Specific circumstances or stressful situations may bring out particular identities. Some patients have histories of erratic performance in school or in their jobs caused by the emergence of alternate personalities during examinations or other stressful situations. Each alternate identity takes control one at a time, denying control to the others. Patients vary with regard to their alters' awareness of one another. One alter may not acknowledge the existence of others or it may criticize other alters. At times during therapy, one alter may allow another to take control.