Types of Agnosias
The American Psychiatric Association does not officially categorize agnosias in its Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). Agnosias, however, are commonly divided into two broad categories: Apperceptive Agnosias and Associative Agnosias. Some patients, may manifest characteristics of both types of visual agnosia, or even symptoms of visual and non-visual agnosias. A diagnosis of an Integrative Agnosia is typically applied when the losses are primarily visual.
Apperceptive agnosias (also known as visual space agnosias) refer to a condition in which a person fails to recognize objects due to a functional impairment of the occipito-temporal vision areas of the brain. Other elementary visual functions such as acuity, colour vision, and brightness discrimination are still intact. Apperceptive agnosics are unable to distinguish visual shapes and so have trouble recognizing, copying, or discriminating between different visual stimuli. When patients are able to identify objects, they do so based on inferences using colour, size, texture and/or reflective cues to piece it together. For example, in the image below, an apperceptive patient may not be able to distinguish a poker chip from a scrabble tile despite their clear difference in shape and surface features.
Apperceptive agnosia often occurs after recovery from "cortical blindness" due to exposure to toxins such as carbon monoxide. Several subtypes of apperceptive agnosia have been identified, including dorsal simultagnosia, ventral simultanagnosia, and visual hemi-neglect. To learn more about any of these, click on any of the links below.
Although apperceptive agnosia and associative agnosias appear to anchor the ends of a continuum; some patients may have a visual disorder that lies somewhere along that continuum. These are referred to as Integrative Agnosias.
|What Are Agnosias||Go to Associative Agnosias|