orage system with an apparent unlimited capacity with information being held in enactive, iconic or symbolic form. The evidence for separate stores comes from empirical studies of duration, capacity, coding differences, serial position effect, brain damage and forgetting.In regard to duration there have been several studies that indicate separate stages, Sperling (1960) briefly showed participants a display of twelve letters organised in three rows and asked them to immediately recall the letters. It was found that if a tone was presented after the display signalling which row to report "recall was three times better demonstrating that available information disappears very rapidly". This study demonstrates the existence of a sensory memory system where the information is lost through decay. Peterson and Peterson (1959) found that delayed recall of trigams reduces performance from 80% after 3 seconds to 10% after 18 seconds, this is significant in that participants were given a task before recall in order to prevent rehearsal which supports the idea of the short term memory system wherein sensory data is lost rapidly without the involvement of rehearsal. Finally in a follow up study Atkinson and Shiffrin (1971) reported a longer duration of 15-30 seconds suggesting an upper limit for short term memory of 30 seconds, this suggests that any data to be stored for longer than this time would be inevitably stored in the long term memory where the duration time is potentially unlimited- demonstrated by forgetting.Secondly, further evidence for separate stores comes in the area of capacity. The above studies indicate that in terms of duration sensory memory is limited whereas the long-term memory store is potentially unlimited. Miller (1956) suggested that chunks limit the span of the short term memory not bits of information. This could explain why many categories consist of seven items e.g. days of the week, wonders of the world and even tele...
