Perception

Physiology

The billions of signals that the brain receives every second are transformed into something we perceive: a certain object, person, event, etc. We do not perceive everything that influences us but only what our brain considers as the most important at that moment.

As a result of the influence of a physical stimulus (light on the retina, sound waves, air vibrations on the ear membrane, or sensations felt by the skin or tongue), a nerve impulse is created in nerve cells which indicates electrical or chemical changes. A nerve impulse transmits excitation to the brain area, which is called a primary or projection area by neurophysiologists. There are different zones for each modality: visual, acoustic, etc.

Neurophysiologists state that it takes a nerve impulse 30 milliseconds after the initial stimulus influence until it reaches the brain (the projection area). But, those 30 ms are not enough time to create a simple sensation, let alone a whole image. It takes much more time to create an image after the stimulus’s influence – 300 milliseconds.

A few areas of the brain serve as a physiological perception base.

Information about the physical characteristics of the stimulus is transmitted to the projection cortex. Then a nerve impulse transmits excitation to the association cortex and hippocampus – these brain areas compare the received stimulus characteristics with the information stored in memory. If comparison results are considered important, the excitation is transmitted to the emotionally motivational centers of the limbic system and the hypothalamus where the information is marked with an emotional label. Then the excitation returns to the projection cortex where it was created and is superimposed onto the traces of the original primary excitation. This moment corresponds to the time for creating a conscious sensation – about 200 ms after physical influence. Thus, one feels not the whole flow of stimulation but only what the brain considers to be important and deserving attention.

Then a nerve impulse transmits excitation to the frontal lobes where they ensure the singling out of integrity criterion in the received configuration of stimuli and categorization – essentially, the realization of an object or event as a part of a certain class with its own name. This takes about 300-400 ms after the moment of initial stimulus influence.

The basis for a continuous flow of perception is a repeated entry of excitation to the brain area where it began after extra processing in other areas or signal transmissions from the outside environment. It provides an opportunity to compare the old information with the changes that happened.