Sensory Defensiveness and Sensory Integration
In an adult, there is expected be a considerable amount of mediation between stimulus and response. This develops neurologically and psychologically from birth onward in many successive layers. As a culture we emphasize the top most layer of conscious goals and intention, since we believe this is the ultimate determiner of actions.
A very fundamental layer of behavior is the connection between a sensory stimulus and a reflexive action. This layer is dominant at birth, but is still very active throughout life. At birth, most sensations cause the infant to alarm and respond with contraction and withdrawal. This is sensory defensiveness. With experience in a secure environment, sensory discrimination takes place so that by adulthood, much fewer stimuli cause contraction, and a lot more cause pleasure. For instance an adult may experience pleasure with spicy food, whereas infants will cry. The attainment of pleasure keeps the person 'working the edge of sensation,' this is the engine of the development of discrimination. Note that this process has nothing to do with cognitive assessment of the nature or meaning of the stimulus.
Different people have a difference balance between sensory defensiveness and sensory discrimination. It can be readily appreciated that high sensory defensiveness greatly interferes with smooth interpersonal interaction, since such interaction is naturally sensory rich. Chronic interpersonal defensiveness has many layers, but sensory defensiveness often starts the cascade.
To understand this further, think first of a friendly game of 'catch' with two children throwing a baseball back and forth. An early defensive reflex to the sight of the ball coming towards one is to curl into as small of a space as one can so as to avoid getting hit. A somewhat more discriminative reflex is to block or bat the ball away. An even more discriminative reflex is to desire the ball and instinctively reach for it. None of this has to do with conscious choosing. The defensive child will conscious choose to take action to catch the ball and consciously inhibit the reflex to duck or swat it away. This will result is less coordination, less success, and and absence of real pleasure. There will be a mental pleasure of sorts when the defensive child does overcome the difficulty and does catch the ball, but this is less secure, and it doesn't set further discrimination in motion.
High sensory defensiveness impedes sensory integration, which is the ability to work in two sensory channels at the same time in a coordinated way. For instance if I am a building crane operator, I am expected to hear radioed instructions in my ear at the same time that I am feathering the control levers using proprioception. If my sensory integration is low, I must stop all movement, 'get what was said' restart the arm movement, stop the arm movement when I hear something else (even if the instruction was not to stop) ask the speaker to repeat what was said, 'get' what was said, start the arm again, etc.. Also because of muscle tightening caused by some level of bodily alarm, my fine motor control will be impaired.
Anxiety produced by irregular sensory integration affects all human beings and all social systems. Sensory defensiveness and limitation in sensory integration are adapted to in a variety of ways. Often the terms hypersensitivity and hyposensitivity are used. However sensitivity is a confusing word, since it can imply either high discrimination or high alarm, and which from the previous few paragraphs it can be appreciated that these are largely inversely related. Perhaps more useful terms are hypo-responsivity and hyper-responsivity. Whatever the case, useful sensory intake is generally diminished in some way, in quantity but perhaps more so in quality. This state of affairs can be obscured by the fact that the intellect adapts by learning to make high quality surmises from the sensation that is taken in.
One behavioral adaptation is sensory extremism. Examples are rock-climbing, parachuting, and bungee jumping for someone that has proprioceptive defensiveness. Another example is seeking out the spiciest food possible for someone that has mouth sensitivity. Where there is sensory defensiveness, the result is not the development of discrimination, but bodily contraction even though the will is active. The goal of sensory extremism may be denial of the underlying defensiveness or it may be lessening the discomfort by 'jamming' the sensory channels. There may be an adrenaline or an endorphin response that further confuses matters.
Another adaptation. more frequent, is avoidance of strong sensory experience, which can be mistaken for introversion, agoraphobia, quirkiness, or timidity.
High arousal or an increase in sympathetic tone will push all people back toward sensory defensiveness (by Jackson-ian dissolution)
To remediate, the following general steps are necessary, 1) awareness and acceptance of one's response, 2) muscle release because tight muscles interfere with sensory discrimination and set a defensive tone, and 3) mindful, graded exposure to a potentially pleasant stimulus with careful attention to staying an optimal zone of arousal. The construct of sensory defensiveness has been nurtured by the profession of occupational therapy, but is not mainstream even in that profession. An excellent treatment of sensory defensiveness is given in Sharon Heller's book, too loud, too bright, too fast, too tight