“An eight-year-old child crawls like his younger infant brother” is an example…

Concept

Defense mechanisms are unconscious psychological strategies the mind uses to protect itself from anxiety or emotional discomfort caused by an unacceptable impulse, an unresolved conflict, or a stressful situation. Regression is one such mechanism: under stress, a person reverts to behaviour typical of an earlier, more immature stage of development.

Application

Here, an eight-year-old child gives up age-appropriate movement and crawls the way his infant brother does. Such a shift is the reversion to an earlier developmental stage of behaviour that regression theory associates with stress or anxiety (commonly triggered by, though not limited to, a younger sibling's presence) — this reversion is the defining signature of regression.

Cross-check

• Repression blocks a distressing thought or memory from conscious awareness; it does not make a person act like a younger child.

• Rationalization supplies a logical-sounding excuse for a behaviour or failure; it does not involve adopting an infant's behaviour.

• Compensation offsets a perceived weakness in one area by excelling in another; it does not involve reverting to earlier-stage behaviour.

Since the behaviour described is a reversion to an earlier developmental stage rather than a blocked memory, an invented justification, or offsetting a weakness, Regression is the concept that fits.