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LESSON 169

Unilateral and mild loss

Year 2
Spring semester
Pediatric Audiology
Pediatric assessment
Duration: 10:28

Unilateral, mild and high-frequency hearing losses can go unnoticed in a quiet room. In this lesson we look at difficulty understanding speech in noise and locating sound, the effects on school performance and listening effort, how monitoring is planned, and the intervention options.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will learn how unilateral and mild hearing loss can affect a child's development and school life.
Then we will take a broad look at how monitoring is planned and which intervention options exist.
A 1998 study by Bess and colleagues defined minimal sensorineural hearing loss in three groups.
The first group is unilateral hearing loss: one ear hears normally and the other has a loss.
A unilateral loss can be mild, or it can be profound in one ear.
The second group is mild bilateral loss; in this study the pure-tone average was defined as 20 to 40 dB HL.
These children often understand speech well in a quiet room, so the loss is easily missed.
The third group is high-frequency loss, with thresholds above 25 dB HL at two or more frequencies above 2000 Hz.
Definitions vary slightly across studies; what they share is that these losses are easily underestimated in daily life.
This example audiogram shows a moderate loss in the right ear.
The left ear thresholds are within normal limits at all frequencies.
In a quiet room, this child can easily understand speech with the good left ear.
That is why the family and teachers often do not notice a problem.
Bone conduction, and masking when needed, are required to define the type of loss; here we only look at air conduction.
Now let us see, step by step, where this kind of loss causes difficulty in daily life.
Bess and colleagues found a prevalence of minimal loss of about 5.4 percent in third, sixth and ninth grade students.
So in a large school, there may be one or two of these children in every classroom.
The prevalence of permanent hearing loss rises steadily from the newborn period to school age.
Newborn screening is usually designed to detect losses above about 30 to 40 decibels in the speech range.
So milder losses can pass the screening.
A unilateral loss may also be absent at birth and appear later, or it may progress over time.
The clearest effect of unilateral loss appears in noisy settings.
If speech comes from the side of the good ear and noise from the side of the poorer ear, the child is relatively lucky.
In this case the head blocks the noise and creates a sound shadow that weakens the noise at the good ear.
The head shadow effect is strongest at high frequencies; if speech comes from the poorer side, the shadow weakens high-pitched consonants.
A person with two hearing ears benefits by using the ear on the side away from the noise.
A child hearing with one ear does not have this option and needs a better signal-to-noise ratio for the same performance.
Locating a sound depends on the time and level differences between the sounds reaching the two ears.
With one ear these differences cannot be compared, so the child may struggle to tell where a sound comes from.
In a busy conversation, noticing who is talking and switching between talkers is also tiring.
In mild bilateral loss, the main problem is that soft speech from a distance, or speech close to a whisper, is not heard.
Young children also learn language by overhearing the talk around them; these losses can reduce that opportunity.
Not being able to locate warning sounds in settings such as traffic also matters for safety.
The classroom is one of the hardest listening settings for a child with minimal loss.
As the teacher's voice travels farther, it weakens and mixes with reflections.
Students within the critical distance hear the direct sound more strongly.
In the back rows, reverberant sound and background noise come to the fore.
When the teacher turns to the board or walks around the room, the signal the child receives keeps changing.
So for these children, classroom acoustics and distance from the teacher matter as much as the hearing threshold.
In a 1986 study by Bess and Tharpe, about one third of children with unilateral loss had repeated a grade.
In the 1998 study by Bess and colleagues, this rate was 37 percent in children with minimal loss.
The same study found that these children also had more difficulty in areas such as energy, stress and self-esteem.
More recent studies have also shown that language scores may be lower on average in children with unilateral loss.
A child who misses what is said in class may look distracted, uninterested or like someone with an attention problem.
So if the child's hearing status is unknown, the difficulty can be misinterpreted.
On the other hand, not every child with these losses struggles at school; the risk is real, but outcomes vary from child to child.
The mental effort spent filling in unheard sounds from context is called listening effort.
A child with minimal loss may spend more attention and memory than peers to understand what is said in class.
When this extra effort continues all day, it can lead to listening fatigue.
Resources spent on listening mean fewer resources left for learning and remembering.
Some children describe marked tiredness and reluctance after coming home from school.
Over time, avoidance of group activities and social withdrawal may also appear.
The first step is to confirm the loss with ear-specific and frequency-specific tests.
In young children, this is done by combining age-appropriate behavioral tests with objective tests.
The cause is investigated by a physician; imaging, congenital cytomegalovirus and genetic evaluation may be part of this process.
Some unilateral losses progress over time, and in some children a loss may also develop in the other ear.
So it is important to monitor both ears at regular intervals.
The family and teacher are told clearly what the loss means and which settings are challenging.
Language development and school performance are also part of monitoring and are assessed with other specialists when needed.
Preferential seating and acoustic improvements in the classroom are a first step to consider for every child.
A remote microphone system carries the teacher's voice directly to the child's ear and improves the signal-to-noise ratio.
The American Academy of Audiology's 2013 pediatric amplification guideline advises considering remote microphones for minimal loss.
The same guideline recommends that children with an aidable unilateral loss be evaluated as hearing aid candidates.
If one ear has a profound loss, a CROS system that picks up sound on that side and routes it to the good ear may be considered.
But in class, CROS can also route noise to the good ear, so the child's age and ability to control the setting matter.
Bone conduction devices also deliver sound through the skull to the better-hearing cochlea.
In some countries, a cochlear implant is also an option in selected severe unilateral losses; the decision is made by a team.
A tip from the field: when explaining mild or unilateral loss to the family, avoid phrases like "one ear is fine, so there is no problem".
Instead, use concrete examples of where the child may struggle: a noisy classroom, a crowded dinner table, the playground.
A short information note for the teacher keeps the child's difficulty from being mistaken for inattention.
Set the date of the follow-up appointment before the visit ends, because the loss can progress.
Also note the family's observations; changes at school and at home are often the first clue.
In this lesson we learned that minimal loss can appear in three forms: unilateral, mild bilateral and high-frequency loss.
These children may understand well in quiet, but understanding in noise and locating sound become harder.
Research shows an increased risk for school performance, listening effort and fatigue.
Monitoring should be regular, and intervention options are assessed by the team based on the child's loss, age and settings.
Test yourself: in which setting does a child with unilateral hearing loss struggle most?
The correct answer is B: group conversation in a noisy classroom.
A child hearing with one ear cannot use the head shadow and struggles to find the talker, so noise affects them most.
In the next lesson we will see how to share a hearing loss diagnosis with the family and how to plan the first meeting.
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