Hallucinatory palinopsia

Hallucinatory palinopsia
Classification and external resources
[]

Hallucinatory palinopsia (Greek: palin for "again" and opsia for "seeing") is a subtype of palinopsia, a visual disturbance defined as the persistent or recurrence of a visual image after the stimulus has been removed.Palinopsia is a broad term describing a heterogeneous group of symptoms which is divided into hallucinatory palinopsia and illusory palinopsia. Hallucinatory palinopsia refers to the projection of an already-encoded visual memory and is similar to a complex visual hallucination: the creation of a formed visual image where none exists.

Hallucinatory palinopsia usually arises from posterior cortical lesions or seizures and can be the presenting symptom of a serious neurological disease. Hallucinatory palinopsia describes afterimages or scenes that are formed, long-lasting, high resolution, and isochromatic. The palinoptic images are not typically reliant on environmental parameters and often present with homonymous visual field deficits. Hallucinatory palinopsia occurs unpredictably and the persistent images can appear anywhere in the visual field, regardless of the location of the original stimulus. A patient will often have only a few episodes of hallucinatory palinopsia. Visual perseveration is synonymous with palinopsia.

Hallucinatory palinopsia consists of the following four symptom categories. A person often reports symptoms from multiple categories.

Formed image perseveration refers to a single, stationary object that remains fixed in one’s visual field. These pathological afterimages look realistic and have the same color and clarity as the original stimulus. The palinopsia lasts at least 15 seconds, but may persist for hours or days. For example, a patient sees a cat, and an identical copy of the cat remains fixed in the field of view for 30 minutes. A patient commonly complains of the perseverated fingers of an examiner. These afterimages often occur in visual field deficits but may occur anywhere in the visual field, regardless of the location of the original stimulus. The generation of the afterimages is not affected by external conditions such as the length of fixation, stimulus intensity, contrast, or motion. The palinoptic image can appear immediately after seeing the original image or may be delayed in time.

...
Wikipedia