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Visual Agnosia

Visual Agnosia

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 end"...

Prosopagnosia

Prosopagnosia

Prosopagnosia, also known as face blindness, is the inability to recognize faces. In severe cases, individuals with prosopagnosia may not recognize close family members, including parents and spouses, by their faces. For instance, someone with prosopagnosia might walk past their child in a crowd, only realizing their mistake upon noticing their child's distinctive backpack or favorite jacket. Prosopagnosia specifically impairs facial recognition, while the recognition of other objects or...

Photoreceptors and Visual Pathways

Photoreceptors and Visual Pathways

At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...

Perceptual Constancy

Perceptual Constancy

Perceptual constancy is the ability to recognize that objects remain consistent and unchanged even when their appearance varies due to changes in sensory input. There are four main types of perceptual constancy: size constancy, shape constancy, color constancy, and brightness constancy.
Size constancy is the recognition that an object remains the same size, even when its image on the retina changes. For instance, a bus is perceived to be large enough to carry people, even if it looks tiny from...

Depth Perception and Spatial Vision

Depth Perception and Spatial Vision

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.

Vision

Vision

Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.

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Related Experiment Video

Updated: May 28, 2026

A Gaze-Contingent Display Framework for Perceptual Learning Research with Simulated Central Vision Loss

A Gaze-Contingent Display Framework for Perceptual Learning Research with Simulated Central Vision Loss

Published on: April 11, 2025

[Progressive visual agnosia].

Azusa Sugimoto¹, Akinori Futamura, Mitsuru Kawamura

¹Department of Neurology, Showa University School of Medicine, Tokyo, Japan.

Brain and Nerve = Shinkei Kenkyu No Shinpo

|October 12, 2011

Summary

This summary is machine-generated.

Progressive visual agnosia, a neurodegenerative condition, differs from classical forms. Understanding this progressive visual loss aids in diagnosing atypical dementias like posterior cortical atrophy.

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Area of Science:

Neurology
Neuroscience
Ophthalmology

Context:

Progressive visual agnosia is a neurodegenerative symptom, distinct from classical agnosia caused by injury.
Posterior cortical atrophy (PCA) is a condition characterized by progressive visual loss and posterior cerebral atrophy.
Visual agnosia subtypes (apperceptive and associative) are observed in PCA and semantic dementia (SD).

Purpose:

To differentiate progressive visual agnosia from classical forms.
To explore the association of visual agnosia subtypes with PCA and SD.
To highlight the importance of diagnosing atypical dementias like PCA.

Summary:

Progressive visual agnosia results from neurological degeneration, unlike classical agnosia from injury.
PCA is defined by progressive visual loss and posterior cerebral atrophy.
Apperceptive visual agnosia is common in PCA, while SD initially shows associative visual agnosia.

Impact:

Enhanced understanding of the visual system and neural perception.
Improved diagnostic capabilities for atypical dementias.
Facilitation of better patient care through timely diagnosis and support.