What is Sensory Processing Disorder?

Try to imagine a life where touching a wool sweater feels like running your hand across a cheese grater, or the sound of people chewing their food at the dinner table is so overwhelmingly loud and repulsive that it makes you physically sick. Imagine that a common household lightbulb shone with the strength of the noonday sun, or that a door closing softly is like a gunshot in your ear.

This is the world that many with autism spectrum disorder (ASD) live in. Extreme sensory sensitivity is a fundamental element of the disorder and something that many with ASD struggle with to a greater or lesser degree.

Because our senses are the primary way we experience life and understand the world around us, people on the spectrum who suffer with extreme exaggerations in senses and sensations genuinely live in a different world from neurotypical individuals. For them, perfectly normal sensory input that we all encounter daily can be a source of tension and anxiety.

Extremes of High and Low Sensitivity to Sensations

Sensory Processing Disorder (SPD) is not an officially diagnosed disorder, but doctors, applied behavior analysts, and other professionals who work with autistic patients often use the term as a catch-all.

Sensory issues are described as one possible symptom of ASD in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Version 5) criteria, which states that hyper- or hyporeactivity (an exaggerated or minimized response) to environmental stimuli or an unusual interest in them may be a sign of autism.

But the DSM-5 criteria does not delve into the complexity or extremity of sensitivity issues that some ASD patients experience, so many clinicians consider SPD to be a comorbid disorder, separate but very often associated with ASD, just like ADHD or depression.

Some of the earliest descriptions of autism, from psychiatrist Leo Kanner’s pioneering work on investigating and describing the disorder in the 1940s, includes observations of extreme sensitivity to light or sound, or a complete indifference to pain. Going back even further, before autism was formally recognized at all, some historic figures who were thought to have the disorder famously showed sensory sensitivities—Mozart, for instance, was said to draw many of his musical gifts from an extremely honed sense of hearing. Loud noises were known to make him physically sick—classic SPD symptoms.

Sensory processing disorder can reach either extreme in individual cases –from extremely high sensitivity to seemingly no sensory perception at all. Some with ASD have extraordinary sensitivity to sight, sound, or touch, reacting as if the feeling were magnified thousands of times. Others appear to be almost completely numb to the same sensory inputs, as if they feel nothing at all.

People on the spectrum with either form of sensitivity disorder often adopt their own coping mechanisms to help keep life bearable. They may hum to themselves to drown out other irritating or sharp noises, or rock back and forth to feel constant movement. Some prefer to wear tight clothes or like to have their backs or arms rubbed to provide a sensation of touch; others may scream in pain at the lightest pressure and avoid all human contact.

Unfortunately, these responses sometimes lead to self-injury and aggression. Much of what makes ASD so difficult to treat, even for ABAs, is the sensory issues that innately shape the world of their patients into a realm that can only be guessed at.

Sensory Issues for People on the Spectrum May Be Related to Brain Structure

No one can say for sure how many of the behavioral and developmental issues those with ASD deal with are attributable to sensory issues, but all experts acknowledge that sensory processing is an elemental issue in autism. Deficits in verbal communication development and language skills learning, for example, are frequently tied to hearing problems.

The underlying reasons for these sensory issues remain mysterious, however. Studies of hearing issues in particular have had mixed results in determining a physiological basis for delayed processing of auditory input in the brainstem. In 2013, however, a study of 40 boys between the ages of 8 and 11 found that those with sensory sensitivities exhibited atypical white matter connections in the regions of the brain responsible for processing sensory signals—a sign that altered brain structure plays some role in the problem.

The atypical neural activity associated with autistic brains trying to process sensory input could be a direct result of altered brain structure, or something secondary to it. Attention deficits are a separate issue entirely, but are common for those on the spectrum and are known to result from impaired executive brain function. This same impairment could also explain some of the sensory processing issues people on the spectrum deal with.

A meta-study conducted in 2006 reviewed other investigations into sensory issues with autism patients. Their findings revealed a trend toward sensory issues becoming less pronounced with age. With the exception of issues of touch sensitivity, many ASD patients found that their sensory perceptions trended closer to neurotypical baselines as they reached adulthood.

This is promising news to parents who worry that their child’s sensory issues may prevent them from ever interacting with the world in a normal way. The study also concluded that there are significant relationships between different sensory issues. Sight and sound sensitivities, for example, appeared to be interconnected and both improved over time, though not necessarily at the exact same rate.