Humans: skills, capabilities and limitations
3.6 Attention
Attention comprises a number of filtering mechanisms that screen the vast input of information being received by our senses at any one time, generally selecting only that which is relevant to the task in hand. Without this process our senses would be overloaded and irrelevant information would dominate, severely limiting our ability to complete any task. Selective attention is the process in which we direct our attention to the stimuli of interest.
The process of selectively attending to visual information is relatively simple, in that this is achieved by physically orientating our eyes. However, a fixed gaze whilst outwardly stationary is not; rather the eyes move constantly (saccades) to fixate at one point for approximately 300 milliseconds. The fixations tend to seek out sources providing the greatest information and/or items that are novel or unusual.
Filtering of auditory information is more complex. Visual attention is directionally controlled. However, auditory information cannot be filtered so simply; we will hear whatever is within our auditory range no matter what the source. In this case, attention is achieved more by mental than physical means, although the direction from which the sound emanates is used as a cue. We also focus on the characteristics of the sound (pitch, intonation) and for speech, the speaker’s lip movements. In addition, the meaning (especially relevant for speech) will aid attention, and can be used, although with some difficulty, in the absence of other cues.
Unattended information, both visual and auditory, is minimally processed, although there is sufficient input for us to respond and change our direction of atten- tion, for example, hearing our name or other ‘key’ words or phrases, seeing movement or colour change at the periphery of our vision. However, as we remember little if anything of the unattended information, this suggests that it is filtered shortly after the perceptual processing stage. The limited impact of unattended information can have disastrous effects. For example, an Eastern Airlines flight crashed into the Florida Everglades due to the crew selectively attending a single malfunction and in so doing, failing to notice altimeter readings warning of descent [13]. As a result, no one was flying the aircraft with the result that it crashed with considerable loss of life.
Research into attention usually falls within two areas, namely that which looks at how effectively we select certain inputs over others (focused attention), and that which studies processing limitation by examining how we perform when attending to two or more stimuli at once (divided attention). Auditory information appears to be selected early in order to limit the demands on processing capacity. Information outside focal attention continues to be processed, but at a reduced rate. A similar low level of processing appears to occur for unattended visual material. Visual attention is not just a matter of focusing on a specific area; it can be more sophisticated, being able to select only certain stimuli within that area, or important parts of the area (e.g. it is possible to focus on one movie image even when a second movie is also being displayed on the same screen over the top of the first).
Many operational tasks require vigilance, namely focused and sustained atten- tion and concentration. Tasks include those where signals must be monitored over long periods of time and specific targets detected. These may be found in industrial inspections, avionics applications and medical monitoring (for clinical and neuro- logical disorders). It is difficult to maintain peak levels of attention, particularly as tasks are typically monotonous and simple, and the targets are often weak, inter- mittent and unpredictable. There are various vigilance paradigms, including free response where the target events can occur at any time, and inspection where events occur at reasonably regular intervals. In addition, the task may require the detection of changes in auditory or visual intensity, or may be more complex and involve some application of cognitive processing. There are a number of problems associated with
vigilance tasks. The ability to distinguish targets from non-targets declines over time, and the observer may become more or less cautious in their reporting of the target presence. The position of the decision criterion for detection can induce a specific pattern of reporting. For example, a high (less stringent) criterion will encourage reporting of fewer targets and fewer false alarms (identification of a target when it is not), while a low criterion will be reflected by higher target reporting with an increase in false alarms.
Explanations for vigilance decrement include ‘expectancy theory’ [14], ‘resource theory’ (e.g. [15]), and ‘arousal theory’ [16]. For example, operators will adjust to the level of targets based on expectations, and if they miss a target the likelihood of further targets going undetected increases. In addition, the level of resources required in vigilance tasks is high, and the high cognitive workload may be difficult to accom- modate. Arousal theory is supported by findings showing reduced brain activation is related to reduced detection rates, which suggest that prolonged task performance leads to a lowering in the arousal state of the central nervous system. Vigilance perfor- mance will depend on the nature of the task (signal strength, modality, discrimination level, event rate and probability), and can be affected by factors including situa- tional (noise, climate, time-of-day), and personal (operator’s age, sex, experience, personality, whether they have taken stimulants or depressants). In order to maximise vigilance, target sensitivity should be improved either directly, by increasing the salience or varying the event rate, or indirectly by adequately training observers and showing examples to reduce memory load.
Any form of focused attention, including vigilance tasks, can be easily disrupted.
For example, a control room operator can be distracted by the conversations and actions of others in the vicinity, or by a very busy and changing visual display. Any disruption will, in effect, cause attention to be divided between the primary task and the peripheral activities.
The ability to perform two tasks concurrently will depend on the nature of the tasks.
The key is the degree to which the processing involved in one task interferes with that required for the second. For example, it is relatively easy to operate machinery or drive a car (if experienced) whilst holding a conversation, but it is not so easy to converse and compose a letter at the same time, for while both can be achieved it should be noticeable that attention is being constantly switched between the two tasks. The latter occurs because some processing resources (verbal) need to be shared between the tasks resulting in lack of processing capabilities and interference. Minimising the effect of interference between the processes involved in the tasks will increase efficiency in the tasks. Interference is lowest when the two tasks use different modalities, for example, one uses visual processes and the other verbal. Driving a car will involve a combination of visual and procedural (motor skill) processing, while a conversation will engage verbal processing, and hence the limited level of interference. One point to note here is that reading, although a visual act, also uses verbal processing to convert visual symbols into meaningful words; in our brain we effectively say what we read.
There are three main factors that affect dual-task performance, namely task sim- ilarity, task difficulty and practice. As can be seen from the driving and conversing
example, these two tasks are quite different, using different stimulus modalities.
However, similarity extends also to stages of processing (to what degree do the tasks use the same processing at input, internal processing and output), the extent that each rely on the same or related memory codes (e.g. verbal, visual), and the similarity of the response. The more difficult a task, usually the more processing capacity is needed and hence, the reduction in overall efficiency. Practice has the effect of automating some processing and/or responses, thus reducing interference with a second task.
A novice driver or operator of equipment is likely to find it much more difficult to converse at the same time than would someone highly practised. Automatic processes tend to be fast, require limited attention, are usually unavoidable (the response occurs whenever the stimulus is present), and are largely unconscious in nature. Training to achieve a high level of automation for a task is advisable, but practice at being able to switch between automatic and ‘manual’ operation in emergency situations is also important.
It is important that wherever possible, the design of display or auditory systems incorporate features that can help to direct attention when needed. Some systems can give prior warning of a potential target. This cue needs to be timed to permit an appro- priate change in attention prior to the target appearance, and it needs to be of a suitable frequency for auditory systems, or position (central or peripheral) for visual systems.