SENSORY AND PERCEPTUAL SYSTEMS
When the neurobiology dysfunctions, it causes distortions in the sensory system of the body. Without proper neurobiological support, the ability to touch, see, and hear can be distorted. When vestibular and proprioceptive systems are inadequate, such perceptions as the ability to know where one is in space, to have a sense of time, and even to have a sense of humor can be distorted in such a way that the individual has difficulty perceiving the world correctly. Visual, auditory, and tactile responses must be able to perceive, interpret and process information so that a child can learn about the world around him/her. Without good sensory integration, learning and behavior is more difficult and the individual often feels uncomfortable about himself, and cannot easily cope with ordinary demands and stress.1
- The tactile system is responsible for some of the earliest sensations for an infant. Different kinds of receptors in the skin receive sensations of touch, pressure, texture, heat or cold, and pain. The tactile system is the largest sensory system in the body and plays a vital role in human behavior, both physical and mental. Touch sensations flow throughout the entire nervous system and influence every neural process to some extent. Without a great deal of tactile stimulation of the body, the nervous system tends to become "unbalanced." 2 This helps to explain why the tactile system is involved in most disorders of the human brain.3
- The proprioceptive system consists of sensory information caused by contraction and stretching of muscles and by bending, straightening, pulling and compression of the joints between the bones. Because there are so many muscles and joints in the body, the proprioceptive system is almost as large as the tactile system. Most proprioceptive input is processed in areas of the brain that do not produce conscious awareness. Without good automatic responses, such things as eye-hand coordination is very difficult.
- The vestibular system is the sensory system that responds to the position of the head in relation to gravity and accelerated or decelerated movement. There are two types of vestibular receptors in the inner ear in a structure called the labyrinth. One type of receptor responds to the force of gravity. The other type of receptors are in the semicircular canals in the ear. These canals are responsible for our sense of movement. The vestibular system is a unifying system. All other types of sensation are processed in reference to this basic vestibular information. The activity in the vestibular system provides a "framework" for the other aspects of our experience. Vestibular input seems to "prime" the entire nervous system to function effectively. When the vestibular does not function in a consistent and accurate way, the interpretation of other sensations will be inconsistent and inaccurate, and the nervous system will have trouble "getting started."
- The visual system has become our major means of relating to space, but the vestibular, proprioceptive and tactile systems must contribute to visual development and function. Together these systems allow us to move about in space, catch a ball, and process the visual body language of others. In order to process more abstract information such as reading, writing, spelling or calculation, such visual abilities as visual-motor, visual perceptual, visual spatial, visual memory, visual figure-ground and visual closure capacities must be in place. These capacities only work well when the tactile, vestibular and proprioceptive systems are intact.
- The auditory system has lower and higher levels of function. First, the auditory system is closely associated with the vestibular system. These systems deal with gravity and vibration. The higher functions deal with the ability to process information that is heard. This includes auditory memory, auditory sequencing, auditory discrimination, auditory figure-ground and auditory perception. Central auditory processing is a physical response which includes the ability to perceive degraded auditory signals, competing auditory signals, figure-ground and discrimination in noise.
1Ayers, A. Jean. Sensory Integration and the Child, Western Psychological Services, 1979, 191pp. p.51
2 Ibid. p. 34, 35
3 Ibid. p. 39