From SKYbrary Wiki
Perception is the action of apprehending through the mind, information acquired through the senses, and making the connection between events in the external “world” (objects, people, movement, sounds and smells) and our thoughts about them. It is the second stage of Information Processing after “sensing”.
Everything that passes through the senses is not necessarily “perceived”. We tend to perceive things that:
- we are interested in (and therefore looking for, or sensitive to),
- make a large impact on our senses (bright lights, loud noises, irregular movement), and
- signs of potential danger; things that trigger fear.
On the contrary we tend to perceive fewer things that do not interest us, are not making a large impact, and do not induce fear.
Also, we do not always perceive accurately the things that we focus on and think about. This occurs in two distinct ways:
- Due to limitations in the performance of our sense organs and the manner in which our brains re-construct sense data, our perception can be fooled into a false picture of the outside world, but one that we see, believe and literally “feel” to be accurate.
- Because we carry with us assumptions (including what we believe to be facts), past experiences, biases, pre-conceived ideas and prejudices, then we are prone to apply deletions, distortions and generalisations to what we observe. That is, we are often subjective and not objective.
As humans, we are all susceptible to the misperceptions caused by limitations in our senses, and we will generally experience the misperceptions in an identical manner. However, as individuals, with different experiences and personalities, the results and impact of our subjectivity will differ – sometimes quite markedly. In both cases other factors can influence our susceptibility to misperception, such as: illness, stress, fatigue, medication (and other drugs), concentration, motivation, etc.
Importance of Perception for Pilots
Understanding perception is important for pilots: perception is the stage of Information Processing prior to Decision Making and judgment, from which actions are taken. Effective decision making and safe actions rely on accurate perception.
Therefore, it is important that pilots also know how to overcome the two misperceptions introduced above - limitations and subjectivity. In simple terms they can do this by deferring to reliable data. In the first case this is provided by appropriate flight instruments and in the second case other objective sources of data (other crewmembers, ATC, manuals, checklists and documents). However, the pilot will have to counter his/her intuitive feelings: when a pilot believes that his aircraft is in a certain attitude, or position and power state, then his/her mind will try to organise whatever information is available to confirm this belief.
For pilots, we can highlight two distinct, but typical, pathways from sensing, through perception, decision-making and action (see Information Processing).
- When manually flying, the whole pathway is condensed to what feels like “one motion”, where feedback to the pilot is instantly sensed and perceived and corrective actions immediately applied. Of course, when sensed data is misperceived then the actions taken to correct the situation may actually make things worse.
- When making an operational decision e.g. to fly a specific approach, the pilot will consider all the information available to him/her, including subjective opinions about his/her own capabilities and fitness and the capabilities and fitness of other crewmembers. In this case there may be considerable time between making a decision and taking the considered action, however, some decisions become “points of no return” and if the decision is based on misperceptions then pilots can find themselves “painted into a corner”. In other words, if a pilot decides to continue to the planned destination having “perceived” the weather conditions, runway distances, aircraft performance, and his/her own capabilities as acceptable, there may be a point where diversion to a “better” aerodrome is no longer possible.
In the first case actions follow perceptions almost instinctively, based on previous learning. Misperceptions can be detected when corrective actions do not have the expected corrective effect; although there may not be enough time to resolve the situation (e.g. Loss of Control accidents).
In the second case misperceptions may never be detected (or accepted) unless a full investigation is undertaken; something usually reserved for accidents. However, in many situations a pilot may be fully aware that some data is incomplete or unreliable (i.e. that he/she has misperceived); in these cases it is usual for pilots to assess the “perceived” risks associated with all the action options. Misperceptions of risk can be closely associated with inappropriate risk tolerance.
It is worth mentioning a third situation. When a pilot’s knowledge is limited then he/she may misinterpret the objective data. For example, limited knowledge and understanding concerning a Flight Management System may result, fatally, in inappropriate action.
The perceptual illusions that pilots encounter which most affect flight safety relate to misperceptions concerning the position of the aircraft, and projected flight path, in space and in relation to other objects (e.g. runway) and the horizontal plane. These invariably include perception of power (engines/thrust) and aircraft configuration (e.g. landing gear, flaps, slats, air-brakes, trim etc.). This subject is intricately interlinked with Situational Awareness and Spatial Disorientation.
The primary senses through which pilot perception, and misperception, is most critical are Visual, Kinaesthetic, and Auditory, and these will be briefly discussed below. More detailed information is available from the relevant SKYbrary Articles referenced at the bottom of this page.
Visual Illusions occur when a pilot perceives the outside world differently to what it actually is and in such a way that what seem to be natural responses to the situation do not have the expected results. Visual perception depends on colour, tone, contrast, illumination, ambient light levels, shapes, angles, lines, juxtaposition, movement and time.
Some visual misperceptions will occur due to physiological limitations of the eye, such as blind spots, myopia, colour-blindness, after-images and the size, function and interaction of light receptors (rods and cones), especially at night or in extreme brightness. For example, an inability to differentiate colours or tones can have a dramatic effect on how the pilot perceives the runway and associated lights at night.
Other visual misperceptions will occur due to perceptual limitations. This is partly due to transferring the 3-dimensional objective world into a 2-dimensional retina image, and back into a 3-dimensional mental formation; and partly due to the imposition of cognitive influences such as assumptions, inferences and pre-conceived ideas. This latter “interference” can be summed-up by the phrase we see what we expect to see - expectation bias. The same applies to what we hear and what we feel (physically and emotionally). Such optical illusions are numerous and include the misperception of aircraft height above touchdown caused by our inability to differentiate between the length of a runway and its slope.
Our kinaesthetic perception relies on our somatosensory (whole body) system to detect touch and pressure, combined with our vestibular system (the inner ear) to detect movement. In most normal earthbound activities, when combined with sight and hearing, this can be fully relied on to help us perceive the world accurately. However, flying, and especially piloting presents situations and environments in which we cannot fully rely on (trust) our kinaesthetic perception; especially when visual and auditory data is also unavailable.
When pilots perceive a spoken message to be different than that transmitted, e.g. misperceiving an instruction from ATC, or misperceiving an answer from a crewmember it can generally be attributed to one of three things.
- unclear transmission, e.g. a thick accent, unfamiliar language, speedy delivery, ambiguous words, too much information at once, etc.
- unsuitable transmission medium, e.g. badly attenuated radios, atmospheric interference, a noisy environment, etc.
- lack of attention being paid by the receiver, and this includes the willingness (due to convenience) to hear what we expect (and want) to hear – e.g. expectation and confirmation bias.
Our perception of a situation, both in objectivity and context, is known as Situational Awareness. The problems we have in perceiving the world accurately, discussed above, mean that we cannot rely totally on our senses and past experiences for maintaining good situational awareness.
Gaining and maintaining effective situational awareness requires pilots to utilise objective data. That means two things:
- relying on flight instruments and FMS in preference to vision, balance, sensations of movement and other kinaesthetic feelings, and
- seeking, analysing and utilising the most appropriate up-to-date information concerning context, such as weather, aircraft performance, crew performance, runway and aerodrome conditions, en-route conditions, terrain, possible emergencies and contingency plans.
Drafting a plan to protect pilots from their natural human ability and tendency to misperceive is fairly simple to do; ensuring that all pilots apply the lessons when the solution goes against their gut-feelings is less simple to achieve. However, most pilots these days have been exposed (under simulation, and in many cases in reality) to situations where they readily misperceive the objective world. This “shock” can be enough to ensure that effective solutions are applied.
A programme aimed at protecting pilots from misperception can include the following aspects.
- medical examinations to ensure that senses are not unduly limited or deteriorated
- human factors training – basic human performance and limitations
- planned simulator and classroom experience of various illusions
- formal and contextual discussions and analyses of relevant accidents and incidents
- development of procedures and/or practices for pilots to employ when “uncertain”
- practice in using these procedures and practices in relevant scenarios
- collection and analyses of human factors occurrences and incidents
- continuing awareness and training programme updated from feedback.
In most commercial airlines many of these steps will be covered within licencing and training requirements e.g. Crew Resource Management (CRM) and Human Factors training and qualification programmes, as well as regular medical examinations. Procedures may exist to ensure that during critical flight periods and during emergencies one pilot is always monitoring the flight instruments. Some airlines may have introduced advanced training programmes (ATQP) where operational data (including human factors) is fed back with the specific intention of adjusting the flying training e.g. LOFT.
To address the misperception of one’s own capabilities and fitness, then an airline will need to encourage regular self-assessment, personal feedback from trainers, supervisors and colleagues, and to integrate these principles into the application of CRM.
- Visual Illusions
- Lessening the Effects of Visual Illusions
- Runway Visual Perspective
- Night Visual Approaches
- Spatial Disorientation
- Somatogravic and Somatogyral Illusions
- Acceleration Effects
- Flight Safety Foundation. 2009. Visual Illusions: Briefing Note 5.3, ALAR Toolkit.
- Understanding Spatial Disorientation - presentation.
- Understanding Visual Illusions and Disorientation – presentation.
- Managing Visual Somatogravic Illusions – presentation.
- FAA. Spatial Disorientation. Briefing Note.
- Australian Transport Safety Bureau. 2007. An Overview of Spatial Disorientation as a Factor in Aviation Accidents and Incidents. Investigation Report: Aviation Research and Analysis Report – B2007/0063.