Agnosia

1. Agnosia PSY 3108 B Suad Mohamed

2. Introduction • Agnosia (What is it?) • 3 Forms (visual, auditory, somatosensory) • Further research

3. Agnosia • “ the inability to recognize people or objects even when basic sensory modalities are intact” • Perception= normal • Recognition of objects???

4. 3 Forms of Agnosia • 1) Visual agnosia: person has difficulty recognizing objects, faces, and words • 2) Auditory agnosia: inability to define/ recognize sounds • 3) Somatosensory agnosia: the person has difficulty perceiving objects through tactile stimulation

5. Visual Agnosia • lesions in the left occipital and temporal lobe • Their main impairment is failure to recognize visually presented objects despite having intact perception of that object • Video • “Recognition without Meaning”

6. Types of Visual Agnosia • Depends on location of lesion • Colour Agnosia: • Lesion in the left occipito-temporal region of the brain • Leads to impaired ability to name and distinguish colours, even though basic vision mechanisms are intact • Tests

7. Prosopagnosia • Inability to recognize faces despite good basic vision and intelligence • Usually due to lesion in the inferior medial temporal-occipital area of the brain (lesioned inferior longitudinal fasciculus which is connected to the temporal and occipital lobes) • Facial recognition is complicated

8. Prosopagnosia cont. • Can recognize facial expressions, but not a face as a whole • example • Mr P. in Oliver Sack’s (neurologist) “The Man who Mistook His Wife for a Hat and other clinical tales”

9. Research has shown that not being able to recognize someone’s face could be an indicator of the inability to recognize individual features or members of a more general category • Example: a bird catcher who can’t tell the difference between the birds anymore; your car from other cars

10. Types of Visual Agnosia cont. • Visual hemi-neglect • Inability to pay attention to or notice stimuli from one-half of the visual field • Occurs on the left side of the visual world as a result of right parietal lobe damage • Stroke • Short vs long term effects after stroke • Have problems with attention and poor working memory

11. ApperceptiveAgnosia • Usually occurs after recovery from “cortical blindness” due to exposure to carbon monoxide • Also known as visual space agnosia, which is a condition in which a person fails to recognize objects due to functional impairment of the occipito-temporal visual areas of the brain, while other visual functions are intact such as: acuity, colour vision, brightness discrimination (Kline 2004)

12. Auditory Agnosia • Inability to recognize sounds as symbols, words, or music • 3 sub-types: • Auditory/verbal information agnosia: inability to hear words • Auditory: inability to hear environmental sounds such as a car starting or dog barking • Receptive amusia: inability to hear music

13. Nonverbal vs verbal auditory agnosia • Verbal: pure word deafness • Comprehend written language, unable to comprehend spoken language in the absence of hearing difficulties • Damage involving the primary auditory cortex or connections between the thalamus and this area • Article: “Speech perception in an individual with verbal auditory agnosia” • Conducted tests a week and a month post onset of diagnosis • May be affected by unilateral as well as bilateral lesions • Non Verbal: dissociation between language and environmental sound comprehension

14. Somatosensory Agnosia • Caused by lesions of the somatosensory cortex (post central gyrus) • Cannot tell an object through touch; its basic features such as size, weight and texture • Patients able to draw and recognize the object pictured in the drawing, even if not by touch • Experiment

15. Further Research • Is a bilateral lesion necessary to cause agnosia in prosopagnosia? • Ongoing debate in tactile agnosia research, what cues are most effectively for the patients to determine what the object is (pictorial cues vs distance cues) • The relationship of acquired verbal auditory agnosia in childhood, to “pure cortical deafness” in adulthood (Rapin, 2008)