Memory is critical to our ability to act consistently and to learn new things. Without
memory, we could not capture a ‘stream’ of information reaching our senses, or draw
on past experience and apply this knowledge when making decisions.
Memory can be considered to be the storage and retention of information, experiences
and knowledge, as well as the ability to retrieve this information.
Memory depends on three processes:
• registration - the input of information into memory;
• storage - the retention of information;
• retrieval - the recovery of stored information.
It is possible to distinguish between three forms of memory:
a) ultra short-term memory (or sensory storage);
b) short term memory (often referred to as working memory)
c) long term memory.
Ultra short-term memory has already been described when examining the role of
sensory stores. It has a duration of up to 2 seconds (depending on the sense) and is
used as a buffer, giving us time to attend to sensory input.
Short term memory receives a proportion of the information received into sensory
stores, and allows us to store information long enough to use it (hence the idea of
‘working memory’). It can store only a relatively small amount of information at one
time, i.e. 5 to 9 (often referred to as 7 ±2) items of information, for a short duration,
typically 10 to 20 seconds. As the following example shows, capacity of short term
memory can be enhanced by splitting information in to ‘chunks’ (a group of related
items).
A telephone number, e.g. 01222555234, can be stored as 11 discrete digits, in which case
it is unlikely to be remembered. Alternatively, it can be stored in chunks of related
information, e.g. in the UK, 01222 may be stored as one chunk, 555 as another, and 234 as
another, using only 3 chunks and therefore, more likely to be remembered. In mainland
Europe, the same telephone number would probably be stored as 01 22 25 55 23 4, using
6 chunks. The size of the chunk will be determined by the individual’s familiarity with the
information (based on prior experience and context), thus in this example, a person from
the UK might recognise 0208 as the code for London, but a person from mainland Europe
might not.
The duration of short term memory can be extended through rehearsal (mental
repetition of the information) or encoding the information in some meaningful
manner (e.g. associating it with something as in the example above).
The capacity of long-term memory appears to be unlimited. It is used to store
information that is not currently being used, including:
• knowledge of the physical world and objects within it and how these behave;
• personal experiences;
• beliefs about people, social norms, values, etc.;
• motor programmes, problem solving skills and plans for achieving various
activities;
• abilities, such as language comprehension.
Information in long-term memory can be divided into two types: (i) semantic and (ii)
episodic. Semantic memory refers to our store of general, factual knowledge about
the world, such as concepts, rules, one’s own language, etc. It is information that is
not tied to where and when the knowledge was originally acquired. Episodic
memory refers to memory of specific events, such as our past experiences (including
people, events and objects). We can usually place these things within a certain
context. It is believed that episodic memory is heavily influenced by a person’s
expectations of what should have happened, thus two people’s recollection of the
same event can differ.
Motor Programmes
If a task is performed often enough, it may eventually become automatic and the
required skills and actions are stored in long term memory. These are known as
motor programmes and are ingrained routines that have been established through
practice. The use of a motor programme reduces the load on the central decision
maker. An often quoted example is that of driving a car: at first, each individual action
such as gear changing is demanding, but eventually the separate actions are
combined into a motor programme and can be performed with little or no awareness.
These motor programmes allow us to carry out simultaneous activities, such as
having a conversation whilst driving.
Situation Awareness
Although not shown explicitly in Figure 8, the process of attention, perception and
judgement should result in awareness of the current situation.
Situation awareness is the synthesis of an accurate and up-to-date 'mental model' of one's
environment and state, and the ability to use this to make predictions of possible future
states.
Situation awareness has traditionally been used in the context of the flight deck to
describe the pilot’s awareness of what is going on around him, e.g. where he is
geographically, his orientation in space, what mode the aircraft is in, etc. In the
maintenance engineering context, it refers to1:
• the perception of important elements, e.g. seeing loose bolts or missing parts,
hearing information passed verbally;
• the comprehension of their meaning, e.g. why is it like this? Is this how it should
be?
• the projection of their status into the future, e.g. future effects on safety,
schedule, airworthiness.
An example is an engineer seeing (or perceiving) blue streaks on the fuselage. His
comprehension may be that the lavatory fill cap could be missing or the drainline leaking. If
his situation awareness is good, he may appreciate that such a leak could allow blue water
to freeze, leading to airframe or engine damage.
As with decision making, feedback improves situation awareness by informing us of
the accuracy of our mental models and their predictive power. The ability to project
system status backward, to determine what events may have led to an observed
system state, is also very important in aircraft maintenance engineering, as it allows
effective fault finding and diagnostic behaviour.
Situation awareness for the aircraft maintenance engineer can be summarised as:
• the status of the system the engineer is working on;
• the relationship between the reported defect and the intended rectification;
• the possible effect on this work on other systems;
• the effect of this work on that being done by others and the effect of their work on
this work.
This suggests that in aircraft maintenance engineering, the entire team needs to have
situation awareness - not just of what they are doing individually, but of their colleagues’
activities as well.
Information Processing Limitations
The basic elements of human information processing have now been explored. It is
important to appreciate that these elements have limitations. As a consequence, the
aircraft engineer, like other skilled professionals, requires support such as reference
to written material (e.g. manuals).
Attention and Perception
A proportion of ‘sensed’ data may be lost without being ‘perceived’. An example with
which most people are familiar is that of failing to perceive something which
someone has said to you, when you are concentrating on something else, even
though the words would have been received at the ear without any problem. The
other side of the coin is the ability of the information processing system to perceive
something (such as a picture, sentence, concept, etc.) even though some of the data
may be missing. The danger, however, is that people can fill in the gaps with
information from their own store of knowledge or experience, and this may lead to
the wrong conclusion being drawn.
Once we have formed a mental model of a situation, we often seek information which will
confirm this model and, not consciously, reject information which suggests that this model
is incorrect.
There are many well-known visual ‘illusions’ which illustrate the limits of human
perception. Figure 9 shows how the perceptual system can be misled into believing
that one line is longer than the other, even though a ruler will confirm that they are
exactly the same.
Decision Making, Memory, and Motor Programmes
a) Attention and perception shortcomings can clearly impinge on decision making.
Perceiving something incorrectly may mean that an incorrect decision is made,
resulting in an inappropriate action. Figure 8 also shows the dependence on
memory to make decisions. It was explained earlier that sensory and short-term
memory have limited capacity, both in terms of capacity and duration. It is also
important to bear in mind that human memory is fallible, so that information:
• may not be stored;
• may be stored incorrectly;
• may be difficult to retrieve.
All these may be referred to as forgetting, which occurs when information is
unavailable (not stored in the first place) or inaccessible (cannot be retrieved).
Information in short-term memory is particularly susceptible to interference, an
example of which would be trying to remember a part number whilst trying to recall
a telephone number.
It is generally better to use manuals and temporary aides-memoires rather than to
rely upon memory, even in circumstances where the information to be remembered
or recalled is relatively simple. For instance, an aircraft maintenance engineer may
think that he will remember a torque setting without writing it down, but between
consulting the manual and walking to the aircraft (possibly stopping to talk to
someone on the way), he may forget the setting or confuse it (possibly with a
different torque setting appropriate to a similar task with which he is more familiar).
Additionally, if unsure of the accuracy of memorised information, an aircraft
maintenance engineer should seek to check it, even if this means going elsewhere to
do so. Noting something down temporarily can avoid the risk of forgetting or
confusing information. However, the use of a personal note book to capture such
information on a permanent basis can be dangerous, as the information in it may
become out-of-date.
“Once the Controller and fitter had got to T2 and found that this supportive material [Task
Cards and AMM extracts] was not available in the workpack, they would have had to return
to Base Engineering or to have gone over to the Line Maintenance office to get it. It would
be, in some measure, understandable for them to have a reluctance to recross the
exposed apron area on a winter’s night to obtain a description of what they were fairly
confident they knew anyway. However, during the course of the night, both of them had
occasion to return to the Base Maintenance hangar a number of times before the task had
been completed. Either could, therefore, have referred to or even drawn the task
descriptive papers before the job was signed off. The question that should be addressed,
therefore, is whether there might be any factors other than overconfidence in their
memories, bad judgement or idleness which would dispose them to pass up these
opportunities to refresh their memories on the proper and complete procedures.”
memory, we could not capture a ‘stream’ of information reaching our senses, or draw
on past experience and apply this knowledge when making decisions.
Memory can be considered to be the storage and retention of information, experiences
and knowledge, as well as the ability to retrieve this information.
Memory depends on three processes:
• registration - the input of information into memory;
• storage - the retention of information;
• retrieval - the recovery of stored information.
It is possible to distinguish between three forms of memory:
a) ultra short-term memory (or sensory storage);
b) short term memory (often referred to as working memory)
c) long term memory.
Ultra short-term memory has already been described when examining the role of
sensory stores. It has a duration of up to 2 seconds (depending on the sense) and is
used as a buffer, giving us time to attend to sensory input.
Short term memory receives a proportion of the information received into sensory
stores, and allows us to store information long enough to use it (hence the idea of
‘working memory’). It can store only a relatively small amount of information at one
time, i.e. 5 to 9 (often referred to as 7 ±2) items of information, for a short duration,
typically 10 to 20 seconds. As the following example shows, capacity of short term
memory can be enhanced by splitting information in to ‘chunks’ (a group of related
items).
A telephone number, e.g. 01222555234, can be stored as 11 discrete digits, in which case
it is unlikely to be remembered. Alternatively, it can be stored in chunks of related
information, e.g. in the UK, 01222 may be stored as one chunk, 555 as another, and 234 as
another, using only 3 chunks and therefore, more likely to be remembered. In mainland
Europe, the same telephone number would probably be stored as 01 22 25 55 23 4, using
6 chunks. The size of the chunk will be determined by the individual’s familiarity with the
information (based on prior experience and context), thus in this example, a person from
the UK might recognise 0208 as the code for London, but a person from mainland Europe
might not.
The duration of short term memory can be extended through rehearsal (mental
repetition of the information) or encoding the information in some meaningful
manner (e.g. associating it with something as in the example above).
The capacity of long-term memory appears to be unlimited. It is used to store
information that is not currently being used, including:
• knowledge of the physical world and objects within it and how these behave;
• personal experiences;
• beliefs about people, social norms, values, etc.;
• motor programmes, problem solving skills and plans for achieving various
activities;
• abilities, such as language comprehension.
Information in long-term memory can be divided into two types: (i) semantic and (ii)
episodic. Semantic memory refers to our store of general, factual knowledge about
the world, such as concepts, rules, one’s own language, etc. It is information that is
not tied to where and when the knowledge was originally acquired. Episodic
memory refers to memory of specific events, such as our past experiences (including
people, events and objects). We can usually place these things within a certain
context. It is believed that episodic memory is heavily influenced by a person’s
expectations of what should have happened, thus two people’s recollection of the
same event can differ.
Motor Programmes
If a task is performed often enough, it may eventually become automatic and the
required skills and actions are stored in long term memory. These are known as
motor programmes and are ingrained routines that have been established through
practice. The use of a motor programme reduces the load on the central decision
maker. An often quoted example is that of driving a car: at first, each individual action
such as gear changing is demanding, but eventually the separate actions are
combined into a motor programme and can be performed with little or no awareness.
These motor programmes allow us to carry out simultaneous activities, such as
having a conversation whilst driving.
Situation Awareness
Although not shown explicitly in Figure 8, the process of attention, perception and
judgement should result in awareness of the current situation.
Situation awareness is the synthesis of an accurate and up-to-date 'mental model' of one's
environment and state, and the ability to use this to make predictions of possible future
states.
Situation awareness has traditionally been used in the context of the flight deck to
describe the pilot’s awareness of what is going on around him, e.g. where he is
geographically, his orientation in space, what mode the aircraft is in, etc. In the
maintenance engineering context, it refers to1:
• the perception of important elements, e.g. seeing loose bolts or missing parts,
hearing information passed verbally;
• the comprehension of their meaning, e.g. why is it like this? Is this how it should
be?
• the projection of their status into the future, e.g. future effects on safety,
schedule, airworthiness.
An example is an engineer seeing (or perceiving) blue streaks on the fuselage. His
comprehension may be that the lavatory fill cap could be missing or the drainline leaking. If
his situation awareness is good, he may appreciate that such a leak could allow blue water
to freeze, leading to airframe or engine damage.
As with decision making, feedback improves situation awareness by informing us of
the accuracy of our mental models and their predictive power. The ability to project
system status backward, to determine what events may have led to an observed
system state, is also very important in aircraft maintenance engineering, as it allows
effective fault finding and diagnostic behaviour.
Situation awareness for the aircraft maintenance engineer can be summarised as:
• the status of the system the engineer is working on;
• the relationship between the reported defect and the intended rectification;
• the possible effect on this work on other systems;
• the effect of this work on that being done by others and the effect of their work on
this work.
This suggests that in aircraft maintenance engineering, the entire team needs to have
situation awareness - not just of what they are doing individually, but of their colleagues’
activities as well.
Information Processing Limitations
The basic elements of human information processing have now been explored. It is
important to appreciate that these elements have limitations. As a consequence, the
aircraft engineer, like other skilled professionals, requires support such as reference
to written material (e.g. manuals).
Attention and Perception
A proportion of ‘sensed’ data may be lost without being ‘perceived’. An example with
which most people are familiar is that of failing to perceive something which
someone has said to you, when you are concentrating on something else, even
though the words would have been received at the ear without any problem. The
other side of the coin is the ability of the information processing system to perceive
something (such as a picture, sentence, concept, etc.) even though some of the data
may be missing. The danger, however, is that people can fill in the gaps with
information from their own store of knowledge or experience, and this may lead to
the wrong conclusion being drawn.
Once we have formed a mental model of a situation, we often seek information which will
confirm this model and, not consciously, reject information which suggests that this model
is incorrect.
There are many well-known visual ‘illusions’ which illustrate the limits of human
perception. Figure 9 shows how the perceptual system can be misled into believing
that one line is longer than the other, even though a ruler will confirm that they are
exactly the same.
Decision Making, Memory, and Motor Programmes
a) Attention and perception shortcomings can clearly impinge on decision making.
Perceiving something incorrectly may mean that an incorrect decision is made,
resulting in an inappropriate action. Figure 8 also shows the dependence on
memory to make decisions. It was explained earlier that sensory and short-term
memory have limited capacity, both in terms of capacity and duration. It is also
important to bear in mind that human memory is fallible, so that information:
• may not be stored;
• may be stored incorrectly;
• may be difficult to retrieve.
All these may be referred to as forgetting, which occurs when information is
unavailable (not stored in the first place) or inaccessible (cannot be retrieved).
Information in short-term memory is particularly susceptible to interference, an
example of which would be trying to remember a part number whilst trying to recall
a telephone number.
It is generally better to use manuals and temporary aides-memoires rather than to
rely upon memory, even in circumstances where the information to be remembered
or recalled is relatively simple. For instance, an aircraft maintenance engineer may
think that he will remember a torque setting without writing it down, but between
consulting the manual and walking to the aircraft (possibly stopping to talk to
someone on the way), he may forget the setting or confuse it (possibly with a
different torque setting appropriate to a similar task with which he is more familiar).
Additionally, if unsure of the accuracy of memorised information, an aircraft
maintenance engineer should seek to check it, even if this means going elsewhere to
do so. Noting something down temporarily can avoid the risk of forgetting or
confusing information. However, the use of a personal note book to capture such
information on a permanent basis can be dangerous, as the information in it may
become out-of-date.
“Once the Controller and fitter had got to T2 and found that this supportive material [Task
Cards and AMM extracts] was not available in the workpack, they would have had to return
to Base Engineering or to have gone over to the Line Maintenance office to get it. It would
be, in some measure, understandable for them to have a reluctance to recross the
exposed apron area on a winter’s night to obtain a description of what they were fairly
confident they knew anyway. However, during the course of the night, both of them had
occasion to return to the Base Maintenance hangar a number of times before the task had
been completed. Either could, therefore, have referred to or even drawn the task
descriptive papers before the job was signed off. The question that should be addressed,
therefore, is whether there might be any factors other than overconfidence in their
memories, bad judgement or idleness which would dispose them to pass up these
opportunities to refresh their memories on the proper and complete procedures.”
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