Studies of saccadic suppression and induced motion have suggested separate representations of visual space for perception and visually guided behavior. Because these methods required stimulus motion, subjects might have confounded motion and position. We separated cognitive and sensorimotor maps without motion of target, background, or eye, with an "induced Roelofs effect": a target inside an off-center frame appears biased opposite the direction of the frame. A frame displayed to the left of a subject's center line, for example, will make a target inside the frame appear farther to the right than its actual position. The effect always influences perception, but in half of our subjects it did not influence pointing. Cognitive and sensorimotor maps interacted when the motor response was delayed; all subjects now showed a Roelofs effect for pointing, suggesting that the motor system was being fed from the biased cognitive map. A second experiment showed similar results when subjects made an open-ended cognitive response instead of a five-alternative forced choice. Experiment 3 showed that the results were not due to shifts in subjects' perception of the felt straight-ahead position. In Experiment 4, subjects pointed to the target and judged its location on the same trial. Both measures showed a Roelofs effect, indicating that each trial was treated as a single event and that the cognitive representation was accessed to localize this event in both response modes.Several topographic maps represent the visual world in the cortex (Felleman & Van Essen, 1991). This characteristic of the visual system raises a question for visual physiology: do all of these maps work together to create a single representation of visual space, or are they functionally distinct? If they are distinct, how many functional maps are there and how do they communicate with one another? This paper presents psychophysical evidence for at least two functionally distinct representations of the visual world in normal humans; under some conditions, the two representations can simultaneously hold different spatial values. The paper also demonstrates some of the ways in which the representations communicate with one another.An early hint that cognitive and sensorimotor systems are separable in normal humans came from studies of eye movements. On the one hand, subjects are unaware ofsizable displacements of the visual world if they occur during saccadic eye movements, implying that information about spatial location is degraded during saccades (Bridgeman,
Background-Cognitive dysfunction is a common and disabling sequela of subarachnoid hemorrhage (SAH). Although several clinical and radiographic findings have been implicated in the pathogenesis of cognitive dysfunction after SAH, few prospective studies have comprehensively and simultaneously evaluated these risk factors. Methods-Between July 1996 and March 2000, we prospectively evaluated 113 of 248 consecutively admitted nontraumatic SAH patients alive at 3 months with a comprehensive neuropsychological evaluation. Summary scores for 8 cognitive domains were calculated to express test performance relative to the entire study population. Clinical and radiographic variables associated with domain-specific cognitive dysfunction were identified with forward stepwise multiple regression, with control for the influence of demographic factors. Results-The study participants were younger (Pϭ0.005), less often white (Pϭ0.006), and had better 3-month modified Rankin scores (Pϭ0.001) than those who did not undergo neuropsychological testing. The proportion of subjects who scored in the impaired range (Ͼ2 SD below the normative mean) on each neuropsychological test ranged from 10% to 50%. Predictors of cognitive dysfunction in 2 or more domains in the multivariate analysis included global cerebral edema (4 domains), left-sided infarction (3 domains), and lack of a posterior circulation aneurysm (2 domains). Other variables consistently associated with cognitive dysfunction in the univariate analysis included admission Hunt-Hess grade Ͼ2 and thick SAH in the anterior interhemispheric and sylvian fissures. Conclusions-Global cerebral edema and left-sided infarction are important risk factors for cognitive dysfunction after SAH. Treatment strategies aimed at reducing neurological injury related to generalized brain swelling, infarction, and clot-related hemotoxicity hold the best promise for improving cognitive outcomes after SAH.
Cognitive impairment impacts broadly on functional status, emotional health, and QOL after SAH. The TICS may be a useful alternative to more detailed neuropsychological testing for detecting clinically relevant global cognitive impairment after SAH.
Epilepsy occurred in 7% of patients with SAH, was predicted by subdural hematoma and cerebral infarction, and was associated with poor functional recovery and quality of life. Our findings indicate that focal pathology, rather than diffuse injury from hemorrhage, is the principal cause of epilepsy after SAH.
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