Pupil Dilation

Pupil Dilation

Article Information
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Last modified:
20.Jun.2022
Article UID:
32318
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Description

Pupil Dilation can be measured at the same time as eye-movement. (Most eye-trackers offer an image of the pupil as an alternate measure). It is accepted that the pupils dilate when the eyes are directed at a pleasing object, and that they contract when mental effort is required.

Discussion/References

It is received wisdom that the pupils of the eyes dilate when their owner is presented with a positive stimulus (Morris, 1982). It is also generally accepted that pupils contract during mental work. The pupils are, however, mainly affected by physical circumstances, such as glancing towards a window, or a positively illuminated monitor screen.

Bradshaw (1968) in a laboratory-style task found that pupil constriction followed the solution (or response to) mental problems.

Casali and Wierwille (1983) monitored respiration rate, mean pulse rate, pulse rate variability, pupil diameter and eye-blinks, and found only pupil diameter was sensible to communications workload.

Stein (1992) found no relationship between pupil size and subjective or objective workload in Air Traffic controllers.

Categories
Human Factors Methods
Generics
Type of method Eye observation
Target of method Strain
Strictly speaking, ‘Stress’ refers to the external factors influencing the controller, which are relatively easy to measure, while ‘Strain’ refers to the effects that the Stress causes on the controller.
Time Scale of method Minutes
Since blinking occurs at a relatively slow rate, a certain time is necessary for it to be possible to detect a change of blink rate.
Portability of method No
At present, blink rate is measured using eye movement or EEG equipment (see descriptions). These are rarely portable.
Observer Effect No
Although the controller is aware that he is being measured, particularly if he is obliged to wear a tightly fitting helmet, the movement of the eyes is not under conscious control.
Context of studies
Laboratory studies Use
 
Simulation studies Avoid
 
Field studies Avoid
 
Potential problems with the method
Failure risk Moderate
Depending on the method, there may be a considerable risk of failure. Systems requiring remote head tracking may lose the position of the eye, and require manual steering back to track. EEG measures are always subject to a risk that electrodes will fall off.
Bias risk Moderate
Blinking is triggered not only by strain, but also by environmental factors, which may affect the drying of the cornea. In principle, this should not affect the use of blinking to assess differences between similar situations, but it is possible that slightly different experimental layouts might make a considerable difference to blink rates if sharp differences in luminance are involved.
Ethical problems None
 
Costs of the method
Staff Cost High
No available eye movement system or EEG can handle more than one controller under observation. At least one specially trained operator, and possible an additional technician, is needed.
Set-up Cost High
EEG and Eye-movement systems have prolonged installation and calibration phases.

Usually, re-calibration is required before each exercise, and can take up to fifteen minutes.
Running Cost High
EEG and Eye movement studies require constant supervision, and may require interventions in the course of the exercise.
Analysis Cost High
At present blinks are counted by visual inspection of EEG or eye movement records. It is possible that modern eye-movement analysis methods may solve this.
Analysis data
Analysis Speed Slow
Manual analysis is slow Automated eye-movement analysis, which can determine where the eye is pointing, may be able to count blinks, where the eye is not visible.
Data Automation Used
The collection of EEG and eye-movement data using electronic devices is inherently automated.
Analysis Automation Used
Most data analysis is more or less automated in the current circumstances. However, total automation is not yet practical.
Status Tentative
Tentative - under consideration, has not been tried in ATC contexts.

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