What psychological condition is characterized by experiencing non-existent stimuli as real?

The psychological condition characterized by experiencing non-existent stimuli as real is hallucinations. Hallucinations are sensory perceptions that occur without an actual external stimulus, meaning a person may see, hear, or feel things that aren’t present. This can manifest in various forms, such as auditory hallucinations (hearing voices) or visual hallucinations (seeing things that aren't there), and is often associated with disorders like schizophrenia, severe depression, or substance abuse.

Understanding hallucinations is crucial in the study of neuroscience, as they provide insight into the brain's interpretation of sensory information and the ways in which this interpretation can be altered by psychological conditions. In contrast, conditions like depression, anxiety, and bipolar disorder may involve a range of symptoms such as low mood or altered energy levels, but they do not fundamentally involve the perception of non-existent stimuli as real. Thus, they do not define the condition focused on in this question.