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Human Memory

Lesson 3

Introduction to Encoding in STM Produced by

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STM Encoding •Visual

converted to acoustic code

Encoding •Semantic Encoding •Acoustic

Study Conrad (1964)

Encoding •Acoustic


Encoding in STM • When information arrives in sensory memory, it is still in its original form, e.g. as visual image or as a sound or touch experience. • The sensory store, as we saw earlier, has separate stores for different modalities (a modality is a particular form of sensory experience such as vision, sound or touch). • Atkinson and Shiffrin envisaged STM as a unitary store, i.e. as a single storage space with no separate compartments.


• Psychologists have been interested in finding out what happens to the stimulus once it arrives in STM and seems likely that is recoded into a form that the STM can recognise and manipulate. • Three main types of encoding in memory are: acoustic coding: the sound of a stimulus  visual coding: the physical appearance of a stimulus semantic coding: the meaning of a stimulus


• Research has shown that the main way of encoding in STM is by sound. • Much of the evidence on encoding has come from substitution errors. These occur when people substitute a different item for a similar one on the list to be learned. • The rationale for this is that people are likely to confuse items that sound alike if they are using an acoustic code, whereas they confuse items that look similar if they are using visual code or items that mean the same thing if they are using a semantic code.


Key Study : Conrad (1964) • Conrad showed participants a random sequence of six consonants. He projected them in a very rapid sequence on the screen. • There were two conditions in his study:  Letters were acoustically similar (e.g. B, G, C, T, D, V)  Letters were acoustically dissimilar (e.g. F, J, X, M, S, R)


• Immediately after the presentation, participants were asked to write the letters down in correct serial order. • Remember the the normal digit span is about seven digits, so participants should have found the recall task quite easy. • However, Conrad found that participants frequently made errors during recall.


• The majority of errors involved substitution of a similar sounding letter (e.g. a V or D). • Participants found it more difficult to recall strings of letters that sounded the same then letters that sounded different. • Remember that letters had been presented visually. • Conrad concluded that we must convert visually presented material to an acoustic code in STM and that we then find it difficult to distinguish between words that sound the same, i.e. there is acoustic confusion.


Methodical Issues • This was a well controlled experiment and therefore has high internal validity but low external validity. • It used artificial stimuli – we do not have to remember string of consonants in everyday life and therefore lacks ecological validity • He used students as his participants who might not be a representative of the general population and therefore lacks population validity.


• The study can be replicated and therefore is reliable. • If a repeated measures design was used there could be practice effects and participants could have performed better in the second task.


Ethical issues • There are no serious ethical issues in this kind of study but investigators have to gain consent from participants and to debrief them and advise them of their right to withdraw.


Cognitive Psychology - Encoding in STM