What are perceptions without external causes, often associated with schizophrenia or drug use, called?

Perceptions without external causes are termed hallucinations. These experiences involve seeing, hearing, or feeling things that are not actually present in the environment, and they can occur in various forms, including auditory hallucinations (hearing voices) and visual hallucinations (seeing things that are not there). Hallucinations can be associated with psychiatric conditions like schizophrenia or can result from substance use, where the brain's interpretation of sensory information is altered.

Understanding hallucinations is crucial in neuroscience because they illuminate how sensory processing and perception can dramatically differ from reality, highlighting the complexities of the brain's functioning when influenced by psychological disorders or external substances. The other terms, while related, do not accurately describe perceptions devoid of any external stimuli.