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Visual Agnosia

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Visual agnosia is a condition characterized by the inability to recognize visually presented objects despite having normal vision. For instance, a person with visual agnosia can describe the shape and color of an object but cannot identify or name it. This impairment does not affect their visual field, acuity, color vision, brightness discrimination, language, or memory. An example of this condition in a social setting is someone at a dinner party asking for "that silver thing with a round...
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Hallucinogens and Psychedelics01:27

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Hallucinogens are psychoactive substances that profoundly alter perceptual experiences, generating unreal visual and sensory images. Often referred to as psychedelic drugs — a term derived from the Greek words "psyche" (mind) and "delos" (revealing) — these substances include marijuana and lysergic acid diethylamide (LSD), among others. These drugs vary in intensity and effects.
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Positive Symptoms Schizophrenia: Hallucinations and Delusions01:26

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Schizophrenia is a complex psychiatric disorder characterized by a range of symptoms that significantly impact cognition, behavior, and emotional regulation. Among these, the positive symptoms stand out as they involve the addition or exaggeration of normal mental functions, deviating markedly from typical behavior and perception. Hallucinations and delusions are prominent positive symptoms, each profoundly affecting the individual's experience of reality.
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Depth perception is the ability to perceive objects three-dimensionally. It relies on two types of cues: binocular and monocular. Binocular cues depend on the combination of images from both eyes and how the eyes work together. Since the eyes are in slightly different positions, each eye captures a slightly different image. This disparity between images, known as binocular disparity, helps the brain interpret depth. When the brain compares these images, it determines the distance to an object.
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Related Experiment Video

Updated: Dec 28, 2025

Development of a Gaze-Contingent Display Framework Designed for Perceptual and Oculomotor Research with Simulated Central Vision Loss
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Development of a Gaze-Contingent Display Framework Designed for Perceptual and Oculomotor Research with Simulated Central Vision Loss

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[Visual snow in hallucinogen-persisting perception disorder].

Hannah Schatten1, Nicole Eter2, Nataša Mihailovic2

  • 1Klinik für Augenheilkunde, Universitätsklinikum Münster, Domagkstr. 15, 48149, Münster, Deutschland. hannah.schatten@ukmuenster.de.

Der Ophthalmologe : Zeitschrift Der Deutschen Ophthalmologischen Gesellschaft
|February 21, 2020
PubMed
Summary
This summary is machine-generated.

A young woman experienced persistent visual snow after consuming a drug cocktail. She was diagnosed with hallucinogen-persisting perception disorder, a condition with limited treatment options.

Keywords:
Eye flickeringHallucinogensNarcoticsNeuroophthalmogyPalinopsia

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Area of Science:

  • Neuro-ophthalmology
  • Psychiatry

Background:

  • Hallucinogen-persisting perception disorder (HPPD) is a rare condition characterized by persistent visual disturbances.
  • This case highlights the potential for severe visual and psychiatric sequelae following recreational drug use.

Observation:

  • A 24-year-old female presented with a 1.5-year history of constant, disturbing visual flickering, likened to "visual snow."
  • Standard ophthalmological and neurological examinations, including cranial MRI and pattern-VEP, were unremarkable.
  • The patient had a history of schizophrenia, which began concurrently with the visual disturbances after ingesting a "narcotic cocktail."

Findings:

  • The patient was diagnosed with type II hallucinogen-persisting perception disorder (HPPD).
  • The onset of HPPD was temporally linked to the consumption of amphetamines, hallucinogens, and alcohol.

Implications:

  • This case underscores the importance of a thorough drug history in diagnosing persistent visual disturbances.
  • Limited treatment options exist for HPPD, emphasizing the need for further research into effective interventions.
  • The co-occurrence of schizophrenia and HPPD warrants further investigation into potential shared neurobiological pathways.