What are perceptions without a direct external cause called?

Perceptions without a direct external cause are referred to as hallucinations. Hallucinations occur when an individual perceives something that isn't present in the external environment; these can involve any of the senses, including seeing things that aren’t there (visual hallucinations) or hearing sounds (auditory hallucinations). This phenomenon is often associated with various mental health conditions, neurological disorders, or substance use, where the brain generates experiences that lack an actual stimulus from the surroundings.

In contrast, illusions involve misinterpretations of real external stimuli; for example, a shadow might be perceived as a threatening figure, but in actuality, it is just a shadow. Delusions are firmly held beliefs that are not based in reality, reflecting a disorder of thought rather than distorted perception. Memories pertain to the past and involve recalling previously experienced events or information rather than generating new perceptions. Thus, hallucinations distinctly represent the experience of sensation without any real external cause.