Memory

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Forgetting in STM

Trace Decay Theory - Peterson and Peterson (1959) and Brown (1958)

The STM can only hold information for around 18 seconds. Without rehearsal, the information decays (fades away). It is called trace decay as it assumes memories leave a physical trace in the brain. This trace is some sort of physical and/or chemical change in the nervous system. Forgetting occurs as a result of the automatic decay or fading of this memory trace. Trace decay theory is all to do with time and the limited duration of STM. There is very little direct support for decay theory as an explanation for the loss of information from STM and LTM. One of the problems with decay theory is that it is more or less impossible to test it. In practice, it is not possible to create a situation in which there is a blank period of time between presentation of material and recall. Having presented information participants will rehearse it. If you prevent rehearsal by introducing a distracter task it results in displacement (interference).

Displacement Theory - Waugh and Norman (1965), Miller (1956) and Murdock (1962)

Old information is literally displaced by new information. It is based on Miller's magic number (7 +/- 2). When STM is 'full', new information displaces or 'pushes out' the old information and takes its place. It is assumed that information that has been there the longest is the first to go (supported by primacy and recency effect by Murdock (1962)). This theory suppers the MSM of memory. This only really words if the MSM is correct. It doesn't take into account the phenomenon that interesting and unusual information doesn't get displaced. Also, it is difficult to differentiate between decay and displacement. It takes time to present new information to displace the old meaning it could have actually dust decayed.

Waugh and Norman (1965)

Participants recall items nearer the end of the list much better (80%) than at the start of the list (about 20%). Participants found it ever so slightly easier to recall the later probe when the items were presented at a rate of 4 per second. The difference is small but significant.

Interference Theory Baddeley (1999) and Keppel and Underwood (1962)

This theory is applies much more to LTM but in theory can apply to STM. Information is not displaced but instead stays and interferes with the newer information. This creates confusion in memory; new information is 'muddled up' with old information.

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Forgetting in LTM

Decay Theory - Lashley (1939) and McKenna and Glendon (1985)

Do we forget things in the long term merely because the 'trace' of the memory has decayed and disappeared? People with damage to their brain suffer from memory loss, because the area where the 'trace' was is now gone. If LTM truly does decay over time, how is it people are able to remember things from a long time ago? Bahrick et al (1975) showed that after 48 years people can still have 70% accuracy of recall. Decay cannot account for how some memories fade and others don't at all, it appears to be random.

Lashley (1939)

He taught rats how to get through a maze. He then removed different parts of their brain and continued to put them in the maze. The more brain he removed, the harder they found it to remember how to get through the maze.

McKenna and Glendon (1985)

They taught 215 workers CPR. They tested them after 3 months and continually tested them for up to 3 years. Many forgot CPR skills after 3 months and after 3 years the skills were almost completely gone.

Interference Theory - Baddeley (1977) and Keppel and Underwood (1962)

Information is not displaced, but instead stays and interferes with the newer information. This creates confusion in memory; new information is 'muddled up' with old information. There are two types of interference:

proactive interference - when you can't learn something new because you keep remembering the old stuff

retroactive interference - when you forget something old, because you learnt something new

However, interference theory explains how you get confused sometimes between two things, but it doesn't explain how you forget something altogether. Also, it is possible to have retroactive interference and then not have it later. If someone gives you clues you can recover from retroactive interference. So did you every really forget it?

Baddeley (1977)

He did a natural experiment on rugby players and confirmed that interference and not decay makes people forget past events. He had 2 groups of rugby players, one team had been to all the games and the other had missed some. The same period of time had passed for both groups; if decay theory is correct, they should all recall a similar percentage of information. If interference is correct, the ones that attended more games should have forgotten more, because of interference. Baddeley found the latter was the case. A real life example of interference is when you move your books to the other side of your bedroom and keep going to the old place to find them.

Cue-Dependent Forgetting Theory

Decay theory and interference theory suggest that we forget things because they are no longer there in our LTM. They are no longer available. But what about the things we can't remember now , but can remember at a later date? The memory is there in you LTM, you just can't access it right now. You forget things because of retrieval failure - your brain can't retrieve the information at this time. You have insufficient cues but with a hint you remember. There are 2 kinds of cue:

external cues (context-dependent learning) - Godden and Baddeley (1975) - familiar things external to you cue your memories like the room you were in or the person you were with

internal cues (state-dependent learning) - Goodwin et al (1969) - what state you were in when you learnt it will cue the memory like if you were drunk or angry. Hardman (1998) - what you were doing when you learnt it will trigger the memory

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Short Term Memory

Encoding

The preferred method of encoding in STM is acoustic - Conrad (1964). This is supported by Baddely et al (1966). However, where acoustic coding is not possible, visual coding is used, for example Spreeder (Bradimonte (1992)).

Capacity

Miller's magic number (7 +/- 2). Miller also claimed that this was true of chunks of information. Chunking increases the capacity of STM but may reduce its accuracy. The limited capacity of STM is backed up further by the primacy and recency effects. This was by Galnzer and Cunitz (1966). Participants are more inclined to remember the first piece of information they are presented with (primacy), as well as the last piece of information (recency). Recency effect was eliminated if the participant is asked to do something else (none memory related) and no other aspects of recall were affected. Baddeley et al (1975) ran an experiment to find out if pronunciation time has anything to do with STM. He found that 1 Millar 'item' is whatever can be pronounced acoustically in 2 seconds. These findings were repeated/confirmed by Schweikert and Boruff (1986). In some languages, you can remember more information in your STM (Naveh-Benjamin and Ayres (1986)).

Duration

The duration of STM is less than 30 seconds if rehearsal is prevented (thereby making sure the information is not encoded into the LTM). The technique used to prevent rehearsal is the Brown-Peterson Technique (Peterson and Peterson (1959)). If no effort is made to retain the information, it is actually lost in seconds (Sebrechts et al (1989)). Capacity affects duration - it is not the sumber of individual items but the number of chunks of information.

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Long Term Memory

Encoding

Baddeley (1966) gave participants one of four lists that had different words: acoustically similar (A), acoustically dissimilar (B), semantically similar (C), semantically dissimilar (D). For immediate recall list A did the worst and 20 minutes later list C did the worst. Baddeley (1966) did exactly the same experiment as STM, except conducted 20 minutes later. Participants performed way better with semantically dissimilar words. They performed worst with semantically similar words. Acoustically similar and acoustically dissimilar words had the same performance. This shows that LTM is semantic.

Capacity

The estimate of human brain capacity is 2.5 petabytes (Reber (2010)). "No human yet exists who can use all the potential of his/her brain. This is why we don't except any estimates of the limits of the human brain." - Anokhin (1973).

Duration

Bahrick et al (1975) asked 400 participants (aged 17-74) the names of the people they went to school with. He then asked participants to put names to faces in yearbooks. The results were that 15 years after school there was 90% recall for both. After 48 years there was 80% name recognition and 70% facial recognition. This shows that duration in LTM is potentially permanent. Waganarr and Groeneweg (1990) showed that concentration camp prisoners could remember some details very accurately even after all this time but couldn't remember other things and the remembered things was random. You obviously can't remember eveyrthing. The main constraint appears to be accessibility, rather than availability. But then there are factors that affect duration considerably: childhood amnesia, initial learning (Bahrick and Hall (1991)) and recognition (Bahrick et al (1975)).

Types of LTM

Tulving (1972) thought that everyone was being far too simplistic about LTM. He stated that there is more than one kind: semantic (meanings) and episodic (day to day memory). Semantic shows little decline at all whereas episodic does. Cohen and Squire (1990) stated that semantic and episodic memory is declarative knowledge and that procedural memory is knowing how to do things. Amnesiac patients show little to no procedural memory decline and they can even learn new skills. This demonstrates they must be different types of memory involving different parts of the brain.

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Multi-Store Model of Memory

Atkinson and Shiffrin (1968) proposed the multi-store model. It is a linear model that shows how information flows through the processes of memory. There are three main components to the model and it is assumed that information must pass through each of these fixed stages to be remembered. There are capacity and duration limitations at each stage. It also identifies ways in which information is forgotten. The three separate stores are:

sensory memory store/register

short term memory

long term memory

Each store had a specific and relatively inflexible function. Information is simply rehearsed in the STM and if rehearsed sufficiently is transferred to LTM. Information to be recalled from LTM passes back through STM producing the associated response.