Of even more importance to basic flight training are the changes brought about by moving into a visually expansive environment. Accurate control of the aircraft relies heavily on visual cues and these are usually related to the horizon. Most people do not have a lot of experience with the vista presented in flight and have to learn, when, where, and how to look, and to a certain extent what to look for. Students often require some time to adjust to these changes and experienced pilots often need to reacquaint themselves to life in the sky after only brief absences from this environment. While it is obvious that you need good vision to fly, the demands are greater than you might expect. It is not just a case of identifying other aircraft quickly. Depth perception cues are often absent or distorted when aloft. Such things as cloud sizes and reflective landing surfaces such as water or snow covered fields are the most deceptive. It is worthwhile therefore, to spend some time understanding how the eye works to get a better understanding of its capabilities and limitations.