"Our perceptions differ qualitatively from the physical properties of stimuli because the nervous system only extracts certain information from a stimulus and then interprets this information in the context of its earlier experience. We experience electromagnetic waves of different frequencies not as waves but as actual colors that we see: red, blue, or green. We experience objects vibrating at different frequencies as tones that we hear. We experience chemical compounds dissolved in air or water as specific smells or tastes. Colors, tones, smells, and tastes are mental reconstructions created by the brain out of sensory experience. They do not exist, as such, outside of the brain….does a sound exist when a tree falls in the forest, if no one is near enough to hear it? We now believe that the fall causes vibration in the air but not sound. Sound only occurs when pressure waves from the falling tree reach and are perceived by a living being."
- PRINCIPLES OF NEURAL SCIENCE, 3RD EDITION., EDS.. KANDEL, SCHWARTZ, & JESSELL, P. 330