The brain continuously receives input from the environment and the body, a neurological process known as sensory processing. This process typically organizes and interprets sensations to allow for smooth, functional interaction with the world. When the central nervous system struggles to efficiently manage these sensory signals, the result is Sensory Processing Disorder (SPD). This difference in processing leads to uncoordinated or unexpected behavioral responses to everyday stimuli. Clinical understanding organizes this condition into three distinct patterns.
Understanding the Foundation of Sensory Processing Disorder
Sensory Processing Disorder is a neurological challenge impacting a person’s ability to receive, organize, and use sensory information effectively. It is a difference in how the nervous system functions, creating a “traffic jam” that prevents appropriate responses. The clinical framework used to categorize these difficulties was developed by Dr. Lucy Jane Miller and the STAR Institute. This model separates the disorder into three main patterns based on the primary area of dysfunction: modulation, discrimination, or motor function. SPD is considered a distinct diagnostic entity, focusing specifically on the inefficiency of sensory integration.
Sensory Modulation Disorder
Sensory Modulation Disorder (SMD) is the most common pattern, involving difficulty regulating the intensity, duration, and nature of responses to sensory input. Individuals with SMD struggle to maintain an optimal level of arousal, leading to responses that are disproportionate to the stimulus. This pattern is divided into three distinct subtypes based on the individual’s reaction to sensation.
Sensory Over-Responsivity (SOR)
In SOR, the nervous system perceives ordinary sensations as too intense, leading to a quick and exaggerated reaction. A person with SOR might find the sound of a hand dryer painful or a clothing tag unbearable. This often results in withdrawal or avoidance behaviors, leading these individuals to be described as sensory avoiders.
Sensory Under-Responsivity (SUR)
SUR is characterized by a muted or delayed response to sensory input. Individuals with SUR may appear sluggish, withdrawn, or oblivious to their surroundings. They may fail to notice pain or extreme temperatures, requiring significantly more intense or prolonged stimulation to register a sensation.
Sensory Seeking/Craving (SS)
This subtype involves an intense need for large amounts of sensory input. These individuals actively seek out sensations by constantly moving, spinning, crashing into objects, or touching everything. This seeking behavior does not effectively organize or regulate the nervous system, and the person may appear disorganized despite high activity levels.
Sensory Discrimination Disorder
Sensory Discrimination Disorder (SDD) involves issues with the quality of sensory processing. The brain struggles to accurately interpret the subtle characteristics of sensory input, focusing on the “what” and “where” of a sensation rather than the strength of the reaction. SDD can affect any of the eight sensory systems:
- Visual
- Auditory
- Tactile
- Gustatory
- Olfactory
- Vestibular
- Proprioceptive
- Interoception
Auditory discrimination difficulties, for example, make it challenging to distinguish between similar-sounding words, hindering the ability to follow verbal directions. In the tactile domain, a person may struggle with stereognosis—identifying an object by touch alone, like determining a coin’s value in a pocket. Proprioceptive discrimination issues affect body awareness, making it difficult to grade force or apply the correct pressure for tasks like writing.
Sensory-Based Motor Disorder
Sensory-Based Motor Disorder (SBMD) is defined by difficulties with motor skills arising from the inaccurate processing of sensory information, particularly from the vestibular and proprioceptive systems. This pattern manifests as disorganized motor output. The muscles and joints are physically healthy, but the brain struggles to use sensory information to plan and execute movement. SBMD is divided into two distinct subtypes: Postural Disorder and Dyspraxia.
Postural Disorder
Postural Disorder involves a challenge in maintaining body position, stability, and balance against gravity. This is due to poor processing of vestibular and proprioceptive signals. Individuals often exhibit low muscle tone and poor core strength, leading to slumping or leaning on furniture for stability. They may fatigue quickly and struggle with movements requiring standing on one foot or walking on uneven surfaces.
Dyspraxia
Dyspraxia, also known as developmental coordination disorder, is a specific difficulty with motor planning. This involves problems with ideation, sequencing, and execution of unfamiliar motor tasks. A person with dyspraxia may appear clumsy and struggle to learn new skills like riding a bike or tying shoes. This is a neurological difficulty in organizing the body’s movements in response to environmental demands.
Next Steps: Seeking Diagnosis and Intervention
Recognizing sensory processing challenges is the initial step toward finding support. If these difficulties interfere with daily functioning, an Occupational Therapist (OT) specializing in sensory integration is the appropriate professional. A comprehensive evaluation by an OT determines the specific pattern and subtypes of SPD, guiding a personalized intervention plan.
The most recognized approach is Occupational Therapy using an Ayres Sensory Integration (ASI) approach. This therapy involves structured, play-based activities within a sensory-rich environment. The goal is to help the nervous system process input more efficiently, enabling more adaptive and functional responses in daily life.