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What Do We Know about Noise Sensitivity in Autism?

Marina Sarris
Interactive Autism Network at Kennedy Krieger Institute
Date Last Revised: 
May 19, 2016
Date Published: 
June 15, 2015

Drawing of vacuum for article about noise sensitivity in autismDonald was "perfectly petrified of the vacuum cleaner." So was Elaine, who would not venture near the closet where her family’s vacuum was stored. Richard, Barbara and Virginia, on the other hand, ignored sound to the point that others wondered if they were deaf.1

These were autism’s first children,2 described in the landmark 1943 article by Leo Kanner that gave a name and description to a disorder that now affects 1 in 68 American children.3 Dr. Kanner, an American psychiatrist, created a new diagnosis for these children, some of whom had been assumed to have intellectual disability.

Among other things, most of the children he studied shared an unusual relationship to sound – either ignoring or fearing it. Today, under- or over- reacting to one’s own senses is a symptom of autism spectrum disorder (ASD), according to the American psychiatric diagnostic manual published in 2013.4 These senses include sight, touch, smell, movement and taste, but for many people, the stereotypical image of autism involves the sense of hearing. It's the image of a child with his hands covering his ears, blocking out noise. In fact, that's what Elaine did when she heard the rumble of the vacuum cleaner. Today she would be called hyper(over)-responsive to noise. Richard, Barbara and Virginia would be described as hypo(under)-responsive, because they barely acknowledged many sounds.

Six decades have passed since Dr. Kanner described this phenomenon, but scientists still have many questions about it. Chief among them: What causes sound sensitivity in autism and what treatments work? How does this affect someone's ability to engage in everyday life?

What do we know?

Studies say from 30 percent to more than 90 percent of people with autism either ignore or overreact to ordinary sights, sounds, smells or other sensations.5-9 Among children who took part in the Simons Simplex Collection autism research project, about 68 percent had unusual sensory interests and 65 percent were sensitive to noise.10

Generally speaking, researchers have had trouble being much more specific. After all, no one single type of sensory problem is "consistently associated with ASD."11

A decade ago, two prominent autism researchers, Sally J. Rogers and Sally Ozonoff, reviewed 75 research papers published on the subject since 1960. They found more evidence that children with autism underreact to their senses, but said they could not draw firm conclusions. That's because the studies they reviewed used different methods, tested different things, and relied on different scientific standards over the decades. In the last decade, other studies have sought to advance our understanding of what Drs. Rogers and Ozonoff called "sensory dysfunction."6

How do we process sensory information?

Photo of tuba being playedThink of your brain and nervous system as a controller, taking in information from your senses, deciding what's important, and choosing how to react. Example: Your boss comes to your cubicle to talk. A florescent light flickers overhead, a co-worker laughs in the next cubicle, and a microwave whirrs in the break room. However, your brain filters out those sights and sounds so you can focus on what your boss is saying. You also tune out the sound of a siren outside, but when you smell and see thick smoke, you and your boss respond to that "sensory input" and leave the building.

Someone with autism may process information from their senses differently. He may be unable to filter out irrelevant noises or sights, such as, in the previous example, the microwave or flickering light. Or he may find certain sounds, lights, or textures to be severely distracting or uncomfortable. Some suspect that sensory problems may be triggers for other behaviors often found in autism, such as extremely picky eating habits12 or even wandering.

Studying the auditory system

Researchers have tried to measure and quantify the sensory symptoms common to autism, using parent surveys, skin conductance tests, hearing exams and brain scans. Is there something different about the way people with autism hear or process sound?

A group of British researchers wondered if teenagers with autism were more sensitive to the pitch, loudness and duration of sounds than other teens. They found that most teens with autism did not differ from typically developing teens in the ability to discriminate between sounds overall. However, they made interesting discoveries when they divided the teens with ASD into subgroups based on their differences from each other. About 20 percent of them had exceptional pitch, the ability to distinguish one musical tone from another. Meanwhile, another subgroup had trouble determining the loudness of a tone; those teens also had more problems coping with noise in everyday life.13

Other researchers wanted to see how children's autonomic nervous systems, which control largely involuntary actions, reacted to noise. For this experiment, they measured skin conductance – the response of sweat glands on the hand – in children with and without autism. The scientists found that children with autism had stronger autonomic reactions than typically-developing children when they heard noises – but also when they didn't.5 The stronger physiological response in ASD may trigger greater behavioral responses to sound, they concluded.

At the University of California Los Angeles, scientists used yet another test to study the senses of hearing and touch in autism. They took scans of children's brains while exposing them to two relatively mild annoyances, noisy traffic sounds and scratchy wool fabric. The youth with autism showed greater activity in certain brain regions than typically developing children on a functional Magnetic Resonance Imaging (MRI) scan, they discovered.14 Those regions included the amygdala, which is involved in social and emotional behavior, and the cortices that process sensory information.

So some studies suggest that the nervous system of a child with autism may react differently to sound. But is his hearing any better or worse than a typically-developing classmate?

Can you hear me now?

Photo of outdoor horns, to illustrate noise sensitivity in autismOne research group administered a battery of tests to find out. They detected no difference in the hearing of children with and without autism – at least in tests that did not require a behavioral response from the children.

However, things got trickier when they administered a test that required the children to indicate by their behavior that they heard a particular sound. In those tests, 41 percent of the children with ASD acted as though they didn’t hear normally at least once.15 They repeated the tests, and got different results on some of the same children. This failure to respond normally and consistently to sound may be caused by a problem with attention, rather than with hearing or sensory processing, they and other scientists have theorized.15-17

That research group cautioned parents and teachers that children with autism may appear to have abnormal hearing on tests that require a behavioral response, even though their hearing is fine. They also said their findings may undercut some of the assumptions behind a "highly controversial treatment, auditory integration training (AIT)" that claims to treat the "auditory 'difficulty'" of children with autism. That's because children with autism may perform unreliably on behavioral hearing tests that might be given before and after AIT.15

The National Autism Center has classified AIT, as well as another common treatment, sensory integration therapy, as "unestablished interventions" in a 2015 report. That means there is little or no reliable scientific evidence of their effectiveness for autism.18

The American Speech-Hearing-Language Association took a similar position on AIT. It said that AIT has not met scientific standards for effectiveness to justify its use by audiologists and speech-language pathologists.19

But where does that leave people with autism who prefer treatments that have solid scientific proof behind them?

Treatment for Children with Autism

Occupational therapists have been in the forefront of sensory processing since one of their own, A. Jean Ayres Ph.D., began describing and theorizing about it some 50 years ago.20 In autism, a child’s language and social delays may make it hard for him to identify and communicate which sounds, sights and sensations bother him. Sometimes it can take a little detective work on the therapist's part to determine the cause of a child's sensory behavior.

A therapist tries to help the child organize sensory information so he can respond appropriately and take part in everyday activities. In some clinics and schools, occupational therapists work with speech-language pathologists and behavior analysts to craft a multi-disciplinary treatment approach for a child with autism. They also train parents on steps to take at home to help their child participate fully in play, family, recreational and other activities.

Safe(ty) and sound: A new avenue for autism research

The National Autism Association (NAA) teamed up with the Interactive Autism Network (IAN) to research auditory sensitivity in autism – and how that might trigger incidents of wandering or provoke other dangerous situations. Some parents had reported that their children wander or bolt in response to certain sounds, said NAA President Wendy Fournier. "We feel really strongly that auditory sensitivities are playing a role in safety issues."

IAN surveyed parents of 814 children with autism for the study and reported preliminary results in Spring 2016.21 Being over- or under-reactive to noise caused 43 percent to 52 percent of the children, respectively, to be in an unsafe situation, according to their parents. Noise sensitivites provoked some children to hurt themselves or others, or led to accidental injuries. More than 40 percent of noise-sensitive children tried to run away from sounds that bothered them, and a fourth tried to hide. Similarly, an earlier study by IAN found that some children bolt to escape uncomfortable sensory experiences.22

Ms. Fournier said she hopes more research will lead to better interventions, something beyond just wearing headphones to block out noise, as many people with autism do. The 2016 study found that about half of the parents were satisfied with ear buds/headphones with music, and ear muffs; however, most parents were not satisfied with ear plugs.21 "We're hoping that, with the data collected, it will lead to the development of devices that could help relieve sound sensitivity and the pain that goes along with it," she said.

The IAN study explored strategies used by parents of noise-sensitive children. Most avoided their child's trigger sounds and took quiet breaks with their child. Still, roughly a third of the parents said the condition led to social isolation by limiting their child's ability to take part in family, community or school activities.

Thank you to the families who participated in IAN Research's survey on auditory sensitivity and child safety.

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References: 
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  2. Donvan, J. & Zucker, C. (October 2010) Autism’s First Child. The Atlantic. Retrieved from http://www.theatlantic.com/magazine/archive/2010/10/autisms-first-child/308227/
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