Reflection can generally be divided into two categories: unconditioned reflex and conditioned reflex. According to the nature of the signal system, conditional reflection can be divided into reflection of the first signal system and reflection of the second signal system.

Unconditioned reflex refers to the innate reflex that people are born with. It is a relatively low-level neural activity that can be completed with the participation of nerve centers below the cerebral cortex (such as the brainstem and spinal cord). Knee jerk reflex, blink reflex, hand withdrawal reflex, baby's sucking, urination reflex, etc. are all unconditioned reflexes. Plums are a very sour fruit, which makes your mouth water when you eat them. This kind of reflex activity is something people are born with and can do without learning, so it is an unconditioned reflex.

Conditioned reflex is an acquired reflex that is gradually formed in the course of life after birth. It is based on unconditioned reflex and completed with the participation of the cerebral cortex through a certain process. It is an advanced form of reflex. Neural activity is the basic way of high-level neural activity. People who have eaten plums many times will also salivate when they see plums. This is what he can do on the basis of drooling after eating plums, so it is a conditioned reflex. You can imagine what the ending would have been like if none of Cao Cao's soldiers had ever eaten plums, and no one had ever told them that plums were sour.

According to the type of signal that causes conditioned reflexes, conditioned reflexes can be divided into reflections of the first signal system and reflections of the second signal system. Caused by various specific signals of vision, hearing, touch, smell, and taste, it is called the reflection of the first signal system. It is unique to humans and animals.

In the process of human beings struggling with nature, language emerged in groups. The brain became more and more developed, and a language center was formed in the cerebral cortex. As a result, human beings can form conditioned reflexes to abstract language and words. This is a reflection unique to humans and belongs to the second signal system, such as talking about plum blossoms to quench thirst.

The process of establishing conditioned reflexes is as follows: use an unrelated stimulus (such as a ringtone) alone for a few seconds, then combine it with an unconditioned stimulus (such as eating), and both act at the same time for a certain period of time. . After being combined several times, the irrelevant stimulus alone can cause a reaction originally caused by an unconditioned stimulus (such as salivation). Here, the ringing has become a conditioned stimulus for salivation, and the conditioned reflex is formed.