This note comments on the confusion caused by the ambiguity of the words used by Rasmussen to describe types of cognitive processes.
April 1989
There are two types of difficulty with Rasmussen's S/R/KB formulation :
a. the words 'skill', 'rule' and 'knowledge' are very rich and used with many meanings. This
has had the result that, although Rasmussen himself may use these words with consistent
meaning, there is no consensus among other people about which of these categories any
particular type of behaviour might be assigned to.
b. there are limitations to this schema as a model of human information processing.
This note will concentrate on the first of these issues, the use of terms. The usages which will
be mentioned have not all been used in published papers, but people have used them in
discussion with me. I have come across all the possible combinations - people who call
rule-based what other people call skill, people to who call knowledge-based what other people
call rule, etc. This may occur because of differences in nuance when translating between
different European languages, for example there is no simple way of translating 'skill' into
French.
There is some ambiguity about whether, by the word 'rule', Rasmussen means behaviour which follows a standard sequence which has been developed through experience, or behaviour which follows instructions devised by someone else. Actually 'instruction following' is not a unique type of cognitive behaviour but is a type of task, which may be done using any of the cognitive mechanisms, as discussed in the last section.
Perceptual-motor Skills (LB)
These are actions which after practice become 'automatic', they require no conscious
monitoring.
1. Skill based : Rasmussen apparently uses the word 'skill' in this limited sense, to refer to this
type of behaviour. Both in British industry and among psychologists, the word 'skill' has a
much more general meaning, referring to the increased speed, accuracy and efficiency which
can develop in any type of behaviour after practice.
2. Rule based : some people say that perceptual-motor skills are examples of rule-based
behaviour, on the grounds that this type of behaviour appears like, and can be modelled by, the
operation of a production rule (if-stimulus-then-action).
3. Knowledge based : some people say that perceptual-motor skills are examples of
knowledge-based behaviour, on the grounds that they can only be done by someone who has
learned a great deal about the task, so they express a person's knowledge of the task.
Familiar Cognitive Skills (LB)
All skills other than perceptual-motor ones are cognitive, they involve cognitive processing.
The clumsy term 'familiar cognitive skills' refers particularly to the type of cognitive skill
which arises in repeated task situations, when a person has developed a standard method for
doing the task, after experience.
1. Skill based : evidently this is a type of skill, as behaviour becomes more efficient after
practice.
2. Rule based : as I understand it, this is the type of behaviour which Rasmussen is usually
referring to when he uses the term 'rule-based'.
3. Knowledge based : see above under perceptual-motor skill. also standard methods for doing
a cognitive task can make use of back-up reference knowledge, for example a mental model of
the structure or function of an industrial process, or knowledge about where its components are
within the building.
Prototype-using Skills (LB)
Rasmussen does not include this type of behaviour as a distinct category.
Problem-solving Skills (LB)
People can be more or less skilled in reacting to situations for which a standard method of
working has not yet been, or cannot be, devised. People can develop problem solving
strategies, and frameworks for organising knowledge in a way which makes it convenient to
refer to for a particular purpose.
1. Skill based : problem solving, i.e. dealing with non-standard situations, is behaviour which
can improve with experience. In UK industry, the 'skilled' tradesman is someone who can
formulate e their own approach to making or doing something.
2. Rule based : some people assign problem solving behaviour to the rule-based category, on
the grounds that it makes use of knowledge which is expressed in production rule format.
3. Knowledge based : Rasmussen himself uses the term 'knowledge based' to refer to these
more knowledge intensive types of behaviour.
Instruction Following
The task of following instructions illustrates the difficulty of assigning a particular type of task
to any one of Rasmussen's three categories. It is frequently assumed that giving instructions to
people minimises the amount of cognitive processing they have to do, but this is in fact not
necessarily the case.
1. Skill based : Written instructions essentially cannot be followed by using perceptual-motor
skills, as understanding language involves the use of working memory. Instructions conveyed
by picture or gesture may be responded to in this way.
2. Rule based : well designed instructions in familiar formats could be followed by using a
standard strategy for interpreting the instructions.
3. Knowledge based : understanding unfamiliar instructions can involve a considerable amount
of problem solving, see Bainbridge, 1989.
©1997 Lisanne Bainbridge
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