In 1963, Dr. Jean Ayers began using the term sensory integration.  She refined her theory through years of practice and research, based on empirical studies that had been completed indicating that neurobehavioral processing and integrating sensory inputs strongly affects development.  

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Clinicians, researchers and scholars in the field of OT have continued to explore how Ayer's work in sensory integration can be better understood and developed, leading to the new classification of sensory processing disorder (SPD).

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"Sensory processing disorder exists when sensory signals do not get organized into appropriate responses and a child's daily routines and activities are disrupted" (Miller, LJ 2006). "It is the inability to integrate, modulate, discriminate, coordinate, and/or organize sensations adaptively, leading to difficulties in learning, development, and behavior." (Kranowitz, C., 2005). Subsequently this results in difficulty understanding and responding appropriately to sensory inputs.  

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Sensory processing disorder (SPD) is an umbrella term which covers three specific classifications or subtypes of SPD; Sensory Modulation Disorder, Sensory-Based Motor Disorder and Sensory Perception/Discrimination Disorder.