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And yet what a potentially dangerous device, what a terrible opportunity to bury valuable, even vital sensory information beneath the fears and prejudices and suppressions of the higher brain! We absolutely must exercise constant discrimination upon the steady barrage of sensations if they are to take on any meaningful form and direct sequential activities; but what bizarre, even ghastly shapes this discrimination is free to invent. Attitudes, moods, neuroses, fixations, and avoidances of all kinds contribute to the sensitivity of the ascending sensory pathways themselves, so that minor irritations can be magnified to overwhelming proportions, pleasures can be erased or actually turned into torments, serious internal difficulties can be blotted completely out of consciousness. The principle of selectivity is crucial to organized behavior, but the possibilities for its abuse are enormous. The mind is capable of distorting incoming information to almost any degree, and it can actually construct a body image that has very little to do with the bulk of sensory data which the body is providing. These two directions of sensory transmission are both occurring all the time, and we cannot say that our idea of reality is more clearly established by one than by the other. Or, if we have to make a choice, we must admit that it is the descending, centrifugal sensory current that is the more important one: We all receive stimulation from the same external world through identical sensory devices, but it is the process of selection and interpretation which makes us respond differently, makes each of us the unique individuals that we are. In this process, discriminating mind descends into and is active in every synapse of the sensory system. The two processes of transmitting data through the nervous system and of interpreting it cannot be separated. Information is processed at each synaptic level of the afferent pathways. There is no one point along the afferent pathways or one particular level beneath the central nervous system below which activity cannot be a conscious sensation and above which it is a recognizable, defineable sensory experience. Perception has many levels, and it seems that the many separate stages are arranged in a hierarchy, with the more complex stages receiving input only after they are processed by the more elementary systems.13 And the more elementary systems are in turn facilitated or inhibited by the higher, more complex ones. The conclusions towards which these observations push us seems unequivocal. The cognitive, associational processes of the higher brain have just as much to do with our construction of physical reality—both within us and outside of us—as do our sensory devices and their specific stimulations. And remember, it is the perception of this sensory reality which initiates and directs our motor responses, our postures, and our behavior.
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