Understanding HCI


An understanding of memory is one of the most important aspects of human information processing for those concerned with the development of human-computer systems. Like so much of human psychology, memory is a fascinating and highly complex subject. For the student of HCI it is of the utmost importance that the users memory is not over taxed.

Memory Systems

There are three basic types of memory systems:

  • working memory
  • long term memory
  • sensory memory

Working Memory

  1. Working memory is the area of conscious memory where current processing takes place - Think of it as the ‘processor’ part of a computer
  2. It can be fed by memories stored in long term memory, or by sensory input.
  3. WM has a role to play in both language understanding and calculation.
  4. In both these cases there is a need to hold information in your head while the process of interpretation of the words or calculation is being carried out.
  5. STM is an aspect of working memory (WM).
  6. Short term memory (STM) is as an area of memory that is able to hold limited information for a short time.
  7. STM was thought to be limited to the ‘magic number’ 7 plus or minus 2 pieces of information - Miller’s magic number
  8. Later research suggests that the capacity of working memory is only about 3 or 4 items - words, phrases or images

Phonological Loop

  1. like a loop of audio tape.
  2. e.g. when trying to dial an unfamiliar phone number, tend to repeat the numbers
  3. limited capacity and duration - < 30 seconds unless refreshed

Visuo-Spatial Scratch Pad

  1. visuo-spatial scratch pad is the visual/spatial equivalent of the phonological loop
  2. e.g visualising a route through a town, building, menu

Long Term Memory

  1. Long term memory (LTM) is an area of memory where information is stored and can be retrieved over very long periods of time - Think of it as the ‘hard drive’ of a computer.
  2. LTM is effectively infinite.
  3. Items from LTM have to be retrieved and brought into working memory before they can be used - This is called activation.
  4. Items in working memory can be processed more easily than information that has to be retrieved from LTM, thus any system that requires recall from LTM will slow down the activity of the user.
  5. The inability to retrieve information as desired, what is termed forgetting, could be viewed as very long retrieval times.
  6. Electrical stimulation of the brain has been said to evoke long-lost memories.

Examples of LTM

  • autobiographical memory - what I did on my first day at school
  • procedural memory - e.g. the knowledge of how to ride a bike or use Word

Sensory Memory

  1. Sensory memory is an area of conscious memory that deals with information from the senses – eyes, ears, tongue, nose & haptic (touch).
  2. When we watch a film we ‘see’ thousands of still frames, which are converted by our brain into a moving image.
  3. Other examples include light traces and audio play-back.
  4. As yet, computer systems do not use taste or smell, however in the future virtual reality systems may wish to use them in order to create the atmosphere of a real experience.

Examples of Sensory Memory

  • auditory encoding, e.g. music
  • haptic encoding, e.g. the sting of a burn
  • olfactory and gustatory encoding, e.g. identifying fresh and rotten food

Types of Memories

There are two basic types of memories

  • episodic
  • semantic

Episodic Memory

Episodic memory involves memory of events – what you had for dinner, what you did last weekend.

Semantic Memory

Semantic memory is knowledge about the world – what different words mean, how many inches in a foot.


  1. accessibility - retrieving information, main problem for long term memory.
  2. availability - whether stored or not, main problem in working memory
  3. Imagine trying to find a specific book in a library
    1. you find it (memory is retrieved)
    2. it’s not in the library (memory is unavailable)
    3. it’s in the library but has been mis-shelved (not accessible)
  4. Working memory
    1. decay - memory simply fades with time
    2. displacement - working memory limited in capacity: if try to add another item or two, a corresponding number of items are squeezed out
    3. Also a number of clinical conditions affecting different aspects of memory
  5. Long term memory
    1. Disuse - no evidence to support this
    2. Interference - forgetting influenced by what we have done before or after learning for example moving from word processor version I to version II - version II has reorganised menus. Having learned version I interferes with learning version II
    3. Retrieval failure

Memory Experiments

The Digit Span

  1. The subject is presented with a series of digits and asked to repeat them back in the same order.
  2. The number of digits is gradually increased until finally the subject always fails to recall the list accurately.
  3. The sequence length at which the subject is right half the time is the digit span.

Exercise - Digit Span

Conduct the digit span experiment on a partner and have them do it to you using the second list. Call out each line of numbers and have your partner repeat them immediately. Record the results and derive your digit span. The sequence length at which the subject is right half the time is the digit span.

  1. digit span 1
  2. digit span 2


  1. Experiments have shown that the capacity of STM is 7 ± 2 (may be outdated).
  2. More information can be remembered in information that is chunked.
  3. For the computer designer, this means that it would be inadvisable to require the user to recall more than this amount of information.
  4. Also, passwords of more than 5 to 9 characters are inadvisable unless chunking is possible.
  5. Example, remembering the number 051594737 is easier if remembered in this form: 051 – 594 – 737, as a telephone number. That is, remembering 3 chunks, instead of 9 individual numbers.
  6. Similarly the letters HMSEDIODUA are more easily remembered as HOUSEMAID (HOUSE and MAID make 2 chunks)


  1. Recalling lists in any order is known as free recall.
  2. In these experiments, there is a tendency for the first one or two words to be remembered well – this is called the primacy effect. These words tend to be rehearsed and enter LTM.
  3. Words in the middle will be remembered less well, and
  4. those at the end will be remembered well. This is called the recency effect.
  5. The words at the end are remembered well because they are either still in the auditory loop or in WM.
  6. Rare words are less likely to be remembered than common words.
  7. Words that have associated images (like elephant) tend to be remembered better.

Exercise - Recall

Choose a list at random from the 4 below and call the words out slowly and steadily to a partner. Have the partner repeat the list in any order and tick off the words. Do you notice any pattern? Have your partner repeat the experiment on you with a different list.

  1. Recall List 1
  2. Recall List 2
  3. Recall List 3
  4. Recall List 4

The Stroop Effect

  1. Trying to read the words at the same time as processing their (counter-intuitive) meaning
  2. normally presented as a series of colour coded words, with each word reading a colour different to their actual colour

Exercise - Stroop Effect

The link below goes to an interactive stroop experiment. Try to read the colour without being affected by the meaning of the word.

  1. Stroop effect experiment

Guidelines for Interfaces


  1. User interfaces need to be consistent.
  2. The user should not be expected to remember a different sequence of events for similar actions.
  3. The user interface should behave in consistent ways at all times for all screens
  4. Terminology, icons and use of colour should be consistent
  5. Examples:
    1. Keyboards are similar in form and structure to the typewriters they evolved from;
    2. The date format should be presented to American users in the form mm/dd/yy and to European user in the form dd/mm/yy

Cues & Feedback

  1. Human beings like to know when a task is done since they are now free to move onto the next stage and forget about what they have just done. This is called closure.
  2. It is important to build closure into systems since this acts as a means of allowing processes to be grouped or chunked in memory.
  3. The process later becomes a whole chunk for the expert user.
  4. The act of providing feedback is also a means of giving feedback to the novice user, aiding the learning process.
  5. Visual and audible clues should be given when a user is succeeding in the task as well as erring
  6. Provide reminders, or warnings as what stage an individual is at in an operation.
  7. Provide ongoing feedback on what is and/or just has happened.
  8. Example:
    1. computers beep when an error is made.
    2. When we copy a file, we see an icon representing the file in a new position in the file manager as well as an alert box signalling the copying process if the file is large.

Recognition Versus Recall

  1. Use picklists when trying to recall something which is on the tip of the tongue or ambiguous (one of the London airports) or
  2. when spelling is difficult


  1. To minimise the load on working memory, use persistence, so do not flash important information onto the screen for brief time periods.
  2. Get the user to click ‘OK’ – even if she does not think that it is.
  3. ‘OK’ is this instance really means – ‘I acknowledge the message’

Reducing Load

  1. Supporting memory by prompts reduces load
    1. use wizards to prompt the user and to help recall steps to complete a task
    2. user need only supply relatively small amounts of information at any one time
    3. has the advantage of an error correction system (i.e. use of the back and next steps)
  2. Organise information into a small number of "chunks"
  3. Try to create short linear sequences of tasks
  4. Organise data fields to match user expectations, or to organise user input (e.g. the auto-formatting phone numbers)
  5. Do not ‘overwrite’ the contents of working memory by giving additional tasks to the users

Using Images

  1. There is evidence to suggest that humans recall pictures better than they can recall words.
  2. This has led to the development of iconic interfaces, rather than command-line interfaces.


  • A user interface must encourage a relaxed attitude since users are more likely to succeed with the system if they are not under stress.
  • People are more likely to recall information if they are in the same situation in which it was learned

Further Reading

  • Anderson, J. (1995) Learning and Memory
  • Baddeley, A. (1994) Your Memory: A User’s Guide
  • Gleitman, H. (1992) Basic Psychology
  • Rose, S. (1992) The Making of Memory