Psychologist Sets Designs On Optimizing Warning Systems
May 16, 2012
by Robin Tricoles
Human noises pervade intensive care units and so do the railing and pinging of machines. Hospital staff become accustomed to the racket, sometimes too accustomed, meanwhile, patients and families become unnerved.
Designing good auditory warning systems is complex. The variables are abundant, the settings diverse.
Enter scientist Carryl Baldwin. Baldwin is a human factors psychologist and an expert in auditory cognition, the way our brains process sound. She designs alarm sounds for warning systems such as those in cars, airplanes, and hospitals.
In doing so, she must keep in mind the sound’s purpose, its degree of urgency, the anticipated ambient noise surrounding it, and whether it’s better to have an ongoing or intermittent warning sound. For example, is the alarm’s purpose to call attention to an emergency such as an impending collision or something less critical, say a refrigerator door left ajar?
Likewise, should the sound be loud and high-pitched or moderately so? Too loud and high, it could startle the user. Too soft and low, it may not be heard or taken seriously. So, Baldwin must search for the optimal pitch, frequency, and volume to match the task at hand.
One option: a constant low-level warning whose sound changes when something is amiss. For example, hospital alarms often use continuous low-level sound to indicate a patient’s state. So, if the patient’s state changes, the change is immediately detectable through a shift in pitch, frequency, or volume.
Likewise, designers must find the appropriate balance between a sound and the urgency of a situation, says Baldwin. “We call it hazard matching. You want to make sure the perceived urgency of the sound matches the hazard level the sound is supposed to represent.” In other words, you don’t want your collision warning system playing a nice, soft melody, and you don’t want your drier screaming at you.
Psychologists must also keep in mind that the more urgent a sound is, the more annoying it tends to be. And when sounds become too annoying people tend to ignore them, or if they can, disable the warning system itself. But, says Baldwin, there are ways to increase urgency without increasing annoyance.
Baldwin says changing the frequency of a sound makes it annoying faster than it makes it more urgent. Whereas, changing the pulse rate, or rhythmic pattern, is more desirable. “We perceive things as more urgent when the pulse rate speeds up. But our annoyance with the sound doesn’t increase as fast as our perception of urgency.”
She is now working on equipping cars with a navigational system that uses tactile pulse rates, rather than auditory ones. So far, she says, no one trying out the system has reported feeling annoyed.
Baldwin is an associate professor of psychology at George Mason University and serves on the FABBS Council of Representatives representing the Human Factors and Ergonomics Society.