1/6. Dissociated perceptual-sensory and exploratory-motor neglect.A patient with a right sided parietal lobe infarction manifested left sided sensory extinction in the visual, auditory, and tactile modalities but had only mild exploratory-motor neglect. In contrast, another patient with a right frontal haemorrhage demonstrated only left sided exploratory-motor hemispatial neglect. Tasks that combined perceptual and exploratory features elicited varying degrees of neglect in each patient. These two cases with dissociated neglect behaviour lend further evidence for behavioural specialisation within components of a cortical network for directed attention: sensory-representational aspects mediated primarily by the parietal component, motor-exploratory primarily by the frontal component. These cases also highlight the need to include and distinguish among several different measures of neglect in the clinical investigation of patients with hemispatial inattention.- - - - - - - - - - ranking = 1keywords = behaviour (Clic here for more details about this article) |
2/6. Blindsight in children: does it exist and can it be used to help the child? Observations on a case series.Damage to the occipital lobe of the brain results in hemianopia when unilateral, and cerebral blindness when bilateral. However, in some cases a degree of visual function persists in the blind visual field. This aim of this study was to describe this phenomenon of 'blindsight' in a cohort of children with brain-damage and to relate the clinical features to their visual evoked potentials. We performed a retrospective analysis of 541 case records of children referred to a tertiary vision-assessment clinic in the Royal Hospital for Sick Children, Glasgow, UK from 1992 to 2002. A total of 541 patients were analyzed (243 females, 298 males; age range 2 mo to 19 y 6 mo, mean 6 y 2 mo). In 19 children with profound visual impairment and four children with hemianopia (12 females, 11 males; age range 1 to 18 y, mean age 8 y 3 mo), evidence of perception of movement in the blind visual field was found and is described. Flash visual evoked potentials varied from no response to normal and was not correlated with visual behaviour. Recognition, detection, and use of this phenomenon in children is vital to their rehabilitation and interaction with their surroundings.- - - - - - - - - - ranking = 0.5keywords = behaviour (Clic here for more details about this article) |
3/6. Rejection behaviour: a human homologue of the abnormal behaviour of Denny-Brown and Chambers' monkey with bilateral parietal ablation.A unique behavioural syndrome in humans followed two separate strokes involving both parietotemporal regions. The behavioural alterations resemble those of Denny-Brown and Chambers' monkey with bilateral ablation of the parietal lobe which were characterised by strong withdrawal or refusal to be touched on the limbs and head. In both humans and animals, touch on the limbs or head elicited exaggerated withdrawal movements and refusal to be touched on the lips and tongue resulted in difficulty in feeding. These behavioural alterations can be interpreted as loss of exploratory activities towards extrapersonal space, or more positively, as rejection of contact with the environment. This rejection behaviour in which tactile, visual, and/or gustatory exploration tendencies are altered, is a counterpart of human frontal lobe syndrome and human kluver-bucy syndrome.- - - - - - - - - - ranking = 6keywords = behaviour (Clic here for more details about this article) |
4/6. Complex visual hallucinations in the hemianopic field.From 120 patients with an homonymous hemianopia 16 experienced complex visual hallucinations in the hemianopic field. The brain lesion was located in the occipital lobe, though damage was not limited to this area. Complex hallucinations appeared after a latent period. They were weak in colour and stereotypical in appearance, which allowed differentiation from visual hallucinations of other causes. Different behaviour after saccadic eye movement differentiated between complex visual hallucinations in the hemianopic field and visual auras of an epileptic origin.- - - - - - - - - - ranking = 0.5keywords = behaviour (Clic here for more details about this article) |
5/6. Behavioural and electrophysiological chromatic and achromatic contrast sensitivity in an achromatopsic patient.OBJECTIVES--In cases of incomplete achromatopsia it is unclear whether residual visual function is mediated by intact striate cortex or results from incomplete lesions to extrastriate cortical visual areas. A patient with complete cerebral achromatopsia was tested to establish the nature of his residual vision and to determine the integrity of striate cortex function. methods--Behavioural contrast sensitivity, using the method of adjustment, and averaged visually evoked cortical potentials were measured to sinusoidally modulated chromatic and achromatic gratings in an achromatopsic patient and a normal observer. eye movements were measured in the patient using a Skalar infrared monitoring system. RESULTS--The patient's chromatic contrast sensitivity was normal, indicating that despite his dense colour blindness his occipital cortex still processed information about spatial variations in hue. His sensitivity to achromatic gratings was depressed particularly at high spatial frequencies, possibly because of his jerk nystagmus. These behavioural results were reinforced by the nature of visually evoked responses to chromatic and achromatic gratings, in which total colour blindness coexisted with an almost normal cortical potential to isoluminant chromatic gratings. CONCLUSIONS--The results show that information about chromatic contrast is present in some cortical areas, and coded in a colour-opponent fashion, in the absence of any perceptual experience of colour.- - - - - - - - - - ranking = 0.5keywords = behaviour (Clic here for more details about this article) |
6/6. Seeing only the right half of the forest but cutting down all the trees?Unilateral neglect following damage to the right hemisphere of the brain can be characterized by failure of the global attentional mechanisms of the right hemisphere to direct the local detail processors of the left hemisphere towards the contralesional left hemispace. This is suggested by patients who recognize the global form of the left side of shapes (the forest) but fail to cancel out its local details (the trees). Here we report the opposite behavioural dissociation in a patient (Q.M.) with damage to the right hemisphere of the brain. Q.M. detected local details (such as the tail of a dog) on the left or right side of visual shapes, regardless of whether these details belonged to predefined target shapes (a dog in this case) or to distractor shapes differing on the opposite side (a dog with a swan's neck and head, for example). Psychological testing showed an abnormal tendency of this patient to respond to local features, but perfect accuracy in interpreting global features when the local features could not interfere in global processing. The results indicate that the left hemisphere can integrate multiple local features simultaneously but loses global awareness as soon as local features individually compete for response selection. However, awareness of the whole is not necessary for the sequential processing of the parts.- - - - - - - - - - ranking = 0.5keywords = behaviour (Clic here for more details about this article) |