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Human Information Processing

In Chapter 3, I introduced the concept of cognitive load and its three components: information processing, time on task and task switching. These components lie at the heart of performance at the individual level in a system. The efficacy of actions is a measure of the success of the individual in meeting the demands posed by balancing cognitive load. In this next section, I want to address the first component: information processing. Psychologists have a long tradition of studying the way humans receive and handle information from the outside world. The classical model of information processing, illustrated in Figure 5.8, has six basic components: inputs, perception, attention, processing, storage and outputs. The model argues that the first stage in

making sense of the world is perception. Stimuli from the external environment generate sensory inputs that are detected by our sense organs. These stimuli are held in sensory registers and processed to varying degrees. The processing of inputs takes two forms. One mechanism, called bottom-up processing, entails the direct analysis of the stimulus and is constrained by the availability of sensory inputs. What this means is that if the signal is of insufficient strength or is not detected in the first place, then it will be overlooked, irrespective of its significance. The second type of processing, top-down, involves a search for expected features in a stimulus based on past knowledge and the current context. This first stage of information processing, then, is constrained by the physical properties of the sense organs and shaped by our prior experience. This can lead to erroneous perception of events, but at the same time, it allows us to fill in the gaps if a stimulus is of very brief duration or degraded in some way. Signal salience describes the extent to which a signal stands out from the general noise. The significance of a signal suggests its importance in terms of what we are trying to achieve, but the significance is a construction, not necessarily a reality. Stress and fatigue will affect perception, as we saw with the B-727 at East Midlands Airport.

The inputs available to the captain of the B-777 on approach to Heathrow would have included:

Visual: Views of the outside world (planned gate, buildings under the approach path, airfield dimensions), instrumentation and annunciators, the position of the thrust levers, the position of flap and gear levels.

Aural: Engines, transmitted signals and messages, warnings and crew utterances.

Kinaesthetic: Acceleration detected by semi-circular canals (buffet and turbulence), stick shaker and reaching for controls.

These sensory inputs were perceived and attended to. As the aircraft descended, the captain was processing stimuli concerning a variety of tasks. Initially, processing was framed by expectations derived from a model of normal procedures - searching the visual field to see whether the assigned gate was free. Once the captain became aware of the unusual situation, his attention was directed towards, first, resolving ambiguities and then, second, to the relationship between the current path of the aircraft and the likely point of contact with the ground. The specific stimuli attended to were relevant to the task goal in play at that time. Initially, the goal was related to planning the arrival on the parking stand. Stimuli from inside the aircraft were not being attended too. The FO’s initial comment - ‘was it doing this when you were flying’ - was processed in a top-down manner’. The ambiguity in the message was resolved by comparing it with the captain’s own prior experience of the turbulence on the approach and its effect on the thrust levers. The outcome had sufficient congruence such that the comment did not trigger any additional information-seeking behaviour. The second comment by the FO, however, was dissonant and triggered additional behaviour. The captain then went through two cycles of searching for information about aspects of the aircraft’s condition. At this point, the captain started to process in a bottom-up manner. He scanned the available information and tried to make sense of it. None of the information matched his prior experience or his understanding of the aircraft’s systems. Finally, the captain attended the stimulus associate with the performance of the aircraft in relation to the ground.

Only the stimuli reaching a particular signal strength are attended to. Throughout the episode, some available data were not processed. For example, the fact that the autopilot was still engaged was missed and was only disengaged when the stick shaker was triggered. The aircraft’s speed was slowing because of the reduced power from the engines and the fact that the autopilot was trying to maintain the ILS glideslope. Although there was some attempt to understand the cause of the power loss, the task was traded off against the more salient task of reaching a safe place to land. The implication of speed was not appreciated until the stick shaker was activated. Attention, then, is a process of recognition, of isolating out certain aspects of the environment. It is possible to attend to multiple stimuli by allocating attention according to the demands of signal processing. We can manipulate attention to a degree. Focussed attention allows us to concentrate on a specific stimulus but at the expense of processing other stimuli. Divided attention allows us to track multiple stimuli. The effectiveness of divided attention is a function of the difficulty of the tasks being monitored and the degree of practice we have had in those specific tasks. In the example we have just explored, the crew were at the end of a long flight from Beijing, and we need to accept the insidious nature of psychological fatigue in relation to information processing. It is an understatement to say that stress was also probably elevated given that the situation they were presented with was outside of any procedural or training framework they had ever encountered. These factors all had an impact on the attentional capacity and attention management tactics of the crew.

Returning to our model of information processing, inputs attended to are brought into the working memory (WM) and manipulated. The WM is where we extract order from the mass of data presented to us. It is where we analyse inputs, make decisions about what to move into storage, prepare responses to inputs and generally manage tasks. Once processed, some information is then retained in the long-term memory (LTM). If we consider the captain’s analysis of his options for reducing drag, thereby extending the track of the aircraft, we can see the interplay between the WM and LTM. Having processed the available stimuli, he identified a possible course of action, which was to retract the undercarriage. However, knowledge of the operation of the undercarriage, its associated doors and the drag implications, held in LTM, was recalled, but the applicable constraint - no action should increase drag - could not be met. He then considered the implications of raising the flaps, to reduce drag, in relation to the aircraft’s performance. Because the aircraft speed was below the standard target speed, the margin between the minimum speed for the new flap setting, held in LTM, and the actual speed would be narrower than usual. In fact, we have another trade-off. In this case, we see the need to extend the range being traded off against the performance margins associated with the aircraft’s condition. The output from this processing activity was an act that reconfigured the aircraft: it was a decision.

To summarise then, a pilot interprets signals from the environment, some of which are mediated through aircraft sensors, systems and indicators, and makes inputs to the aircraft to reconfigure the device as appropriate for the local needs. The role of the pilot is two-fold: first, it is to execute a plan determined in advance and, second, it is to respond to perturbations in the environment in real time. Accurate information processing is underpinned by robust knowledge structures. Fundamental to safe operations is the importance of sense-making. We need to remember that the model of information processing outlined above was heavily influenced by early work on computers. Unfortunately, humans are not computers.

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