Cases reported "Perceptual Disorders"

Filter by keywords:



Filtering documents. Please wait...

1/7. Alternative brain organization after prenatal cerebral injury: convergent fMRI and cognitive data.

    The current study presents both longitudinal behavioral data and functional activation data documenting the effects of early focal brain injury on the development of spatial analytic processing in two children, one with prenatal left hemisphere (LH) injury and one with right hemisphere (RH) injury. A substantial body of evidence has shown that adults and children with early, lateralized brain injury show evidence of spatial analytic deficits. LH injury compromises the ability to encode the parts of a spatial pattern, while RH injury impairs pattern integration. The two children described in this report show patterns of deficit consistent with the site of their injury. In the current study, their longitudinal behavioral data spanning the age range from preschool to adolescence are presented in conjunction with data from a functional magnetic resonance imaging (fMRI) study of spatial processing. The activation results provide evidence that alternative profiles of neural organization can arise following early focal brain injury, and document where in the brain spatial functions are carried out when regions that normally mediate them are damaged. In addition, the coupling of the activation with the behavioral data allows us to go beyond the simple mapping of functional sites, to ask questions about how those sites may have come to mediate the spatial functions.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)

2/7. Canceling out both the real and the spectral lines.

    Neglect patients typically show motor perseveration while canceling targets on the ipsilesional side. This behavior can be influenced by the presence vs. absence of targets on the (neglected) contralesional side (). As alternative explanations, the authors proposed (i) directional hypokinesia--the patient cannot perform reaching movements towards detected left-sided targets, and thus carries on canceling on the right side, and (ii) allochiria--the patient misperceives left-sided targets as located on the right side, and cancels them there. We report here data from a patient (EZ) that might confirm the second hypothesis. EZ was presented with 19 displays in which the number and position of cancellation targets on both sides were varied systematically. EZ showed motor perseveration while canceling, but this tendency did not vary across conditions. Interestingly though, EZ also drew cancellation marks in the empty space between the ipsilesional targets, and this phenomenon was significantly more intense when there were more targets on the neglected side. As EZ's comments suggested, such a behavior might reflect the attempt to cancel out delusional targets. Our speculation is that those objects were generated by allochiria.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)

3/7. Ipsilesional attentional-approach neglect or crossover effect.

    patients with ipsilateral neglect (IN) bisect lines toward contralesional space. It has been posited that IN might be induced by an attempt at compensation, as part of the crossover effect, where patients with an ipsilesional bias when bisecting long lines, cross over and develop a contralesional bias on short lines or as a release of an approach (grasp) behavior that might be attentional or intentional. To test these alternative hypotheses we had a patient with IN from a right medial frontal lesion bisect lines that contained no cue, a left-sided cue, a right-sided cue, and bilateral cues. If this patient had ipsilateral neglect (IN) because of a crossover effect or compensation, right-sided cues should have influenced bisection more than left-sided cues. We, however, found that only left-sided cues induced a significant change (left-sided deviation) providing support for the attentional-approach (grasp) hypothesis. Further support of this contralesional attentional grasp hypothesis comes from the observation that this patient also had ipsilesional extinction to simultaneous stimuli.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)

4/7. Spatial compression in visual neglect: a case study.

    In the standard account of left neglect, some manner of attentional boundary is postulated such that elements to the left of that boundary are cognitively neglected. We propose an alternative model in which space is distorted ('compressed') in neglect. A new task is devised whereby the subject must follow 'in imagination' the direction of an arrowhead across 'empty' space to its corresponding position in a numerical target array. The two-dimensional array is Euclidian and all four arrow/array relationships are incorporated (arrow to the left/right of a vertical array, arrow to the top/bottom of a horizontal array). Normal subjects perform at ceiling, with excellent accuracy in all orientations and positions. A patient with severe left neglect (consequent upon lesion of the right temporo-parietal region) shows systematic deflections in her judgement of target positions. These distortions are fully consistent with a model whereby points in 'left space' are compressed rightwards; the compression function is linearly proportional to the coordinates of Euclidian space.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)

5/7. Successful treatment of phantosmia with preservation of olfaction.

    A 26-year-old woman had an 8-year history of phantosmia in her left nostril. The phantosmia could be eliminated by nostril occlusion or cocainization of the olfactory epithelium on the involved side. Because her symptoms and testing suggested a peripheral problem, a full-thickness "plug" of olfactory epithelium from under the cribriform plate (including all the fila olfactoria) was excised. At 5 weeks postoperatively, the phantosmia was completely gone, and her olfactory ability had returned to preoperative levels. Either the removal of abnormal peripheral olfactory neurons from the nose or the interruption of incoming signals to the olfactory bulb eliminated the phantosmia. This form of therapy for phantosmia offers an alternative to more radical procedures such as olfactory bulbectomy and may offer a significant sparing of olfactory ability.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)

6/7. Cognitive-perceptual abilities of a neurologically impaired infant: an alternative assessment strategy.

    A 26-month-old boy with quadriplegia, untestable using traditional developmental tests, was assessed using a visual-discrimination paradigm (i.e. habituation-dishabituation). The results were interpreted as evidence that this infant could visually attend to, and discriminate between photographic slides varying in shape and/or colour. It is suggested that this paradigm may eventually be used as an alternative clinical testing protocol for assessing the perceptual-cognitive abilities of CNS-damage infants.
- - - - - - - - - -
ranking = 5
keywords = alternative
(Clic here for more details about this article)

7/7. Guidance of locomotion on foot uses perceived target location rather than optic flow.

    What visual information do we use to guide movement through our environment? Self-movement produces a pattern of motion on the retina, called optic flow. During translation, the direction of movement (locomotor direction) is specified by the point in the flow field from which the motion vectors radiate - the focus of expansion (FoE) [1-3]. If an eye movement is made, however, the FoE no longer specifies locomotor direction [4], but the 'heading' direction can still be judged accurately [5]. Models have been proposed that remove confounding rotational motion due to eye movements by decomposing the retinal flow into its separable translational and rotational components ([6-7] are early examples). An alternative theory is based upon the use of invariants in the retinal flow field [8]. The assumption underpinning all these models (see also [9-11]), and associated psychophysical [5,12,13] and neurophysiological studies [14-16], is that locomotive heading is guided by optic flow. In this paper we challenge that assumption for the control of direction of locomotion on foot. Here we have explored the role of perceived location by recording the walking trajectories of people wearing displacing prism glasses. The results suggest that perceived location, rather than optic or retinal flow, is the predominant cue that guides locomotion on foot.
- - - - - - - - - -
ranking = 1
keywords = alternative
(Clic here for more details about this article)


Leave a message about 'Perceptual Disorders'


We do not evaluate or guarantee the accuracy of any content in this site. Click here for the full disclaimer.