Sensory Processing Disorder (SPD) is a complex neurological disorder characterized by the brain's impaired ability to effectively organize, integrate, and interpret sensory information from multiple modalities, including tactile, auditory, visual, olfactory, gustatory, and vestibular senses. This dysfunctional sensory integration manifests in difficulties in accurately perceiving, prioritizing, and adaptively responding to stimuli in one's external environment. The resultant sensory dysregulation significantly impacts an individual's daily functioning across a variety of contexts—ranging from academic and occupational settings to social interactions and interpersonal relationships. As a consequence, individuals with SPD often experience heightened challenges in effectively navigating the complexities of day-to-day life, potentially complicating their emotional well-being and overall quality of life.

History of SPD

Sensory processing disorder is a unique type of abnormal functioning that was first outlined by occupational therapist Anna Jean Ayres. Ayres developed a conceptual model for this disorder, initially named Sensory Integration Dysfunction, based on six sets of data analyses involving children with learning and perceptual motor disabilities, as well as typically developing children.

Ayres identified different subtypes of sensory issues:

1. Dyspraxia: This involves difficulties in motor planning, especially tied to the vestibular system and proprioception, which relate to balance and the sense of one's body position in space, respectively.
2. Poor Bilateral Integration: This involves the ineffective use of both sides of the body at the same time.
3. Tactile Defensiveness: This subtype refers to an aversive response to touch-related stimuli.
4. Visual Perceptual Deficits: This includes difficulties in perceiving forms and spaces, as well as problems with visual-motor coordination.
5. Somatodyspraxia: Similar to dyspraxia, this also involves poor motor planning but is attributed to unreliable information from the tactile (touch) and proprioceptive (body position) systems.
6. Auditory-Language Problems: Issues related to auditory processing and language comprehension.

It should be noted that both visual perceptual and auditory-language deficits were believed by Ayres to have a strong cognitive aspect and only a weak link to sensory processing issues, which is why they are not often considered core deficits in various models of sensory processing.

In a study conducted in 1998, Mulligan confirmed the presence of these patterns through a different type of data analysis known as confirmatory factor analysis.

Another conceptual model was proposed by Dunn, who categorized sensory issues based on two criteria:

1. Response Type: Whether the individual's response to sensory stimuli is passive or active.
2. Sensory Threshold: Whether the individual has a low or high sensitivity level to stimuli.

Dunn’s model identifies four subtypes:

1. High Neurological Thresholds
   • Low Registration: These individuals have a high tolerance for sensory stimuli but do not actively engage with their environment.
   • Sensation Seeking: These individuals also have a high threshold but are active in seeking sensory-rich experiences.
2. Low Neurological Threshold
   • Sensitivity to Stimuli: These people have a low tolerance and find sensory input distracting and unsettling, although they don't necessarily avoid it.
   • Sensation Avoiding: These individuals have a low tolerance and take active steps to avoid sensory input, often acting as their own regulators of sensory exposure.