Short-term memory
Short-term memory (or "primary" or "active memory") is the capacity for holding a small amount of information in an active, readily available state for a short interval. For example, short-term memory holds a phone number that has just been recited. The duration of short-term memory (absent rehearsal or active maintenance) is estimated to be on the order of seconds. The commonly cited capacity of 7 items, found in Miller's Law, has been superseded by 4±1 items.[1] In contrast, long-term memory holds information indefinitely.
Not to be confused with working memory.Short-term memory is not the same as working memory, which refers to structures and processes used for temporarily storing and manipulating information.
Synaptic theory[edit]
Various researchers have proposed that stimuli are coded in short-term memory using transmitter depletion.[14][15] According to this hypothesis, a stimulus activates a spatial pattern of activity across neurons in a brain region. As these neurons fire, the available neurotransmitters are depleted. This depletion pattern represents stimulus information and functions as a memory trace. The memory trace decays over time as a consequence of neurotransmitter reuptake mechanisms that restore neurotransmitters to prior levels.
Relationship with working memory[edit]
The relationship between short-term memory and working memory is described by various theories, but the two concepts are generally considered distinct. Neither holds information for long, but short-term memory is a simple store, while working memory allows it to be manipulated.[16] Short-term memory is part of working memory, but is not the same thing.
Working memory refers to structures and processes used for temporarily storing and manipulating information. Working memory has been termed working attention. Working memory and attention together play a major role in the thought process. Short-term memory in general refers to the short-term storage of information, and it does not encompass memory manipulation or organization. Thus, while short-term memory components appear in working memory models, the concept of short-term memory is distinct from other concepts.
Within Baddeley's influential 1986 model of working memory two short-term storage mechanisms appear: the phonological loop and the visuospatial sketchpad. Most of the above research involves the phonological loop, because most of the work on short-term memory uses verbal material. Since the 1990s, however, research on visual short-term memory[17] and spatial short-term memory has expanded.[18]
Duration[edit]
The limited duration of short-term memory (~18 seconds without rehearsal)[19] suggests that its contents spontaneously decay over time.[20] The decay assumption is part of many theories of short-term memory. The most notable one is Baddeley's model of working memory. The decay assumption is usually paired with the idea of rapid covert rehearsal: to retain information for longer, information must be periodically repeated or rehearsed, either by articulating it out loud or by mental simulation. Another type of rehearsal that can improve short-term memory is attention-based rehearsal. Information is mentally searched in a particular sequence.[16] Once recalled, the information re-enters short-term memory and is then retained for a further period.
Nairn and Lewandosky et. al. dispute that spontaneous decay plays any significant role in short-term forgetting,[21][22] and the evidence is not conclusive.[23]
One alternative asserts that several elements (such as digits, words, or pictures, or logos) are held in short-term memory simultaneously, their representations compete with each other for recall, degrading each other. Thereby, new content gradually replaces older content, unless the older content is actively protected.[24]