Virtual reality allows users to interact with simulated environments, whether based on real or imaginary places. Most VR is primarily a visual experience shown on screens or special displays, though some systems include sound and limited tactile feedback. While technical limitations currently make high-fidelity VR difficult, improvements in processing power, resolution and bandwidth are expected to overcome these issues over time. VR has applications in training, scientific visualization, medicine, education and more. Recent advancements include contact lenses and software that allow existing graphics applications to run on VR devices without source code access.