Life used to be simple when man was in direct contact with the environment. With the variety of sensors provided by evolution, we were able to explore the world surrounding us at ease. However, it has recently become possible to explore virtual environments in which we are not physically present. Here, the direct contact with the environment is lost, and all informa-tion on the layout of the environment is presented by displays. Unfortunately, such displays often present only a cumbersome representation of the virtual environment. Due to the limited capacity of image generators and display system, images are presented with a low resolution, for a narrow field of view, and for an arbitrary viewing direction. In simulators, remotely piloted vehicles, and endoscopic surgery, this frequently leads to pof (self) motion and disorientation. To improve the realism and effectiveness of virtual environments, two principles were followed in this thesis. First, tailoring the available information to the properties of the human visual system. Second, focussing on the visual information that is required in the task at hand. Below, two typical studies of the thesis are described. The effectiveness of a display system with a narrow field of view may be improved by changing the virtual viewing direction. In that case, the observer is enabled to explore the virtual environment in different directions, increasing his effective field of view. If such images are presented on a stationary monitor, however, a change in virtual viewing direction is not accompanied by a change in the viewing direction of the observer. This results in a percept of an unstable world, swinging to and fro when viewing direction is changed. In a simulator experiment it was shown that a Head-Slaved Display, which presents the images in the correct viewing direction, substantially improves performance. Another method to improve the effectiveness of a display with a narrow field of view is introduce sparse visual information in the periphery of the image. In this way, the available visual information is distributed according to the processing capacities of the visual system. In two simulator experiments, it was found that with this display system steering performance and spatial awareness were just as good as with a traditional wide display at a uniform level of detail. The operators of unmanned vehicles face similar problems. Due to the limited capacity of the data-link, video images are presented at a low update-rate and for a small, zoomed-in, field of view. It has been found that this leads to poor performance in tracking and searching targets, and frequently results in complete disorientation. The traditional methods of operator support, by means of quantitative displays and dials indicating camera heading and pitch are not effective. The information presented by these displays has to be converted into a sense of spatial orientation of the camera. This is in conflict with the apparent ease at which we are able to perceive our viewing direction in our natural environments. Therefore, an ecological display was used to present spatial information to the operator. Using the camera position and orientation data from the remote vehicle, a schematic computer generated environment can be presented to augment or extend the camera image. Thus, visual information is presented that is virtually identical to the visual information that is normally used in tracking, searching and spatial orientation. Since it is generated at the control station, the update-rate and field of view can be chosen to suit the task at hand. In two experiments, it was found that tracking and spatial orientation performance became independent of update rate when the camera image was augmented with a computer generated gter generated grid. In a third experiment it was found that search performance improved substantially if the (zoomed-in) camera image was surrounded with a normal view on such a computer generated environment. In contrast, traditional displays were found not to be effective in improving search performance. To summarise, by tailoring the available visual information to the properties of the human visual system, and by concentrating on only the visual information that is required in the task at hand, the effectiveness of a virtual environment may be substantially improved.