Perception as information-processing

In order to behave appropriately in the environment the individual needs to have information about its layout. The environment is best thought of as an arrangement of surfaces, one lying in a horizontal plane, the other two lying at some angle in relation to one another in the vertical plane. In mobility, for example, the task of the traveller is to maintain contact with the horizontal surface while avoiding contact with the vertical ones. Jansson (1985) has analysed the task of mobility into walking towards, walking along and walking around. To this one needs to add walking upon, and it is the business of safely walking upon surfaces which presents the blind traveller with the greatest challenge.