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However in this lies the danger of expectation. When beginning to hear a familiar message we tend to assume that the end of the message will contain the same information to which we have become familiar. Thus we forecast/assume what is to come and our concentration tails off the further we get into the transmission message. These kind of assumptions have caused many an aircraft accident.
Information from our senses is compared to the model as part of our control process. If we detect a mismatch, then we have a problem to resolve. Often we try to shape the data to the model and errors occur. But when perception matches reality one is situationally aware.
An inherent danger in this system is that, having built a mental model, we will tend to seek only information that confirms our model (confirmation bias) and ignore other information that may cast doubt on its accuracy.
A good example of confirmation bias is a pilot, when temporarily unsure of his/her position but hopes that the aircraft is where it is meant to be, tries to fit the map to the ground. As discussed in CRM, this loss of situational awareness is the time when leading questions start to appear. “That was Witney, wasn’t it ?” The phenomenon tends to be brought on by stress.
Three Dimensional Models
Our visual system has many cues to provide us with a three dimensional model. These include:
•Convergency - the amount that our eyes converge to bring an object into focus onto each fovea.
•Stereopsis - objects at close range provide a different picture on each retina than distant objects.
•Obscuration - near objects occlude far objects.
•Atmospheric Perspective - objects at a distance lose their colour and clarity.
•Retinal Size - the angle subtended at the retina becomes smaller with increasing distance. Retinal size is of particular importance to the pilot. For example, in the final stages of an approach, the pilot is likely to judge his height above the ground from the retinal size of the runway. To make this judgement, however he must have a stored expectation of the likely size of the runway. If the runway is wider or narrower than he expects it to be he may over or underestimate his height.
Short-term Memory (Working Memory)
Introduction
The attention mechanism will select what information is passed to the short-term memory. This memory enables information to be retained for a short period of time and will be lost in 10 to 20 seconds unless it is actively rehearsed and deliberately placed in our long-term memory. Unless rehearsed these items are lost by interference from new information or even from information previously stored.
Acoustic information is considered easier to retain than visual information as it is easier to rehearse sounds than data in a visual form.
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Limitations of Short-term Memory
The capacity of our short-term memory is limited. The maximum number of unrelated items which can be maintained is about 7 ± 2. Once this limit is exceeded one or more of the items are likely to be lost or transposed. This is of importance when designing checklists or deciding on the contents of an RT message. As anyone who has received a complicated departure clearance is aware, much of the information cannot be memorised but must be written down.
Short-term memory is also highly sensitive to interruption. For example, if a frequency is passed to a pilot and very soon after reception an interruption takes place, instant retention is possible but is immediately lost and the pilot has to request that the information is re-transmitted.
Methods of Increasing Short-term Memory
The two main tools to increase short-term memory are:
•Chunking
We can expand the number of items retained in our short-term memory by a system of ‘chunking’ any related material. Chunking works best when the individual is familiar with the information (mental model). A long telephone number may contain ten or more digits e.g. 012357176204 but can be chunked to 0123 5717 6204; only three items to be held. An example of this is the French telephone directory in which numbers are printed in separated blocks making good use of this tool. When asked for a telephone number a Frenchman will sometimes pass it in chunks, each chunk consisting of three figures.
•Association
This technique is used by many when remembering spoken lists of items. A wild and bizarre association is imagined and attached to each item on the list. Many politicians make use of this method when putting faces to names.
•Mnemonics
The use of mnemonics, the art of making up a word, phrase or sentence in order to remember many points, is useful.
Typical examples of items stored in the short-term memory in flight are : radio frequencies, heights and pressure settings prior to selection, short ATC instructions and verbal responses to checklists prior to execution.
Long-term Memory
Introduction
If the information in the short term memory is rehearsed, it will be transferred into the longterm memory. It is believed that information is stored in the long-term memory for an unlimited time period although frequently there are retrieval problems. One major disadvantage is the time it takes to access.
The long term memory contains information which can be classified into three types:
•Semantic memory.
•Episodic memory.
•Procedural memory (motor programmes).
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Semantic Memory
Semantic memory stores general knowledge of the world, storing information to such questions as: Are fish minerals? Do birds fly? Do cars have legs? It is believed that semantic memory holds concepts that are represented in a dense network of associations. Language is also held in semantic memory. It is generally thought that once information has entered semantic memory it is never lost. It is certainly more accurate than episodic memory. When we are unable to remember a word it is because we are unable to find where the item is stored, not because it has been lost from the store.
Episodic Memory
Episodic Memory is a memory of events or ‘episodes’ in our life; a particular flight, meeting, or incident.
Motor Programmes
Although most experts in the field of information processing agree that long term memory consists of episodic and semantic memories only, there are those that include motor programmes within the make-up of the long term memory and thereby include these as a third constituent of the LTM. It would appear that EASA concur with the latter viewpoint, thus these notes have included procedural memory as part of the long-term memory.
Factors Affecting Long-term Memory
•Expectation
One of the features of episodic memory is that the information does not remain static but is heavily influenced by our expectation of what should have happened. This tendency to remember what should have happened, rather than the actual series of events, causes problems to investigators of accidents or even to police investigations. For example, an experienced pilot witnessing an aviation accident will have a much stronger expectation of a likely set of events than a lay observer, and his recollection may be more biased to his interpretation of his observations than the non-expert’s recollection of the events themselves.
•Suggestion
It should also be noted that our recollection of events will be modified by the circumstances of suggestion and recall. Two observers having witnessed the same event may recall different ‘facts’ depending on the questions asked. Ask one his estimate of a vehicle’s speed as it ‘came’ around the bend and he will invariably give a lower figure than the second witness who is asked to judge the speed as it ‘screeched’ around the corner. Subconsciously the responder may give a reply that he thinks the questioner wants.
Suggestion can be inferred as was shown by an experiment in 1981. Some undergraduates were asked to wait for several minutes in a small cluttered office of a graduate student. When later asked to recall everything that was in the office, most students mistakenly “remembered” that books were present, even though there were none.
•Repetition
A third factor affecting long-term memory recall is that of repetition. For example, a person telling friends of a very amusing episode he experienced, may over the years of repetition add small embellishments to make the story even more amusing. Eventually the narrator will be unable to distinguish from what were the exact facts of what took place and the embellishments.
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•Amnesia
Amnesia, or loss of memory, commonly affects only episodic memory. The sufferer may be unable to recall events in his life; is he married? - what is his job? - where does he live? However, if asked to ‘take the third door on the left and sit in the blue chair’ he will remember the meanings of words and numbers which are held in his semantic memory.
Central Decision Maker and Response Selection
Once information has been perceived a decision must be made as to the response. For example on hearing a warning sound the operator may switch off the system (a selected response) or hold the information in memory whilst a search is made for the problem which has triggered the warning.
Information is continuously entered into and withdrawn from both the long and short memories to assist the decision process. For example ATC may require a change to a new frequency. The frequency required will be stored in the short-term memory whilst how to select a frequency will be stored in the long-term memory.
We sometimes feel that we can make several decisions at the same time. This is strictly untrue since the central decision maker can only process one decision at a time and this is its chief limitation. This is known as single channelled processing. If the human being was limited to single channelled processing, multi-tasks (such as flying an aircraft and holding a conversation) would not be possible. To satisfy this fundamental requirement of life we are able to learn skills through motor programmes.
Motor Programmes (Skills)
Introduction
Motor Programmes, or “skills”(sometimes referred to as procedural memory), are behavioural sub-routines which are learnt by practice and/or repetition and are held within the long term memory and can be carried out without conscious thought. For clarity, the information processing model (Figure 8.1) shows them separated from the long term memory.
A skill is an organized and coordinated pattern of activity. It may be physical, social, linguistic or intellectual.
Developing Motor Programmes
To develop a motor programme or skill, there are three distinct phases:
•The cognitive phase in which the learner thinks consciously about each individual action.
•The associative phase in which the separate components of the overall action become integrated.
•The automatic phase when the total manoeuvre can be executed smoothly without conscious control.
These skills, or motor programmes, are essential in many tasks. It is only the ability to fly the aircraft using these skills that enables the pilot to send and receive RT messages without losing control of the aircraft. The motor programmes fly the aircraft, the central processing unit deals with the communication. If however flying the aircraft becomes non-routine, then the
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central decision maker is required to fly the aircraft and the transmission must stop (see next paragraph).
Transition between the Phases
Motor programmes help to offload the central decision maker and thus increase a pilot’s capacity. For example, a pilot in the cognitive phase of learning has no surplus capacity as the central decision maker is working to maximum capacity.
Once the pilot has achieved the automatic phase, he/she can fly without conscious thought thus freeing the central decision maker for the many other vital activities that have to be looked after in the cockpit. However, when the process of flying the aircraft becomes nonroutine (an emergency or turbulence), the pilot must concentrate on his/her flying and may slip back into the associative stage until conditions return to normal and a return is made to the automatic phase once again. It can be said that stress and lack of practice are the two most common causes of this temporary transition.
Note: A good example of the use of all three parts of long-term memory occurs in tennis. Knowing the rules of the game or how many sets are needed to win a match involves semantic memory. Remembering which side served last requires episodic memory and knowing how to lob or volley involves procedural memory/motor programmes.
Non-declarative Knowledge
Motor programmes are normally held as ‘non-declarative knowledge’, that is the possessor of the skill may not be able to explain the components of the skill, causing difficulty if he wishes to pass the skill on to others. Further, if he wishes to modify the skill, he may find that thinking about his actions spoils the execution of the skill and he may have to go back almost to the beginning to bring about change.
Errors Associated with Motor Programmes
There are two errors associated with motor programmes:
•Action Slip. Action slips usually occur at the selection stage. For example, an ‘engine failure’ drill may be executed perfectly when a ‘loss of hydraulic pressure’ drill is required. One of the most common examples of an action slip is selecting flaps instead of lowering the landing gear. Another might be a student who knows the correct answer to a multi-choice question but marks an erroneous option on the answer sheet.
•Environmental Capture (Habituation). Environmental capture is made when an action is frequently made in the same environment such as confirming “three greens” on final approach without selecting the landing gear down while practising a number of circuits. When questioned after making this error pilots are convinced that they saw three green lights whereas the landing gear was never selected down.
The only way to avoid these two errors, (which are the major disadvantages of motor programmes), is for pilots to constantly monitor both their own and each others motor actions and lastly to carry out drills and checks diligently - never automatically.
Note: Action slip and environmental capture are sometimes referred to as routine errors i.e. routine errors are any errors immediately associated with a motor programme (skill).
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Actions - Response and Feedback
Actions
Actions can be taken as a result of information emanating from:
•Motor Programmes via the Attention Mechanism - a skilled pilot flying straight and level.
•Motor Programmes via the Central Decision Maker - when carrying out a fire drill.
•Directly from the Central Decision Maker - when solving a non-routine or unfamiliar problem.
Note: The above are respectively examples of Skill Based, Rule-based and Knowledge Based Behaviour which are dealt with in the next chapter.
Feedback
The feedback mechanism is continually in use. Even when motor programmes are being used to fly the aircraft in straight and level flight and in visual conditions, the senses continually scan the environment to maintain the desired configuration.
Response
Any action undertaken will cause a detectable change which, in turn, will be noted by the senses. This feedback may alter the action being taken. As an example, a pilot banking the aircraft will receive feedback from the visual or artificial horizon. From the rate of bank detected the pilot may increase or decrease the control forces, and when the desired angle of bank is reached the feedback will cause the pilot to return the controls to the neutral position.
When there is pressure to make a rapid response, perhaps in an emergency, there are a number of factors to be borne in mind which include:
•There will frequently be a trade off between speed and accuracy. A delay in some situations could be dangerous (engine failure after take-off). There will also be pressure to make a response before sufficient information has been processed.
•High arousal level leads to faster but less accurate responses.
•Auditory stimuli (noises) are more likely to attract attention than visual stimuli but they are also more likely to be responded to in error.
•An increase in age between 20 and 60 years tends to lead to slower but more accurate responses.
Response Error (Error of Commission)
If we expect a stimulus and prepare a response, we will respond more quickly if the expected stimulus occurs. If however, an unexpected stimulus occurs we will be more likely, under pressure, to make the prepared response (an error of commission).
For example: a pilot may have noticed engine instrument variations showing parameters approaching out of limits. He/she will mentally prepare the engine shut down drills if the limits are exceeded and any stimulus, perhaps as simple as the noise of a tray falling, may be sufficient for the pilot to shut down the engine.
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