1,721,087 research outputs found
The interaction between time and number in a temporal bisection task: A reply to Vicario (2011)
Full text linkAbstract.We discuss the results of Vicario (2011, Perception 2011, 40, 23-29), in the light of an experiment designed to bypass some of the limits of that study. There, participants were asked to perform a temporal bisection on numerical stimuli (small or large digits) presented either for 700/900 ms
or 2000/2200 ms. For the two longest durations only, bisections of larger digits occurred later than those of smaller digits. Here, subjects judged the temporal position of a flick occurring during the visual presentation of a digit (1, 5, or 9) which lasted on the screen for either 700 ms or 2000 ms. Results revealed no difference in the perceived temporal midpoints of large compared to small digits. In contrast, they showed a response bias: only with the shortest-duration stimuli the digit's magnitude affected the subject's response
Increased attentional load moves the left to the right
Full text linkIntroduction: Unilateral brain damage can heterogeneously alter spatial processing. Very often brain-lesioned patients fail to report (neglect) items appearing within the contralesional space. Much less often patients mislocalize items' spatial position. We investigated whether a top-down attentional load manipulation (dual-tasking), known to result in contralesional omissions even in apparently unimpaired cases, might also induce spatial mislocalizations. Method: Nine right-hemisphere-damaged patients performed three computer-based tasks encompassing different levels of attentional load. The side of appearance of visual targets had to be reported either in isolation or while processing additional information (visual or auditory dual task). Spatial mislocalizations (from the contralesional hemispace towards the ipsilesional unaffected one) were then contrasted with omissions both within and across tasks, at individual as well as at group level. Results: The representation of ipsilesional targets was accurate and not affected by dual-tasking requirements. Contralesional targets were instead often omitted and, under dual-task conditions, also mislocalized by four patients. Three cases reported a significant number of left targets as appearing on the right (alloesthesia). Two of these patients perceived more targets (albeit to a wrong spatial location) under dual- than under single-task load. In a fourth patient, increased visual load resulted in synchiria, the (mis)perception of single, contralesional targets as being two (one on each side). Conclusions: When the neural circuitry subtending spatial processing is damaged, an increase in task load can lead to either a disregard or a bias in the processing of contralesional hemispace. The spatial bias subtending mislocalizations seems to index a more severe deficit than neglect, as if contralesional space would be completely erased rather than merely ignored
Unveiling residual, spontaneous recovery from subtle hemispatial neglect three years after stroke
Full text linkA common and disabling consequence of stroke is the difficulty in processing contralesional space (i.e. hemispatial neglect). According to paper-and-pencil tests, neglect remits or stabilizes in severity within a few months after a brain injury. This arbitrary temporal limit, however, is at odds with neglect's well-known dependency on task-sensitivity. The present study tested the hypothesis that the putative early resolution of neglect might be due to the insensitivity of testing methods rather than to the lack of spontaneous recovery at later stages. A right hemisphere stroke patient was studied longitudinally for three years. According to paper-and-pencil tests the patient showed no symptom of hemispatial neglect one month post stroke. Awareness of spatially lateralized visual targets was then assessed by means of computer-based single- and dual-tasks requiring an additional top-down deployment of attention for the parallel processing of visual or auditory stimuli. Errorless performance at computer-based tasks was reached at month 12 and maintained until month 30 after stroke. A bottom-up manipulation was then implemented by reducing target diameter. Following this change, more than 50% of contralesional targets were omitted, mostly under dual-tasking. At months 40 and 41 the same task revealed a significant (but not complete) reduction in the number of contralesional omissions. Ipsilesional targets were, in contrast, still errorless detected.The coupling of a bottom-up (target change) and a top-down (dual-tasking) manipulation revealed the presence of a long-lasting spontaneous recovery from contralesional spatial awareness deficits. In contrast, neither manipulation was effective when implemented separately. After having excluded the potential confound of practice effects, it was concluded that not only the presence but also the time course of hemispatial neglect strongly depends on the degree of attentional engagement required by the task
Neglect and extinction depend greatly on task demands: A review
Full text linkThis review illustrates how, after unilateral brain damage, the presence and severity of spatial awareness deficits for the contralesional hemispace depend greatly on the quantity of attentional resources available for performance. After a brief description of neglect and extinction, different frameworks accounting for spatial and non-spatial attentional processes will be outlined. The central part of the review will describe how the performance of brain damaged patients is negatively affected by increased task demands, which can result in the emergence of severe awareness deficits for contralesional space even in patients who perform normally on paper-and-pencil tests. Throughout the review neglect is described as a spatial syndrome that can be exacerbated in the presence and severity by both spatial and non-spatial tasks. The take-home message is that the presence and degree of contralesional neglect and extinction can be dramatically overlooked based on standard paper-and-pencil testing, where patients can easily compensate for their deficits. Only tasks where compensation is made impossible represent an appropriate approach to detect these disabling contralesional deficits of awareness that become subtle in post-acute stroke phases
The sharp drop in the number of faculty positions is compromising the future of neuroscience
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Unveiling contralesional omissions six years after stroke. Effects of top-down and bottom-up manipulations
Full text linkWe examined how spatial processing is affected by attentional load during multitasking in a chronic patient who suffered a right hemisphere stroke six years before the testing. We employed standard paper-and-pencil tests for neglect along with a new version of a well-established computerized dual-task paradigm. The latter combined a spatial processing primary task (reporting lateralized visual targets) with a concurrent secondary task (categorizing visual/auditory stimuli). Attentional load was manipulated through top-down (secondary task) and bottom-up (target size in primary task) factors. Paper-and-pencil tests did not reveal contralesional omissions. In contrast, the dual-task paradigm demonstrated greater sensitivity in detecting asymmetric spatial processing. Surprisingly, contralesional omissions occurred despite primary and secondary task stimuli did not overlap in time (i.e., secondary task stimuli were presented after the disappearance of lateralized visual targets lasting 100 ms). While both top-down and bottom-up manipulations induced contralesional omissions, their effects differed according to target size. Increased attentional load from dual-tasking impaired perception of larger contralesional targets, whereas smaller targets elicited omissions even in single-task conditions without additional multitasking effects. In this patient, very different manipulations, the first involving top-down and exclusively cognitive factors and the second involving bottom-up and purely perceptual aspects, independently modulated the level of processing resources. Both can be exploited to exacerbate very subtle (yet potentially hazardous) spatial processing deficits
When time is space: Evidence for a mental time line
Full text link(This is a sample cover image for this issue. The actual cover is not yet available at this time.) This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit
Difficulty matters: Unspecific attentional demands as a major determinant of performance highlighted by clinical studies
No full textThe cognitive impairments shown by brain-damaged patients emphasize the role of task difficulty as a major determinant for performance. We discuss the proposal of Kurzban et al. in light of our findings on right-hemisphere-damaged patients, who show increasing awareness deficits for the contralesional hemispace when engaged with resource-consuming dual tasks. This phenomenon is readily explained by the assumption of unspecific depletable resources
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