In psychology, memory is the processes by which information is encoded, stored, and retrieved. Encoding allows information that is from the outside world to reach our senses in the forms of chemical and physical stimuli. In this first stage we must change the information so that we may put the memory into the encoding process. Storage is the second memory stage or process. This entails that we maintain information over periods of time. Finally the third process is the retrieval of information that we have stored. We must locate it and return it to our consciousness. Some retrieval attempts may be effortless due to the type of information. From an information processing perspective there are three main stages in the formation and retrieval of memory: Sensory memory corresponds approximately to the initial 200500 milliseconds after an item is perceived.