The document discusses the anatomy and functions of the visual cortex, detailing the roles of the dorsal and ventral streams in processing visual information. It elaborates on various visual disorders associated with lesions in these areas, including prosopagnosia, visual agnosia, and Balint syndrome, among others. Additionally, it highlights the impact of specific conditions on visual perception, including color vision abnormalities and hallucinations.

1. DR VAROON

3. 18 : Elaboration and synthesis of visual function
19 : Integration of Visual Information with other
modalities of information, language and memory.
17 : upper and lower bank of calcarine sulcus : striate cortex :
white stria of Gennari, a distinctive stripe visible to the naked
eye that represents myelinated axons from the lateral
geniculate body terminating in layer 4 of the gray matter.

6. Ventral : “What” Recognition of objects,
colours , faces and words
Dorsal : “Where” Visuospatial function, i.e
location, motion etc of stimuli.

8. LESIONS OF OCCIPITAL LOBE AND
EXAMINATION

9. PRIMARY VISUAL CORTEX
• FIELD DEFECTS : HEMIANOPIA, B/L QUADRANTANOPIA, ALTITUDINAL HEMIFIELD
DEFECT
• CORTICAL BLINDNESS
• ANTON SYNDROME
VENTRAL STREAM
• VISUAL OBJECT AGNOSIA , COLOUR VISION ABNORMALITIES, PROSOPAGNOSIA,
PURE ALEXIA ( ALEXIA WITHOUT AGRAPHIA)
DORSAL STREAM
BALINT SYNDROME ; VISUAL DISORIENTATION ; AKINETOPSIA ; ASTEREOPSIS ;
VISUAL EXTINCTION

10. Primary Visual Cortex

11. CORTICAL BLINDNESS
• MACULAR SPARING : SHIFT IN OCULAR FIXATION ; DUAL BLOOD
SUPPLY ( MCA + PCA) ; macular representation ( large cortical)
• Occipital cortex
• Cerebral blindness : Circuits, Double hemianopia ; adrenal
leukodystrophy
Anton-Babinski syndrome (Anton syndrome or ABS)
Visual anosognosia (denial of loss of vision) associated with
confabulation (defined as the emergence of memories of events
and experiences which never took place) in the setting of obvious
visual loss and cortical blindness

12. Field
Defects
b/l altitudinal defect

13. VENTRAL STREAM

14. • Agnosia : Perceptual Disorder where
sensations are preserved but the
ability to recognize a stimulus or
identify its meaning is lost

15. Visual Agnosia
• Apperceptive visual agnosia :
• Abnormality in visual perception and discriminative process, despite
the absence of elementary visual deficits.
• These people are unable to recognize objects, draw, or copy a figure.
• They cannot perceive correct forms of the object, although knowledge
of the object is intact.
• Typically associated with lesions to the parietal, occipital cortex
TESTS : MATCHING ; COPYING

17. Perceptual categorization defect
VISUAL STIMULI
PRIMARY SKETCH
VIEWER CENTERED REPRESENATION
OBJECT CENTERED REPRESENTATION
SEMANTIC CONCEPTUAL
FIELD
VISUAL ANALYSIS
PHONOLOGICAL
LEXICON
Recognize in conventional
orientation

18. Perceptual Categorization Defect : Right
Parietal Lobe
Visual object and space perception battery
Birmingham object recognition battery

19. • Associative visual agnosia :
• Difficulty with understanding the meaning of what they are seeing.
• They can draw or copy but do not know what they have drawn.
• They correctly perceive the form and know the object when tested with
verbal or tactile information, but cannot identify the object.
• They are unable to link the fully perceived visual stimulus to prior
experience to help them recognize the stimulus.
• Usually associated with damage to the bilateral inferior occipitotemporal

20. Question : Picture of object, animal or tool … ask properties , function..
Sorting : according to category
Match visually dissimilar object with same function. Eg Keys, glass.

22. • Optic aphasia is a disconnection syndrome ( Language—Vision) in
which patients are unable to name visually presented objects but
have no difficulty in naming those objects on tactile or verbal
presentation. Left Occipitotemporal
• Prosopagnosia : Inability to identify familiar faces . Fusiform Gyrus.
– B/L damage to fusiform & lingual gyri
– U/L Rt OP lesion
– B/L or U/L anterior temporal lesion
1. Informal test : face identification
2. Benton Facial Recognition Test ( Formal )

25. Colour Vision Abnormalities

26. Achromatopsia : partial or total absence of color vision. People
with complete achromatopsia cannot perceive any colors; they
see only black, white, and shades of gray.
Incomplete achromatopsia is a milder form of the condition that
allows some color discrimination
b/l or non dominant Inf OT lesions : Lingual & Fusiform G with
sparing calcarine cortex
Colour agnosia concerns the inability to
recognise colours despite intact colour perception,
semantic memory for colour information,
and colour naming. Patients with selective colour
agnosia have been described and the deficit is
associated with left hemisphere damage.
Colour Amnesia : Defect in Colour Object Association
Cannot color pictures, naming defective.
Colour Anomia : Naming Defect

29. Simultanagnosia : inability to synthesize separate features of
the visual field into a meaningful whole(Totality of a Scene)

30. DORSAL
large global letter made of smaller local letters
modified letter cancellation test

31. Ventral

32. DORSAL STREAM

33. Disorders of Dorsal stream
1. Balint Syndrome
2. Visual
disorientation
3. Akinetopsia
4. Astereopsis
5. Visual extinction

34. Balint syndrome
• Occurs due to lesion in b/l parieto occipital lesion in the
convexity of the hemisphere
• Components
• Dorsal simultanagnosia
• Oculomotor apraxia : An inability to visualize more than one object in
the visual field at a time (psychic paralysis of gaze or visual inattention
• Optic ataxia : failure to reach an object under visual guidance.
(Misreaching).
• Test : touch examiner`s ear --- own ear

35. Visual disorientation : Egocentric topographic
disorientation
• Error in judging the location and distance of an object, and
in judging the relative distance between the two objects
• Bump into things while walking , Difficulty in finding door
handle
• Problem arises when things are placed at different level.
Test : Two Objects at 15cm distance ---half meter from
eyes--- ask near / far ; Dot at the center of the circle
• Visual disorientation improves with repeated attempts,
differentiating from optic ataxia

36. Astereopsis
• Loss of depth perception
• Depth is computed from binocular
visual information
• Retinal disparity is processed by the
dorsal stream
• Area 18 is primarily concerned with
stereopsis
• Abnormality is seen due to bilateral
damage, more to the right side

37. Akinetopsia
• Aquired defect of motion perception
• Sees moving people here and there
• Difficulty in pouring water from a cup to
bottle as the water appears as ice

38. Visual extinction : Can perceive one object at a time. If both
fields are stimulated , ignores one

39. Other visual phenomenas

40. Peduncular Hallucinosis
• Charcot – Willebrand syndrome
• Vivid,colourful,formed hallucination
of p[eople and animal
• Usually hypnogogic
• Pseudohallucinosis as patient knows they
are unreal
• Also seen in midbrain lesion as a
release hallucination

41. Charles Bonnet Syndrome
• Seen in patients with visual loss due to
ophthalmological condition
• Well defined, organized and vivid scenes of animals,
flowers and people
• Also a pseudohallucination
• Can be abolished by repeated closing and opening of
eyes
• Deafferentiation of visual assdociation areas leading to a
form of phantom vision

42. • Metamorphopsia( distortions of shape)
• Teichopsia( irregular shapes)
• Macropsia and Micropsia
• Palinopsia (perseveration of visual images : continuation of visual
sensation after cessation of stimulus)
• Visual allesthesia (spread of a visual image from a normal to a
hemianopic field)
• Synthesia : Visual Images by auditory or gustatory stimuli