A continuously increasing number of Germans do their work at the computer. In 2001, the amount of the employed population that uses a PC in their job

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3 A continuously increasing number of Germans do their work at the computer. In 2001, the amount of the employed population that uses a PC in their job reached 50 percent for the first time. (German Association for Information Technology, Information, Telecommunications and new Media (BITKOM)) With 60%, Germany is even significantly above the EU average of 50% (European statistical association Eurostat). Behind Germany are countries like the UK (55%) and France (54%). The most recent developments are a good indicator for the technological modernization in Germany; this applies equally to both economics and administration. (BITKOM) The prerequisites for electronic commerce are improving as well since many workstation PCs are also connected to the internet. In the year 2009 the percentage of employees in this country that were able to use their computer to go online increased from 29 (year 2003) to 46 percent. During its investigation, the European statistical association Eurostat surveyed businesses that had at least ten employees. The banking sector was excluded.

4 Carpal Tunnel Syndrome The most important nerve in the hand, the Nervus Medianus, connects with all finger flexor tendons into a type of tunnel that is formed through a cross-running band. The n. medianus provides the thumb, index and middle finger, as well as the portion of the ring finger toward the thumb, with sensation. In addition, the nerve has motor parts for the provision of thenar muscles. In the event of carpal tunnel syndrome, the n. medianus is constricted below this carpal band. Key symptoms include erroneous sensations (pins and needles, numbness) with fingers falling asleep from the thumb to the ring finger. Pain especially occurs during the night and in moments of rest. In the long term, carpal tunnel syndrome can develop into a repetitive strain injury (RSI). Tissue changes and scar formations occur through the slightest injuries. These injuries first lead to symptoms and can be remedied through early treatment. The actual RSI develops with chronic damage and shows a chronic progression. The RSI symptoms particularly occur in humans that work with computers a great deal. Frequently (text processing, data entry) are most affected. In particular, repetitive motions, such as typing or mouse-clicks, are seen as being partially responsible for such injuries.

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7 According to Schnurr (2007), one can distinguish between Stand-Sit-Dynamics and Sit- Stand-Dynamics. Sit-Stand-Dynamics describing the transition from sitting to standing, with the aim of avoiding unilateral loading of the spine by long sitting. The Sit-Stand Dynamics helps to change a work style which is characterized by continuous sitting by alternating between sitting and standing in favor of more motion. Stand-Sit Dynamics on the other hand involves the change from standing to sitting with the aim of avoiding unilateral loading of the spine by long standing. Therefore, Stand-Sit Dynamics helps to change a work style characterized by continuous standing by alternating between standing and sitting in favor of more motion.

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11 Three different input devices were analyzed in a study with 90 test subjects between 20 and 75 years in a two dimensional pointing task. The execution time as well as the mental workload were measured as dependent variables. Based on a start object, the task was to point target objects in different angles as quickly and as accurately as possible. Regarding the execution time, clear age effects have been determined. The elderly test subjects needed significant more time than the younger test subjects. Following a direct comparison of the three input devices, it must be emphasized that, regardless of participants age, the best performance in terms of short execution time results from touch screen information input. Surprisingly mouse input showed the poorest average performance among all subjects. However, the effect of the execution time improvement through alternative input devices (touch screen, eye-gaze) varies in strength among the different age groups. The greatest improvement in performance can be achieved by the 60 to 75 year-olds. These participants need on average twice as long as the 20 to 39 year-olds for information input with the mouse. However, when using a touch screen they reach a performance level similar to that of younger people using a mouse.

12 The slide shows a systematic overview of important display technologies. The technologies can be divided into three categories: projection, direct view and offscreen Direct view displays: With these displays the light emitted from the device is seen directly on the monitor without first being reflected by a projection surface. All CRT, LCD, Plasma TV and computer monitors are direct view displays. These displays work best in bright light and have a greater light output than projection displays. Projection displays: Unlike direct systems, the projection display is based on the projection of an image onto the screen. There are frontal and rear projection systems which are significantly different in terms of screen technology. Frontal projection uses a reflective screen surface, whereas rear projection uses a transmitting surface. Projection displays work best in a dimly lit environment. Frontal projection in particular requires a darker room in order to reach optimal viewing quality. Off-screen displays: These display systems do not require any special projection surfaces. Instead, a natural medium such as glass or even the retina can be used for projection. Offscreen displays are based either on coherent or non-coherent light emission. Coherence is the ability of waves to generate stationary interference phenomena. Normally lasers have a much higher level of coherence than conventional light. VRDs (Virtual Retinal Displays) and 3d holographic Head-up Displays are examples of off-screen display systems.

13 TFT stands for Thin Film Transistor. This describes a set of planar circuit elements that actively control the individual picture elements. The display consists of a matrix with many pixels. Each of these pixels can transmit a predefined photoelectric light color. Usually several fluorescent tubes are used as a backlight behind the matrix. A picture is then created on the front of the elements as a kind of shutter is opened that allows the light for a specific pixel to be either transmitted or blocked. Thus, for electrically responsive liquid crystal are used in a specific layer, the so-called alignment layer (alignment shift). There are two polarizing filter both in front and behind. The light is polarized by the first filter before entering into the alignment layer, i.e. the direction in which the light waves vibrate is fixed in a certain direction. Upon leaving the alignment layer there is another filter which is turned 90. The following filter transmits light waves that are also turned in the same direction. In a de-energized state, the liquid crystal alignment layer rotates the vibration direction of the of the light by 90 so that the light can pass freely (twist).

14 It is necessary to present the information on the screen at a size and quality that is easy to recognize. For characters that appear at an angle of vision between 16 and 31, this demand is fulfilled. An angle of vision of 22 is given when the height of capital letters, without ascender (character height), is equal to the designated viewing distance divided by 155. However, the font height should also not be greater than the viewing distance divided by 110, because fluid reading then becomes more difficult (font height of approximately 4.5 mm at the most at a viewing distance of 500 mm, corresponding to an angle of vision of 31 at the most). At a viewing distance of 500 mm, font heights of 3.0 to 4.0 mm should be strived for.

15 To investigate the age related coherence between acuity of vision and human performance, a symbol detection task was conducted on the basis of three different font sizes (16, 20 and 22 arc minutes). Results from partial correlation analysis point to an age differentiated adaption of font size rather than an adaption based on a measurement of visual acuity. The number of symbols to be detected and the response times of correct responses were analyzed with an analysis of variance. The results were derived from data of 75 subjects between 20 and 75 years, and they show a strong effect of font size and a medium age related effect. Results revealed that regardless of participants age, the best performance in terms of short response time occurs with the biggest font size of 22 arc minutes. The possibility to compensate age related differences in response time by enlarging the font size from 16 arc minutes up to 22 arc minutes supports the approach of age differentiated adaption of the human computer interface.

16 For certain eye diseases, the negativ contrast can improve the legibility of the represented information for the affected people. Retinitis Pigmentosa and macular degeneration belong to these eye diseases. Retinitis Pigmentosa is a retina degeneration where the photoreceptors are destroyed. Macular degeneration includes a group of eye diseases which apply the macula lutea ( the point of sharpest vision, yellow blot ) of the retina and which go along with a gradual loss of function of the gauze. Through these diseases the glare sensitivity can increase and the contrast sensitivity and the ability for adaption can decrease. The negativ contrast reduces the disability glare because less stray light arises in the eye. The character seem larger by negative polarity and thus they are better to read for visually impaired people. Another advantage is the reduction of the flicker. The flicker sensitivity is in the peripheral visual field significantly higher than in the central visual field. That is to say eye diseases with a damage of the central visual field increase the problem of the flicker.

17 Dependence of light density of visual direction: An anisotropic display is referred to as one in which the light density for the visual situation decreases diagonally to the picture level by more than 10% in comparison to the normal viewing position (ISO ). Experiment for recognition performance with TFT displays The goal of Ziefle s study (2004) was to examine the influence of a TFT display s anisotropy on the recognition performance of young adults. To do so, a TFT display was compared with a CRT display. Subjects had to process a visual search task in which objects (similar to Landoltrings) were presented to them. Then, the subjects had to decide whether each object was opened on the top, bottom, right or left. The recognition time for both displays increases with an increase in the viewing angle due to the negative effects of anisotropy. However, the recognition times in the statistical middle are greater for the TFT display and the negative anisotropy effect is stronger for smaller targets.

18 Experimental studies on dual monitor configuration. The subjects task consisted of discriminating ZiSo s (similar to Landolt rings, but square). Study 1: Comparison of horizontal dual monitor configuration (two versus one monitor) The simultaneous monitoring of multiple monitors arranged horizontally (each 50 left and right from the viewer) in comparison to working with only one monitor was analyzed. The recognition of targets on one screen results in significantly faster processing than the recognition of targets in two horizontally aligned monitors. There are no significant differences regarding the processing accuracy. Study 2: Comparison of vertical dual monitor arrangement (arranged above or below) The influence of the viewing angle is detected by the comparison between the upper and lower screen position. The assignment given to the subjects was solved significantly faster when using the lower screen compared to the upper screen. The viewing angle had no influence on the processing accuracy.

19 In this study, the increase in productivity was examined by using multiple screens with a total of 67 subjects. The scenario was the merge of comments in the preparation of a publication. The task of the subjects was to take specific corrective-suggestions and integrate these suggestions in their own text. All groups performed this task on a 19-inch screen as the reference task. After that the same task was either processed at the same working station (group 1: 19 subjects), at a working station with a 22-inch widescreen monitor (group 2: 24 subjects) or at a working station with three 19-inch screens (group 3: 24 subjects). As a measure of productivity, the performance ratio was calculated from the achieved points (correct answers minus errors) per time unit. This serves as the basis for the calculation of the increase in productivity (%) by the use of larger or more screens. For group 1 the average performance ratio increases from task 1 to task 2 by 1,8%. To avoid learning effects, only the differences of the performance ratios related to task 2 were observed and the productivity level of group 1 was used as the base. The increase of productivity was 8,3% for group 2 and 35,5% for group 3. Thus, a larger screen area leads to a significant increase in productivity.

20 Objects that should be perceived by the human eye either have to emit light themselves or reflect light coming from their surroundings. Light is electromagnetic radiation with a wavelength from 400 to 720nm which generates a visual stimulus in the human eye. Light consists of different colors which allocate to different wavelengths. The human eyes color sensitivity depends on the conditional adaption and therefore the environmental lightness. The light-adapted eye is most sensitive in the color range of green to yellow, where it is quite insensitive to blue and red. The dark adapted eye is most sensitive to a color range from blue to green.

21 For adapting to different viewing distances, denoted as accommodation, the ciliary muscle adjusts the eye s lens thickness and therefore its focal length. Increasing the tension of the ciliary muscles increases the lens's thickness which enables near vision. Keeping up this tension gets harder at higher ages since the lens suffers from age-related rigidification. Decreasing or relaxing the muscles tension decreases the lenses' thickness enabling distant vision. Frequent changes in accommodation leads to fatigue which has to be considered as a criterion when designing work systems, e.g. where displays come to use. All displays should preferably have the same distance to the viewer s eyes. Accommodation involves setting the angle of vergence (see next slide).

22 Objects at fixation distance are projected on the corresponding retinal position by muscular regulation of both eyes line of sights. By fixing a very distant object both eyes line of sights are close to be parallel (divergence). By fixing a near object both eyes line of sights are moved towards each other to make the corresponding images projected on the retinal surface being in cover (convergence).

23 The illustration shows how the human eye focuses (e.g. point P located on left side of illustration) and a corresponding image is projected on the eyes retina (points p 1 and p 2 ). An object (Q) being located at further (or closer) distance is projected on the opposite positions of the retina with its corresponding (disparate) positions (points q 1 and q 2 ). The lateral offset is called disparity. The difference between each of the regarding two images generates a stereoscopic image and therefore the spatial impression in the brain s visual cortex. The image received in the visual cortex is reversed diagonally. For a "proper" perception in correspondence to gravity the perceived image is cognitively converted in the visual cortex.

24 Background information: If the horopter is not in compliance with human perception or eyes are receiving contradictive information in any way: Occurrence of "Simulator Sickness with symptoms of nausea; human perception can get used to this phenomenon, a.k.a. "ios7-sickness": Apples operating system "ios7" causes nausea by the usage of the parallax effect, where two images are shifted against each other; symptoms should disappear after a usage of ten days of "ios7" since the users perception gets used to this effect. The effect is caused by a very slight motion of objects on a display which has a very high resolution. Motion and the high image sharpness induce the desired three-dimensional effect. Since the devices tablets or smartphones are perceived as flat and held in the users hands the human perception struggles with the perceived three-dimensional effect and a contradictive perception occurs. Devices e.g. built for desktop purposes generate less dissonance since their depth boldness is higher. Furthermore, the discrepancy between three-dimensional optics and two-dimensional displays have additional effects: The eyes have less ability to gain proper focus which causes stinging in the eyes and general fatigue.

25 With artificial stereoscopy the viewer is shown two pictures of varying visual positions. The natural viewing of different pictures with two eyes is thus reproduced. The different techniques of stereoscopic presentation therefore also have either two separate image areas or else function in a time-division manner. If photos are shown to the observer, the camera distance and angle must already be taken into consideration during photographing. The distance of virtual cameras, the angle of the cameras and the perspective of the generated pictures can be determined for the display of 3D scenes that are first calculated by the computer. The presentation of two different pictures is inherent to all stereoscopic display systems. The first systems, so-called stereoscopes, were primarily invented in the 18th century. Two photographs were required from two different lines of vision. The observer viewed the differently taken images with the stereoscope. In this case, the photo taken from the left side line of vision was presented to the left eye, and the photo taken from the right line if sight to the right eye. Thus, a cognitively created impression of depth occurs through the merge of the two images in the visual cortex. Today s stereoscopic monitors work with similar techniques. The key difference is that the pictures are not static photographs, but rather images on the display which are shown as field images. Field images are images where even and odd lines of the image are separated into different channels resulting into the two different interlaced field images. The haploscopic division, i.e., the transmission of each field image to the specific eye, is achieved using different techniques than used for historic stereoscopes. Currently, and aside from separate displays on two monitors, e.g., through mirror systems or HMDs (head mounted displays), haploscopic division can also be carried out through multiplex procedures. Thus, shutter glasses show the left and right eye a temporally alternating monitor image while auto stereoscopic monitors present the left and right eye with a spatially alternating image.

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29 The principle of alternating half-image presentation can be seen on the left side of the figure. The images for the left and right eye are already interlinked in the computer by graphics card drivers so that only the interlinked image is then transferred to the monitor. The prism masks mode of operation is presented on the right side of the figure. The prisms are laid out in such a way that the alternating pixel gaps are diverted to both the left and right eye. If the eyes of the observer are within the so-called Sweet Spot, i.e., within the region to which the light is diverted, then each eye receives the image specific to that eye, and a spatial impression is created. However, information is lost during the interlinking of the left and right half-image. Basically, the horizontal resolution of the images is halved. This leads to distorted edges, particularly for text. A decrease in depth resolution also occurs for spatial perception due to the halving of the horizontal resolution.

30 In principle, volumetric displays are able to blur the boundaries between illusion and reality the observer dives into the picture. Currently, there are various possibilities for producing a three-dimensional accurate visual impression. Volumetric displays are based on millions of 3D-pixels called voxel (volume + pixel) which either absorb or emitter the light. The three-dimensional picture is produced by projection of the voxels on a rotating screen. An X-Ray-like image of the leaked image data is created. Perspecta 200 individual two-dimensional images come together within a half-sphere made of glass to create a three-dimensional image. These individual images are projected onto a plastic disc rotating transparency screen within the sphere by a projector that produces 4000 frames per second. The human eye then sees the image as being three-dimensional. In contrast to conventional procedures, for Perspecta the observer does not require 3D glasses and is not limited to one specific visual angle.

31 DepthCube A color image from a projector is projected onto consecutively staggered glass panels. The basic material uses 20 standard TFT display panels, which now acts as a single screen. 19 of the layers are translucent, and only one acts as the opaque layer. The 3D image is then built up in layers, always on a different LCD panel. 20 of these successive panels results in a spatial depth of about ten centimeters. The monitor serves as a quasi visual body. The image requires a very powerful projector of the Digital Light Processing (DLP) type, with a capacity of about 800 watts. The large amount of power is needed because the TFT panels only allow low levels of light through. The projector is responsible for the colors. In order to avoid visible transitions between the individual panes, a special algorithm provides for antialiasing in 3D applications.

32 Light is an electromagnetic radiation, which leads to visual stimulation in the eye, in a wavelength range from approximately 380 to 780 nm. Radiators are called light sources if they emit at least partially energy in these spectral range. Light consists of different colours which assign to specific wavelength. The eye is not equally sensitive to all colours. The highest sensitivity for day-seeing is the yellow/green colour range (approximately 550 nm).

33 The illuminance (Lux = Lumen/square meter) corresponds to the relationship of light hitting a certain surface (usually the workspace) to the size of this surface. If a luminous flux of 1 Lumen hits a 1 m2 surface then the illuminance is of 1 Lux (lx). The luminous flux decreases with punctiform light sources with a square of distance between light source and evaluated surface. The reflectance is the relationship of the reflected luminous flux to that hitting the surface. Reflectance reproduces the characteristics of surfaces in order to reflect the light beams appearing. Luminous flux and illumination are known as the radiance emitted from a light source, both generally in all directions (luminous flux) as well as in a specific area (illumination). A particular topic of interest is luminance which lights up a particular surface; the measure of illuminance is used in this case. For radial symmetric bodies with perpendicular occurrence of radiance the following holds true E = I / r², when r expresses the distance between the radiating and the receiving body. Thus, illuminance can be varied quite easily through a change in distance. The luminous intensity (Candela) is the visible radiation from a light source in a particular solid angle, and belongs to the SI base units. The solid angle (Steradiant) is the measurement for the size of the cone-shaped or pyramid-shaped region that contain beams of light. It can be calculated from the relationship between the perpendicularly lit surface to the square of the distance between the surface and the beam s point of origin: = A/r 2.

34 The illuminance (lux = lumens / square meter) is the ratio of the incident luminous flux on a specific area (often the work space) to the size of this area. The illuminance at an area is 1 Lux (lx), if a luminous flux of 1 lumen (lm) falls perpendicularly onto an area of 1 m 2. Reflectance is the ratio of the reflected luminous flux to the incident luminous flux. The illuminance is recipient-related quantity. It is independent of the reflectance of an illuminated surface. The illuminance calculated with the area-illuminating-formula is interpreted as an average because generally the luminous flux is not distributed uniformly over the area. For large ratios of r 2 to A, E can be calculated with the luminous intensity I and the distance r between the light source and the illuminated point. If the ratio of the distance to the light source to the expansion of the light source is higher than 5, it is E=I/r 2. Often, the illuminated area is not positioned orthogonal below the light source. In this case, the resulting illuminance E depends on the angle of the observed surface to the light source and the mounting height r.

35 Generally the luminous flux of a light is not emitted uniformly in all space directions. The luminous flux Φ emitted per solid angle Ω unit to a specific direction is called luminous intensity I. The unit is candela [cd=lm/sr]. The energy which migrates into the eye as visible light is described by the luminance L and is measured in candela per square meter [cd/m 2 ]. The luminance represents the objective physical size which generates a subjective brightness perception. It results from the reflection of an illuminated area or out of the luminous intensity of a luminous body and it is defined as luminous intensity I of a light source in relation to the emitting area of the emitter A. With the exception of the so-called Lambert radiator, the luminance depends on the viewing angle. The Lambert radiator represents the ideal case of constant luminance over the solid angle. The ratio of directional luminous intensity and projected area (perpendicular to the luminous intensity vector) is the same for all directions. The luminance of the surface area for fully scattered reflecting surfaces can be calculated with the illuminance E, the reflectance ρ and the distance r between eye and illuminated area A.

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37 Visual acuity: Visual acuity indicates the ability to recognize small objects, and is expressed as the reciprocal value of the smallest angle (in arc minutes) from which the eye can directly perceive a detail (object). This measure of visual acuity is called visus. Visual acuity is influenced by a variety of factors, such as age, luminance, accommodation, contrast and color of light. Apart from the physical properties of the eye, visual acuity is influenced by central-nervous factors. Thus, in particular the form perception has a significant influence on the recognition performance. Visual acuity is not only dependent on the anatomical resolution grid of the retina; it can not be solely calculated with the diameter of the receptors, too. The essential influencing factors of the visual acuity are the object in view, the location of the image on the retina, the visual field luminance and the luminance ratio. Two visual objects with different luminance can only be perceived by the eye as disconnected when the luminance-difference exceeds a minimum value. The same goes for the visibility relative to the surrounding field. The luminance difference (contrast) between visual object and surrounding field is described with the luminance ratio. It is calculated as the ratio of the luminance of the infield to the luminance of the surrounding field. The visual acuity increases with the luminance of the surrounding field as well as the luminance difference between infield and surrounding field. It is also clear that even at low luminance of surrounding very small luminance differences are sufficient for an increase of visual acuity.

38 The adaption of the eye to the luminance in the visual field is done by photochemical and physiological adaption of the retina as well as a change in the pupil opening. This ability of the eye which is called adaption strongly influenced all the visual functions. The schematic course (time course) of adaption mainly depends on the luminance at the beginning and the end of adaption. A change from bright to dark is called dark adaptation, in the opposite case it is called bright adaptation.

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