Although sensory integration dysfunction (DSI) has been around since 1954 when A. Jean Ayres, PhD pioneered and researched this topic, few have truly understood the depth of which her theory encompassed. Present day neuroscience continues to expand and support the neurobiological meaning which I hope to summarize here. Thus, the term sensory integration is based on the work of Dr. Ayres to describe the theory and the intervention; whereas,
a new nosology is used to describe the diagnostic category of this disorder known as sensory processing disorder (SPD).
Dr. Ayres sought out initially to identify how poor processing of sensory stimuli affected the child, resulting in atypical motor, social/emotional, and functional patterns of behavior. These behaviors were hypothesized to interfere with end product competencies in speech/language, attention, motor. This is best illustrated by the flow chart developed by Ayres below:
Widely recognized is A. Jean Ayres' definition of sensory integration. "Sensory integration is the neurological process that organizes sensations from one's body and from the environment, and makes it possible to use the body to make adaptive responses within the environment. To do this, the brain must register, select, interpret, compare, and associate sensory information in a flexible, constantly-changing pattern" A Jean Ayres, 1989
Simply said, sensory integration is the relatedness of one to others, one to their environment, and one's ability to adjust oneself to function within the environment with oneself, others, and objects within it.
Ayres' theory and intervention is based on categorizing seven neuro sensory systems and the relationship of each with one another. Alfred Tomatis, MD, also developed his framework similarly identifying the same basic systems as Ayres. Current neuroscience research continues to verify and confirm these sensory systems as:
Dr. Ayres further established four categories in the 1960's to classify and refine specific sensory manifestations as seen by sensory modulation dysfunction (SMD), developmental dyspraxia, bilateral integration dysfunction, and generalized dysfunction (a combination of all areas). The SPD global umbrella identifies three primary diagnostic categories as sensory modulation disorder, sensory discrimination disorder, and sensory-based motor disorder.
- Vestibular: Known to be one of the first sensory organs completed in utero, this system provides us with information to help detect and process our sense of movement, the pull of earth's gravity, and position in space. "A well-modulated vestibular activity is very important for maintaining a calm, alert state….The vestibular system also helps keep the level of arousal of the nervous system balanced. An under-active vestibular system contributes to hyperactivity and distractibility because of its modulating influence." A. Jean Ayres Ineffective processing of this system may lead to sensory-based motor disorder or sensory modulation disorder.
- Tactile: As it sounds, this system is responsible for our sense of touch. The tactile system addresses surface area of our body including the skin, hair, hands, feet, and oral motor cavity. Ineffective processing of this system leads to sensory discrimination disorder or sensory modulation disorder.
- Proprioception: This system allows one to process information and gain information from our internal sense which comes from our joints and muscles. One could say this system is a necessary foundation for muscle memory. Generally, problems in the area are associated with tactile and/or vestibular issues which lead to sensory modulation and sensory-based motor disorder.
- Auditory: This system serves as the sensory integrator of two basic systems within the ear (vestibular and cochlear) and is responsible for 90% of our brain's processing, Sixty percent of the stimuli to the brain originate from the bones, joints and muscles through the vestibular system, while the remaining forty percent is from the sound processed through the cochlea. Since the brain needs stimuli to be nourished, the stimuli and significance of it from the ear is the perception of different sound wave frequencies.
- Visual: This system is now known to be reflective of auditory processing and therefore, it is the ability to perceive and make sense of spatial orientation and direction (vertical vs. horizontal), color, shape, assess intensity of light, process form, etc.
- Olfactory & Gustatory: This system is responsible for our sense of smells, odors, and tastes, and measures the intensity of them. Often we find that individuals who seek excessive salt, sweetness, or hot spice are under-reactive, while people who tolerate only very bland, or have a limited repertoire of foods are overly-reactive. Likewise, some demonstrate difficulty with smells which may result in nausea or emesis.
Sensory modulation dysfunction (SMD) is the ability one has to take in sensory sensations be it auditory, visual, gustatory, olfactory, or tactile stimuli, by interpreting what it is and filtering what is important while ignoring what is not by
inhibiting that sensation. Often, as seen in the Today Show video, children with SMD are unable to process information to cause them to have ineffective sensory modulators. Examples which are often reported may be being unable to tolerate smells from the lunch room, or intolerance for noise such as that of other children or fireworks/vacuum cleaners, being unable to move without fear or feeling nauseous, clothes that are intolerable, craving bumping and crashing into things/people. Or, perhaps the opposite is observed where the child does not seem cuddly or recognize when they are hurt, does not seem to hear auditory information, or will not sit still. Often one may hear this being described as being over-reactive or under-reactive.
Developmental Dyspraxia is reflected when a child has a coordination disorder being unable to execute new skilled movements. These children often are unable to visualize mentally a plan (ideation), or know how to complete novel tasks (affordances). Dr. Ayres' later work on dyspraxia identified these children to have underlying sensory processing issues resulting in difficulties with detection, organization, discrimination of sensory information from the tactile (skin), proprioceptive (joints and muscles) and/or vestibular (movement) systems. These children sometimes are moving very quickly but when asked to grade their movements they fall or look clumsy. School age children who may exhibit this are often delayed in learning how to formulate handwriting skills, eat with their fingers because they are unable to negotiate utensils, demonstrate delays cutting, or cannot ride a bike, skate, or perform large muscle actions as they are unable to have the ideation and/or if they do, do not have the affordances. Dr. Ayres believed that intervention addressing the underlying sensory processing issues rather then using and educational process of teaching was more successful. For that reason, rather then working on handwriting (as an example), therapy is focused on the integration of the sensory systems as the primary goal.
Postural-Bilateral Integration Dysfunction is due largely to the immature developmental integration of primitive reflexes and core muscle patterns. This results in an inability to use two sides of the body together, lack of lateral dominance (switches hand use where parents say their child is ambidextrous), and inability to cross the body midline. Often this translates to observing the child to have difficulty with directionality, inability knowing where their body is in space, have difficulty alternating limb movements, poor conjugate eye movements, or extreme gravitational insecurity as seen in .) unusual fear for certain positions (being on their tummies, moving backwards, going downstairs, etc), difficulty executing activities of daily living skills of self dressing as they are unable to button or zip, and/or reversals of letters.