1) Short term memory (STM) lasts only a few seconds unless information is rehearsed, in which case it can be transferred to long term memory (LTM). Peterson and Peterson (1959) found recall of letters was around 90% after 3 seconds but only 2% after 18 seconds without rehearsal. 2) LTM can last from hours to decades. Bahrick et al (1975) found strong recall of classmates' names up to 34 years later, especially with visual prompts. 3) The capacity of STM is around 7 items on average according to studies using digit span tasks. LTM capacity is considered limitless as information is lost through decay and interference over time rather than reaching a

1. Duration, Capacity and Encoding

2. Duration: Short Term Memory
• STM does not last very long
• Rehearsal keeps a memory active
• Verbal rehearsal can allow the memory to
become long term.

3. Studies!
• Peterson and Peterson (1959)
– WRT303 SCX592
– Count backwards from the number in 3s
– Recall the three letters.
– Remembered around 90% after 3 seconds
– Remembered around 2% after 18 seconds
• Nairne et al (1999)
– Found could recall up to 96 seconds. Used the
same items across trials to reduce interference
between items.

4. Duration: Long Term Memory
• Memories that last anywhere from 2 hours to
100 years. Considered to be limitless duration
• STUDY:
– Bahrick et al (1975)
– 392 US high school graduates. Remembered
classmates names w/out pictures and with
pictures.
– Up to 34 years very strong results. Better with
visual prompts
– Dip in recall after 47 years (could be duration or
ageing)

5. Capacity
• LTM = considered pretty much limitless.
Losses happen through decay and interference
not a limit on capacity.
• STM – how are you going to define a unit?

6. Capacity STM
• Jacobs (1887) – Used digit span to show
average recall is around 7 digits
• George Miller (1956) – Tried different
“chunks” 15 letters very difficult but 5 x 3
letter words doable.
• Simon (1974) – Capacity dependent on
chunks. Span less with longer syllable words

7. Encoding
• Information arrives in your sensory memory
as a sound or an image or a feeling
• Three main ways of coding
– Acoustic coding: the sound of a stimulus
– Visual coding: the physical appearance of a
stimulus
– Semantic coding: the meaning of the stimulus
• In general STM seems to use acoustic coding
and LTM uses semantic coding.

8. Studies
• Conrad (1964):
– Showed six consonants: one group similar
acoustically and one group different acoustically.
– Write down in correct order.
– Found the acoustically similar ones harder
– Concluded that in the STM we convert visual
material into an acoustic code and find it difficult
to distinguish between information that sounds
the same.

9. Studies
• Baddeley (1966)
– Participants shown a random sequence of five
words from one of four categories:
• Acoustically similar words
• Acoustically dissimilar words
• Semantically similar words
• Semantically dissimilar words
– Asked to write down after
– Got similar results to Conrad and concluded STM
codes acoustically

10. Studies
• Baddeley (1966) cont.
– Modified the experiment to look at LTM
– Made it ten words long, stopped them rehearsing
by interrupting after each presentation.
– Shown each list four times and tested 20 minutes
later.
– This time acoustic similarity was not significantly
different but semantic similarity was.
– Concluded LTM mainly semantically encoded.