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PubMed1991

The role of sensorimotor experience in object recognition. A case of multimodal agnosia.

Object recognition was studied in a 19-yr-old male patient who presented severe multimodal amnesia and agnosia without significant intellectual, linguistic or perceptual deficits. Bilateral temporal lobe lesions involved medial, polar and anterior infero-temporal structures. Although visual recognition was impaired to various extents for all categories of objects, preservation of certain capacities were demonstrated. In particular, the patient was able to determine specifically how to manipulate certain objects, in spite of his incapacity to define their function or their context of utilization. It is argued that object recognition involves different processing modes such that when direct access to representations of an object is impaired, sensorimotor information activated via alternative cortical and subcortical pathways may provide a limited mechanism for recognition.

Adult↗
PubMed1994

Agnosia, alexia and a remarkable form of amnesia in an adolescent boy.

Childhood cases of global anterograde amnesia, visual agnosia or alexia without agraphia, either alone or in any combination, are extremely rare. Here we report the case of a male adolescent, Neil (a pseudonym), who consequent to a pineal tumour began to exhibit all three disorders in the presence of normal verbal intelligence. The most surprising aspect of Neil's case, however, is his ability to retrieve postmorbid memories through the act of writing without being able to provide any oral account of the content of his written reports. His memory retrieval thus has some of the character of 'automatic writing'. This evidence pointing to Neil's possession of a dissociated form of episodic memory presents a new challenge to our understanding of the organization of memory and of the cerebral systems underlying it.

Adolescent↗
PubMed1995

The functional anatomy of recovery from auditory agnosia. A PET study of sound categorization in a neurological patient and normal controls.

H2(15)O-PET was used to investigate the functional anatomy of recovery in a patient (J.B.) with bilateral perisylvian strokes and auditory agnosia, who partially regained the ability to recognize environmental sounds, but remained clinically word-deaf. The patient and a group of six normal volunteers were scanned in the following three conditions: (i) passive listening to environmental sounds; (ii) categorization of environmental sounds; (iii) at rest. In normal subjects, passive listening as compared with rest was associated with significant activations in the auditory cortices and posterior thalami, and in the inferior parietal lobe and anterior insula/frontal opercular region on the right. In J.B., activations were observed in the spared auditory cortex and inferior parietal lobe of the right hemisphere and in regions adjacent to the perisylvian lesion in the left hemisphere (anterior insula/frontal opercular region, middle temporal gyrus and inferior parietal lobe). The recovered function, as measured by categorization of sounds compared with passive listening, in J.B. was associated with bilateral activation of a distributed network comprising (pre)frontal, middle temporal and inferior parietal cortices, as well as the right cerebellum and the right caudate nucleus. In addition, there was a left-sided activation of the anterior cingulate gyrus. In normal subjects, the same categorization task led to activation of a network comprising (pre)frontal, middle temporal and inferior parietal cortices in the left hemisphere only. These results suggest that bilateral activation (with recruitment of areas homologous to those known to be responsible for normal function), the engagement of peri-infarct regions, and the involvement of a more widespread neocortical network, are mechanisms of functional reorganization after injury that may enable recovery from, or compensation for, cognitive deficits.

Agnosia↗
PubMed1999

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.

Aged↗
PubMed1990

Implications of olfactory agnosia for understanding sex differences in schizophrenia.

In our studies, 50 percent of the male patients with schizophrenia have an olfactory agnosia. This finding is of interest because the olfactory neuroanatomical network involves brain regions found to be abnormal in patients with schizophrenia, and this olfactory deficit appears to be sex dependent. This article reviews conceptual models for assessing olfactory function, describes the neuroanatomical structures involved, and reviews the findings of olfactory performance in patients with neurological dysfunction. The findings are then integrated with neuropathological studies of patients with schizophrenia. Finally, as there is increasing evidence for a sex difference in patients with schizophrenia, a model is suggested to account for these differences based on neuro-developmental and latent lesion hypotheses.

Agnosia↗
PubMed1996

Obstacle avoidance during locomotion is unaffected in a patient with visual form agnosia.

A patient (D.F.) who developed visual form agnosia following carbon monoxide-induced anoxia was assessed on three tests designed to measure her sensitivity to obstacle height in a locomotor task. Although her verbal estimates of the height of the obstacles were correlated with their actual height, the slope of the line relating estimated and actual obstacle height was much shallower than for control subjects. Similarly, when asked to estimate the height of the obstacle by raising one leg while standing nearby, the slope of line relating toe elevation and obstacle height was shallower than in control subjects. In contrast, D.F. was able to negotiate the same obstacles during locomotion as well as control subjects: toe elevation increased linearly as a function of obstacle height with similar slopes and correlation for the line relating toe elevation and obstacle height. These results provide additional support for the proposal by Goodale and Milner that the cortical pathways mediating the required transformations for the visual control of skilled actions are separate from those mediating experiential perception of the visual world.

Adult↗
PubMed1998

Is there semantic specificity in overlapping-figures agnosia?

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.

Agnosia↗
PubMed2002

Dynamic visual speech perception in a patient with visual form agnosia.

To examine the role of dynamic cues in visual speech perception, a patient with visual form agnosia (DF) was tested with a set of static and dynamic visual displays of three vowels. Five conditions were tested: (1) auditory only which provided only vocal pitch information, (2) dynamic visual only, (3) dynamic audiovisual with vocal pitch information, (4) dynamic audiovisual with full voice information and (5) static visual only images of postures during vowel production. DF showed normal performance in all conditions except the static visual only condition in which she scored at chance. Control subjects scored close to ceiling in this condition. The results suggest that spatiotemporal signatures for objects and events are processed separately from static form cues.

Adult↗
PubMed1997

Mirror agnosia.

Normal people rarely confuse the mirror image of an object with a real object so long as they realize they are looking into a mirror. We report a new neurological sign, 'mirror agnosia', following right parietal lesions in which this ability is severely compromised. We studied four right hemisphere stroke patients who had left visual field 'neglect'. i.e. they were indifferent to objects in their left visual field even though they were not blind. We then placed a vertical parasagittal mirror on each patients' right so that they could clearly see the reflection of objects placed in the (neglected) visual field. When shown a candy or pen on their left, the patients kept banging their hand into the mirror or groped behind it attempting to grab the reflection; they did not reach for the real object on the left, even though they were mentally quite lucid and knew they were looking into a mirror. Remarkably, all four patients kept complaining that the object was 'in the mirror', 'outside my reach' or 'behind the mirror'. Thus, even the patients' ability to make simple logical inferences about mirrors has been selectively warped to accommodate the strange new sensory world that they now inhabit. The finding may have implications for understanding how the brain creates representations of mirror reflections.

Aged↗
PubMed1992

Partial imitation and partial sensory agnosia in mentally normal children with convulsive disorders.

Mentally normal 6-9 year old children with or without convulsive disorders were examined using the procedures of the five soft signs (SS) selected from conventional soft neurological signs and Bergès' gesture imitation tasks. In comparisons of SS between the 60 children with convulsive disorders (CD group) and the 38 without (N group), the average number of SS detected in each case and the incidence ratio of the two signs--partial imitation (PI) and partial sensory agnosia (PSA)--were higher in the CD group than the N group. Examinations of relationships between age, IQ, error index (EI; an index taken from the Continuous Performance Test) and SS, and of correlations among the SS, found two kinds of SS: age-related and El-related signs. The former included right-left confusion, clumsiness and PI, which correlated with each other, while the latter included unstableness of lateral gazing and PSA, which did not correlate with each other. Even though several factors belonging to characteristics of convulsive disorders were evaluated concerning the presence or absence of PI and PSA, there was only one relationship: PSA was more common in children with febrile convulsions than in those with epilepsy. We speculated that PSA reflected an immaturity of the brain in children with febrile convulsions.

Agnosia↗
PubMed1979

Prosopo-affective agnosia associated with chronic organic brain syndrome.

Impairment of the ability to recognize facially expressed emotions was studied in 14 chronically disoriented patients with chronic organic brain syndrome (CBS). This impairment was named prosopo-affective agnosia (PAA). A diagnostic requirement was relatively intact neurologic functioning in underlying perceptual-verbal-motor processing. A test was designed for facial-affect recognition in the accurate differentiation of normal persons from chronically disoriented CBS patients. No normal subject made any errors in this test. Despite decades of illness and hospital living, patients with a history of schizophrenia or major affective disorders scored almost at a normal level (95 vs. 100 percent) in this test, and significantly higher (95 vs. 66 percent) than did the disoriented CBS patients. The social and therapeutic implications of the findings are stressed. CBS patients may be impaired with respect to receiving and appreciating elementary aspects of social communications such as recognizing a smile, anger, sadness or disapproval on the faces of people who surround them. This disability requires understanding and a special attitude on the part of the therapeutic team toward such patients.

Aged↗
PubMed1996

Visual form agnosia in multiple sclerosis.

We report a case of multiple sclerosis with visual form agnosia and callosal syndromes. Initially, the patient's visual recognition of object form was severely disturbed at the perceptual stage, in association with left-sided ideomotor apraxia and agraphia. Magnetic resonance imaging showed large white matter lesions in the bilateral frontal and occipital lobes, the latter extending to the occipitotemporal junction, and widespread corpus callosum lesions. Over the course of one year follow-up, neuropsychological examinations indicated that the patient's visual recognition defects occurred not only at the early substage of form perception, but also at the stage of reproducing the shape of objects from visual memory store. The present case suggests that neural connections between the striate cortex and occipitotemporal visual areas are crucial for both the perceptual and associative stages of visual object recognition.

Agnosia↗
PubMed1986

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.

Aged↗
PubMed1998

Separate visual pathways for perception of actions and objects: evidence from a case of apperceptive agnosia.

Recognition of different kinds of visual stimuli was studied in a patient who acquired apperceptive visual agnosia after a bilateral occipitotemporal lesion which partially spared the primary visual cortex. Impairment in recognising static objects perceived visually sharply contrasts with the relatively well preserved ability to recognise objects from gestures illustrating their use, and to recognise actions shown in line drawings. It is suggested that the occipitoparieto-frontal pathway is involved in the recognition of actions, and in the recognition of objects when sensorimotor experience is evoked.

Aged↗
PubMed2003

Radical "visual capture" observed in a patient with severe visual agnosia.

We report the case of a 79-year-old female with visual agnosia due to brain infarction in the left posterior cerebral artery. She could recognize objects used in daily life rather well by touch (the number of objects correctly identified was 16 out of 20 presented objects), but she could not recognize them as well by vision (6 out of 20). In this case, it was expected that she would recognize them well when permitted to use touch and vision simultaneously. Our patient, however, performed poorly, producing 5 correct answers out of 20 in the Vision-and-Touch condition. It would be natural to think that visual capture functions when vision and touch provide contradictory information on concrete positions and shapes. However, in the present case, it functioned in spite of the visual deficit in recognizing objects. This should be called radical visual capture. By presenting detailed descriptions of her symptoms and neuropsychological and neuroradiological data, we clarify the characteristics of this type of capture.

Aged↗
PubMed1977

Distinctive features of unilateral spatial agnosia in right and left brain-damaged patients.

In order to study the distinctive features of unilateral spatial agnosia shown by right and left brain-damaged patients, a test of copying drawings with guiding landmarks was given to 83 control subjects and to 248 patients affected by right (n = 108) or left (n = 140) hemispheric damage. The test enabled us to obtain a quantitative assessment both of the lines omitted ('omissions') and of the lines wrongly traced ('errors') on the half page contralateral to the damaged hemisphere. Results showed that contralaterally to the hemispheric locus of lesion a clear-cut double dissociation can be found between right and left brain-damaged patients: the former showed a striking tendency to omit the lines lying on the left half of the sheet, whereas the latter tended mainly to trace faulty lines on the right half of the drawings.

Agnosia↗
PubMedDate not supplied

Behavioral and neuroimaging evidence for a contribution of color and texture information to scene classification in a patient with visual form agnosia.

A common notion is that object perception is a necessary precursor to scene perception. Behavioral evidence suggests, however, that scene perception can operate independently of object perception. Further, neuroimaging has revealed a specialized human cortical area for viewing scenes that is anatomically distinct from areas activated by viewing objects. Here we show that an individual with visual form agnosia, D.F., who has a profound deficit in object recognition but spared color and visual texture perception, could still classify scenes and that she was fastest when the scenes were presented in the appropriate color. When scenes were presented as black-and-white images, she made a large number of errors in classification. Functional magnetic resonance imaging revealed selective activation in the parahippocampal place area (PPA) when D.F. viewed scenes. Unlike control observers, D.F. demonstrated higher activation in the PPA for scenes presented in the appropriate color than for black-and-white versions. The results demonstrate that an individual with profound form vision deficits can still use visual texture and color to classify scenes-and that this intact ability is reflected in differential activation of the PPA with colored versions of scenes.

Adult↗
PubMed2001

Visual agnosia after treatment of a posterior fossa ependymoma in a 16-month-old girl.

We present the clinical observation of a 16-month-old girl treated for a posterior fossa ependymoma who experienced severe and delayed visual dysfunction. She was initially treated by surgery and conventional chemotherapy. When she relapsed at age 3 years, the salvage treatment combined high-dose chemotherapy, second surgery, and local irradiation. At age 4 years, disturbed gait and dysarthric speech appeared rapidly, and she became unable to recognize objects and people. Computed tomography revealed bilateral calcifications in the cerebellum and temporal and occipital lobes but no relapse. The neuropsychologic evaluations revealed signs of visual agnosia and marked intellectual impairment. The role of the different treatment modalities in the pathogenesis of this unusual syndrome is discussed.

Agnosia↗