WHAT, WHERE,

& HOW SYSTEMSAGNOSIAS!

What, Where, & How Systems

What

Visual Agnosia

Visual Object Agnosia

• Apperceptive

• Associative

Apperceptive Agnosia

• Intact vision:– Acuity, brightness discrimination, color vision, & other

elementary visual capabilities– Sometimes preserved shape from motion

• Deficits:– Abnormal shape perception (pictures, letters, simple

shapes)– Grouping process deficit (that operates over an array

of local features representing contour, color, depth, etc.)

Apperceptive Agnosia

• VIDEO: Apperceptive Agnosia, impaired triangle recognition, subject 1

• VIDEO: Apperceptive Agnosia, impaired object recognition, subject 1

• VIDEO: Object Agnosia 2: Impaired Visual but not tactile identification (naming), subject 2

• VIDEO: Object Agnosia 3: Intact visual movement identification, subject 2

• VIDEO: Object Agnosia 1: Impaired Visual identification (subject given name & array of objects), can’t see objects

Associative Agnosia

Associative Agnosia• Cannot recognize objects by sight alone• Intact general knowledge of objects• Can recognize objects by touch or definition• Visual perception better than in apperceptive

agnosia • Not a naming deficit

(cannot indicate recognition by nonverbal means)

Theories of Associative Agnosia

1. Disconnection between visual representations and language areas

2. Disconnection between visual representations and memory areas

3. Stored visual memories have been damaged

4. A perceptual and memory problem, and the two are inseparable

Intertwined Perception & Memory

• Some visual problems • Copying drawings on line by line• On matching tasks, they rely on slow, sequential featured-

by-feature checking

• In the PDP system, the memory of the stimulus would consist of a pattern of connections strengths among a number of neuron like units. The " perceptual" representation resulting from presentation of the stimulus will depend upon the pattern of connection strengths among the units directly or indirectly activated by the stimulus. Thus, if a memory is altered by damaging the network, perception will be altered as well. Thus, Associative Agnosia may not be the results of an impairment to perception or to memory; rather, the two are in principle inseparable, and the impairment is better described as a loss of high level visual perceptual representations that were shaped by, and embody the memory of, visual experience.

Apperceptive:Localization of Damage

• Diffuse brain damage, often from

• Multiple infarcts or from other global anoxic events: e.g. carbon monoxide poisoning.

Apperceptive Associative

Associative Agnosia

Prosopagnosia

Prosopagnosia

• Compensate by relying on nonfacial cues (voice, gait, clothing..)

• With a few exceptions, they can discriminate a face’s gender, ethnicity, approximate age, and emotion conveyed.

• Patients who do not have problems recognizing faces may have difficulty recognizing the emotion.

Matching Faces Task

Test of Famous Faces

Types Of Agnosia

• Face• Object• Printed Word• Face, or face and object -- right or bilateral• Word, or word and object – left• Maximum overlap in left inferior medial

region (including parahippocampal, fusiform, and lingual gyri)