Psychology - memory - coding, capacity and duration

Short term memory - 

• A temporary memory store for events in the present or immediate present 

• Short duration  small capacity 

Long term memory -

• A more permanent memory store for events that happened in the more distant past

• Long duration + large capacity

Coding -

The way in which information is changed so that it can be stored in memory

Capacity - 

The amount of information that can be stored in memory at a given time 

Duration -

The length of time information remains in storage within memory (how long a memory lasts)

Coding is the format in which…

information is stored in the various memory stores 

Memory is often thought of as a process whereby a…

physical ‘trace’ of information about the past is store

The way that a memory is encoded describes the format that…

‘raw’ information is converted to when storing and retrieving such ‘traces’

The different types of encoding -

• Visual (as an image)

• Acoustic (as a sound)

• Semantic (through its meaning)

Research on Coding -

• Alan Baddeley gave different lists of words to 4 groups of ppts to remember

• 1. Acoustically similar

• 2. Acoustically dissimilar

• 3. Semantically similar

• 4. Semantically dissimilar

Conclusion from experiment -

• STM codes acoustically (as acoustically similar words were recalled the least efficiently)

• LTM codes semantically (as semantically similar words were recalled the least efficiently)

What happened when recalling acoustically similar words for STM?

When the words sound similar, the acoustic traces interfere with each other, making it harder to recall the exact order/which word was present

What happened when recalling semantically similar words for LTM?

When words have similar meanings, the semantic information in LTM overlaps, causing confusion + making it more difficult to retrieve the specific, distinct words that were originally learned

Research on digit span - who?

Jacobs (1887)

What was his research?

• He read out 4 digits and the ppt would try to recall them in the correct order

• If the ppt got it correct, they would up the number of digits to 5 + so on until they made a mistake

• This gives us an indication of their digit span

Conclusion made by Jacobs - 

• Mean span for digits ranges between 9-3 items 

• Mean span for letters ranges between 7-3 

• The STM has a limited storage capacity 

Miller (1956)

• He noticed that many things come in 7s

• He believed that the span of STM is around 7 items (plus/minus 2)

• He noted people can recall 5 letters as easily as they can recall 5 numbers by chunking them together

Miller explanation of chunking highlights that -

the capacity of STM is limited by the number of chunks, not the number of individual, basic units of information

Strengths of Millers research -

• Real-world application in remembering phone numbers for example

Weaknesses - 

• Cowan (2001) reviewed studies + on capacity of STM + concluded that it is limited to 4 chunks 

• Vogel (2001) looked at capacity for visual items + also said it is limited to 4 chunks 

• Simon (1974) found that people had a shorter memory span for large chunks and a longer memory span for small chunks. So it is the size of chunk that matters 

Capacity of LTM -

It is not possible to quantify the capacity of LTM, many psychologists would agree it is limitless

Capacity of LTM research -

• Linton (1975) conducted an autobiographical study using a memory diary to record 6 years of events from her life

• A researcher would randomly select pairs of records once a month + Linton would try to estimate the chronological order in which they occurred + date of each event.

• The average of items tested each month was 150, from amass of 5,500 after 6 years

• Linton found her memory for real-life events decreased at a rate of 5% a year, but she was able to recall a lot more items than expected, suggesting that real-life memories are a lot more durable than those of lab experiments

Duration of STM psychologist name/s

Peterson and Peterson (1959)

Method of research -

• Participants had to try and remember and recall three letter strings e.g. FZX

• When tested after 3 seconds, they could recall 80% of them

• After 18 second, though, they could only remember 10%

• Recall got progressively worse as the delay increased

Conclusion - 

STM lasts from 15-30 seconds (average 18 seconds) 

Strengths of Peterson study - 

• Showed that forgetting in the STM can occur if information is not rehearsed 

• High levels of control —→ high internal validity 

• Replicability —→ increase reliability of results through standardisation 

Weaknesses -

• Trying to memorise consonant syllables does not reflect everyday memory activities so is artificial —→ lacks ecological validity

• Marsh et al. (1997) when participants aren’t expected to be tested, forgetting will occur after just 2 seconds

• Is the study really testing for duration? Or just displacement - The numbers may displace the syllables to be remembered

Who did a study on the duration of LTM?

Bahrick et al. (1975)

What did they find out?

• 90% accuracy in face + name recognition even with those participants who had left high school 34 years previously

• After 48 years this declined to 80% for name recognition and 70% for face recognition

• Free recall was considerably less accurate: 60% accurate after 15 years and only 30% accurate after 48 years

Bahrick et. al results (1975) 

Conclusions -

• Findings show that classmates are rarely forgotten once recognition cues have been given.

  • Thus Bahrick et al.’s aim to demonstrate that people have very long-term memories was supported

• The findings also support the claim that recognition is better than recall

• It can be concluded that memory may not as unreliable + subject to confabulation (inaccuracy) as is often claimed

Strengths of Bahrick et al.’s study -

• Research demonstrates VLTM for a particular type of information - familiar faces that are likely to have emotional significance

• Study uses meaningful stimuli - high school year books - to test memory.

  • Thus research is more representative of natural behaviour —→ high ecological validity

Weaknesses -

• It cannot be concluded that VLTM exists for all types of info - maybe just for emotionally meaningful stimuli

• It is unclear whether the drop off in accuracy is due to limits of duration/general decline with memory as we become older