Understanding Sensory Processing Differences
Sensory processing and integration are complex neurodevelopmental functions that allow children to regulate, perceive, discriminate, and use sensory input experienced from the environment and their bodies to respond, learn, and adapt daily effectively. Sensory processing disorder (SPD) has been described as a distinct neurodevelopmental disorder in the literature (Schoen et al., 2009; Jorquera-Cabrera et al., 2017; Crasta et al., 2020). It now has been recognized in the most recent version of the diagnostic classification of mental and developmental disorders of infancy and early childhood-revised (DC: 0–5, zero to three). Sensory processing abilities develop naturally and play essential roles in child learning, behavior and emotional regulation, motor development, and task performance. Sensory processing disorder has been defined as the brain's inability to organize sensory input for appropriate use. As stated in the DC: 0–5, zero to three-manual, SPD is diagnosed based on difficulties in detecting, modulating, interpreting, or organizing sensory stimuli to the extent that these deficits impair daily functioning and participation. However, the question of whether deficits in sensory processing represent the symptoms of another disorder, such as autism spectrum disorder (ASD), developmental coordination disorder (DCD), or SPD is its distinct condition remains (Borkowska and Sklodowska, 2017).[1]
The American Academy of Pediatrics [AAP], 2012 recommended that SPD generally should not be diagnosed citing that there is no universally accepted framework for the SPD diagnosis. Although sensory processing problems were recognized as important to identify and address, the AAP stated that there lacked evidence to solidly demonstrate that children presenting with sensory-based problems have an actual "disorder" of the brain's sensory pathways. They concluded sensory processing deficits were likely associated with other developmental and behavioral disorders. This view, however, does not account for children who present with sensory processing deficits affecting their daily life who do not meet the diagnostic criteria for any other disorder[1].
Experts in the field characterized tSPD as having three main types: [1]
- sensory modulation disorder (SMD): Sensory modulation refers to the ability to notice and react to, regulate, adapt to, and grade responses that are appropriate to the sensory situations experienced in daily life.
- Sensory discrimination disorder (SDD); Sensory discrimination disorder refers to problems with accurately perceiving and interpreting sensory information coming in or experienced from one or more of the sensory systems (Miller et al., 2007; Lane and Reynolds, 2020; Parham and Mailloux, 2020). Discrimination abilities allow for recognizing qualitative and quantitative sensory features and differences among various objects and experiences processed through the sensory systems. People with this type can register sensory stimuli. However, appreciating or detecting the qualities of a given stimulus is a challenge and can occur with one or more sensory systems.
- Sensory-based motor disorder (SBMD), is further divided into subtypes (Miller et al., 2007).
- Sensory over-responsivity (SOR): Atypical behaviors associated with SOR are characterized by intense, exaggerated responses to sensory events that most children do not perceive as negative or obnoxious, often resulting in withdrawal and avoidance behavior.
- Sensory under-responsivity (SUR): Atypical behaviors with SUR include muted or slowed responses to sensory experiences, often with an apparent lack of awareness, lethargy and/or indifference, or diminished responsivity.
- Sensory craving (SC); is sometimes referred to as sensory seeking. Atypical behavior associated with SC includes a need for more intense sensory input than what one would typically want, or that would naturally occur, often manifesting as inappropriate, disruptive, disorganized and/or risky behavior (Miller et al., 2007, 2017; James et al., 2011; Schoen et al., 2014).
Prevalence estimates of iSPD range from 5 to 16% of children in the general population, while 60–90% of children with coexisting neurodevelopmental conditions such as autism spectrum disorder (ASD) have been estimated to have sensory problems (Ahn et al., 2004; Ben-Sasson et al., 2009; James et al., 2011; Galiana-Simal et al., 2020; Jussila et al., 2020). Mulligan et al. (2019) reported that 20% of the children in their sample had a co-occurring disorder while the remaining 80% had not been diagnosed with another neurodevelopmental disorder. [1]
Unfortunately, there are a limited number of diagnostic assessment tools available to evaluate the sensory processing abilities of children, and no tool is available for explicitly identifying and measuring the SPD types as described by Miller et al. (2007).[1]
Research evidence is building regarding how sensory processing deficits manifest within various populations and how iSPD may be differentiated among children with other neurodevelopmental conditions. As high as 90% of children with ASD have sensory processing difficulties, with the most common pattern of SPD being the SOR modulation subtype (Schoen et al., 2009; Tavassoli et al., 2014; Tomchek et al., 2014; Little et al., 2018). Children with ASD were more under-reactive to auditory stimuli but over-reactive to taste and smell.
Sensory under-responsivity has been associated with depressive symptoms and internalizing behaviors, while externalizing behaviors have been more related to sensory craving, and over-reactivity. Studies demonstrating how the symptoms of children with iSPD differ from those seen in children with other neurodevelopmental conditions, including ADHD and ASD are particularly relevant for supporting SPD as its own diagnostic entity. Miller et al. (2012) compared clinical assessment findings among samples of neurotypicals, children with ADHD, those with SMD, and those with dual diagnoses. All clinical groups had significantly more sensory, attention, activity, impulsivity, and emotional difficulties than typical children. [1]
[1] Mulligan S, Douglas S and Armstrong C (2021) Characteristics of Idiopathic Sensory Processing Disorder in Young Children CC BY
