Delirium (Acute Confusional State): Causes, Identification, Assessment and Management Introduction Here is the definition of delirium from the shorter oxford textbook of psychiatry: “delirium is a global impairment (clouding) of consciousness resulting in a reduced level of alertness, attention, perception of the environment, and thence cognitive performance.” There are several terms used in this definition that can make it difficult to understand at first. It begins with a clouding of consciousness, which they say results in reduced alertness, attention, and perception, and these are cognitive or let's put it simply, mental abilities, so the overall mental abilities or cognitive performance is reduced. Now, let me quickly explain these and some other terms so you can fully comprehend this definition and the other signs and symptoms of delirium that we will be discussing. Terminology Perception Perception occurs when the brain processes the raw sensory stimuli from the environment