What Exactly Is Sensory Integration Dysfunction?
The theory of Sensory Integration Dysfunction (SID) was formulated by A. Jane Ayres (1979), an occupational therapist, to describe a variety (!) of neurological disorders. It attempts to account for the relationship between sensory processing and behavioral deficits. At present SID still remains a theory and has not much recognition and support from the fields outside occupational therapy (OT). Below I will try to answer the 'why is it so' question and see whether skepticism is justifiable or not.
There seem to be several reasons to account for criticism received by the theory of SID. To start with, the choice of the term 'sensory integration dysfunction/disorder' was very unfortunate. On the one hand, SID allows a very broad interpretation as it was introduced to cover a variety of neurological disorders. On the other hand, it effectively narrows the investigation, as it excludes any other disorder labeled by a different term, for example, sensory processing disorders. As a result, despite the theory having been actively developed within the field of OT, it has inevitably ignored a great amount of research in the field of sensory and information processing, as being outside the scope of OT interests. It is no wonder, therefore, to find such statements as "the state of knowledge regarding modulation of sensation was in its infancy during the 1980s" in a review of OT literature. To the contrary of this statement, quite a lot of research was being carried out in the field of sensory dysfunction, including sensory modulation problems, in the 1960s-80s.
Thus, already in the 1960s, Bernard Rimland wrote about impairments in perceptual abilities of autistic children. Edward Ornitz described disorders of perception in autism. In the early 1970s, Carl Delacato put forward the theory of sensory dysfunction in autism, and proposed a classification of abnormal sensory experiences of autistic children. Delacato also pioneered the treatment of sensory abnormalities by 'normalizing' the sensory processing. Though his book The Ultimate Stranger: The Autistic Child (1974) was published more than three decades ago, the basic ideas about sensory dysfunction described in this book are still relevant today. Actually, these ideas 're-appeared' in many works of OT research in the 1980s-90s as 'new discoveries'.
Another drawback of the SID theory was that it was presented to describe a new phenomenon that had not been investigated before. Consequently, it successfully wiped out the research mentioned above, and limited itself to the field of OT. It is important to remember that the SID theory was not new, but the name of it was. Before that, the same concepts were described under the terms of 'sensory perceptual impairments', 'sensory processing disorders/problems', 'sensory dysfunction', 'disturbances of sensory modulation/information processing', etc. etc.
Even now, after several decades of intensive research in the field of OT, there is a great confusion of definitions, concepts, and notions related to SI and SID.
In the OT literature I have been unable to find a single, commonly accepted definition of SI(D). Different authors either use different terminology to discuss identical phenomenon, or apply one and the same term to cover different meanings, depending on the views, expertise, and research interests of the person who uses it.
The definitions of SI(D) presented in the OT literature can be roughly divided into broad and narrow ones.
The broad definitions
Ayres defined sensory integration (SI) as "the neurological process that organizes sensation from one's own body and from the environment and makes it possible to use the body effectively within the environment. The spatial and temporal aspects of inputs from different sensory modalities are interpreted, associated and united." In accordance with this broad definition, some authors describe SI as 'the process by which the nervous system receives, organizes, files, and integrates sensory information in order to make an appropriate response'; 'the ability to take in information through senses, to put it together with prior information, memories, and knowledge stored in the brain, and to make a meaningful response', etc.
And now let us compare these definitions of SI with those of perception and sensory processing: Perception is the process by which an organism collects, interprets, and comprehends information from the outside the world by means of senses. Sensory processing is the ability of the brain to process all sensations so we can interact adequately with our environment. Confusing? You bet!
This broad interpretation of SI leads to broad interpretation of SID, such as the ineffective neurological processing of information received through the senses. (Though some occupational therapists do distinguish between sensory processing dysfunction and SID - where sensory processing is the way the body takes in 'raw data' of sensations from the environment through all of the sense organs; and SI is referred to the way the brain combines and utilizes that raw information in order to provide useful information with which we can make a decision.)
The narrow definitions
Below are just a few examples of narrow interpretation of SI(D). SI is 'distinguishing between sensory experiences, such as touch, movement, body awareness, sight, sound, smell, taste, and the pull of gravity' (Gale Encyclopedia). SID is a disruption in the process of intake, organization and output of sensory information. Inefficient sensory intake is taking in too much or too little information. With too much information, the brain is on overload and causes an individual to avoid sensory stimuli. With too little information, the brain seeks more sensory stimuli (Kranowitz, 1998). This latter explanation coincides completely with Delacato's classification of hyper- and hyposensitivities (though Delacato distinguished a third possibility - 'white noise', as well.)
In a narrow sense, SID is nowadays often used interchangeably with sensory modulation disorder/disruption. This brings even more confusion, as this 'interchange' is not accepted by all the researchers, and some authors interpret 'modulation' as a separate process.
Similarly, we find broad and narrow definitions of 'modulation in the OT literature. In their review of OT literature on sensory modulation, Wilbarger and Stackhouse regret that there is limited information written about sensory modulation, and emphasize the necessity to update "our theories to incorporate the new findings in order to facilitate acceptance of our unique perspective on central nervous system functioning as it relates to human occupation." One should add, it is equally important to incorporate the 'old findings' from the outside of OT, such as, for example, those described by Ornitz - the disturbances of sensory modulation manifested as both underreactivity and overreactivity to sensory stimuli.
All these different interpretations of SID allow highlighting different characteristics and categories. As any aspect of sensory and information processing can be covered by the term of SID, it gives a researcher a free hand to choose whatever they want to study describing it as SID. Some researchers, for instance, discuss various characteristics of SID under four categories: attention and regularity problems, sensory defensiveness, activity patterns, and behavior. Others include into end products of SI such characteristics as the ability to register and modulate stimuli, motor coordination, attention, motor planning ability, balance, eye control, emotional stability, behavioral control, body scheme, and self-esteem. Kranowitz (1998) describes modulation, inhibition, habituation, and facilitation. Myles and colleagues (2001) distinguish five stages of the SI process: registration, orientation, interpretation, organization, and execution of a response. Besides, the authors suggest that sensory modulation (not included by them into the five points of the SI process) supports the "effective performance by further integrating (?) the information to result in a behaviour or action that matches our intent."
Originally, Ayres limited her investigation with "three basic senses" - tactile, vestibular, and proprioceptive ones. Later, some OT researchers included all the senses into the theory.
Ayres introduced the concepts of tactile defensiveness (for tactile sense), gravitational insecurity (vestibular system), and postural insecurity (proprioception). She defined tactile defensiveness as avoiding or negative reactions to non-noxious tactile stimuli and as an imbalance between discriminative and protective sensory processing. Tactile defensiveness is manifested in 'fright, flight, or fight' response or reaction.
However, the concept of defensiveness in the context of SID seems to be misleading as it implies the reaction (i.e. behavior caused by something) rather than the cause(s) of this reaction.
Gradually, the shift from sensory defensiveness to sensory modulation problems (a person's threshold for responsiveness to sensation) was made. Probably, that is why, though OT researchers still write about tactile defensiveness, while describing problems in other sensory modalities they prefer to use 'hypersensitivity' rather than 'visual defensiveness'/'auditory defensiveness', etc. It seems quite logical, as hypersensitivity experienced by the individual causes defensiveness (reaction/behavior).
According to Sensory Integration International, some signs of SID are:
- Oversensitivity to touch, movement, sights, or sounds
- Underreactivity to touch, movement, sights, or sounds
- Tendency to be easily distracted
- Social and/or emotional problems
- Activity level that is unusually high or unusually low
- Clumsiness or apparent carelessness
- Impulsive, lacking in self-control
- Difficulty making transitions from one situation to another
- Inability to unwind or calm self
- Poor self concept
- Delays in speech, language, or motor skills
- Delays in academic achievement
These signs are often complemented with more specific symptoms from all sensory modalities and often coincide with the symptoms of Central Auditory Processing (CAPD) and Scotopic Sensitivity/Irlen Syndrome.
At present there are two distinct views on the 'status' of SID. Some authors argue that numerous psychological, psychiatric and neurological disorders such as schizophrenia, depression, ADHD, autism, etc. appear the same as SID, and that many symptoms of SID look like symptoms of other common disabilities, making it difficult to differentiate one difficulty from another. Others think that referring to the cluster of SI problems as a disorder may be premature as SID has not been identified as having universal and persistent features that are distinct from other established disorders. One can make some suggestions. Instead of trying to embrace all sensory and information processing disorders under one umbrella term, wouldn't it better to distinguish specific patterns of sensory perceptual problems in different 'established disorders'? For instance, though sensory perceptual problems have not been incorporated into diagnostic classifications, very specific and easy-to-describe unusual responses to sensory stimuli have been reported in most autistic children when they are observed prior to 6 years of age or when their parents are questioned about specific behaviors (Ornitz). It would be useful to compile specific patterns of sensory perceptual problems for different developmental disorders in order to find out whether there are differences in their manifestations.
To make the process easier, one could clearly specify and define separate sensory and information processing phenomena. For example, sensory integration dysfunction can be defined as difficulty processing and interpreting information from more than one sensory channel a time; sensory modulation disturbances - as the difficulties to modulate optimal arousal, that is manifested as both under- and overreactivity (hyper- and hyposensitivities) to sensory stimuli, or fluctuation between the two; etc.
Probably, then SID, sensory modulation problems, as well as CAPD, SS/IS and similar conditions will fit perfectly into the theory of sensory perceptual disorders/problems/difficulties.
References:
Ayres, A. J. (1979). Sensory Integration and the Child. Los Angeles: Western Psychological Services.
Kranowitz, C. (1998). The Out of Sync Child. New York: The Berkley Publishing Group.
Myles et al. (2001). Asperger Syndrome and Sensory Issues. Autism Asperger Publishing.
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