A continuously increasing number of Germans do their work at the computer. In 2001, theamount of the employed population that uses a PC in their job reached 50 percent for thefirst time. (German Association for Information Technology, Information,Telecommunications and new Media (BITKOM))

With 60%, Germany is even significantly above the EU average of 50% (Europeanstatistical association Eurostat). Behind Germany are countries like the UK (55%) andFrance (54%). “The most recent developments are a good indicator for the technologicalmodernization in Germany; this applies equally to both economics and administration.”(BITKOM)

The prerequisites for electronic commerce are improving as well since many workstationPCs are also connected to the internet.

In the year 2009 the percentage of employees in this country that were able to use theircomputer to go online increased from 29 (year 2003) to 46 percent.

During its investigation, the European statistical association Eurostat surveyedbusinesses that had at least ten employees.

The banking sector was excluded.

Carpal Tunnel Syndrome

The most important nerve in the hand, the Nervus Medianus, connects with all fingerflexor 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 ringfinger toward the thumb, with sensation. In addition, the nerve has motor parts for theprovision of thenar muscles. In the event of carpal tunnel syndrome, the n. medianus isconstricted below this carpal band. Key symptoms include erroneous sensations (pinsand needles, numbness) with fingers falling asleep from the thumb to the ring finger. Painespecially 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 injuriesfirst lead to symptoms and can be remedied through early treatment. The actual RSIdevelops with chronic damage and shows a chronic progression. The RSI symptomsparticularly occur in humans that work with computers a great deal. Frequently (textprocessing, data entry) are most affected. In particular, repetitive motions, such as typingor mouse-clicks, are seen as being partially responsible for such injuries.

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-StandDynamics helps to change a work style which is characterized by continuous sitting byalternating between sitting and standing in favor of more motion.

Stand-Sit Dynamics on the other hand involves the change from standing to sitting withthe aim of avoiding unilateral loading of the spine by long standing. Therefore, Stand-SitDynamics helps to change a work style characterized by continuous standing byalternating between standing and sitting in favor of more motion.

Three different input devices were analyzed in a study with 90 test subjects between 20and 75 years in a two dimensional pointing task. The execution time as well as themental workload were measured as dependent variables. Based on a start object, thetask was to point target objects in different angles as quickly and as accurately aspossible.

Regarding the execution time, clear age effects have been determined. The elderly testsubjects 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 timeresults from touch screen information input. Surprisingly mouse input showed the poorestaverage performance among all subjects. However, the effect of the execution timeimprovement through alternative input devices (touch screen, eye-gaze) varies in strengthamong the different age groups. The greatest improvement in performance can beachieved by the 60 to 75 year-olds. These participants need on average twice as long asthe 20 to 39 year-olds for information input with the mouse. However, when using a touchscreen they reach a performance level similar to that of younger people using a mouse .

TFT stands for Thin Film Transistor. This describes a set of planar circuit elements thatactively control the individual picture elements. The display consists of a matrix with manypixels. Each of these pixels can transmit a predefined photoelectric light color. Usuallyseveral fluorescent tubes are used as a backlight behind the matrix. A picture is thencreated on the front of the elements as a kind of “shutter” is opened that allows the lightfor a specific pixel to be either transmitted or blocked. Thus, for electrically responsiveliquid 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 firstfilter before entering into the alignment layer, i.e. the direction in which the light wavesvibrate is fixed in a certain direction. Upon leaving the alignment layer there is anotherfilter which is turned 90°. The following filter transmits light waves that are also turned inthe same direction. In a de-energized state, the liquid crystal alignment layer rotates thevibration direction of the of the light by 90° so that the light can pass freely (twist).

To investigate the age related coherence between acuity of vision and humanperformance, a symbol detection task was conducted on the basis of three different fontsizes (16’, 20’ and 22’ arc minutes). Results from partial correlation analysis point to anage differentiated adaption of font size rather than an adaption based on a measurementof visual acuity. The number of symbols to be detected and the response times of correctresponses were analyzed with an analysis of variance. The results were derived fromdata of 75 subjects between 20 and 75 years, and they show a strong effect of font sizeand 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 of22’ arc minutes. The possibility to compensate age related differences in response timeby enlarging the font size from 16’ arc minutes up to 22’ arc minutes supports theapproach of age differentiated adaption of the human computer interface.

Experimental studies on dual monitor configuration. The subjects’ task consisted ofdiscriminating 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 andright 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 therecognition of targets in two horizontally aligned monitors. There are no significantdifferences 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 andlower screen position. The assignment given to the subjects was solved significantlyfaster when using the lower screen compared to the upper screen. The viewing anglehad no influence on the processing accuracy.

Objects that should be perceived by the human eye either have to emit lightthemselves or reflect light coming from their surroundings. Light is electromagneticradiation with a wavelength from 400 to 720nm which generates a visual stimulusin the human eye. Light consists of different colors which allocate to differentwavelengths.

The human eyes’ color sensitivity depends on the conditional adaption andtherefore the environmental lightness. The light-adapted eye is most sensitive inthe color range of green to yellow, where it is quite insensitive to blue and red. Thedark adapted eye is most sensitive to a color range from blue to green.

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

Objects at fixation distance are projected on the corresponding retinal position bymuscular regulation of both eyes‘ line of sights. By fixing a very distant objectboth eyes’ line of sights are close to be parallel (divergence). By fixing a nearobject both eyes’ line of sights are moved towards each other to make thecorresponding images projected on the retinal surface being in cover(convergence).

The illustration shows how the human eye focuses (e.g. point P located on left side ofillustration) and a corresponding image is projected on the eyes‘ retina (points p1 and p2).An object (Q) being located at further (or closer) distance is projected on the oppositepositions of the retina with its corresponding (disparate) positions (points q1 and q2). Thelateral offset is called disparity. The difference between each of the regarding two imagesgenerates a stereoscopic image and therefore the spatial impression in the brain‘s visualcortex. The image received in the visual cortex is reversed diagonally. For a "proper"perception in correspondence to gravity the perceived image is cognitively converted inthe visual cortex.

Background information: If the horopter is not in compliance with human perception oreyes are receiving contradictive information in any way: Occurrence of "SimulatorSickness“ with symptoms of nausea; human perception can get used to thisphenomenon, a.k.a. "iOS7-sickness": Apples operating system "iOS7" causes nausea bythe 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 usersperception gets used to this effect. The effect is caused by a very slight motion of objectson a display which has a very high resolution. Motion and the high image sharpnessinduce the desired three-dimensional effect. Since the devices tablets or smartphones areperceived as flat and held in the users hands the human perception struggles with theperceived 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-dimensionaldisplays have additional effects: The eyes have less ability to gain proper focus whichcauses stinging in the eyes and general fatigue.

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 differenttechniques of stereoscopic presentation therefore also have either two separate imageareas or else function in a time-division manner.

If photos are shown to the observer, the camera distance and angle must already betaken into consideration during photographing.

The distance of virtual cameras, the angle of the cameras and the perspective of thegenerated pictures can be determined for the display of 3D scenes that are first calculatedby 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 viewedthe differently taken images with the stereoscope. In this case, the photo taken from theleft side line of vision was presented to the left eye, and the photo taken from the right lineif sight to the right eye. Thus, a cognitively created impression of depth occurs through themerge of the two images in the visual cortex.

Today’s stereoscopic monitors work with similar techniques. The key difference is that thepictures are not static photographs, but rather images on the display which are shown asfield images. Field images are images where even and odd lines of the image areseparated 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, isachieved using different techniques than used for historic stereoscopes. Currently, andaside from separate displays on two monitors, e.g., through mirror systems or HMDs(head mounted displays), haploscopic division can also be carried out through multiplexprocedures. Thus, shutter glasses show the left and right eye a temporally alternatingmonitor image while auto stereoscopic monitors present the left and right eye with aspatially alternating image.

The principle of alternating half-image presentation can be seen on the left side of thefigure. The images for the left and right eye are already interlinked in the computer bygraphics 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. Theprisms are laid out in such a way that the alternating pixel gaps are diverted to both theleft 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 specificto 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 dueto the halving of the horizontal resolution.

In principle, volumetric displays are able to blur the boundaries between illusion andreality – the observer “dives into” the picture. Currently, there are various possibilities forproducing a three-dimensional accurate visual impression.

Volumetric displays are based on millions of 3D-pixels called voxel (volume + pixel) whicheither absorb or emitter the light. The three-dimensional picture is produced by projectionof the voxels on a rotating screen. An X-Ray-like image of the leaked image data iscreated.

Perspecta

200 individual two-dimensional images come together within a half-sphere made of glassto create a three-dimensional image. These individual images are projected onto a plasticdisc rotating transparency screen within the sphere by a projector that produces 4000frames per second. The human eye then sees the image as being three-dimensional. Incontrast to conventional procedures, for Perspecta the observer does not require 3Dglasses and is not limited to one specific visual angle.

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 singlescreen. 19 of the layers are translucent, and only one acts as the opaque layer. The 3Dimage is then built up in layers, always on a different LCD panel. 20 of these successivepanels 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 LightProcessing (DLP) type, with a capacity of about 800 watts. The large amount of power isneeded because the TFT panels only allow low levels of light through. The projector isresponsible for the colors. In order to avoid visible transitions between the individualpanes, a special algorithm provides for antialiasing in 3D applications.

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 ifthey 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).

The illuminance (Lux = Lumen/square meter) corresponds to the relationship of light hitting acertain surface (usually the workspace) to the size of this surface. If a luminous flux of 1Lumen hits a 1 m2 surface then the illuminance is of 1 Lux (lx). The luminous flux decreaseswith punctiform light sources with a square of distance between light source and evaluatedsurface.

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 beamsappearing.

Luminous flux and illumination are known as the radiance emitted from a light source, bothgenerally 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 ofilluminance is used in this case.

For radial symmetric bodies with perpendicular occurrence of radiance the following holdstrue 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 particularsolid angle, and belongs to the SI base units. The solid angle (Steradiant) is themeasurement for the size of the cone-shaped or pyramid-shaped region that contain beamsof light. It can be calculated from the relationship between the perpendicularly lit surface tothe square of the distance between the surface and the beam’s point of origin: Ω = A/r2.

The illuminance (lux = lumens / square meter) is the ratio of the incident luminous flux ona specific area (often the work space) to the size of this area. The illuminance at an areais 1 Lux (lx), if a luminous flux of 1 lumen (lm) falls perpendicularly onto an area of 1 m2.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 anilluminated surface. The illuminance calculated with the “area-illuminating-formula” isinterpreted as an average because generally the luminous flux is not distributed uniformlyover the area. For large ratios of r2 to A, E can be calculated with the luminous intensity Iand the distance r between the light source and the illuminated point. If the ratio of thedistance to the light source to the expansion of the light source is higher than 5, it isE=I/r2. Often, the illuminated area is not positioned orthogonal below the light source. Inthis case, the resulting illuminance E’ depends on the angle of the observed surface tothe light source and the mounting height r.

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/m2]. 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.

Visual acuity:

Visual acuity indicates the ability to recognize small objects, and is expressed as thereciprocal value of the smallest angle (in arc minutes) from which the eye can directlyperceive a detail (object). This measure of visual acuity is called visus. Visual acuity isinfluenced by a variety of factors, such as age, luminance, accommodation, contrast andcolor of light. Apart from the physical properties of the eye, visual acuity isinfluenced by central-nervous factors. Thus, in particular the form perception has asignificant influence on the recognition performance. Visual acuity is not onlydependent on the anatomical resolution grid of the retina; it can not be solelycalculated with the diameter of the receptors, too. The essential influencingfactors of the visual acuity are the object in view, the location of the image on theretina, the visual field luminance and the luminance ratio. Two visual objects withdifferent luminance can only be perceived by the eye as disconnectedwhen the luminance-difference exceeds a minimum value. The same goes for thevisibility relative to the surrounding field. The luminance difference(contrast) between visual object and surrounding field is described withthe luminance ratio. It is calculated as the ratio of the luminance of the infield tothe luminance of the surrounding field. The visual acuity increases with theluminance of the surrounding field as well as the luminance difference betweeninfield and surrounding field. It is also clear that even at low luminance ofsurrounding very small luminance differences are sufficient for an increase ofvisual acuity.

The adaption of the eye to the luminance in the visual field is done by photo-chemical and physiological adaption of the retina as well as a change inthe pupil opening. This ability of the eye which is called adaption stronglyinfluenced all the visual functions. The schematic course (time course)of adaption mainly depends on the luminance at the beginning and the endof adaption. A change from bright to dark is called dark adaptation, in the oppositecase it is called bright adaptation.