In short-term memory there are two ways in which we forget. One of these ways is displacement.
Displacement is based on the idea that short-term memory (STM) has a limited capacity for information and that because new information comes along it displaces or over-writes the exisiting information. This means that the original information is forgotten.
Norman et al (1965)
Showed evidence for displacement.
They presented participants with a string of 16 numbers. After this, one of the numbers (the probe digit) was made known.
Participants had to recall the numbers that appeared immediately after the probeand it was found that the more numbers that follwed the probe, the more difficult it was to recall the numbers.
This was because the numbers nearer the end had displaced the earlier numbers making them unavailable.
The Decay Theory
Another way in which we forget in STM.
The Decay Theory suggests that memory fades overtime or decay's if it is not rehearsed.
This would explain the results from Peterson et al as no recall was premitted and the information had disappeared from STM after 18 seconds- memory is forgotten through disuse.
Norman et al (The Decay Theory)
Norman et al did the same study but presented the 16 numbers at different speeds. The faster the presentation rate, the less time for the numbers to decay.
As predicted participants found it easier to recall the faster lists. This supports the Decay Theory.
In the Peterson et al study, where participants had to countdown in 3's from a number and then recall a syllable it's possible that information did not disappear (decay) but that it was displaced by the numbers being used to count down.
Reitman (1974)- tried to over the problem of displacement by giving participants a different task in the retention interval. As again, the participants forgot the words, we have further evidence for decay.
Shallice et al- also suggested that displacement and decay explain forgetting in STM but that displacement is more important.
Problems with Displacement and Decay
- It can be argued that studies into displacement and decay, such as Peterson, lack ecological validity and are lab based so particpants are likely to suffer from demand characteristics.
- The use of nonsense trigrams and lists of numbers does not represent learning in everyday life and thus findings cannot be easily generalised.
A way we forget in LTM is called cue-dependent. This states that forgetting in LTM is mainly due to retrieval failure (lack of accessibility rather than availability). This is the failure to find an item of information.
Baddeley et al (1975)
Did research into external cues.
Presented scuba divers with a list of words either underwater or on dry land.
Found that words learned underwater were best recalled underwater and vise versa.
Concluded that recall is better if the environment is the same as the place the information was first learned.
Investigated Baddeley et al's research further.
Arraged for students to be tested in their usual teaching room either by their usual teacher, or a different one.
Other students were tested in a different room by either their usual teacher or a different one.
Those tested by their usual teacher in their usual room performed best, persumably due to the familiar things which acted as memory cues.
Glenbery et al (1985)
Tried to replicate studies by Baddeley and Abernethy but never found consistent support for cue-dependant effects, decreasing the reliability of the studies.
Internal cues and Goodwin (1969)
Internal cues occur through state dependant learning. This suggests that the psychological state a person is in can effect recall.
Goodwin (1969)- examined this effect with alcohol.
Participants who hid money whilst drunk were more likely to remember the hiding place when they were back in their orginal drunken state rather than when they were sober.
Darley et al (1973)- found similar effects. This demonstrates good reliability as studies have similar findings.
We have different theories as to why we forget things and these theories reflect the complexity of memory.
It is perphaps more logical to consider all theories as each individual is different and may forget for different reasons.