Final answer:
The defense mechanism where a person returns to a more immature behavioral stage when faced with anxiety is known as regression. It's an unconscious effort by the ego to reduce stress by adopting behaviors from an earlier developmental period.
Step-by-step explanation:
The ego defense mechanism where a person reverts to a previous developmental stage's behaviors to cope with stress or anxiety is called regression. This is an unconscious process where the ego seeks to reduce anxiety by adopting more child-like behaviors, which are deemed safer or more comfortable. An example of regression is an older child who starts wetting the bed during a stressful period after having been consistently dry at night.
Freud's theory of defense mechanisms suggests that they are a way for the ego to protect itself against anxiety arising from conflicting demands of the id and superego. These mechanisms are unconsciously employed by individuals to distort reality and thus reduce feelings of anxiety.
Other ego defense mechanisms include reaction formation, projection, and rationalization, each serving as a way to cope with anxiety by transforming it into a less threatening form, sometimes by altering one's perception of reality.