Short Term Memory

Introduction

Short term memory is a vital device to allow us to cope with the wealth of information that is constantly presented to us. It allows us to temporarily store information and then discard what is irrelevant in order to preserve the capacity of our long term memory and allow for faster and more efficient retrieval and perception. According to Miller (1956) the capacity of short term memory is seven items (plus or minus two). Miller later developed his theory to incorporate the idea of "chunking" whereby individual items could be chunked together to form one larger item or "chunk", allowing more information to be stored in short term memory. However the size of these chunks are also a factor in determining how many can be stored (Naveh-Benjamin & Ayres, 1986). A chunk was defined as something that could be pronounced in under one and a half seconds.

The duration of short term memory is around thirty seconds (Atkinson and Shiffrin, 1971). Evidence for this includes the ability of anterograde amnesiacs to retain information for up to around 30 seconds but no longer (also indication separate systems for short term and long term memory). As shown by Peterson and Peterson (1959), the ability to recall decays significantly over time when rehearsal is prevented using the brown Peterson, Peterson technique.

An updated model for short term memory was proposed by Baddeley & Hitch (1974). It redefined short term memory as working memory; an active rather than passive store of information relating to the current objectives of an individual. They proposed that the storage of information in working memory was divided into two categories or sub-stores that do not interfere with each other. They showed this by asking participants to recall a sequence of digits while simultaneously performing a spatial reasoning task. They found that the number of digits that participants were asked to recall had no effect on the number of errors in the spatial reasoning task. The Visuospatial sketchpad deals with visual and spatial stimuli while the Phonological Loop, deals with sounds. The combined input to these sub-stores is integrated by the central executive.

The evidence for the Phonological Loop is derived from phonological confusion (Badderley, 1966). This is where the number of errors in recalling acoustically similar words is higher than in acoustically dissimilar or semantically similar words. This suggests that stimuli are stored phonetically in working memory. This