This Briefing Note (BN) discusses the important safety-related cognitive processes of attention and vigilance. It includes definitions and discusses factors that influence attention and vigilance levels.
Attention is a cognitive process that is important to virtually every activity people perform. It is one of the most studied processes in cognitive psychology and neuroscience and is considered to be the gateway to perception and all other higher level cognitive processes. Without attention, we could not selectively process information and discriminate important information from the unimportant “noise” that surrounds us. In turn, because we can control our attention, we can be vigilant and be prepared for dangers when they arise. Over the last few years, attention and vigilance studies have become recognized as vitally important to human factors, especially in aviation, because of the growing use of automation in modern aircraft. Such automation requires less action but more monitoring on the part of the crew who must retain the ability to act when necessary if a situation arises. This type of monitoring activity requires a great deal of attention and vigilance on the part of the crew.
Attention and vigilance are key components of situational awareness. As such, the accident data displayed in the situational awareness BN are representative of data related to attention and vigilance.
Definitions and Other Related Terms
Definitions of attention vary slightly depending on the field from which the definition is taken. All of the definitions, however, share the central theme of attention involving the concentration of thinking (cognitive processes) on a single object or thought to the exclusion of other stimuli or thoughts. In simpler terms, attention is the ability to focus and maintain interest in a given task or idea while avoiding distractions.
Vigilance is a concept closely related to attention; in fact, the word attention is often used when defining vigilance. One definition of vigilance describes it as the process of paying close and continuous attention. It is often described as a quality or state of alertness or watchfulness. Vigilance can also be thought of as the extent of readiness to detect, or the likelihood of detecting, a stimulus that is imperative to safety.
Several concepts related to attention and vigilance have been studied, and a well-informed crew should at least be familiar with the concepts:
- Overt versus covert attention. Overt attention is the act of directing the senses (vision, hearing, smell, etc.) toward a stimulus source to gather information. Covert attention is an internal act that involves mentally focusing on a particular stimulus to enhance the information once we have sensed a stimulus.
- Selective attention. It involves focusing on a specific stimulus while ignoring other competing or distracting stimuli. Selective attention can be conscious or unconscious. Often a person can be selectively attending to an object without realizing it, especially if he or she is expert in the particular task where attention is required.
- Controlled and automatic attention processes. Controlled processes of attention are those used when we are faced with a new task. These processes require effort and are limited by short-term memory. With training, attention becomes more automatic; i.e., it requires less effort and is not limited by short-term memory. This explains why after sufficient training we are able to do several things at the same time (e.g., listening to the radio while driving).
- Sustained attention. It is the ability to direct and focus cognitive activity on specific stimuli for an extended period of time.
- Alternating attention. It is exactly what it sounds like and refers to instances when an individual switches attention between tasks that require different thought processes.
- Divided attention. It refers to instances when an individual must conduct multiple tasks at the same time, and the tasks compete for limited attention resources. This situation is often referred to as multitasking and can be very dangerous since attention resources are strained when an individual attempts to complete multiple tasks simultaneously.
Main Factors Affecting Attention and Vigilance
Attention and vigilance are relatively fragile in nature and can be adversely affected by many factors. The primary factors that affect attention and vigilance and their consequences are presented below.
Time on task
One of the first experiments showing the effect of time on task on attention was conducted by Mackworth in 1950. In this experiment, subjects were asked to watch a clock and detect every critical signal (the double jump of the needle) while ignoring the non-critical signals (the single jumps). Human operators were shown to have a limited ability to maintain vigilance over extended periods of time.
Another important factor that may affect performance in a vigilance task is the rest to activity ratio. Figure 1 shows that a short rest activity cycle (20 minutes of activity/20 minutes of rest) is better than a long rest activity cycle (60 minutes of activity/60 minutes of rest) especially when alertness tends to be low, e.g., during night.
Figure 1. Performance (reaction time in the detection of aircraft) of air traffic controllers as a function of the rest-activity cycle and, time of the day and time on task
The effects of the frequency of critical and non-critical signals on vigilance have been tested and shown to be related to performance on a vigilance task. Figure 2 shows that a low number of critical signals significantly reduces performance (expressed in reaction time) during a vigilance task. Figure 3 demonstrates that the lower the number of non-critical signals per minute, the higher performance will be (expressed in percentage of detection). That is to say, more non-critical signals per minute results in greater distraction and greater difficulty in identifying critical signals. These results demonstrate that level of performance is significantly influenced by signal-to-noise ratio.
Figure 2. Effects of the number of critical signals on vigilance.
Figure 3. Effects of the number of non-critical signals on performance at a vigilance task.
Noise. The effects of noise on attention are complex. The following examples illustrate these effects:
- In the first example (Figure 4) subjects were asked to perform a classic clock monitoring task. In this experiment, two levels of noise were tested with either one or three clocks:
- One-clock condition with 113 dB noise level versus 79 dB,
- Three-clock condition with 113 dB noise level versus 79 dB
Study results showed that noise level had no significant effect on performance in the one-clock condition. In the three-clock condition, however, performance decreased significantly at the higher noise level. This result supports the idea that higher levels of noise tend to decrease the ability to share attention when several tasks are being conducted simultaneously.
Figure 4. Effects of noise exposure on performance in a clock test.
Another study examined the effects of noise on the simultaneous performance of a tracking task and a detection task. For the tracking task, a higher percentage of time spent on target indicated better performance. For the detection task, performance was expressed as the percentage of signals detected in a variety of positions in the visual field. Results showed that a higher level of noise helped to maintain performance on the tracking task over time. For the detection task, a higher level of noise improved performance for signals located in the center of the field, but decreased performance when a signal was in the periphery. See Figure 5.
Figure 5. Effects of noise exposure on performance in a double task test.
The effects of heat on the performance of a vigilance task were studied as far back as the 1950s in work by Mackworth and Pepler The studies indicated that performance degrades significantly when temperatures reach 30°C. Performance is affected much less at a temperature of 26°C. In addition to degrading performance, higher temperatures also result in significant physiological changes (thermoregulation) such as a shift of blood volume to the periphery. These changes increase heart rate and blood pressure, which can affect an individual’s performance.
Sleep loss is known to affect performance on a wide variety of tasks. Related to attention, sleep loss has been shown to induce lapses. As an individual gets sleepy (s)he functions normally until a microsleep occurs, which leads to a lapse.
The effects of sleep loss can often be seen very shortly after a task has been started. Akerstedt examined this effect in a 34-minute visual vigilance task given to twelve subjects every three hours over a 64-hour period without sleep. After 24 hours of being awake, even the very first sets of tests showed decrements in subject performance when compared to baseline measures where subjects were well-rested. These results demonstrate that there is no "safe" duration for a monotonous task if the situation is undemanding/boring and the subject has substantial sleep loss.
Noise and Sleep Loss
Wilkinson compared the performance of subjects during a vigilance test across four conditions that combined a noise factor with a sleep deprivation factor. Subjects had either normal sleep or were sleep deprived for 32 hours. They then carried out a task in silence or with a high level of noise.
- sleep deprivation for 32 hours - task carried out in silence,
- sleep deprivation for 32 hours - task carried out with noise (100 dB),
- normal sleep - task carried out in silence,
- normal sleep - task carried out with noise (100 dB).
The results, shown in Figure 6, indicate that the best performance occurred in the condition combining normal sleep and silence. Noise produced a positive effect when the subjects had been deprived of sleep and a negative effect when they had slept normally. When the subjects have not been deprived of sleep, noise degrades their performance since their activation levels exceed the optimum level. Conversely, when deprived of sleep, noise improves performance, at least for a brief period, since it increases alertness levels above the required activation threshold. These results indicate that an external agent such as noise does not produce the same effects in all situations; rather the effects are dependent on factors such as the operator's sleep deprivation and alertness.
Figure 6. Effects of sleep loss and noise on performance
Motivation plays a very important role in task performance. Motivation is generally referred to as being either intrinsic or extrinsic to the individual. Intrinsic motivation comes from internal factors and involves a willingness or desire to achieve a certain level of performance for personal satisfaction. In a vigilance task, this motivation can be enhanced by giving feedback after each response (e.g., the response was good or bad, quick or slow). When such feedback or knowledge of results is given, performance is typically higher than when no feedback is given.
Extrinsic motivation is related to factors external to the individual and generally involves rewards (or punishment) for performance. Figure 7 demonstrates that, depending on information given to an individual, performance can change dramatically. Subjects were told that they were either involved in a recruitment process where they were being tested or were involved in a laboratory research project. Those people that were told they were being recruited performed much better than those that were told they were simply participating in a laboratory experiment. The external motivation of being “recruited” and the potential for reward stimulated the participants to perform better.
Figure 7. Effects of instructions given to subjects on performance on a vigilance task: recruitment test versus laboratory experiment.
The following key points relate to attention and vigilance:
- Attention is a fundamental cognitive process that is important to higher level cognitive processes
- Vigilance requires attention and describes an individual’s state of alertness, watchfulness and preparedness to attend to critical information that is not yet present
- Attention and vigilance are not constant and may be impacted by environmental factors such as noise and temperature.
- Physiological factors such as sleep loss, high blood pressure, etc. can affect attention and vigilance
- Motivation, intrinsic or extrinsic, can affect attention and vigilance
- Task factors such as frequency of signals can affect performance on attention and vigilance tasks.