SIMPLE HALLUCINATION

Also referred to aselementary hallucination. Both terms are used to denote a hallucination of the lowest degree of complexity. In the auditory modality, simple hallucinations are known as * akoasms. Common examples of akoasms are clicking sounds, the sound of the door bell ringing, rustling noises, and buzzing. Akoasms may occur in the context of both peripheral and central conditions. In * tinnitus, akoasms tend to have a chronic and sometimes highly disturbing character. In the visual modality, simple hallucinations may take the form of *Eigengrau, *flickering scotomata, *photopsia, etc.Photopsia comprises a group of elementary visual phenomena such as * phosphenes, luminous rays, coruscations, heat waves, *snow lights, and * Moore's lightning streaks. Some of these simple phenomena can be provoked by gentle pressure to the eyeball (as in * pressure phosphenes) or caloric vestibular stimulation (leading to *vestibularly evoked visual hallucinations). It may therefore be tempting to believe that simple visual hallucinations invariably fall into the class of * entoptic phenomena. But again many of them are associated with both peripheral and central conditions. The same holds true for simple hallucinations occurring in the tactile modality, such as *paraesthesias, * formicative hallucinations, and *cocaine bugs. The term simple hallucination derives from a classification of hallucinations which employs complexity as a guiding principle. It is used in opposition to the terms *organized (or *formed) hallucination and *complex hallucination. By their nature, * olfactory and * gustatory hallucinations defy categorization based on degrees of complexity. The same holds true for *vestibular hallucinations, *proprioceptive hallucinations, *kinaesthetic hallucinations, and many *somatic and * sexual hallucinations.

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