An object is characterized by a triple representation: formal, semantic, lexical. The clinical, cognitive, pathophysiological analysis lead to distinguish 3 types of visual agnosia. 1) Aperceptive visual agnosia: patients see badly with morphological errors; the disorder concerns visual informations processing that is a necessary condition for identifying the formal representation of the object; the lesions are bilateral and involve the occipito-temporal cortex. 2) Associative visual agnosia: patients can copy, are not aphasic, but give erroneous verbal responses; the disorder concerns the links between formal representations and semantic, lexical representations; the lesions are unilateral and involve the left gyrus angularis connections. 3) Asemantic visual agnosia: patients have lost the meanings of objects and words; the disorder concerns semantic representations; the lesions are bilateral and involve the temporo-limbic cortex.     

Optic Aphasia: Evidence of the Contribution of Different Neural Systems to Object and Action Naming

Visual stimulus naming was studied in a 66-year-old male patient with optic aphasia subsequent to left occipito-temporal infarction. While having difficulty in naming objects perceived visually, he was able to name objects by viewing gestures illustrating their use, and to name actions shown in pictures. These results suggest that naming performance depends on the kind of stimulus that is visually presented (object vs. action). The present findings lend support to cognitive models which postulate the existence of visual and functional semantic systems.     

The role of local and global processing in the recognition of living and nonliving things

We report a study on a patient (DW) with integrative visual agnosia and a category-specific recognition impairment for living things. We assessed DW's local and global processing and tested if his integrative agnosia could have led directly to his category-specific impairment. The main findings were: (i) DW was faster at identifying local compared to global letters. (ii) DW showed no local-to-global (or global-to-local) interference effects in selective attention tasks. (iii) DW showed a congruency effect in a divided attention task, suggesting that, when his attention was cued to both levels, he could process information simultaneously and integrate local and global information. (iv) Controls were poorer at naming nonliving compared to living things when presented with silhouettes. These data suggest that local and global information are differentially weighted in the visual recognition of living and nonliving things, and that an impairment in processing the overall shape of an object can lead to a category-specific deficit for living things. Crucially, this implies that category-specific impairments do not necessarily reflect damage to the semantic system, and models of semantic memory based on this assumption need to be revised.     

Disconnection and recognition of faces. A case with lesions of the left visual cortex and the splenium

We report the clinical findings in a case of alexia without agraphia, due to a left posterior cerebral artery infarction, in which C.T. showed occipital and splenial lesions. There were in addition a right homonymous hemianopsia and agnosia for colors, objects and pictures, with both associative and disconnective aspects. The hypothesis of an occipito-occipital disconnection, depriving the left visual associative areas of inputs, could explain this agnosia. The most striking findings in this case was, besides an anomia for faces, a peculiar difficulty to recognize her own face. The patient seemed to recognize herself. The patient spoke about herself in the third person, giving genuine autobiographical details, without being able to say: "it is me". This phenomenon is discussed in terms of disconnection: the right hemisphere sending information from the semantic field evoked by her own face, through the anterior part of the corpus callosum, to the left hemisphere. We discuss the hemispheric contribution within cognitive experience, and the role of language concerning the conscious experience in man.     

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.     

Visual agnosia: the dual deficit of perception and recognition

This case of visual agnosia is of special interest because of its causation by trauma, of the unusually long follow-up (10 1/2 years), and the evidence for dual deficits of recognition and perception. Although most of the findings were characteristic of associative visual agnosia with preserved perceptual function, the poor copying, contrasted to better spontaneous drawing, suggested apperceptive agnosia as well. Prosopagnosia, alexia without agraphia, Balint's syndrome, visual static agnosia and simultanagnosia were also observed. The patient had persisting amnestic syndrome, but no dementia or aphasia. The responses to visual stimulation were perseverations, form confusions and confabulations. Visual evoked potentials were severely, bilaterally abnormal and computerized tomographic localization showed bilateral lesions also. The stages of recognition are analysed through this case of visual verbal disconnection and the importance of memory in perception is highlighted.