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  • Updated 07.08.2019
  • Released 04.07.1999
  • Expires For CME 07.08.2022

Visual agnosias

Introduction

This article includes discussion of visual agnosias, apperceptive visual agnosia, associative visual agnosia, prosopagnosia, simultanagnosia, object agnosia, topographagnosia, topographical disorientation, pure alexia, and cortical dyschromatopsia. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Agnosia is a group of neurologic disorders in which a person cannot recognize or identify an object, face, sound, word, or environment despite intact consciousness, language, memory, and fundamental sensory functions (45). Visual agnosia is a subtype of the agnosic syndromes where the deficit is specific to a visual target. In this article, the authors review different types of visual agnosia with respect to clinical characteristics, pathogenesis, structural localization, differential diagnosis, diagnostic evaluation, and rehabilitation.

Key points

• Visual agnosia is a rare neurologic deficit in recognizing or identifying a visual target despite intact consciousness, language, memory, and fundamental sensory functions.

• The 2 main streams of visual pathway from the primary visual cortex to its associative cortex are the dorsal stream (“where” pathway) and the ventral stream (“what” pathway).

• Visual agnosia is classified into 2 major categories: apperceptive visual agnosia and associative visual agnosia.

• Subtypes of visual agnosia are named according to the deficit in different visual targets.

• Specific rehabilitation programs targeting visual training improve ability in visual processing among persons with visual agnosia.

Historical note and terminology

One of the first descriptions of a visual agnosia was provided by Munk in 1881. Munk noted that following bilateral partial occipital lobe ablation, a dog had a change in his responsiveness to familiar objects such that the dog could see but could not recognize. In 1890 Lissauer distinguished between 2 forms of visual agnosia: apperceptive and associative (70). In 1891, Freud introduced the term "agnosia," which was later defined as failure to recognize objects, not attributable to a defect in visual acuity, impaired cognition, or aphasia (08).

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