Memory

• Short-term memory (STM)

  The limited-capacity memory store. In STM, coding is mainly acoustic (sounds), capacity is between 5 and 9 items on average, duration is about 18 seconds.
• Long-term memory (LTM)

  The permanent memory store. In LTM, coding is mainly semantic (meaning), it has unlimited capacity and can store memories for up to a lifetime.
• Coding

  The format in which information is stored in the various memory stores.
• Capacity

  The amount of information that can be held in a memory store.
• Duration

  The length of time information can be held in memory.
• Research on Coding- Group outline

  Alan Baddeley (1966a, 1966b) gave different lists of words to four groups of participants to remember:

  • Group 1 (acoustically similar): words sounded similar
  • Group 2 (acoustically dissimilar): words sounded different
  • Group 3 (semantically similar): words with similar meanings
  • Group 4 (semantically dissimilar): words with different meanings.
• Research on Coding- Procedure

  Participants were shown the original words and asked to recall them in the correct order. When they did this task immediately, recalling from short-term memory (STM), they tended to do worse with acoustically similar words. When they recalled the word list after a time interval of 20 minutes, recalling from long-term memory (LTM), they did worse with the semantically similar words. These findings suggest that information is coded acoustically in STM and semantically in LTM.
• Strengths of Baddeley‘s research into Coding

  It identified a clear difference between two memory stores. Later research showed that there are some exceptions to Baddeley's findings. But the idea that STM uses mostly acoustic coding and LTM mostly semantic has stood the test of time. This was an important step in our understanding of the memory system, which led to the multi-store model
• Limitations of Baddeley‘s research into coding

  It used quite artificial stimuli rather than meaningful material. For example, the word lists had no personal meaning to participants. So Baddeley's findings may not tell us much about coding in different kinds of memory tasks, especially in everyday life. When processing more meaningful information, people may use semantic coding even for STM tasks. This suggests that the findings from this study have limited application.
• Research on Capacity- Digit Span

  Joseph Jacobs (1887) found out how much information can be stored by measuring digit span. For example, the researcher reads out four digits and the participant recalls these out loud in the correct order. If this is correct the researcher reads out five digits and so on until the participant cannot recall the order correctly. This indicates the individual's digit span. Jacobs found that the mean span for digits across all participants was 9.3 items. The mean span for letters was 7.3.
• Research on capacity- Span of memory chunking

  George Miller (1956) made observations of everyday practice. For example, he noted that things come in sevens: seven notes on the musical scale, seven days of the week, seven deadly sins, etc. Miller thought that the span (i.e. capacity) of STM is about 7 items, plus or minus 2. But he also noted that people can recall five words as easily as they can recall five letters. We do this by chunking - grouping sets of digits or letters into units or chunks.
• Strengths of Jacob’s study on capacity- digit span

  It has been replicated. The study is a very old one and early research in psychology often lacked adequate controls. For example, some participants' digit spans might have been underestimated because they were distracted during testing (confounding variable). Despite this, Jacobs' findings have been confirmed by other, better controlled studies since (e.g. Bopp and Verhaeghen 2005). This suggests that Jacobs' study is a valid test of digit span in STM.
• Limitations of Miller’s research onto capacity-

  Miller may have overestimated STM capacity. Nelson Cowan (2001) reviewed other research and concluded that the capacity of STM is only about 4 (plus or minus 1) chunks. This suggests that the lower end of Miller's estimate (five items) is more appropriate than seven items.
• Research on duration of STM

  Margaret and Lloyd Peterson (1959) tested 24 students in eight trials each. On each trial the student was given a consonant syllable (such as YCG) to remember. They were also given a 3-digit number. The student counted backwards from this number until told to stop. The counting backwards was to prevent any mental rehearsal of the consonant syllable (which would increase the duration of STM memory for the syllable). On each trial they were told to stop after varying periods of time: 3, 6, 9, 12, 15 or 18 seconds (the retention interval).
• Research on duration of STM- Findings

  The findings were similar to the student data. After 3 seconds, average recall was about 80%, after 18 seconds it was about 3%. Peterson and Peterson's findings suggested that STM duration may be about 18 seconds, unless we repeat the information over and over (i.e. verbal rehearsal).
• Research on duration of LTM

  Harry Bahrick et al. (1975) studied 392 American participants aged between 17 and 74. High school yearbooks were obtained from the participants or directly from some schools. Recall was tested in various ways, including:

  • A photo-recognition test consisting of 50 photos, some from the participants' high school yearbooks.
  • A free recall test where participants recalled all the names of their graduating class.
• Research on duration of LTM- Findings

  Participants tested within 15 years of graduation were about 90% accurate in photo recognition. After 48 years, recall declined to about 70% for photo recognition. Free recall was less accurate than recognition - about 60% after 15 years, dropping to 30% after 48 years. This shows that LTM may last up to a lifetime for some material.
• Limitations of Peterson and Peterson’s study on duration of STM

  The stimulus material was artificial. The study is not completely irrelevant because we do sometimes try to remember fairly meaningless material (e.g. phone numbers). Even so, recalling consonant syllables does not reflect most everyday memory activities where what we are trying to remember is meaningful. This means the study lacked external validity.
• Strengths of Bahrick et al.’s research on the duration of LTM

  It has high external validity. This is because the researchers investigated meaningful memories (i.e. of people's names and faces). When studies on LTM were conducted with meaningless pictures to be remembered, recall rates were lower (e.g. Shepard 1967). This suggests that Bahrick et al's findings reflect a more 'real' estimate of the duration of LTM.
• The Multi-Store model (MSM)

  A representation of how memory works in terms of three stores called the sensory register, short-term memory (STM) and long-term memory (LTM). It also describes how information is transferred from one store to another, what makes some memories last and what makes some memories disappear.
• Sensory Register

  The memory stores for each of our five senses, such as vision (iconic store) and hearing (echoic store). Coding in the iconic sensory register is visual and in the echoic sensory register it is acoustic (sounds). The capacity of sensory registers is huge (millions of receptors) and information lasts for a very short time (less than half a second).
• Richard Atkinson and Richard Shiffrin's (1968, 1971) multi-store model (MSM) describes how Information flows through the memory system. The model suggests that memory is made up of three stores linked by processing.
• Sensory Register

  Coding in each store is modality-specific (i.e. it depends on the sense). For example, the store coding for visual information is iconic memory and the store coding acoustically (i.e. for sound) is echoic memory. There are other sensory stores for touch, taste and smell information. Duration of material in the SRs is less than half a second. The SRs have a very high capacity, for example over one hundred million cells in one eye, each storing data. Information passes further into the memory system only if you pay attention to it (so attention is the key process).
• Short-term memory (STM)

  Information in STM is coded acoustically and lasts about 18 seconds unless it is rehearsed, so STM is a temporary store. It is a limited-capacity store, because it can only contain a certain number of 'items’ before forgetting occurs. The capacity of STM is between five and nine items of information, though Cowan's research suggests it might be more like five instead. Maintenance rehearsal occurs when we repeat material to ourselves over and over again. We can keep the information in our STMs as long as we rehearse it. If we rehearse it long enough, it passes into LTM.
• Long term memory (LTM)

  This is the potentially permanent memory store for information that has been rehearsed for a prolonged time. LTMs are coded mostly semantically (i.e. in terms of meaning). Its duration may be up to a lifetime. The capacity of LTM is thought to be practically unlimited. According to the MSM, when we want to recall information from LTM, it has to be transferred back into STM by a process called retrieval.
• Episodic Memory

  A long-term memory store for personal events. It includes memories of when the events occurred and of the people, objects, places and behaviours involved. Memories from this store have to be retrieved consciously and with effort.
• Semantic memory

  A long-term memory store for our knowledge of the world. This includes facts and our knowledge of what words and concepts mean. These memories usually also need to be recalled deliberately.
• Procedural memory

  A long-term memory store for our knowledge of how to do things. This includes our memories of learned skills. We usually recall these memories without making a conscious or deliberate effort.
• Endel Tulving (1985) was one of the first cognitive psychologists to realise that the multi-store model's view of long-term memory (LTM) was too simplistic and inflexible. Tulving proposed that there are in fact three LTM stores, containing quite different types of information. He called them episodic memory, semantic memory and procedural memory.
• Episodic memory

  This refers to our ability to recall events (episodes) from our lives. These memories are complex. They are 'time-stamped - in other words you remember when they happened as well as what happened. They store information about how events relate to each other in time. Your memory of a single episode will include several elements, such as people and places, objects and behaviours. All of these memories are interwoven to produce a single memory. You have to make a conscious effort to recall these memories.
• Semantic Memory

  This store contains our shared knowledge of the world. Your semantic memory contains your knowledge of an impressive number of concepts such as 'animals, love' and 'Frozen'. These memories are not 'time-stamped. Semantic knowledge is less personal and more about facts we all share. It contains an immense collection of material which, given its nature, is constantly being added to. According to Tulving, it is less vulnerable to distortion and forgetting than episodic memory.
• Strengths for Tulving’s research into LTM

  There is evidence from the case studies of HM (Henry Molaison) and Clive Wearing. Episodic memory in both men was severely impaired due to brain damage (caused by an operation and infection respectively). But their semantic memories were relatively unaffected. They still understood the meaning of words. Their procedural memories were also intact. This evidence supports Tulving's view that there are different memory stores in LTM - one store can be damaged but other stores are unaffected.
• Counter argument to clinical evidene as a strength of Tulving’s research into LTM

  Studying people with brain injuries can help researchers understand how memory is supposed to work normally. But a major limitation is that they lack control of variables. The brain injuries experienced by participants were usually unexpected. The researcher had no way of controlling what happened to the participant before or during the injury. Therefore, it is difficult to judge exactly how worse it is afterwards, as they had no idea what the memory was like before.
• Limitations of Tulving’s research into LTM

  There are opposing findings linking types of LTM to areas of the brain. E.g. Randy Buckner and Steven Petersen (1996) reviewed evidence regarding the location of semantic and episodic memory. They concluded that semantic memory is found in the left side of the prefrontal cortex & episodic memory on the right. But, other research links the left prefrontal cortex w/ encoding of episodic memories & the right prefrontal cortex w/ episodic retrieval (Tulving et al. 1994). This challenges the use of neurophysiological evidence to support types of memory.
• Strengths of Tulving’s research into LTM

  • Understanding types of LTM allows psychologists to develop treatments to help people with memory problems. E.g. , as people age, they experience memory loss. But research has shown this seems to be specific to episodic memory - it becomes harder to recall memories that occurred recently, though past episodic memories remain intact. Sylvie Belleville et al. (2006) devised an intervention to improve episodic memories in older people. The trained participants performed better on a test of episodic memory after training than a control group.
• Working memory model (WMM)

  A representation of short-term memory (STM). It suggests that STM is a dynamic processor of different types of information using subunits co-ordinated by a central decision-making system.
• Central Executive (CE)

  The component of the WMM that co-ordinates the activities of the three subsystems in memory. It also allocates processing resources to those activities.
• Phonological loop (PL)

  The component of the WMM that processes information in terms of sound. This includes both written and spoken material. It's divided into the phonological store and the articulatory process.
• Visuo-spatial sketchpad (VSS)

  The component of the WMM that processes visual and spatial information in a mental space often called our 'inner eye’.
• Episodic buffer (EB)

  The component of the WMM that brings together material from the other subsystems into a single memory rather than separate strands. It also provides a bridge between working memory and long-term memory.