Biomedical subjects

Dorothe A Poggel

Publications and source records attributed to Dorothe A Poggel.

6 recordsLinked to original sources

PubMed2006

Improving residual vision by attentional cueing in patients with brain lesions.

Visual attention is crucial for almost all processes of visual perception, particularly when perception is difficult. We were interested in the effects of cueing spatial attention in patients with cerebral lesions who face difficulties in visual perception in areas of residual vision at the border of visual field defects. In 23 patients with visual field loss due to post-geniculate brain lesions, stimulus detection performance and reaction times were mapped with high-resolution computer-based perimetry. A cueing procedure using Gestalt completion to attract attention to areas of residual vision was implemented in this test and performance compared in attended and unattended conditions. Stimulus detection and reaction times in areas of residual vision improved significantly under attended conditions. The extent of this effect depended on the size of areas of residual vision within the cued field. Unexpectedly, facilitation was also observed, though to a lesser extent, in invalid cueing conditions, suggesting an unspecific increase of alertness in unattended areas. Our findings show that top-down influences are relevant for visual field testing. Visuo-spatial attention may change patterns of neural activation and induce short-term plasticity not only in the intact visual system but also in the presence of visual field loss after brain lesions. Attentional cueing induces a co-activation of the lesioned visual system and (intact) attentional networks in the brain inducing immediate facilitation of visual perception. This effect may be relevant for designing new strategies to permanently improve vision during neuropsychological rehabilitation.

Adult↗

PubMed2006

Increasing the temporal g(r)ain: double-pulse resolution is affected by the size of the attention focus.

Spatial cueing of transient attention has recently been shown to reduce temporal sensitivity. We investigated how the size of the sustained attentional focus influences double-pulse resolution (DPR) thresholds mapped across the visual field in a sample of 95 healthy subjects using a 9-fold interleaved adaptive algorithm (YAAP). Peripheral DPR thresholds increased for measurements between 2.5 degrees and 20 degrees eccentricity. Additionally, central DPR thresholds increased at a similar rate when measured with increasingly larger stimulus displays for peripheral measurements. This latter effect suggests that temporal resolution decreases with a larger sustained attention focus and cannot be explained by retinal characteristics only.

Adolescent↗

PubMed2006

A mirror in the mind: a case of visual allaesthesia in homonymous hemianopia.

We report the case of a 61-year-old female patient with intracranial bleeding in left parietal and parieto-temporal regions and a history of epilepsy and migraine. MR images showed lesions of the optic radiation, but primary visual cortical areas were intact. Perimetric testing revealed an incomplete right hemianopia. The patient claimed that visual percepts from her intact field were projected as "mirror images" into the hemianopic field. The illusory images were weak and sometimes difficult to detect, but focusing spatial attention on the "mirror" image increased its saliency. Drawings the patient made of her pseudo-hallucinations revealed that the illusions were lateral transpositions instead of mirror images of real objects. The illusions were tilted in clockwise direction and were never colored, although color discrimination was unimpaired in the patient's left hemifield. We quantified the characteristics of the pseudohallucinations in several experiments: The patient was asked to adjust the position, rotation angle, and size of a white test card in her blind field so that it corresponded with the illusory projection of a card of standard size and position that was presented in the intact field. The test card was compressed in horizontal size by 20% and positioned 17 degrees visual angle to the right of the standard, shifted 1.5 degrees upward or downward, and rotated in clockwise direction by 22.6 degrees on average. Large objects in the intact field were projected incompletely into the blind area. Our patient's symptoms are similar to those reported in earlier case studies of visual allaesthesia. We hypothesize that the "mirror image" is induced by sparse input from contralesional V1 via the corpus callosum upstream of the lesion site and a lack of inhibition or hyperexcitability of ipsilesional early visual areas after deafferentation. The rotation of the illusions may be induced by the parietal lesions causing faulty co-ordinate computations, e.g., an inability to integrate visual and otholitic input.

Female↗

PubMed2004

Attentional cueing improves vision restoration therapy in patients with visual field defects.

BACKGROUND: In patients with postgenicular lesions of the visual system, areas of residual vision (ARVs) are the main predictor of recovery induced by vision restoration therapy (VRT). In these partially defective regions, the elevated perceptual thresholds can be acutely reduced by attentional cueing. OBJECTIVE: To examine whether directing attention to ARVs using a visuospatial cue also increases long-term neural plasticity and thus enhances permanent training outcome. METHODS: In a prospective, randomized clinical trial, treatment outcome was compared in patients with postgenicular visual system lesions who received either standard VRT (control group [CG]; n = 10) or VRT with attentional cueing (experimental group [EG]; n = 9). Visual field size was determined before and after a 6-month treatment period using Tubingen Automated Perimetry and computer-based high-resolution perimetry (HRP) and in regular intervals throughout this period by HRP and detection performance in VRT. RESULTS: In the area of the cue, restoration of vision was significantly greater than during VRT without cueing: cued patients showed a much more pronounced shift of the visual field border toward the blind area than that observed in the CG or in uncued regions of the EG. Focusing attention at ARVs during treatment changed topographic and temporal patterns of recovery as compared with uncued regions of the visual field. CONCLUSIONS: Use of a visuospatial cue to focus attention at areas of residual vision amplifies long-term neuronal plasticity. The authors propose that top-down signals preactivate partially damaged areas of V1, thus linking visual and attentional neuronal networks, with the effect of permanently increasing conscious visual perception.

Adult↗

PubMed2004

Visual perception in space and time--mapping the visual field of temporal resolution.

To characterize temporal aspects of information processing in the human visual field, we studied the topographical distribution of temporal and non-temporal performance parameters in 95 normally sighted subjects. Visual field maps of double-pulse resolution thresholds (DPR) (the minimum detectable temporal gap between two light stimuli) and simple visual reaction times (RT) (measuring the speed of reaction to a light stimulus) were compared to maps of luminance thresholds determined by standard perimetry. Thus, for the first time, the topography of a visual variable without temporal constraints (perimetry) could be compared to visual variables in the temporal domain, with (RT) and without (DPR) motor reaction. The goal of the study was to obtain and to describe the pattern of co-variation of performance indicators. In all three measures, performance was best in the central visual field and dropped significantly towards the periphery. Although the correlation between DPR and RT was significant, shared variance was low, and we observed large topographical differences between these two temporal-performance variables. In contrast, DPR and perimetric thresholds correlated more substantially, and visual field maps were similar. The Gestalt of DPR maps shares characteristics of basic visual processing (e.g., light sensitivity), but it also reflects top-down influences, i.e., from spatial attention. Although the correlation between DPR and RT suggests common characteristics between these two temporal variables, the topographic distributions reveal significant differences, indicating separate underlying processing mechanisms.

Adolescent↗

PubMed2003

Neglect and hemianopia superimposed.

In patients with posterior-parietal brain damage it is often difficult to decide whether left-sided omissions in perimetry are due to primary visual loss or due to visual neglect. We investigated 11 patients with combined neglect/hemianopia and 11 patients with pure hemianopia using a visual search task with single or double stimulation conditions. The second stimulus was either the fixation point itself (like in perimetry) or a distractor appearing in the hemifield opposite to the target. The fixation point did not worsen left-sided perception, but its disappearance led to a bias of exploration towards the right side in neglect patients but not in pure hemianopics. A distractor in the intact hemifield worsened the performance to left-sided stimuli, that is, neglect patients behaved as if they were completely hemianopic, even in intact parts of the visual field (VF). Three of the neglect patients showed unconscious processing of the distractor in the left VF, suggesting that the visual field defect was produced by neglect mechanisms rather than primary visual loss. This visual search paradigm appears to be helpful in understanding of the nature of hemianopia versus neglect deficits in individual patients.

Adult↗