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What Are Sensory Processing Difficulties & When Should I Be Concerned?

In my blog last month, I introduced the concept of the sensory systems and talked about how we actually have 8 senses (rather than the 5 that most of us know about). I figured it would be pertinent to do a ‘part 2’, to chat more about what exactly sensory processing difficulties are, some strategies to get you started, and when to get support.

Review of Sensory Processing

Remember, we live in a sensory-rich world. Everything we learn and take in from our environment comes into our body (and brain) through our senses, and once the brain has integrated or processed this information, we act on it1. The sensory system is actually comprised of the brain, spinal cord, and neurons. It is the neurological wiring by which we perceive and process sensory information coming from outside and even inside our bodies.

Most of us are familiar with the 5 senses, but people are surprised to learn we actually have 8 senses!

We receive sensory input from the external world via the most famous 5 senses : tactile (touch), visual (vision), auditory (hearing), olfactory (smell), and gustatory (taste). 

Then! There are the 3 body senses that give us information about our internal world: Vestibular (movement/balance), Proprioception (body awareness/body position), and Interoception (internal organs, body rhythms such as hunger/thirst, sleep cycles, bowel/bladder, etc).

You can read more about these 8 sensory systems in my blog from last month – What You Need to Know about the 8 Senses and Sensory Processing in Babies.

All 8 of the systems working together provide you with the “optimal level of arousal”, which means you are able to perceive, process, and react to sensory stimuli, interpret the information, and form a response (either a motor response, language, cognition, etc)1.

It is important to know that sensory processing and integration is not an either/or matter.  We don’t have perfect sensory integration or none at all. None of us organizes sensations perfectly. Some people have especially good sensory integration, others just average or poor.

However, when a person or child is having difficulty perceiving and/or interpreting information from these senses, this is often referred to as sensory processing differences, issues, or concerns.  The brain does not receive all of the sensory information necessary to do an effective job. And, as a result, there will be more effort and difficulty in every day activities, and less success and satisfaction.

When it is significant enough to affect their overall functioning and/or the functioning of the family, then they may get a label like Sensory Processing Disorder.

What Exactly Is Sensory Processing Disorder?

Unfortunately Sensory Processing Disorder did not make it into the DSM-V, the Diagnostic & Statistical Manual that doctors use to diagnose. This means that hard diagnostic criteria doesn’t technically exist, and a lot of recommendations are based on clinical observation. However it is often recognized, referred to, and somewhat understood in much of the medical and therapy community.

The term Sensory Processing Disorder actually came from the original condition that was once called Sensory Integrative Dysfunction, which was defined by Dr. Jean Ayres, an Occupational Therapist, who was the forerunner of sensory integrative theory and research back in the 1950s and 1960s. Dr. Ayres had a keen interest in how the brain worked and spent many years pursuing doctoral studies, doing research and writing books about this concept of sensory integrative abilities (aka sensory processing).  She also developed sensory integration intervention programs using specialized techniques and offered specific certifications in her approach.

Dr. Jean Ayres’ sensory integrative theory had the following underlying concepts or assumptions:

1.  Development is affected by our ability to process sensory information

2.  Impaired processing can be inferred via behavioural responses and motor output

3.  Sensory processing can be improved with controlled sensory input provided through meaningful activities that yield adaptive responses. 

Since Jean Ayres developed the theory of sensory integration, there have been a few Occupational Therapists and research professionals that have made great strides in building on this theory and who have developed various models to try to better explain sensory processing and sensory integration.

Two of the most well known models are:

Winnie Dunn’s model

Lucy Jane Miller’s model

Without getting into too much of the nitty gritty of each model, I did want to discuss some basic concepts of sensory processing differences and how they may present in babies, and kids (and yes, even in adults).

What Does Sensory Processing Disorder Look Like?

There are technically different sub-types of sensory processing disorder including sensory modulation, sensory discrimination disorder, postural-ocular disorder, and even dyspraxia.  However, most of the time, when we start looking at sensory processing difficulties in terms of understanding the child and what strategies might be helpful we start with the sensory modulation subtype. 

There are essentially 4 types of responses at this sensory modulation level, when it comes to how the brain responds to sensory input.

  • Low arousal/under-registration with high activity
  • Low arousal / under-registration with low activity
  • High arousal / over-registration with high activity
  • High arousal / over-registration with low activity

What is Arousal Level?

Arousal refers to a person’s state of alertness or awareness. As the body processes sensory input from the environment such as sounds, movement, or smells, the brain takes it in, which causes the person to respond to that input. Some people may over respond or under respond to this input or not register the input at all.

Low Arousal/Under-Registration of Sensory Input

Let’s start with low arousal, or under-registering of sensory input.

A child whose sensory system is under-aroused (also sometimes known as hypo-arousal or with a ‘cold brainstem’) has a high threshold to sensory input and their brains under-respond to certain input in their environment.  Think of this as their sensory system being ‘asleep’ and not effectively registering the sensory input coming in from daily life. Because their sensory systems are not registering this input properly, their brain is not able to make the best use of new information or the learning environment itself.

A child with this type of sensory dysfunction may require more physical activity to “awaken” his or her nervous system.

This low arousal or under-registration type can be a child with low activity or high activity, and each of those subtypes have their own characteristics.

The child with Low Arousal Low Activity is often more ‘passive’ or quiet, and described as a ‘good or easy’ child, never getting into mischief or trouble. As babies they don’t really fuss much, rarely cry, and may just ‘be’. They may be slower to move and react, possibly meeting milestones on the later end. They are usually happy to stay back and observe rather than be in the action. 

As they get older, they are often slouching in chair, leaning their heads on their desk, or lying in the floor. They may be inconsistent in responding to their names, have a flat affect, seem a bit withdrawn, or even difficult to engage.


Well these kids are under-registering input and not really noticing it coming in at all. So they don’t have the motivation (or want/need) to act on it.

The child with Low Arousal High Activity is often more of the ‘sensory seeker’ and may appear to be impulsive and somewhat of a risk taker. These are the kids who are usually bouncing off the walls, jumping on the bed, climbing on everything, sort of like the Tazmanian Devil.

They often don’t have great body awareness and so are clumsy & tripping/falling – the ‘bull in the china shop’. These kids are the active kids in the classroom, running around & not able to sit still.


Well they are LOOKING for more input to help their body feel grounded in space & against gravity & their daily life input is just not enough because they are under-registering it (in their brain & nervous system).

Which means that, in general, low arousal kids actually need MORE sensory stimulation to essentially ‘wake up’ their brain and bodies or to notice the sensory information coming in.

  • More tactile play with paint, sand, and shaving cream
  • More vestibular input with swinging, spinning, and upside down
  • More body work input like jumping, marching, and stomping

High arousal (with high or low activity)

Children whose sensory systems are in a high arousal state (also sometimes known as hyper-arousal or a ‘hot brainstem’) have a low sensory threshold and therefore over-respond or overreact to certain input that most people’s nervous systems would typically be able to cope with.  This results in becoming hyper-sensitive or sensory-defensive to the specific input.

Their system goes into “overload” with too many messages to the brain, which results in increased adrenaline and cortisol. A child with this type of sensory arousal often requires more calming, rhythmical sensory input that is familiar and predictable, so they feel safe.

This high arousal or over-registration type can be a child with low activity or high activity, and each of those subtypes have their own characteristics.

The child with High Arousal with High Activity is the one ‘attacking’ or ‘fleeing’ – they are sensitive to sensory input and are over-registering it. Their bodies feel sensation too easily or too intensely. For example if they are touched unexpectedly or there is a loud noise, they see it as ‘dangerous’ and a threat and it activates their fight (attack) or flight (flee) response.

The child with High Arousal with Low Activity is one who avoids. They are also sensitive to the sensory input and over-register it, but rather than fight or flight, they just avoid this input. They ‘shut-down’ easily, withdraw from the input. They might avoid different textures or movement. Perhaps they refuse to go to certain places or even birthday parties (because the noise or visual stimulation is too much).

For these children it is really important to tune in and understand their triggers.

And knowing that the proprioceptive, tactile, and vestibular systems, those three ‘foundational senses’ that help to organize the body (and the other senses) will be key in helping them feel grounded and calm.

These children benefit from:

  • Deep touch (or firmer pressure/touch) is better received and less irritating than light touch)
  • Being approached from the front (so they can see you) versus from behind (this is less scary and unpredictable
  • Lots of heavy work and body work – pushing, pulling, lifting, carrying to ‘calm’ the system

It really is so interesting & complex. 

I should also mention that although the sensory systems do work together, each system can have their own sensory threshold.  So it is quite normal to have a child who is hyper-responsive to some of the sensory systems and hypo-responsive or under-responsive to others.

When Should I Be Concerned & Seek Help?

I know it sounds complicated and it is to a certain extent, which is why you definitely want someone trained in this area to be assessing your child should you suspect any concerns.

This is a big part of how I work with clients as at the root of a lot of ‘behaviours’ & difficulties with functioning in various daily tasks is a sensory system that is not working optimally.

In terms of when to seek out additional help, well, I tell parents to trust their instincts.

Seek out more information if your baby, toddler, or even older child has symptoms that are occurring frequently. Especially if it is impacting your child’s overall daily functioning, well-being, relationships and even the family’s dynamics and routines compared to other children the same age.

And remember, what is disruptive to one child and one family might not be the same for another family, so please please please trust your mama instincts!

Sensory Processing is something I have been passionate about learning over my 12-year career as a pediatric occupational therapist.  I’ve gained so much valuable experience from working in a variety of settings – from early intervention, to nursery and elementary schools for kids with Autism, to private sensory clinics, with kids of all ages.

If you suspect that your baby or young child might have some sensory issues going on, but aren’t sure whether they warrant intensive therapy in a clinic or sensory gym – I’ve got you!

I’ve made an easy to consume Sensory 101 course that takes you through the development of the sensory systems in babies. Not meant to replace an outside professional, but offering tips and tricks and activity ideas along the way. It even includes a whole lesson on how sensory processing may affect sleep, with lots of strategies to make bedtime better. This course can provide tons of knowledge and tips to get you started.

And, of course, I offer 1:1 virtual consultations if you want to talk through some symptoms and get some individualized education and ideas for strategies to try. And I will help you find additional resources if my resources don’t fit the needs of your child and family. 


Ayres, J. Revised and updated by Pediatric Therapy Network. (2005). Sensory Integration and the Child: Understanding Hidden

Sensory Challenges. (25th Edition).

Faure, M, & Richardson, A. (2002). Baby Sense: Understanding Your Baby’s Sensory World – The Key To A Contented Child.

Miller, L. J., Nielsen, D. M., Schoen, S. A., & Brett-Green, B. A. (2009). Perspectives on sensory processing disorder: a call for translational research. Frontiers in integrative neuroscience3, 22. https://doi.org/10.3389/neuro.07.022.2009

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Kaili Ets

I help overwhelmed and exhausted moms create a clear action plan around their baby's sleep, developmental, reflux, and overall functioning so they can tune into and trust their mama instincts and feel like the confident super moms they are.

hi! I'm Kaili!

Lovingly known as the Holistic Baby Guru. I have a passion for normalizing and bringing clarity around baby sleep, development, reflux, and more. Wife and mom of two, I understands the importance of trusting your mama instincts. I am on a mission to help mamas tune into their intuition and feel like the confident super moms they are. I like to think of myself as an approachable authority on all things baby-related, as that I provides down-to-earth advice that makes everyone feel like they can do this parenting thing!

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