In psychology, memory is the process in which information is encoded, stored, and retrieved. Encoding allows information from the outside world to reach the five senses in the forms of chemical and physical stimuli. In this first stage the information must be changed so that it may be put into the encoding process. Storage is the second memory stage or process. This entails that information is maintained over periods of time. Finally the third process is the retrieval of information that has been stored. Such information must be located and returned to the consciousness. Some retrieval attempts may be effortless due to the type of information, and other attempts to remember stored information may be more demanding for various reasons. From an information processing perspective there are three main stages in the formation and retrieval of memory: Encoding or registration: receiving, processing and combining of received information Storage: creation of a permanent record of the encoded information Retrieval, recall or recollection: calling back the stored information in response to some cue for use in a process or activity The loss of memory is described as forgetfulness or, as a medical disorder, amnesia.