IN THE study of sensation it is seldom emphasized that there is a continuous stream of sensory impulses to the thalami and cortices, and that any new stimulation is merely a phasic activity of this continuous process.1If this stream of impulses from the exteroceptive and interoceptive systems were reported to the consciousness, one would be constantly occupied in evaluating these barrages of messages, and constructive activity would be very difficult. A mechanism must exist to regulate these incoming impulses, to permit only the important and the urgent to reach the consciousness, especially when the attention is focused elsewhere. It is here proposed that this mechanism is supplied by the sensory suppressor systems originating in the sensory strip areas of the cortex. It is likewise proposed that the phenomenon of "sensory extinction" to bilateral simultaneous stimulation is a manifestation of such physiologic suppression. The existence of distinct projections from