The theory of Sensory Integration (SI) proposed by Jean Ayres explains that how the senses are processed will affect other aspects of child development, such as social, emotional, physiological & neurological development. She hypothesised that motor learning was based on sequential developmental stages and could only be achieved if the necessary incoming sensations were received by the body.
There are two main sensory processing pathways in the body, the Dorsal Column Medial Lemniscal pathway (DCML) and the Anterolateral system (AL). [AL is sometimes called the Spinothalmic pathway.] These transmit the information received by the sensory systems from the body to the brain and vice versa.
- receptors respond to mechanical stimuli
- neurons transmit tactile, vibration, pressure, proprioceptive information
- receptors respond to rough touch stimuli (rubbing, squeezing, pinching), tissue damage stimuli, temperature including neutral warmth, tickle sensation
- neurons transmit pain, temperature and crude touch information (=detection of an object but not further info such as movement)
There is also the Vestibular pathway which controls the movement of the head, coordination of the eyes, balance, and detection of speed and direction of movement. The Trigeminothalamic pathway deals with touch, temperature and pain from the face area.
There are eight sensory system in the human body. The Auditory system detects and localises sound; and the Visual pathway detects and processes light into images. This is is done by receptors called cones in day vision, and rods for night vision. Olfatory is smell; Gustatory is taste, and Interoception which is awareness of internal body sensations such as hunger, thirst, need to urinate or a pounding heart. The main systems that Jean Ayres focuses on in SI theory are Vestibular which deals with balance and your position in space; Proprioception which processes the movement and orientation of your joints & limbs; and also Tactile which deals with touch.
Sensory Processing Disorder (SPD)
People with SPD do detect stimuli (unlike someone who is eg deaf), but their sensory pathways are unable to organise it into an appropriate response. This causes them to have abnormal responses to normal stimuli.
They therefore perceive the same sensory information in a different way to the majority of people. Some problems with sensory processing can include under-responsiveness to sensation, sensory over-responsiveness or aversive responses to normal movement/gravitational insecurity.
Examples of symptoms associated with problems are:
- Over-responsiveness– a flight or fight response to normal intensity stimuli, where the sympathetic nervous system is reacting unnecessarily. May recoil from being touched or cover ears/eyes to block out sounds/sights.
- Under-responsiveness– a disregard for sensory input from the environment. Could appear clumsy, withdrawn, uncoordinated, may not notice pain or too hot/too cold.
Bundy A, Lane S, Murray E and Fisher A (2002) Sensory Integration: Theory and practice (2nd edition) Philadelphia: F.A. Davis.