Search

The term visual agnosia is used to refer to recognition disorders that are confined to the visual modality, that are not due to an impairment in sensory functions, and that cannot be explained by other cognitive deficits or by general reduction in intellectual ability. Here, we describe the different types of visual agnosia that have been reported (form agnosia, integrative agnosia, associative agnosia, transformational and orientation agnosia as well as category-specific impairments such as pure alexia and prosopagnosia) and how they relate to the current understanding of visual object recognition. Together with related disorders such as simultanagnosia, texture agnosia, aphantasia, and optic aphasia, these visual perceptual impairments can have severe consequences for those affected. We suggest how in-depth assessment can be carried out to determine the type and the extent of these impairments. In the context of clinical assessment, a step-by-step approach reflecting a posterior to anterior gradient in visual object recognition, from more perceptual to more memory-related processes, is suggested. Individually tailored interventions targeting the identified impairments can be initiated based on the results of the assessment.

Visual agnosia is a neuropsychological impairment of visual object recognition despite near-normal acuity and visual fields. A century of research has provided only a rudimentary account of the functional damage underlying this deficit. We find that the object-recognition ability of agnosic patients viewing an object directly is like that of normally-sighted observers viewing it indirectly, with peripheral vision. Thus, agnosic vision is like peripheral vision. We obtained 14 visual-object-recognition tests that are commonly used for diagnosis of visual agnosia. Our “standard” normal observer took these tests at various eccentricities in his periphery. Analyzing the published data of 32 apperceptive agnosia patients and a group of 14 posterior cortical atrophy (PCA) patients on these tests, we find that each patient's pattern of object recognition deficits is well characterized by one number, the equivalent eccentricity at which our standard observer's peripheral vision is like the central vision of the agnosic patient. In other words, each agnosic patient's equivalent eccentricity is conserved across tests. Across patients, equivalent eccentricity ranges from 4 to 40 deg, which rates severity of the visual deficit. In normal peripheral vision, the required size to perceive a simple image (e.g., an isolated letter) is limited by acuity, and that for a complex image (e.g., a face or a word) is limited by crowding. In crowding, adjacent simple objects appear unrecognizably jumbled unless their spacing exceeds the crowding distance, which grows linearly with eccentricity. Besides conservation of equivalent eccentricity across object-recognition tests, we also find conservation, from eccentricity to agnosia, of the relative susceptibility of recognition of ten visual tests. These findings show that agnosic vision is like eccentric vision. Whence crowding? Peripheral vision, strabismic amblyopia, and possibly apperceptive agnosia are all limited by crowding, making it urgent to know what drives crowding. Acuity does not (Song et al., 2014), but neural density might: neurons per deg2 in the crowding-relevant cortical area.

Introduction: Patients who have difficulties recognising visual form stimuli are usually labelled as having visual agnosia. However, recent studies let us identify different clinical manifestations corresponding to discrete diagnostic entities which reflect a variety of deficits along the continuum of cortical visual processing. Development: We reviewed different clinical cases published in medical literature as well as proposals for classifying deficits in order to provide a global perspective of the subject. Here, we present the main findings on the neuroanatomical basis of visual form processing and discuss the criteria for evaluating processing which may be abnormal. We also include an inclusive diagram of visual form processing deficits which represent the different clinical cases described in the literature. Lastly, we propose a boosted decision tree to serve as a guide in the process of diagnosing such cases. Conclusions: Although the medical community largely agrees on which cortical areas and neuronal circuits are involved in visual processing, future studies making use of new functional neuroimaging techniques will provide more in-depth information. A well-structured and exhaustive assessment of the different stages of visual processing, designed with a global view of the deficit in mind, will give a better idea of the prognosis and serve as a basis for planning personalised psychostimulation and rehabilitation strategies. Resumen: Introducción: Los pacientes que presentan dificultades para el reconocimiento visual de formas estimulares son considerados habitualmente como pacientes con agnosia visual. No obstante, estudios recientes permiten identificar diferentes manifestaciones clínicas que podrían corresponderse con entidades diagnósticas que reflejan déficits diferenciados a lo largo del continuo del procesamiento visual cortical de las formas. Desarrollo: Revisamos diferentes casos clínicos publicados en la literatura científica así como propuestas de clasificación de este déficit con la finalidad de dar una visión integradora del mismo. Exponemos los principales hallazgos en cuanto a las bases neuroanatómicas del procesamiento visual de formas y discutimos acerca de los criterios para evaluar dicho procesamiento cuando pueda estar alterado. Asimismo, presentamos un esquema de los déficits de procesamiento visual de formas que pretende integrar los distintos casos clínicos descritos en la literatura científica. Finalmente, proponemos un árbol de decisión que puede ser útil para guiar el proceso diagnóstico de estos casos. Conclusiones: Existe un amplio consenso en cuanto a las áreas corticales y circuitos neuronales que participan en el procesamiento visual, aunque futuros estudios con las nuevas técnicas de neuroimagen funcional permitirán profundizar en este aspecto. Una evaluación estructurada y exhaustiva de las diferentes etapas del procesamiento visual realizada a partir de una visión integradora del déficit nos facilitara un diagnóstico más objetivo, lo que nos permitirá conocer mejor el pronóstico y será de utilidad para guiar el diseño de estrategias individualizadas de psicoestimulación o rehabilitación. Keywords: Visual form agnosia, Associative agnosia, Integrative agnosia, Transformational agnosia, Classification of visual form agnosia, Pseudo-agnosia, Palabras clave: Agnosia visual de formas, Agnosia asociativa, Agnosia de integración, Agnosia espacial de transformación, Clasificación de agnosia visual de formas, Seudoagnosia visual

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.

Cerebral Palsy is defined as a movement alteration result of a non progressive damage witch is permanent in anencephalon that has not acquired its final maturation. Patients that suffer cerebral palsy present learning disabilities,that varies between being completely normal to severe as a consequence of memory, gnosis, praxis, perceptive andlanguage impairments. Nevertheless the consequences of this disease are not always predictable. This paper pretendsto make a description of the cognitive and behavioral deficits that overcomes along with the manifestation of thecerebral palsy and its possible treatment. We used a complete neuropsychological battery to evaluate a 7 years oldpatient who was diagnosed of cerebral palsy and spastic diplegia finding some cognitive impairment in fields such asmnesic, gnosic and attention processes.

The extent to which imagery and perceptual processes overlap in the brain has been the focus of a number of studies using different experimental methodologies (e.g., studies of functional brain activation and studies of patients with selective deficits following brain damage). Here we report the results of a number of different experimental investigations exploring visual memory in a patient with a severe perceptual deficit (HJA). We demonstrate that HJA can perform imagery tasks well that require judgements about a single object or object part; however, he experiences difficulty on tasks where he has to respond to the spatial relations between the local parts of objects. He experiences similar difficulties in perceptual processing. We argue that the bottom-up coding of visual images is influenced by the same intermediate visual processes that serve object recognition.

General Background. Motion Blindness. Cerebral Achromastopsia. Integrative Agnosia. Apperceptive Agnosia: A Deficit of Perceptual Categorisation of Objects. Vision and Visual Mental Imagery. Category-specific Recognition Impariments for Living and Nonliving Things. Optic Aphasia: A Review of Some Classic Cases. Covert Recognition and Anosognosia in Propagnosic Patients. Relations Among the Agnosias.

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.

Integrative agnosia is a type of visual agnosia associated with bilateral occipital lesions and characterized by the inability to identify stimuli in complex backgrounds, especially when it comes to overlapping or interlocking shapes. There are difficulties in coding and grouping the whole from the parts of the stimulus. We report a case of a 14 year-old female, with integrative agnosia as consequence of refractory symptomatic focal epilepsy with left occipital epileptogenic focus. Clinical features and the visual recognition processes are analyzed and discussed from different theoretical models that attempt to explain visual perception. La agnosia integrativa es un tipo de agnosia visual asociada a lesiones occipitales bilaterales que se caracteriza por la incapacidad para identificar estímulos en fondos complejos, especialmente, cuando se trata de formas superpuestas o entrelazadas. Existen dificultades para codificar y agrupar el todo a partir de las partes del estímulo. Se presenta un caso de una paciente de 14 años, con una agnosia integrativa como consecuencia de una epilepsia focal sintomática refractaria, con un foco epileptogénico occipital izquierdo. Se plantean las características clínicas de la paciente y se hace un análisis de sus procesos de reconocimiento visual discutidos a partir de los diferentes modelos teóricos que tratan de explicar la percepción visual.

The performance of two patients with visual agnosia was compared across a number of tests examining visual processing. The patients were distinguished by having dorsal and medial ventral extrastriate lesions. While inanimate objects were disadvantaged for the patient with a dorsal extrastriate lesion, animate items are disadvantaged for the patient with the medial ventral extrastriate lesion. The patients also showed contrasting patterns of performance on the Navon Test: The patient with a dorsal extrastriate lesion demonstrated a local bias while the patient with a medial ventral extrastriate lesion had a global bias. We propose that the dorsal and medial ventral visual pathways may be characterized at an extrastriate level by differences in local relative to more global visual processing and that this can link to visually based category-specific deficits in processing.

We report the case of a patient with a major defect in visual object recognition after vascular damage in posterior regions of both cerebral hemispheres. We conclude that our subject suffered from integrative agnosia, according to the terminology recently proposed by Humphreys and Riddoch (1987). However, there were several features by which our subject differed from the previous cases of integrative agnosia: he displayed analogous difficulties in tactile modality, he tended to recognise objects when they were actually used by the examiner, and he seemed to have access to semantic knowledge of objects from a partial analysis with no access to the structural knowledge. The implications of the case for current accounts of agnosia and visual object recognition are discussed.

How complex multipart visual objects are represented perceptually remains a subject of ongoing investigation. One source of evidence that has been used to shed light on this issue comes from the study of individuals who fail to integrate disparate parts of visual objects. This study reports a series of experiments that examine the ability of two such patients with this form of agnosia (integrative agnosia; IA), S.M. and C.R., to discriminate and categorize exemplars of a rich set of novel objects, "Fribbles", whose visual similarity (number of shared parts) and category membership (shared overall shape) can be manipulated. Both patients performed increasingly poorly as the number of parts required for differentiating one Fribble from another increased. Both patients were also impaired at determining when two Fribbles belonged in the same category, a process that relies on abstracting spatial relations between parts. C.R., the less impaired of the two, but not S.M., eventually learned to categorize the Fribbles but required substantially more training than normal perceivers. S.M.'s failure is not attributable to a problem in learning to use a label for identification nor is it obviously attributable to a visual memory deficit. Rather, the findings indicate that, although the patients may be able to represent a small number of parts independently, in order to represent multipart images, the parts need to be integrated or chunked into a coherent whole. It is this integrative process that is impaired in IA and appears to play a critical role in the normal object recognition of complex images.

We present a case (SE) with integrative visual agnosia following ischemic stroke affecting the right dorsal and the left ventral pathways of the visual system. Despite his inability to identify global hierarchical letters [Navon, D. (1977). Forest before trees: The precedence of global features in visual perception. Cognitive Psychology, 9, 353-383], and his dense object agnosia, SE showed normal global-to-local interference when responding to local letters in Navon hierarchical stimuli and significant picture-word identity priming in a semantic decision task for words. Since priming was absent if these features were scrambled, it stands to reason that these effects were not due to priming by distinctive features. The contrast between priming effects induced by coherent and scrambled stimuli is consistent with implicit but not explicit integration of features into a unified whole. We went on to show that possible/impossible object decisions were facilitated by words in a word-picture priming task, suggesting that prompts could activate perceptually integrated images in a backward fashion. We conclude that the absence of SE's ability to identify visual objects except through tedious serial construction reflects a deficit in accessing an integrated visual representation through bottom-up visual processing alone. However, top-down generated images can help activate these visual representations through semantic links.

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.

La parálisis cerebral se define como una alteración del movimiento que resulta por un daño (o lesión) no progresivo y permanente en un encéfalo inmaduro. Por otro lado el paciente con parálisis cerebral presenta dificultades de aprendizaje, que varían entre lo normal y una afección profunda como consecuencia de déficit mnésicos, gnósicos, práxicos, perceptivos y lingüísticos. Sin embargo las consecuencias de esta enfermedad no son siempre predecibles. Por esta razón el presente artículo busca hacer una descripción de sus características, su posible tratamiento y los principales déficit que se derivan de la aparición de la misma, mediante la evaluación neuropsicológica de un paciente de siete años que fue diagnosticado con parálisis cerebral y diplejía espástica y quien presenta secuelas cognoscitivas secundarias a la enfermedad que comprometen procesos gnósicos, mnésicos y atencionales. Cerebral Palsy is defined as a movement alteration result of a non progressive damage witch is permanent in an encephalon that has not acquired its final maturation. Patients that suffer cerebral palsy present learning disabilities, that varies between being completely normal to severe as a consequence of memory, gnosis, praxis, perceptive and language impairments. Nevertheless the consequences of this disease are not always predictable. This paper pretends to make a description of the cognitive and behavioral deficits that overcomes along with the manifestation of the cerebral palsy and its possible treatment. We used a complete neuropsychological battery to evaluate a 7 years old patient who was diagnosed of cerebral palsy and spastic diplegia finding some cognitive impairment in fields such as mnesic, gnosic and attention processes.

The current manuscript takes a critical look at the case of Goldstein and Gelb's patient, Schn, reported to be the first well-defined example of apperceptive visual agnosia. While doubts have been cast on the validity of the original investigations, we propose that perhaps the case of Schn should be reclassified as an example of integrative agnosia. Be that as it may, what is not in doubt is that the case of Schn has had a lasting impact on the development of neuropsychological theorem.

A CASE of apperceptive visual agnosia, revealing difficulties only in the performance on a standard overlapping-figures test, has been studied. Unusually, the patient demonstrated difficulties only with two semantic categories of the overlapped figures (clothes and school accessories) ; preserving, however, the knowledge of the same figures when presented isolated. We propose that the underlying deficit is only of a pseudo-semantic nature and is actually due to certain similarities of the two overlapping combinations, creating difficulties still on the apperception level only.

Normal observers process individual faces holistically, meaning that facial features are processed simultaneously over a face-wide perceptual span and that the face is represented as a single perceptual unit. Acquired prosopagnosia, an impairment of face recognition following brain damage is thought to be caused by a problem with holistic processing of faces (Sergent & Villlemure, 1989). However, previous studies have only demonstrated an impairment of interactive processing of features in patients who, in addition, present general visual integrative agnosia (e.g., Boutsen & Humphreys, 2002; Levine & Calvanio, 1989), so that direct evidence for a deficit in holistic face processing in prosopagnosia is lacking. In an experiment with a brain damaged case of prosopagnosia (PS, Rossion et al., 2003), we used two gaze-contingent techniques allowing manipulation of the amount of information that was simultaneously available. First, a gaze-contingent foveal mask, prevented the use of foveal, high resolution information, necessary for detailed investigation of the facial features, but allowed holistic processing based on lower resolution peripheral information. Second, a gaze-contingent foveal window covering all peripheral information, prevented the simultaneous use of several facial features, but allowed detailed investigation of each feature individually. In a face matching task, normal control participants showed increased errors and RTs with a foveal window in comparison to conditions with a foveal mask or with a full face. PS, on the contrary, was almost unimpaired by a foveal window relative to a full face, while she had major difficulties recognizing faces with a foveal mask. Moreover, the eye movement data confirmed the findings from previous studies, that for face recognition, PS mainly relies on the mouth region, while normal observers attend to the region just below the eyes. These data provide direct evidence for impairment of holistic face processing in acquired prosopagnosia.

A single case study of a patient with visual agnosia is presented. The patient had a marked impairment in visual object recognition along with good tactile object identification and a preserved ability to copy. Detailed investigations demonstrated impaired perceptual processes, with the patient's identification strongly affected by duration of stimulus exposure and by using overlapping figures. However, his stored knowledge of objects was shown to be intact. The results demonstrate that agnosia may be determined by a specific deficit in integrating form information; and that the input description for visual object recognition, disrupted in this patient, is functionally separate from stored object descriptions, which are intact. The implications of the results for understanding visual agnosia and for theories of normal visual object recognition are discussed.

Integrative agnosia is a type of visual agnosia associated with bilateral occipital lesions and characterized by the inability to identify stimuli in complex backgrounds, especially when it comes to overlapping or interlocking shapes. There are difficulties in coding and grouping the whole from the parts of the stimulus. We report a case of a 14 year-old female, with integrative agnosia as consequence of refractory symptomatic focal epilepsy with left occipital epileptogenic focus. Clinical features and the visual recognition processes are analyzed and discussed from different theoretical models that attempt to explain visual perception. La agnosia integrativa es un tipo de agnosia visual asociada a lesiones occipitales bilaterales que se caracteriza por la incapacidad para identificar estímulos en fondos complejos, especialmente, cuando se trata de formas superpuestas o entrelazadas. Existen dificultades para codificar y agrupar el todo a partir de las partes del estímulo. Se presenta un caso de una paciente de 14 años, con una agnosia integrativa como consecuencia de una epilepsia focal sintomática refractaria, con un foco epileptogénico occipital izquierdo. Se plantean las características clínicas de la paciente y se hace un análisis de sus procesos de reconocimiento visual discutidos a partir de los diferentes modelos teóricos que tratan de explicar la percepción visual.