Sensations or information from each of the senses have two important attributes, stimulus and perception. The stimulus is measurable and consistent across individuals. The amount of light in a room, the volume of the school bell, the pressure of a pat on the back and the amount of spiciness in a Mexican dinner are examples of a sensory stimulus. The stimulus does not change across two individuals as they experience the same phenomena. The stimulus could be measured systematically if we wanted to know the brightness of a light or the degree of spiciness in a meal. Perception of sensation or sensory stimuli on the other hand is the subjective appraisal of sensory input which varies both within and between individuals. One person might think a room was not bright enough while another might feel the need to get dark glasses to ward off the glare. Some people love hot peppers while others avoid them because they burn their mouths. You may have heard a child say that they don’t like cinnamon or peppermint gum because it is “hot” and burns their mouth.

Additionally, our subjective appraisal of sensations can change from day to day, hour to hour or even minute to minute. Think about your own nervous system as you drive to the mall on a Saturday compared to driving home from work in heavy traffic. Do you grip the wheel a bit more tightly; do you turn down the radio so you can concentrate on your driving? The incoming sensations are essentially the same on both occasions, but the state of your nervous system is different so it perceives the incoming sensations differently. As you are reading this, you may be thinking of situations you have experienced with a particular child or even in yourself that exemplify differences in the perception of sensory stimuli. As a parent or professional working with children with autism spectrum disorders, learning to notice and appreciate your own sensory preferences or avoidances is an important first step. This will help you better analyze and appreciate sensory challenges in your child or the children you work with.

The delivery of sensory messages to the central nervous system is the avenue for input from experiences and interactions with the environment. These experiences can be external (outside the body; event in the environment) or internal (inside the body; headache, hunger pains). As messages travel along neural pathways, specific regions of the brain serve to compare or combine (integrate) information from the senses to make appropriate responses. This information is integrated so the brain can formulate a response. This response may be a motor action, a thought, an emotional reaction or a combination of these.

Each of the sensory systems has two important functions, discrimination and protection, that contribute to our ability to learn and be safe in the world. The discriminative function supplies details to the central nervous system for consideration and comparison. For example, when a person touches (tactile) an object, the discriminative function of the tactile system tells the person whether the object is hard, soft, fuzzy, smooth, round, angular, and so on. Accurate information about these details will help us learn about the object in a useful manner, so we know whether it is to hold carefully, without squishing it (a ripe peach), or to grasp it firmly (a baseball). The sensory perception of objects in our environment then becomes part of the memory we have for these objects.

The systems also have a protective function that helps to keep us away from danger or harm. For example, when we reach into a boot and detect something soft and fuzzy, the tactile system may signal us to move our hand quickly to keep from being bit by a brown recluse spider. The sensory systems operate in a way that seeks to maintain of a state of equilibrium. If a child misinterprets sensory information his state of equilibrium may be disrupted. Depending on the child and the situation, their reaction might be mild (flinch, say “go away”, cover eyes or ears) or extreme (run, scream, hit, withdrawal from situation). These reactions, the behaviors that we see (and don’t see), come from what and how that person sees, feels, hears, or otherwise interprets sensory events in his world.