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​Sensory Processing 'Disorder' in Tourette syndrome and ASD

Dysfunction of sensory integration, now often referred to as sensory processing 'disorder' or SPD, is common in individuals with Tourette syndrome and autism spectrum disorders (ASD). A number of studies indicate that sensory 'difficulties' are not only reported by the majority of individuals with TS but can involve all sensory modalities. Different combinations of modalities may be affected in different individuals. The 'five' senses are well known but the nervous system processes sensory input from many sources including vibration, pain, temperature, positional attitude (proprioception) sensors as well as being involved intimately in many neuro-hormonal or neuroendocrine processes within the body.
There is a subtle difference between the way the world is and the way in which we perceive it. Information which is derived from our ability to sense or detect the world around us, is processed within our brains by integrating disparate sources of complex information whilst matching them with 'experience' to make a useful perception of the state-of-things. It is the way in which we determine the 'meaning' of sensory input and what it is we are experiencing and forms the basis for our subsequent responses and actions. Dysfunction in this area of neural processing can have profound consequences
In many cases, sensory-processing 'dysfunction' in TS is considered a greater impairment than motor tics.
Sensory processing dysfunction is of particular importance to educational progression and in speech, language and social development and functioning. Although recognised by educators (and educational psychologists) as a separate 'disorder' in the case of SPD and as 'core' or comorbid symptoms in ASD, there is a poorly-understood reluctance to acknowledge their role in Tourette Syndrome, a neuro-developmental disorder as common as ASD. Studies suggest that sensory 'impairments' in Tourette syndrome may be more marked than in ASD, in specific sensory modalities (including auditory and visual).
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A particularly common symptom is sensory hypersensitivity in which sensory input may be experienced at a greater intensity than others perceive. Sounds may appear unpleasantly loud or distorted, or confusing and muddled when there are several competing sound sources. This can lead to a sensory 'defensiveness' where the individual prefers to avoid or shut out unpleasant stimuli (loud or particular noises, bright/flashing lights, being touched or having to touch certain textures). Tactile hypersensitivity may include a dislike for clothing, shoes, bed covers or certain fabrics and materials. A dislike of certain foods due to texture or taste can occur or aversions to certain smells. Sound sensitivity may be associated with an increased startle response to sudden noises and abnormally intensified reactions. Hypersensitivity to sound is sometimes termed misphonia.
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Understanding speech may be impaired by auditory processing difficulties even though hearing tests show no appreciable deficit in sound reception. In such cases, hearing enhancement technologies may actually have a negative impact on the problem. Although speech may be heard loudly due to hypersensitivity it may not be easily comprehended. Hearing aids may exacerbate this rather than lead to better speech definition.
Research findings suggest tactile hypersensitivity can be selective. It may vary between light touch and more intense contact, with responses to the former being perceived as 'unpleasant' and distracting whereas, in contrast, firm tactile sensation or even massage may be experienced as being pleasant. Neuro-anatomically, light touch sensation signalling may be carried by different neural tracts. Pressure is sensed by special neural endings and it's 'correct' interpretation is vital to many fine-motor skills including writing, typing, drawing and manipulating objects.
Evidence shows that reading speed in TS is frequently lowered on standardised tests and is likely to be a consequence of impaired visual processing. A recent study (N=12), showed that children with TS may be helped by using coloured overlays over text. Increases in average reading speed were recorded in a majority of children with TS tested, and increases appeared greater than those achieved when compared to individuals with ASD tested similarly. It must also be considered that the additional cognitive and motor activity intrinsic to TS can act to distract or draw focus from processing tasks that require heightened concentration such as reading and writing.
Little research has been done on reading impairment using screen-based text in this context in particular when in relation to the commonly-used 'light-emitting' displays. Many individuals report that backlit, scrollable and pixelated text is significantly more difficult to read and, importantly, much slower to process than printed text.
In dyslexia, some font styles appear 'easier' to read especially when there is an emphasised/emboldened base to the text to enhance line tracking and a non-serif font is used with wider line-spacing. It is possible that fonts such as open-dyslexic and lexia may benefit readers with TS or ASD also but preliminary analysis of these solutions are unconvincing, do not apply universally and indicate that font consistency i.e. sticking to a particular or preferred typeface, may be more important to reading/typing efficiency. Dyselexia and dysgraphia also affect handwriting and may be helped by typing/word-processing. Both however can be co-occuring components in TS in some cases. Technically any processing impairment that hinders reading is a 'dyslexia' (literally faulty/difficult reading). TS also presents unique difficulties for reading in the form of tics (simple/complex and cognitive) which similarly can affect writing and typing.
For the student with TS who has difficulties reading screen-based text and/or using keyboards efficiently, an insistence on only typed/word-processed assignments rather than allowing handwritten work will place that student at a strong disadvantage and affect not only the time taken to fulfill assignments but increase their stress and TS symptoms and risk adversely affecting their quality of work and resulting marks.
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Lighting can be be perceived as overly bright or flickering due to mains electricity frequency or low refresh rates on TVs and computers. Low-latent inhibition may result in sensory clutter, in which the environment is perceived in unusual detail leading to an impaired ability to focus on salient features and an over-awareness of less relevant details. This has, potentially, the consequence of an 'attention deficit' where attention is less focused due to distraction and sensory cluttering - not seeing 'the wood for the trees.'
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Research indicates that in Tourette syndrome it is not a problem with the apparatus of sensory reception (ears, eyes, tactile sense etc.) but a consequence of central-processing dysfunction within the brain which leads to impaired sensory integration and altered perception.
It is becoming apparent that many aspects of TS symptomatology involve inhibitory dysfunction which reduces 'control' or selectivity of neural activity. Where most people can filter out 'unwanted' incoming information to an appropriate/manageable level, this may be impaired in TS.
In TS and TS-related obsessive-compulsive symptoms, this dysregulation may also involve thoughts/cognition - repetitive and intrusive thoughts can be experienced which are poorly controlled and are not consistent with their own preferred thoughts or personality or that cause distraction and 'interfere' with other cognitive processes. Some experience thought-blocking or speech-blocking where fluency is disrupted. Motor and vocal tics may be another, often very outward, expression of neural inhibitory dysfunction or dysregulation. Some studies indicate a possible defect in neuronal-gating in TS, which normally would serve as an inhibitory 'valve' controlling or selectively filtering signal-transmission through neurons (nerve cells).
TS: Educational Considerations
A tendency for autistic individuals to avoid eye contact (the oft used phrase here is 'look into') has been discussed and researched widely. There is much confusion about the causes of this behaviour but too frequently an unwillingness to listen to what those with the disorder say about it. A tendency to lip-gaze in some individuals with TS has been noted, a behavior also often present in ASD.
In autistic subjects, when eye movements and gaze direction are tracked digitally, there is a tendecy to focus more on the mouth than the eyes during social interaction. A significant part of this mouth-directed visual preference could be due to a need to watch the speaker's lips to improve understanding of speech due to difficulties with comprehension through auditory sensory input alone. This is of course well-known among people with deafness. An individual who shows a reluctance to look into the eyes, is therefore, not always only shying away from 'social contact' as is often thought (because they are autistic).
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In autism there do seem to be difficulties with the intensity of mutual visual-gaze which appears to cause an intense emotional response for some and that some individuals with sensory integration problems find the continual movements of other's eyes to be a source of sensory stress. Avoidance of eye-gaze in TS/SPD may be, in part, a consequence of increased lip-gazing.
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Many teachers will persistently tell an autistic child "look into my eyes when I'm talking to you" and further compound the transgression by pointing to their own eyes with two fingers! It may not be helpful to the SEN child with these difficulties to undergo considerable effort and frustration in attempting to comply with a seemingly pointless and inconvenient requirement, perhaps only so we are able to say 'look how he/she is progressing' they have much better eye contact now!
There was once an insistence in many schools for the deaf, that using sign language should be forbidden (this was almost universal at one time) in order to 'encourage' the child to learn to communicate verbally. This was purely for the convenience of 'hearing' individuals who did not wish to learn sign language or were unwilling to provide the necessary accommodations to properly 'include' deaf children. For many deaf children this removed the best channel for effective development of communication and learning with the result that many deaf children became severely 'learning delayed'. More importantly, for many, they did not develop speech and language abilities sufficiently during the normal period of early neuro-developmental plasticity of the brain (to language development) which, once passed, precludes their fully achieving their original language potential and thus experienced an impairment throughout their lives. Sign-languages use the same area of the brain as spoken language and hence promote it's neural development.
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​An aspect of sensory processing difficulties in children (and older students) with TS or ASD (also ADD), in the learning environment, is that they may find it difficult to hear speech clearly when exposed to additional ambient background noise, music or distracting visual stimuli (this may also apply to tactile and other sensory modalities). Conversely they may not be able to read effectively if you are talking or process visual input efficiently. Concerns regarding the over-use of IT and audio-visual teaching aids raises specific concerns in this regard. Multi-media presentation of learning materials can represent a 'sensory onslaught' to some individuals.
Another oft-ignored problem is the use of low-frequency (50-60Hz) flourescent lighting in the teaching environment or at home. To an individual with SP difficulties these can represent something akin to a disco stroboscope as they can often perceive the flickering. The same problem arises with using many desktop computer screens that contain flickering light sources. Television with low screen refresh rates may also represent a source of sensory over-stimulation. Experiments in schools that involved removing standard flourescents and replacing them with high-frequency (300Hz) versions resulted in improvements for many SEN children but, more remarkably, improved 'behavioural' problems in the non-SEN children also! For children with these difficulties, replacing the lighting in the area where they study (and live) may bring benefits. Incandescent lights (with filament bulbs) are becoming rarer but are an option in bedrooms and for desklights for homework etc.
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The impact of newer LED lighting has not been properly evaluated in this context.
For those with TS and sensory problems computers may not always help all areas of difficulty. Unlike the difficulties associated with dyslexia and dyspraxia which can make handwriting a significant challenge and also result in poor legibility, some students with sensory processing issues may be better able to undertake handwritten assignments. Keyboards in particular may present their own difficulties. Unlike handwriting where the action is direct - the text appears immediately at the tip of the pen precisely where they are looking, keyboards involve selecting and pressing multiple keys in a different position and plane to the text being produced. TS brings it's own unique problems to word-processing. In addition to sensory difficulties and distractive or cognitive interference due to tics, many with TS have complex tics and related symptoms that are provoked or exacerbated by a "tray full of plastic buttons" and a mouse and also the complexity of the many buttons and menus of the software itself.
Most students do not learn to touch-type, especially boys. For the non touch-typist, the querty keyboard layout involves moving, physically and visually, from one side to the other. Some complain that it would be easier if the letters were in alphabetic order and so easier to find! This is particularly problematical in single or two-finger typing. Querty keyboards were actually designed to slow down typing speed for the earlier mechanical machines that had a capability limited by mechanics.
Laptop computers and tablets are becoming available with displays with reduced flicker (these vary and have differing light sources and screen refresh rates). Higher definition displays, importantly, can help reduce pixel-awareness and hence visual information-intensity and perceptive clutter. High-definition tablets have been used for information processing, with success, in a number of neuro-developmental disorders including autism. Newer high definition models such as the iPad retina are more costly.
Frequently, TS individuals experience an increase in the severity of their tics when using computer screens and particularly when watching television. This is reported by a high percentage of TS patients.
Normal computer monitors are backlit, so reducing reading efficiency (sometimes severely) when sensory difficulties are present. This applies similarly to backlit tablet devices most of which have LED screens. In these circumstances they may be better able to read from paper or printed media and from ePaper based eReaders (e.g Kobo, Nook and Kindle) which use a non-illuminated background and well-defined eInk text. The new generation of eReaders with built in illumination can also give rise to similar problems with text being more difficult to read with the light is switched on or if too bright - in this case an external light source or front-lighting is preferable. Higher definition eInk devices are becoming available but at significantly higher cost. None of these devices currently permit the use of an external keyboard or have adequate word-processing software. A low-cost experimental eInk device that provides this capability is currently under development.
A particularly problematic form of sensory dysfunction, involves altered proprioception (joint-position, muscular tension/movement sense). This may cause impairment of fine-motor skills and hence difficulty not only with writing/typing but also any activity involving manual dexterity. Gross-motor skills and gait may be affected in some. Conversely however many individuals with TS can have quantifiably enhanced reaction times with increased speed and accuracy of movement. This may explain why some with TS are outstanding athletes, dancers, musicians and, some may think surprisingly, surgeons.
Vestibular sensory input is derived from the inner ear and carries information relating to the position or movement of the head. This is integrated with other sensory input such as visual, auditory and proprioceptive information. Problems with this type of processing, which do occur in TS and ASD, can give rise to impairments involving balance, orientation, motor performance and gait.
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Prosopagnosia is a type of sensory processing dysfunction that reduces a person's ability to recognise faces. This may be so even when the person being 'encountered' is well known to them. It is often referred to as face-blindness and can have obvious negative consequences in social interaction and professional life. The difficulty can be specific to facial recognition while the ability to recognise other 'objects' or patterns is intact. Prosopagnosia occurs for varying reasons in people without other neurological disorders but has been reported by many with ASD or Tourette syndrome.
For the child with Tourette Syndrome their sensory difficulties are compounded immeasurably by having to suppress or control their tics during class or examinations where they are expected to sit still and quietly for extended periods, a 'tall order' in itself. They will often concentrate so hard on achieving this that they will not be able to focus their attention on the task at hand, read written material efficiently or listen to the teacher effectively or more importantly perform academic tasks to their best ability. They will, frequently, incur some degree of academic deficit as a result.
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Other topics/tags relevant to this article: non-verbal learning difficulties, low-latent inhibition, obsessive thought behaviours, complex tics, sensory defensiveness
​Tourette syndrome Symptomatology:
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