Physiological investigation reveals that all perception depends on very complex processes of detection by sense organs and of transmission of signals from them to the brain. There is much neurophysiological evidence that a conscious experience arises only when there is some specific cerebral activity. For every experience it is believed that there is a specific spatio-temporal pattern of neuronal activity in brain. The kinesthetic information from all the movements as well as the sensory information from the vestibular apparatus are synthesized with the retinal information. This chapter re-examines nature of sensory perceptions, it is evident that these give the so-called facts of immediate experience and that the so-called "objective-world" is a derivative of certain types of this private and direct experience. The electroencephalogram reveals that in states there may be either a very low level of neuronal activity, as in coma, concussion, anesthesia, and deep sleep, or a very high level of stereotyped and driven activity, as in convulsions.