Cathleen Grimsen

Cathleen Grimsen
Universität Bremen | Uni Bremen · Higher education development and capacity planning

Dr. rer. nat.

About

33
Publications
3,249
Reads
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295
Citations
Additional affiliations
October 2002 - September 2013
Universität Bremen
Position
  • Researcher

Publications

Publications (33)
Article
Full-text available
We present the results of 51 stroke patients with free central visual fields of which about half suffer from clear deficits of midlevel vision undetected by standard clinical tests. These patients yield significantly elevated thresholds for detection and/or discrimination between forms defined by motion, colour, or line orientation (‘texture’). As...
Article
After a stroke involving the left occipitotemporal cortex our patient shows a word-length effect and has problems to identify letters or numbers in strings of symbols. But he is normal in identifying isolated letters and in non-verbally categorizing even complex images such as faces or natural scenes. His cortical lesion is stretching from the visu...
Article
Full-text available
Since scenes in nature are highly dynamic, perception requires an on-going and robust integration of local information into global representations. In vision, contour integration (CI) is one of these tasks, and it is performed by our brain in a seemingly effortless manner. Following the rule of good continuation, oriented line segments are linked i...
Data
Complete trial from Peak condition, with added markers indicating contour location.
Data
Complete trial from Peak condition.
Data
Complete trial from Long condition, with added markers indicating contour location.
Data
Complete trial from Long condition.
Poster
Contour integration (CI) is an integral part of visual information processing requiring the combination of aligned edge configurations into coherent percepts. Subjects are efficient at detecting contours, reaching peak performances for stimulus presentation times of 100-200ms. CI research usually employs flashed static stimuli, making this an artif...
Article
Full-text available
In human and nonhuman primates, goal-directed behavior requires the selection of relevant pieces of information from the multitude of simultaneous sensory inputs. Feature-based attention (FBA) plays a crucial role in this selection by improving the neuronal representation of an attended stimulus feature. Of particular interest for understanding the...
Conference Paper
Contour integration is an integral part of visual information processing requiring observers to combine aligned edge configurations into coherent percepts. Human observers are efficient in detecting contours, reaching peak performances for stimulus presentation times as low as 100ms. However, studies depicting these findings used flashed static sti...
Conference Paper
Full-text available
Background / Purpose: Patients with unilateral occipito-temporal damage show object recognition deficits in both visual fields, which are accompanied by strong neural alterations in object-selective cortex. Here we investigate whether intact early visual cortex is functionally affected by remote lesions. Main conclusion: Early visual areas sho...
Article
Full-text available
It is widely agreed that in object categorization bottom-up and top-down influences interact. How top-down processes affect categorization has been primarily investigated in isolation, with only one higher level process at a time being manipulated. Here, we investigate the combination of different top-down influences (by varying the level of catego...
Article
Full-text available
Temporal visual processing is strongly deteriorated in patients with schizophrenia. For example, the interval required between a visual stimulus and a subsequent mask has to be much longer in schizophrenic patients than in healthy controls. We investigated whether this deficit in temporal resolution is accompanied by prolonged visual persistence an...
Article
Full-text available
Neuropsychological deficits after occipital infarction are most often described in case studies and only a small sample of studies has attempted to exactly correlate the anatomical localization of lesions with associated neuropsychological symptoms. The present study investigated a large number of patients (N = 128) in order to provide an overview...
Conference Paper
Full-text available
Background / Purpose: We investigated a large number of stroke patients (N=128) to better characterize neurological and neuropsychological deficits caused by occipital damage. The aim was 1) to provide a systematic description of subacute clinical and neuropsychological deficits and 2) to correlate the exact localization of lesions with specific...
Conference Paper
Background / Purpose: Most patients with unilateral damage to occipito-temporal cortex do not suffer from major object recognition deficits. The aim of this study was to investigate whether unilaterally-damaged, non-agnostic patients show subtle deficits in object categorization and to find the underlying neural correlates. Main conclusion: Un...
Article
In a figure identification task, we investigated the influence of different visual cue configurations (spatial frequency, orientation or a combination of both) on the human EEG. Combining psychophysics with ERP and time-frequency analysis, we show that the neural response at about 200ms reflects perceptual saliency rather than physical cue contrast...
Article
Orientation selective neurons in the primary visual cortex typically respond to a range of orientations that covers 20 degrees or more, while in psychophysical experiments, orientation bandwidth is often clearly narrower. Here, we measure the orientation specificity of perceptual learning for vernier discriminations. More than 70 observers, in sepa...
Article
Perceptual learning is defined as a long-lasting improvement of perception as a result of experience. Here we examined the role of task on fast perceptual learning for shape localisation either in simple detection or based on form discrimination in different visual submodalities, using identical stimulus position and stimulus types for both tasks....
Thesis
Full-text available
The present work concentrates on different aspects of disturbed visual information processing. The patients examined have either a cerebral lesion or a psychiatric disease (schizophrenia). Patients and groups of patients are distinguished based on supposed site of disruption on an early or else a late visual processing stage.The second chapter cons...
Article
Spatial representations rely on different frames of reference. Patients with unilateral neglect may behave as suffering from either egocentric or allocentric deficiency. The neural substrates representing these reference frames are still under discussion. Here we used a visual search paradigm to distinguish between egocentric and allocentric defici...
Article
Schizophrenic patients show aberrancies of contextual processing over a broad range. Of particular importance are low level contextual deficiencies since they might cause higher level processing deficits. It was previously found that schizophrenic patients reveal diminished contextual facilitation in visual detection tasks taken as an indication of...
Article
In this study we systematically explored the impact of left hemisphere (LH) lesions on array-centered and item-centered spatial attention.We investigated 16 LH first ever stroke patients, focusing on strokes of the Middle Cerebral Artery (MCA), and 15 healthy control subjects with a parallel and serial search paradigm. None of the LH patients had a...
Article
To compare the neuropsychological deficits of primary progressive multiple sclerosis with those of relapsing-remitting and secondary progressive multiple sclerosis. Sixty-five patients with different clinical courses of MS were neuropsychologically tested for language, attention, memory and executive functions. Discriminant analysis was used to pre...
Article
The term "visual form agnosia" describes a disorder characterized by problems recognizing objects, poor copying,and distinguishing between simple geometric shapes despite normal intellectual abilities. Visual agnosia has been interpreted as a disorder of the magnocellular visual system, caused by an inability to separate figure from ground by sampl...

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Project (1)
Project
Understanding behavioral and neuronal dynamics and top-down modulation of change detection