Localization is the ability to determine the direction and
distance, direction alone, or distance alone of a sound. Localizing is important for safety and detecting
danger. For example, being able to
determine where the truck with the back-up alarm is coming from is important in
preventing accidents. The outer ear plays an important role in localizing
sounds. When the ear is covered by an
earmuff, it is harder to localize sounds. An earplug can distort the frequency
of a sound making it difficult to identify the direction of a sound. For Service
members, the direction and distance to gunfire is also critical in detecting
the location of enemies. HPDs and other
equipment such as helmets may interfere with cues that help with localization. Some HPDs are designed to allow for
localization. Selecting HPDs based on localizing as well as noise attenuation
capabilities may be mission critical.
For devices on the HPD EPL, we compare the ability to
localize with the open ear, to how well those same people are able to localize
with HPDs being tested. Three measures
Percent angular error
reversals occurs when a person confuses the direction of a sound by 180o.
Most people can easily distinguish between a noise in front of them versus one
behind them. A normal hearing person who
is not wearing hearing protection will confuse sounds in front of them for a
sound behind them less than 5% of the time.
angular error is the percent of angle off from the direction of a sound.
Percent angular error is a measure of how precise a person can localize. Normal hearing people with the open ear will
have a percent angular error of less than 5%. As the angular error increases, a person may
take longer to find a target or mistake the direction of a sound
Guided Visual Search (AGVS) measures the time required to find a
visual target that is co-located with a sound source in the presence of other
visual targets. Response time is important because it measures the functional
impact HPDs have on localization capabilities.
Without a sound, people will take an average of 12 seconds to find the
visual target. With the sound paired
with the visual target, people with normal hearing will take less than two
seconds to find the target. We use the
term spatial awareness to describe localization on the HPD EPL. The below rating system is used for spatial
awareness. Note the smaller the number,
the better the device will help the wearer to localize a sound. Further
explanation is available in the guidebook.