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J Zihl

Publications and source records attributed to J Zihl.

60 records · Page 4Linked to original sources

Diurnal variation of visual field size in patients with postretinal lesions.

Perimetry at various times of day in patients with large visual field defects due to postretinal lesions showed significant variations of visual field size. The largest visual fields were observed at noon, the smallest in the evening. Such systematic variations were observed only in patients who showed a gradual increase of increment threshold between the intact parts of the visual field and the scotoma. In two patients who showed an abrupt transition between intact and blind areas of the visual field, no obvious diurnal variation was observed. It is suggested that an endogenous modulation of neuronal sensitivity coupled to a hypothetical circadian oscillator is the basis of the diurnal variation.

Adolescent↗

Use of visually evoked responses in evaluation of visual blurring in brain-damaged patients.

Pattern visual evoked potentials were recorded in brain-damaged patients who complained of fluctuation of vision causing visual blurring. Continuous prolonged pattern stimulation revealed marked variability of P100 amplitudes. In contrast, normal subjects and brain-damaged patients who did not complain of visual blurring showed stable P100 amplitudes. Fluctuation of vision thus seems to have an electrophysiological correlate in terms of P100 amplitude lability, which can be objectively assessed by prolonged continuous recording of pattern visual evoked potentials.

Adult↗

Neuropsychological assessments before and after treatment in patients with anorexia nervosa and bulimia nervosa.

In psychiatric patients the identification of cognitive deficits which predict a poor clinical outcome is important for the development of specific treatment strategies aimed at the amelioration of these impaired cognitive functions to increase the likelihood of full clinical remission. However, such attempts are absent in bulimia nervosa (BU), are scarce in anorexia nervosa (AN) and, furthermore, provide conflicting results. In the present prospective study we investigated the neuropsychological demands in 12 patients with AN and in 14 patients with BU before, during, and after a treatment period. At the initial testing session, both patients samples showed similar and impaired performance levels on tasks measuring attentional demands and problem solving abilities, while their mnemonic functions were preserved. At the final testing session, which took place 7 months thereafter, the impaired cognitive functions had improved to a similar degree in the AN and the BU subgroups. However, although the eating disorder symptomatology had ameliorated in parallel, no direct associations could be established with the initial neuropsychological demands and their rectification, respectively. On an individual level, 11 patients initially showed obvious cognitive deficits. However, the clinical characteristics of this subgroup differed not from that found in the 15 'good performers'. These findings indicate that the cognitive functions in the acute AN and BU are similarly impaired, but also ameliorate in a similar manner with clinical remission. Because no associations were obvious between cognitive and clinical rectifications, significant contributions of mediating factors (e.g., changes in metabolic brain turnover and in steroid hormones) are suggested.

Adult↗

A neurodynamical model of visual attention: feedback enhancement of spatial resolution in a hierarchical system.

Human beings have the capacity to recognize objects in natural visual scenes with high efficiency despite the complexity of such scenes, which usually contain multiple objects. One possible mechanism for dealing with this problem is selective attention. Psychophysical evidence strongly suggests that selective attention can enhance the spatial resolution in the input region corresponding to the focus of attention. In this work we adopt a computational neuroscience perspective to analyze the attentional enhancement of spatial resolution in the area containing the objects of interest. We extend and apply the computational model of Deco and Schürmann (2000), which consists of several modules with feedforward and feedback interconnections describing the mutual links between different areas of the visual cortex. Each module analyses the visual input with different spatial resolution and can be thought of as a hierarchical predictor at a given level of resolution. Moreover, each hierarchical predictor has a submodule that consists of a group of neurons performing a biologically based 2D Gabor wavelet transformation at a given resolution level. The attention control decides in which local regions the spatial resolution should be enhanced in a serial fashion. In this sense, the scene is first analyzed at a coarse resolution level, and the focus of attention enhances iteratively the resolution at the location of an object until the object is identified. We propose and simulate new psychophysical experiments where the effect of the attentional enhancement of spatial resolution can be demonstrated by predicting different reaction time profiles in visual search experiments where the target and distractors are defined at different levels of resolution.

Attention↗