When light waves are emitted by a light bulb or when sound waves are emitted by a radio, our “sensory organs”, in this case our eyes or ears, intercept them. The intercepted energy then travels to the brain. How does this happen? Of course, light or sound waves do not bounce back inside our skull! So how do they get to the brain?
The brain uses its own form of energy, an “electrochemical energy” (see Chapter 3). It is this energy that allows neurons to communicate with each other and to act. Therefore, in order for the brain to decipher the different forms of energy received by our sensory organs, each form of energy must go through a transformation process called “transduction,” which converts it into electrochemical or “neural” energy. It is the presence of certain types of cells, i.e. “receptors”, in the sensory mechanisms
that make transduction possible. Each sensory mechanism has its own type of receptor cells. Once environmental energy is converted, a neural signal communicates information through a “sensory nerve” to the area of the brain responsible
for processing and analyzing this type of information. Is there only one tone in the music or human voices we hear? Does the light we see have only one color? Of course not! Each of these sensory experiences, or stimuli, is made up of a complex set of light wavelengths, sound frequencies, olfactory or taste intensity, etc.
But don’t panic! Our sensory mechanisms are up to the job. Thanks to a “coding and representation process”, the brain is able to grasp the complexity of all the environmental stimuli it receives. Each characteristic of the stimulus translates into a specific pattern of neural activity. According to the “theory of specific energies”, each sensory mechanism provides information for only one sense, regardless of the nerves stimulated. In other words, the area of the brain responsible for light processing will always perceive the stimulus as light.
With the help of neurosurgeons, psychologists have carried out experiments on patients who, for other reasons, require the removal of part of the skull, an operation that allows direct access to the brain. Using an electrode, they emitted an electrical discharge on several parts of the brain. And the results were astonishing. For example, after an electrical shock, one patient said, “I hear chickens clucking. “If the electrode had been placed on the area of the brain responsible for taste processing, the patient might have said,
“Hmm… Tomato soup is good! “How is that possible? When this area of the brain is stimulated, the brain thinks it is receiving taste information from the corresponding sensory organ, even though this is not the case. Each sensory mechanism is connected to a certain area of the brain to allow the brain to differentiate between sound and light,
for example. The different aspects of a stimulus are coded in the brain according to the neurons that are activated and the structure of this neuronal activation. If it is the neurons of the visual mechanism that are activated, then the brain is able to perceive light. If the structure of the neuronal activation changes, the brain will perceive different wavelengths or intensities of light, allowing the brain to distinguish between daylight and candlelight. The sensory process ends with a neural “representation” of sensation in a specific area of the brain. At this point, we hear music or see colors ;