In psychology, affect describes emotions that are expressed and therefore observable by others.
For example, flat effect is a psychiatric symptom in which individuals have no displayed emotions whatsoever. Depressed affect is a mental and physical state that frequently occurs among persons who feel trapped in their emotional or physical condition.
Examples include prisoners, abuse victims, or isolated individuals (such as a submarine crew) - it is believed the lack of stimulation is linked to depressed affect. This causes the person to shift into a mental and physical state of neutrality that can extend to extreme apathy and disregard for normal tasks such as eating/caring for oneself, etc. In its most extreme form it can actually lead to the death of the victim.