If we are to understand the brain, we might well begin by discovering how information is taken in and how responses are generated. Humans have at least nine senses and we will not have time to study them all. Vision is our choice for this course because there is more known about that sense than about any other and because more of the primate brain is devoted to vision than to any other sense. Judging by brain space, humans are primarily visual animals. Every sense system, from audition to the vestibular senses, has a set of receptors that can receive stimuli.
Brain cells understand only the language of nerve impulse patterns.
Shine a visual image directly onto the visual cortex of the brain and all you will accomplish is to dry out the tissue. The firing of neurons in your receptor organs does not, in itself, generate any conscious sensations in your mind. However, every sense has a pathway from its receptor organs to the cerebral cortex of the brain where the conscious mind does reside. These pathways are called projection systems. A sensory projection system is the path from the receptors to the area of the cortex for that sense.