CCC- AGNOSIA & PROSOPAGNOSIA

Agnosia

A disorder of object recognition despite intact basic vision, intelligence, and memory.

What agnosia is not

It is not caused by poor acuity, visual field loss, or loss of object knowledge.

Cause of agnosia

Typically results from damage to occipital or inferior temporal cortex in the ventral stream.

Significance of agnosia

Different forms reveal how object recognition is organised in the brain.

Ventral stream role

Supports object and face recognition.

Dorsal stream role

Supports action and visuomotor control.

Preserved abilities in agnosia

Patients can navigate environments and grasp objects accurately.

Apperceptive agnosia

where a person can see but cannot process visual information to form a complete perception of an object

Key deficit in apperceptive agnosia

difficulty in the brain's ability to combine individual visual attributes, such as color and shape into a unified and coherent perception of an object

Behaviour in apperceptive agnosia

Poor copying, matching, and shape discrimination.

Processing stage affected in apperceptive agnosia

Damage occurs early, before stable shape representations form.

Associative agnosia

A failure to link perceptual representations with stored object knowledge.

Key deficit in associative agnosia

Object knowledge is intact but cannot be accessed visually.

Behaviour in associative agnosia

Copying and matching are intact, but naming and recognition fail.

Processing stage affected in associative agnosia

Damage occurs after perceptual processing, at the object knowledge stage.

Limits of apperceptive–associative distinction

The distinction is useful but oversimplifies agnosia types.

Prosopagnosia

A selective impairment in recognising faces.

Key feature of prosopagnosia

Inability to recognise familiar faces visually while other modalities remain intact.

Covert face recognition

Unconscious physiological responses to familiar faces despite no overt recognition.

Capgras delusion

A condition where faces are recognised but lack emotional familiarity, leading to impostor beliefs.

Two-route model of recognition

Overt ventral route supports conscious recognition; covert dorsal route supports affective response.

Prosopagnosia vs Capgras

Prosopagnosia reflects ventral damage; Capgras reflects disrupted affective signalling.

Overall conclusion

Object and face recognition are modular, distributed, and rely on multiple interacting pathways.