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Psychophysik und Physiologie des Farbensehens

Certain aspects of colour science and colour physiology are presented from the point of view of a linear transfer theory. The following struc­tures are introduced for this purpose: a set of (physical) colour sti­muli, an instrumental colour space, a fundamental colour space, and an opponent colour space. The linear transfer is described by means of mathematical linear mappings between these structures. An important part is played by certain types of colour blind observers, the so-cal­led dichromats. The blue colour mechanism receives a special treatment. The psychophysical results are compared with biophysical and electro­physiological findings. Finally, we present a critique of the colour system CIE 1931.
Horst Scheibner, Elmar Wolf

Die Funktion der Akkommodation des menschlichen Auges

A good visual acuity in different distances not only requires a high resolution of the retina but as well a good function of convergence and accommodation. Whereas convergence can be controlled intentionally in most cases, this cannot be done for accommodation. Our knowledge of accommodation and convergence is based on subjective and objective methods and also on functional anatomic investigations.
Convergence and accommodation are loosely connected with each other. Only deviations from the ideal connection must be corrected by fusion. Each artificial manipulation of this connection between convergence and accommodation is combined with additional effort of fusion. The resting value of accommodation is not the far point but a myopic one. It is determined by the dynamic equilibrium of the sympathetic (desaccommodation) and the parasympathetic (accommodation) nervous system. The resting point drifts towards the far point with increasing age. It is unstable. Recognition rate for small targets does not reach 100%.
Accommodation varies around values which shift towards the resting point with increasing unsharpness of targets. Therefore unsharp targets should be avoided. Accommodation shows chromatic errors like the eye-optics. This error increases with the saturation of colours. Edges of different spectral colours of equal luminance give uncertain values of accommodation. The dynamic amount of accommodation and its velocity decrease at the age of 40 to 55 years. Latency increases. The dynamic values of convergence remain constant.
Very slow variations of target distances result in unremarkable asymmetric responses of convergence and accommodation.
Helmut Krueger

Kontrastübertragung des Auges als Filterfunktion für die Diskrimination visueller Reizmuster

The ergonomic design of visual displays is an important task in the development of the man-machine interface with complex vehicle or process guidance systems. One aspect of this task is the design of symbol sets. At present there is no known method by which the suitability of a symbol set can be evaluated without conducting expensive and time-consuming psychophysical tests. The algorithm presented in this paper allows first order prediction of ranking visual stimuli with regard to form discrimination performed by humans. As an essential feature this model comprises the use of the human visual modulation transfer function (MTF) as a filter of the spatial frequency components of the stimuli. The procedure generates a distance metric upon which visual discrimination errors are predicted or against which human errors can be correlated. The method is tested on the results of a recognition task with thermal images.
Karl Reinhard Kimmel

Das visuelle System als Merkmalfilter

The visual system is considered as an information processing system where the information processing task may consist in the localization and recognition of objects in the 3-dimensional physical world. After some definitions concerning terms like physical world and its projection, image,feature, and segmentation the processing in the first stages of the visual system (low-level vision) is discussed. A computational theory of retinal filtering is presented and related to the anatomy and physiology of the retina as well as to psychophysical results suggesting that a spatial-frequency filtering is performed in the human visual system. Furthermore neurophysiological and psycho-physical data suggest that the segmentation is the next stage after retinal processing. Here surface elements are extracted which follow from motion, texture, or the depth of objects (Stereopsis) relative to the observer. Some results of our simulation of low-level vision (retina, primary visual cortex) are presented for natural images. Particularly these results are related to the extraction of contour points, and edges for the reconstruction of the original gray values and the description of forms, and to the evaluation of statistical parameters for the description of textures in different spatial-frequency domains.
Axel Korn

Zusammenspiel des fovealen und peripheren Sehens bei Informationsbelastung

The detection performance of human peripheral vision depends on presentation angle and additional informational load by foveal vision. This is modeled based on signal detection theory and investigated experimentally in a perimeter. As a result the influence of additional visual load is described consistently as increased noise level for the detection task, expressed in terms of brains internal noise by a workload factor. This workload factor can be interpreted as contrast multiplier needed for constant detection performance. Furthermore the workload factor of a given informational load by foveal vision can be calculated from the detection rates of peripherally presented light stimuli measured with and without this informational load. On this background a method to measure mental workload by visual information is developed; a special spectacle frame is used to present peripheral light stimuli. Experimental results of this measurement method are discussed and compared with other workload indicators. The results show a good discrimination of different demand levels in very different workload situations. By averaging repeated measurement intervals of short duration the temporal resolution of this method is in the order of seconds. The properties of this measurement method are well suited to practical applications.
Manfred Voss

Sehfunktion und Bilddarbietung

This paper attempts to survey some important facets of visual function as related to optical and electro-optical image display. It is demonstrated that there are many problems associated with the observer-display interface which can, however, be approached from the present understanding of early image processing carried out by the visual system.
A comprehensive model of visual performance thresholds code-named ORACLE which in its present extended version includes effects of rastered image display can be used to predict either the performance thresholds of image display systems or the frequency of seeing or the suprathreshold factor (called visibility) under specified conditions.
Ian Overington

Codierung optischer Information

Coding of visual information is an important step in designing man-machine dialogues. After an analysis of the coding and decoding procedures the human properties in information transmission tasks are described by applying the Shannon-Wiener measure of information. The strongly limited human capacity for absolute judgements in information transmission tasks leads to the recommendation of a rather small number of coding steps when using single stimulus dimensions. In a comparison different codes like analogue, digital, alphanumerical, chromatic, pictorial and blinking signals are discussed in order to give application-oriented design rules.
Georg Geiser

Zeichenkontrast und visuelle Leistung am Bildschirm

The generation of characters on VDU’s exhibits specific raster problems in view of contrast and visibility evaluation. The luminance modulation of rasters is theoretically and experimentally analysed, resulting in the specification of local inner, local outer and mean contrast of characters. An analytical model of contrast thresholds is presented including the effects of background luminance, size, stimulus duration etc. in order to estimate the visibility of characters.
On the basis of detection, identification and search experiments as well as of subjective appraisals it is shown, that the inner local contrast of characters is the determinant for the effect of contrast on visual performance and acceptance. The inner local contrast also provides an adequate criterion to optimise the adjustment of contrast of VDU’s in a given environment.
Siegfried Kokoschka

Strukturaspekte der Informationsgestaltung auf Bildschirmen

Structuring information on visual display units (VDUs) is a major ergonomic aspect in man-machine communication. Following a theoretical exposé on establishing models for visual analysis of scenes and structures, a description is given of experiments conducted to evaluate alphanumerically coded screen masks. Evidence is presented to show that the structure of these masks has a considerable influence on users in accepting information displays and also on their performance. In conclusion, some practical aspects of picture configuration are illustrated.
Peter Haubner


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