Although ASI theory and practice are complex and integrated, the author displays SI in three levels in Figure 19.1, in an attempt to construct it in a more comprehensible manner. Figure 19.2 divides the levels of SI further in an attempt to explain the different levels (processes) involved in SI that support function. Although it is staggered hierarchically, these processes are interdependent and cannot always be separated as it is done theoretically.

The first level in Figure 19.1 represents registration, arousal and modulation which are viewed as overarching modulation although it can be debated whether registration is part of modulation. For sensory information to be modulated, it needs to be registered, and for the purpose of this model, registration of sensory information is seen as the first part in the process of modulation. When sensory information is modulated, it contributes to the ability to focus on and concentrate and engage in those activities that are in the foreground at a given moment in time.

The second and next level of SI is that of discrimination and perception that provides information on spatial and temporal qualities of sensory information received. Discrimination and perceptual abilities allow for a ‘higher’ and more involved level of participation in activities as cognitive involvement is also required. An example would be ‘what am I touching?’, ‘what are the qualities of the object that I am touching?’ and also ‘when did I touch it?’ and then ‘how do I need to react?’ Cognitive recognition, meaning and decision-taking now form an important part of the process.

Following on that, is the third level that represents refined use that is possible when integration of sensory information contributes and supports motor skills and praxis. On this level, more advanced motor and cognitive functioning are required for successful interaction and engagement in activities. The requirements for successful participation also become more complex. An example of skilled action could be the ability to ride a bicycle, and that of praxis the ability to perform new motor actions with a fair amount of success, for example, to attempt to jump with a skipping rope for the first time. As soon as the action becomes learnt because of practice and repetition, it becomes a skill and no longer requires praxis abilities.

All three levels of SI processes play an important role in occupational performance.

In an effort to understand the contribution of SI to function and dysfunction, the levels are further explained in Figure 19.2.

Schaaf et al. in Kramer and Hinojosa (2010, p. 99) state that although the theory of SI has expanded and evolved over the years, the ‘basic premise that the sensory systems and the integration of their inputs are important contributors to learning and behaviour remains the key postulates’ within the theory of SI.

Sensory registration (see level 1 of Figure 19.2)

Sensory registration refers to the point where the brain registers sensory information/becomes aware of incoming sensory information. According to the research done by Dunn (1999), the point where the brain registers sensory information is referred to as the neurological threshold. Neurological thresholds are viewed to be on a continuum, where on the one side of the continuum, a low neurological threshold would imply that very little sensory information is needed before the brain registers it, whereas on the other side, a high neurological threshold would imply that a lot of sensory information is needed before the brain registers it. Neurological thresholds can differ within each sensory system with the implication that an individual’s sensory profile is in a certain sense like a fingerprint. No two individual’s sensory profiles are exactly the same, but research has indicated that there are typical behaviours linked to neurological thresholds. Low neurological thresholds can result in avoidant or sensitive behaviours pertaining to that specific sensory system, and high neurological thresholds can result in poor registration or seeking/craving behaviour. An example of this could be that a child could crave for movement activities due to the high neurological threshold for movement, but would not want to play in a group on play equipment due to a low neurological threshold for auditory information. All the screaming and shouting bothers the child, and playing on play equipment alone or with only a few friends present would be preferred.

Sensory modulation (see level 1 of Figure 19.2)

Sensory modulation refers to the brain’s ability to adapt to sensory information (from inside the body or from the environment) in such a way that it supports optimal engagement in meaningful daily activities. It includes the brain’s ability to habituate to non-threatening/unimportant sensory information or sensitisation to threatening/harmful sensory information. Modulation is also a brain function that needs to happen within all the different sensory systems. Sensory modulation plays an important role in daily functioning especially in terms of the ability to focus, concentrate and be ready for engagement in the task at hand.

Adequate modulation of sensory information supports the capability of the individual to sustain engagement in activities despite variability within the body and/or the environment (Schaaf et al. in Kramer & Hinojosa 2010, p. 112), and it is thus of great importance in the learning process of a child. Sensory modulation also supports optimal levels of arousal to engage in activities. It further contributes to not only stability in emotions but also impacts on behaviour.

Dunn’s Sensory Profile (1999) described the neurological thresholds and how they contribute to modulation and behaviour. She also describes the four different sensory profiles that have emerged from her research, namely, low registration and sensory seeking (SS) (representative of high neurological thresholds) and sensory sensitive and sensory avoiding (representative of low neurological thresholds).

The Sensory Profile Measure (SPM) is the other well-researched sensory processing measurement instrument that is used in practice (Parham et al. 2006). It measures sensory processing, praxis and social participation at home, school and community settings and is done according to structured and unstructured observations. Dysfunctions are described according to the work of Miller et al. (2007), namely, sensory over-responsivity (SOR), sensory under-responsivity (SUR) and SS.

Disorders in sensory modulation are reflected in behaviour. Disorders can be present in one or more of the sensory systems and can involve responses from internal or external sensations.

The common grounds between the works of Dunn (1999) and Miller et al. (2007) are high neurological thresholds and under-responsivity and low neurological thresholds and over-responsivity. The ‘category’ of SS is described in the work of both authors and is seen by researchers as a need for sensory input that is much more than that of the typical child.

Tactile defensiveness is one of the SI dysfunctions that is well described in the literature. Tactile defensiveness is linked to poor limbic or reticular processing within the brain and fight-or-flight reactions that are elicited by tactile sensation that others would consider non-noxious. This type of dysfunction is attributed to the anterolateral system of the central nervous system. This system is responsible for the mediation of pain, crude touch, light touch and temperature. Most of the fibres of the anterolateral system terminate in the reticular formation (Bundy et al. 2002). The reticular formation is responsible for arousal, emotional tone and autonomic regulation. Projections are sent from the reticular formation to the thalamus. The thalamus is also an integrating centre that assists with the coordination of information. From there, information is relayed to the cortex and the limbic system. The limbic system is responsible for emotional tone and motivational aspects of behaviour, arousal, attention and regulation.

Defensiveness can occur in any of the sensory systems, and sensory defensiveness is an over-response to sensory stimulation causing the child to experience anxiety, fear and aggression. The sensory defensive child thus avoids these sensory stimulating activities.

A type of sensory modulation dysfunction (SMD) that was already described by Ayres (1972) is that of gravitational insecurity. The child becomes fearful when their feet leave the ground or on an unstable, raised surface or when their head is tilted into ‘unfamiliar’ positions, especially into backward space. May-Benson and Koomar (2007) have done further work on this type of SI dysfunction. Another type of dysfunction, described by Ayres, is that of intolerance to movement where the child is disorganised by any movements that are unfamiliar. Although both dysfunctions are related to low neurological thresholds (over-responsivity) within the vestibular system, the difference is that the child that experiences problems with gravitational insecurity likes movement but his/her body needs to be secure in terms of gravitational pull. The child with aversion/intolerance to movement problems dislikes movement and is in general overwhelmed by movement.

Children experiencing SMD can demonstrate hyper-responsivity, hypo-responsivity or fluctuations in response to sensory stimuli. Children with SMD are not only restricted in terms of processing sensory information but also in terms of their ability to attend and concentrate, their emotional control and activities of daily living such as toileting dressing, feeding, bathing and socialising. Their levels of arousal do not only impact on their ability to engage in occupations, but it also influences their emotions. Emotions that are seen include anxiety, lability, fear, aggression, depression and hostility.

Sensory discrimination and perception (see level 2a and level 2b of Figure 19.2)

Sensory discriminatory abilities are abilities that are supported by and dependent on all the different sensory systems. Discriminatory abilities allow for the individual to ‘interpret and differentiate between the spatial and temporal qualities of sensory information’ (Schaaf et al. in Kramer & Hinojosa 2010, p. 113). An example of discriminatory abilities within the tactile system would be when a child is able to identify where he/she has been touched, what is it that touched him/her and when did it touched him/her. In the process of discrimination, past experiences and memories need to be utilised to form associations about the spatial and/or temporal qualities of what he/she is experiencing and then act on that information. Sensory discriminatory abilities add meaning to sensations and support the forming of perceptions.

Discrimination within the auditory system can vary from basic discrimination abilities such as knowing from which direction a sound came to abilities such as a soft or a hard sound or hearing a ‘b’ or ‘d’.

Visual discrimination is the foundation of form and space discrimination and in the development of visual perception skills and visual-motor skills.

Within the vestibular system, there are two discriminatory processes occurring:

1. Otolithic processing that is concerned with the pull of gravity and provides types of discrimination that has to do with postural accommodations, together with where the body is in space when vision is excluded, for example, whether vertical or horizontal when in a swimming pool.
   
2. Semicircular canal processing that is concerned with the detection of head movements through space. This type of processing contributes to three-dimensional (3D) spatial experiences and spatial orientation.

Proprioceptive discrimination is concerned with aspects where muscles, tendons and joints are working and where the brain needs to decide on actions such as adjusting posture when sitting in a chair, how hard to press when writing with a pencil or how far to stretch the elbow to pick up something.

Discrimination within the tactile system is complex and can range from identifying where touched to manipulation of a small bead to be able to thread it. Within the mouth area, tactile discrimination ranges from the food’s texture to finding a small piece of bone in food that is in the mouth.

Taste and smell discrimination also ranges from basic discriminatory abilities to very refined discrimination, memories often playing an important role in function. A child who is a fussy eater and who has had a bad experience with the taste and smell of a certain food will become anxious just by visually seeing the food.

From the aforementioned, it is clear that discriminatory functions within the different sensory systems can vary from simple to very refined and these functions also evolve with development. Discriminatory functions can depend on only one sensory system but can also be dependent on combinations of sensory systems such as the visual and vestibular systems that together provide a stable visual field during head movements. Postural–ocular control involves the activation and coordination of muscles ‘in response to the position of the body relative to gravity and sustaining functional positions during transitions and while moving’ (Schaaf et al. in Kramer & Hinojosa 2010, p. 114). Here, the combination of the visual, vestibular and proprioceptive systems supports function.

Poor processing of vestibular–proprioceptive input is believed to impede the development of postural and ocular control (Bundy et al. 2002). A postural–ocular disorder is described as the behavioural manifestation of a vestibular–proprioceptive processing disorder and is hypothesised to be the basis for the bilateral integration and sequencing (BIS) disorder. Difficulties with postural-related demands like righting and equilibrium reactions, flexion and extension postures, postural stability and lateral flexion and rotation are experienced by these children. Poor ocular control impacts on activities where a stable visual field is needed. When following an object with the eyes, visual fixation is needed with dissociation of the eyes from the head movements. Poor ocular control will also delay the development of form and space perception and eye–hand coordination.

In the literature, it is assumed that posture is the observable manifestations of vestibular and proprioceptive processing. There are also schools of thought that postural dysfunctions reflect the basis for deficits in BIS and sometimes for somato-dyspraxia (Bundy et al. 2002). Observable postural indicators include extensor muscle tone (observed in a standing position), prone extension, proximal stability, ability to move the neck into flexion against gravity (part of supine flexion), equilibrium and post-rotary nystagmus. This cluster of indicators is referred to in some cases as ‘postural–ocular’ components. Postural control and stability are usually problematic for these children described by Bundy et al. (2002), and they experience problems such as maintaining their posture and relying on their environment to support them with the postural demands. These children will lean against a wall when in the upright position, curl their legs and feet around chair legs or assume a ‘lying’ position in a chair.

Motor skills (see level 3 of Figure 19.2)

Although postural–ocular abilities are seen as discriminative abilities, it is difficult to draw a line where the abilities end and motor skills start. More advanced postural–ocular abilities such as those used when riding a bicycle can also be viewed as skill.

There is currently a debate on whether or not BIS are motor skill functions or functions supported by praxis abilities. The latest research indicates that a BIS dysfunction is a separate type of dysfunction to the visuo- and somato-praxis factors that are identified in current research (Mailloux et al. 2011; van Jaarsveld et al. in press). There is however consensus on what these functions entail and what it allows for:

• The effective use of the two sides of the body whether on a level of navigating the body through space or on a more skilled level
  
• Similar use of the two hands, skilled in each, for example, skilled hand function and good hand function relative to hand skill
  
• Cooperative use of hands together
  
• Symmetrical rhythmic movements of arms, hands and feet
  
• Coordinated bilateral asymmetric movements of limbs
  
• Ability to coordinate rhythmic sequences of movements

Children experiencing problems with BIS will have difficulties in using the two sides of the body in a coordinated manner, crossing of their midline and adequate establishment of dominance. Difficulties with the sequencing of motor actions, and specifically anticipatory projected movements, can be experienced. Anticipatory projected actions are very much feedforward dependent, meaning that they depend on past experiences and the ability to anticipate what is coming. Vestibular and proprioceptive system functions are the basis for adequate BIS actions, and the visual system also plays an important role in directing motor actions (Bundy et al. 2002). Children with BIS dysfunctions also suffer emotionally because of their inability to experience success. They usually have a low self-esteem and their motivation is low.

In terms of other motor skills, many examples of it are to be found in the literature. The important question is whether a child can perform skilled motor actions related to his/her age norm and to what extent it influences their function and engagement in occupations.

Praxis (see level 4 of Figure 19.2)

Ayres defined developmental dyspraxia as a ‘motor planning disorder’ and as a ‘disorder of sensory integration interfering with ability to plan and execute skilled or non-habitual motor tasks’ (Ayres & Cermak 2011, p. 51). Praxis was also described by Ayres (1989) as the process that includes conceptualisation or ideation, motor planning and execution of a novel or new motor action. Praxis abilities are crucial in successful interaction with the environment to execute action plans and adapt/correct motor actions to achieve the desired outcomes (Schaaf & Smith-Roley 2006).

Ayres (1989) stated that the conceptualisation or ideation part of the praxis process is a cognitive function, partially dependent on the integration of sensory information. She also described that children’s knowledge of objects and their affordances (potential use) are dependent on the purposeful use of the body in activity and with objects in the environment. More work on the ideational component of the praxis process was done by May Benson and Cermak (2007) who developed the Test of Ideational Praxis (TIP). They also state that ‘ideation underlies planning, sequencing and organization of actions and ideational abilities may influence how a child engages in activities and occupations’ (May-Benson & Cermak 2007, p. 152). Difficulties with ideation will present itself in a child’s inability to know or make use of the affordances of objects in 3D space.

Visuo-praxis is mainly dependent on the visual system but also relies on the vestibular system in terms of providing a stable visual field. Somato-praxis is dependent on the support of the proprioceptive and tactile systems. Visuo- and somato-dyspraxia have been described in Ayres’ original work on the Sensory Integration and Praxis Test (SIPT). This is also one of the ‘clusters’ of dysfunctions that are described in the SIPT Manual (2004). These two types of dyspraxia are still seen as factors evolving from current research (Mailloux et al. 2011; van Jaarsveld et al. in press).

A child affected by poor SI abilities will experience difficulties with engaging in daily occupations during play, school, personal independence, recreation, sleep and interpersonal relations. The degree of difficulties can and will depend on the level/levels of difficulties or dysfunction as displayed in Figure 19.2 and discussed earlier. A generalised SI dysfunction is also described in research as a combination of dysfunction where a child obtains below-average scores on tests involved in BIS, visuo-dyspraxia and somato-dyspraxia.

Children with praxis dysfunction can experience difficulties with body scheme, gross and fine motor skills and oral-motor control (Lane 2012). They appear clumsy in performing motor actions, are accident-prone, mouth objects or drool and depend on using their vision for successful completion of tasks. Their behaviour varies from controlling and demanding to apathetic. Emotions that they frequently have to deal with include frustration, aggression or apathy. Academic problems such as perceptual and visual-motor difficulties (inclusive of reading and writing) can also be a direct result of these disorders.

Visuo-dyspraxia is a deficit in visual perception abilities that affects constructional skills. The visual as well as the proprioceptive systems are involved in this dysfunction. Children with visuo-dyspraxia experience difficulties with visually planning space on 3D and two-dimensional (2D) levels, which impacts on mapping space and organising their own personal space (Lane 2012). Drawing and writing are usually problematic and can be observed in their management of their working space.

Somato-dyspraxia causes children to have difficulty with motor tasks in terms of creating ideas of the how or what is possible, the planning of the actions and the execution of it. They do not receive feedback from their body and the environment after the action is completed, namely, its success or lack of success. The quality of their feedforward mechanisms is also poor (before an action is carried out, information is needed from the nervous system on the ‘how’ of the actions, e.g. in an action like catching a ball, the individual needs to get his/her limbs to a particular place in time to catch it). Any activity that depends on intact somatosensory feedback, for example, identifying shapes by touch without seeing them, will pose problems for a child with dyspraxia. Fine motor abilities are often also affected (Schaaf et al. 2010).

Functional, organised behaviour and occupation

Developmentally appropriate, organised behaviour and motor actions relative to time and space are what Ayres has termed ‘end products’ of SI. This includes the ability to concentrate, ability to organise, good self-esteem, self-control and self-confidence, academic learning abilities, capacity for abstract thought and reasoning as well as specialisation of each side of the body and the brain (Schaaf et al. in Kramer & Hinojosa 2010, p. 100). This implies that when a child is able to participate meaningfully and developmentally appropriately in daily activities and occupations, SI processes in the brain are supporting function. This is represented in the top section of the model in Figure 19.2.

Sensory integration difficulties and dysfunctions in child psychiatric conditions

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