11/348. Pathological perceptual completion in hemianopia extends to the control of reach-to-grasp movements. The neuropsychological phenomenon of blindsight is observed when patients who are cortically blind exhibit residual visual processing capabilities for stimuli presented within their scotoma to which they are otherwise unaware. Cortically blind patients may also exhibit the phenomenon of pathological visual completion in which, paradoxically, they can become aware of a complete visual stimulus even when a significant portion of that stimulus falls within their blind hemifield. In this study, the ability of a blindsight patient (G.Y.) to use visual information to control reach-to-grasp movements to static objects presented within his blind hemifield was investigated. The results indicate that while G.Y. was insensitive to variations in object size when reaching for objects presented entirely within his blind hemifield, his ability to accurately grasp objects located within his blind field was vastly improved if part of the object to be grasped extended into his seeing hemifield. This finding demonstrates that visual awareness can facilitate the visuomotor processing of object form within G.Y.'s apparently blind field, and suggests that the primary deficit in blindsight may be an impairment of visual consciousness rather than an absolute loss of visual function. ( info) |
12/348. Akinetopsia from nefazodone toxicity. PURPOSE: To investigate two cases of selective impairment of motion perception (akinetopsia) induced by toxicity from the antidepressant nefazodone, a new drug that blocks serotonin reuptake and antagonizes 5-HT2 receptors. methods: case reports. RESULTS: A 47-year-old man receiving nefazodone (Serzone; Bristol-Meyers Squibb, new york, N.Y.) (100 mg twice daily), reported a bizarre derangement of motion perception. Moving objects were followed by a trail of multiple "freeze-frame" images, which dissipated promptly when motion ceased. A 48-year-old woman receiving nefazodone (400 mg daily at bedtime) reported a similar phenomenon, with visual trails following moving objects. In both patients, vision returned to normal after the dosage of nefazodone was reduced or eliminated. CONCLUSIONS: Nefazodone toxicity can result in akinetopsia, characterized by the inability to perceive motion in a normal, smooth fashion; persistence of multiple, strobelike images; and visual trails behind moving objects. In this rare syndrome, stationary elements are perceived normally, indicating that nefazodone causes selective impairment of pathways involved in motion processing in the visual system. ( info) |
13/348. Ipsilesional intentional neglect and the effect of cueing. BACKGROUND: Contralesional hemispatial neglect may be induced by an attentional deficit where patients are inattentive to or unaware of stimuli in contralesional hemispace, an intentional deficit where patients are unable to act in or towards contralesional hemispace, or both. The deficits associated with ipsilesional neglect have not been as well characterized. Because cueing may be used as a rehabilitative assistive device, we wanted to learn whether the efficacy of an attentional or intentional cue was related to the type of bias. methods: We studied a patient with a right frontotemporal stroke who had ipsilesional neglect by using a video apparatus that dissociates sensory-attentional and motor-intentional systems. We also performed a cueing experiment with primarily sensory-attentional cues (i.e., read the letter at the end of the line) and primarily motor-intentional cues (i.e., touch the end of the line). RESULTS AND CONCLUSIONS: Ipsilesional neglect was primarily a motor-intentional deficit with a motor-action bias to the left and a secondary sensory-attentional bias for stimuli to the right. With cueing we found a double dissociation: the rightwards motor-intentional cue improved the primary left-sided intentional bias and the leftwards sensory-attentional cue improved the secondary right-sided attentional bias. Effective rehabilitation strategies need to address both sensory-attentional and motor-intentional deficits in patients with neglect. ( info) |
14/348. Oscillopsia and pseudonystagmus in kidney transplant patients. PURPOSE: Modern immunosuppressants have improved the success of kidney transplantation for renal failure patients. They also may induce neurotoxic effects including tremor. We report two cases of pseudonystagmus and oscillopsia in transplant patients caused by immunosuppressant-induced head tremor and gentamicin-induced vestibulotoxicity. methods: case reports. head tremor, static visual acuity, and dynamic visual acuity were measured. Vestibular function was evaluated with ice water calorics. RESULTS: Both patients had significant head tremor and pseudonystagmus. head stabilization improved static visual acuity. Dynamic visual acuity revealed a 4-line and 10-line loss of visual acuity, respectively. CONCLUSIONS: These findings of pseudonystagmus and oscillopsia are likely to become more prevalent as more renal failure patients receive transplants. Improvement may be seen with reduction of immunosuppressant, reduction of stimulant intake, use of medications to reduce head tremor, and vestibular rehabilitation. ( info) |
15/348. A category-specific deficit of spatial representation: the case of autotopagnosia. Following a vascular lesion in the parietal cortex of the language dominant hemisphere (right in one case), two patients showed a striking dissociation between spared naming, recognition and use of their body parts and an inability in localising on verbal command the same body parts on themselves and on a mannequin (Autotopagnosia, AT). The patients were submitted to a modified version of Reed and Farah Test (1995), a test that taps the ability to encode changes of body position as opposed to changes of position of objects. Their performance differed from normal controls, showing a specific deficit in encoding body position.It is suggested that AT could be the consequence of a lesion in a specific neural circuit, located in the language dominant hemisphere, whose function is to encode the body position for both oneself and others. ( info) |
16/348. blindness to form from motion despite intact static form perception and motion detection. We studied the motion perception, including form and meaning generated by motion, in a hemianopic patient who also had visual perceptual impairments in her seeing hemifield as a result of a lesion in ventral extrastriate cortex. She was unable to recognise 2- or 3-dimensional forms, and even borders, generated by motion alone, failed to recognise mimed actions or the Johannson 'biological motion' display, and ceased to recognise people well-known to her when they moved. Her performance with static displays, although impaired, could not explain her inability to perceive shape or derive meaning from moving displays. Unlike a motion-blind patient, she can still see and describe the motion, with the exception of second-order motion, but not what it creates or represents. ( info) |
17/348. The automatic updating of egocentric spatial relationships and its impairment due to right posterior cortical lesions. The non-visual updating of body-centred spatial relationships was investigated in an experiment in which blindfolded patients had to point to previously seen targets after a body rotation in the absence of vision. patients with lesions to the right dorsal (RD) area were impaired at updating their positions relative to non-RD patients and normal subjects: they tended to underestimate systematically the angle through which they had turned. The results are interpreted in terms of impoverished locomotor input and/or systematically biased processing or locomotor proprioception in the RD patients, which prevented accurate tracking of changes in egocentric spatial relationships. ( info) |
18/348. Faces call for attention: evidence from patients with visual extinction. Three patients with left spatial neglect and visual extinction from right brain damage were studied to determine whether faces are privileged in summoning attention. In a first experiment, either a face, a name, or a meaningless shape were briefly presented in the right, left or both visual hemifields. On bilateral trials, all patients extinguished a left-side face much less often than a left-side name or a left-side shape. Conversely, they extinguished a left-side shape more often when it was accompanied by a right-side face rather than a right-side name. In a second experiment, either a face or a scrambled face could appear in the right, left or both hemifields. Again, on bilateral trials, a left-side face was less likely to be missed than a scrambled one. These results suggest an advantage of faces in capturing attention and overcoming extinction, which may be related to their special biological and social value, or to the very efficient and automatic operation of specific perceptual processses that extract facial organization in extrastriate visual areas. These findings also demonstrate that the distribution of spatial attention and extinction can be modulated by the relevance of visual stimuli. This implies that substantial analysis and categorization may take place in the visual system before information from the contralesional field is selected for, or excluded from, attentive vision. ( info) |
| A case of bipolar disorder subsequent to a mild head injury in a 15-year-old girl is reported. review of the literature indicates that this is an extremely rare outcome. Lack of adequate follow-up studies makes it difficult to accurately predict type and severity of psychiatric outcome. Assessment and management involves ongoing consideration of both organic and psychosocial factors even after initial negative investigations. ( info) |
20/348. Neglect and constructive disorder. A 61 year-old right handed man, who suffered from right cerebral infarction with evidences of visual-spatial neglect and constructive disorder, was reported. When copying simple geometric designs, he omitted to copy figures on the left side of the page; he tended to bisect the line to the right of the line's real center; after memorizing the familiar pictures he mainly mentioned the pictures on the right side of the page; when copying the "Rey Complex" he also ignored the structures on the left side. The relations of the neglect and construction disorder are discussed. ( info) |