What are our senses and what do they control?
Most people will know our five basic senses – vision, hearing, smell, taste and touch. However, there are 3 other less known senses – the vestibular sense, proprioception and interoception. As mentioned in previous pages, it’s best to think of autism in the social model of disability. This means considering how the environment is disabling to an autistic individual. Autistic people may be described as having sensory issues, but sensory differences is more accurate in describing the variety of ways our community processes the environment around us.
Our eyes allow us to see and perceive what is going on around us as well as allowing us to form a sense of distance and depth. Our brain merges the information from both of our eyes to create our visual perception. Our eyes also work closely with the vestibular system which is our balance system to help us know in which direction we are moving and to keep our eyes and head steady, so our brain can make sense of the information more easily. Autistic individuals appear to gather a lot more detail from their environment visually than neurotypical people i.e. autistic individuals tend to notice more detail in their surroundings whereas neurotypical people may filter this information out.
Similarly to our vision, our brain combines the information it receives from both of our ears to perceive the sounds we are hearing. The way our brain processes these sounds allows us to interpret where the sound is coming from. This also contributes to our sense of body awareness, for example, if we hear a sound is becoming louder, we perceive that thing as getting physically closer to us. Our hearing system also filters out unimportant background noise. However, this appears not to be the case for autistic individuals and is one of the most well-known sensory differences they experience. Autistic people can often be very sensitive to sounds, particularly sounds coming from lots of directions like in busy places e.g. shopping centres or schools and lower frequency sounds such as handryers or hairdryers. This can present difficulty with perceiving where a sound is coming from, and an autistic individual may pay attention to all sounds in an environment at once making if difficult to concentrate or respond to someone talking to them or indeed sensory overload in some instances (see below).
Taste and Smell
Our senses of taste and smell are highly connected. Our senses of taste and smell are important for keeping us safe and play a key role in our dietary and eating habits. Our body naturally dislikes bitter or sour tastes as a way of keeping us safe from eating foods that may not be safe for us to eat. Our bodies are naturally attracted to sweet and salty foods which the body finds comforting. It is common for autistic individuals to be sensitive to the smell, taste and texture of food which often impacts the range of foods they can tolerate.
Our sense of touch provides us with lots of different information. Without using our other senses we can understand where we are being touched, the pressure of the touch, and the temperature of touch. Two pathways deliver these touch messages to our brain to be interpreted, the first (known as the anterolateral system) carries information relating to pain and extreme temperatures and crude touch and the second (known as the dorsal column medial lemniscal pathway) carries information about deep pressure touch/proprioception, vibration and fine touch. We have all had the experience of getting a small cut (such as a paper cut) and applying pressure to it instinctively to stop the discomfort. This is because the 2 pathways intersect in the brain. When we apply pressure to the injured area, the pressure messages reach the brain first and block the brain from receiving any more pain messages.
In autistic individuals who are sensitive to touch, we think that the brain is mis- interpreting every-day touch, like the feel of clothes as uncomfortable or painful. Hence, many interventions to decrease sensitivity involve using deep pressure or proprioception.
The Vestibular Sense
Our vestibular sense tells us how and when we are moving. The receptors for the vestibular sense are in our inner ear. Three very small semi-circular tubes filled with fluid allow us to interpret what direction we are moving in and how fast. We can interpret this as the fluid in our vestibular system will move as we do, sending signals to the brain. Our vestibular system is able to perceive tiny movements of the head (that happen all the time-even when sitting still!) and instruct the body to make small adjustments to our muscle tone (the tightness of our muscles) to keep us upright and balanced. This is also important for keeping the head and eyes steady so the brain can interpret the information from the eyes more easily and not feel dizzy.
If the vestibular system is not working efficiently, this can cause difficulties with balance, low muscle tone and tolerating movement. The person might also seek out movement in order to stimulate their vestibular system or indeed have difficulty with balance and often coordination.
The vestibular system is also like a gate keeper or traffic warden for information coming in from the other senses. The vestibular system filters information from the senses as it enters the brain and ‘decides’ which information is passed up the brain so we are aware of it. Again, if the vestibular system is inefficient, the brain can be overwhelmed with sensory information. This is why many programmes or interventions to improve sensory processing involve movement e.g. swings, trampolines etc.
Proprioception is our sense of body awareness. Each time we move our bodies, receptors in our muscles and joints allow us to perceive where our body is even if our eyes are closed. If an individual’s proprioception system isn’t interpreting information from their proprioceptive system efficiently, they may need to use other senses such as vision, movement and touch in order to allow them to have a clear sense of body awareness/where there body is. For example, they may need to bump or touch objects whilst moving around a building, or wrap their legs around the legs of the chair they are sitting on, for example.
Interoception describes our sense of what is going on inside our body. This sense allows us to interpret our heartbeat, our breathing, our emotions, whether we are hungry and when we need to use the bathroom. While we are constantly perceiving what goes on inside of us we are not always alerted to these changes. We often only receive an ‘alert’ when our brain is letting us know that our body needs something or our status has changed, for example, when we get hungry. If an individual struggles with interoception they may not receive these alerts. For example, they may forget to eat as they are not automatically reminded that they need to eat or may not notice that they need the bathroom until it’s too late.