What and Where visual Pathways presentation by Optom Girma Shallo

1. Presentation on: What & Where Pathways
Presenter: Girma Shallo
(BSc, MSc in COptom 1st year stud.)
University of Gondar
College of Medicine and Health Sciences
Jan 2020
Gondar, Ethiopia
Department of Optometry
Moderator:
Fisseha Admassu, MD
Assist prof in Ophthalmology
(Cataract and Glaucoma)

2. What and Where pathway 2

3. Objectives
After this presentation you are expected to:
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• Understand the “What” and “Where” pathways
• Compare the “What” and “Where” pathways
• Describe disorders of the “What” and “Where” pathways
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4. Outlines
▪Visual pathways
▪What pathways (ventral streams)
▪Disorders of What pathway
▪Where pathways (dorsal streams)
▪Disorders of Where pathway
▪Comparison
▪References
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5. The Visual Pathway
▪ It is the pathway over which a visual sensation is transmitted from the
retina to the brain.
▪ It includes:
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• Lateral Geniculate Nucleus (LGN)
• Optic Radiations, and
• Striate Cortex
• The Retina
• Optic Nerve
• Optic Chiasm
• Optic Tract

6. The Visual Pathway… 6

7. The Visual Pathways (Streams)
• Starting from 1960s, scientists had the ideas that the visual system
could be divided into two separate components (Held, 1968;
Schneider, 1969)
• The first empirical evidence on the existence of ventral and dorsal
streams provided in 1982 (Ungerleider & Mishkin)
• The first and most influential report came in 1991 (Goodale & Milner).
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8. The Visual Pathways (Streams)…
• The two functionally and anatomically distinct visual processing
pathways (streams) originating in the occipital cortex are:
1. The What pathway ("ventral stream")
2. The Where pathway ("dorsal stream")
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9. What and Where pathways
Are concerned with visual perception and cognition
processes which take place in the brain.
Visual analysis occurs through
these two principal paths.
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10. What pathway
• Located on the junction of the occipital
and temporal lobes.
• Extends into more anterior and ventral
portions of the temporal lobe.
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11. What pathway…
• It is associated with carrying visual information related to object form
and recognition from primary visual cortex (V1) to the temporal lobe.
• This stream deals with the general problem of object recognition
• Neurons in this stream respond selectively to visual features needed for
object identification (color, shape, texture, etc).
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12. Disorders of What pathway
▪Damage to the What pathway (ventral stream) can cause inability to
recognize faces or interpret facial expression.
▪The specific clinical syndromes due to occipitotemporal lesions include:
 Visual object agnosia
 Prosopagnosia
 Achromatopsia
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13. Disorders of What…
▪Visual object agnosia
⁎ Can not translate the image they see into an idea in their minds
⁎ Severely impaired in shape and form discrimination
⁎ Caused by extrastriate lesions in occipital and temporal cortex.
⁎ Can have preserved VA and minor VF defects,
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14. Disorders of What…
▪Prosopagnosia: from Greek, ‘prosop’ – ‘face’ and ‘agnosia’ -'ignorance’
• also known as face-blindness,
• is an inability to recognize familiar faces
• Caused by right anterior inferior occipital lesions in the region of the
occipitotemporal junction.
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15. Disorders of What…
▪ Achromatopsia: cortical color blindness.
• is characterized by a partial or total absence of color vision.
• People with partial achromatopsia can perceive color but have
difficulty distinguishing between certain colors, such as red and green.
• People with complete achromatopsia cannot perceive any colors, but
only black, white, and shades of gray.
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16. Disorders of What…
❑Patients with achromatopsia can experience
 Photophobia,
 Nystagmus,
 Low visual acuity,
 Hyperopia,
 Myopia, (less common)
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17. Where Pathway
⁎Where pathway (“Dorsal”, or “how” stream)
• Located on the junction of the occipital and parietal lobes.
• Stretches from V1 in the occipital lobe into the parietal lobe.
• It contains a detailed map of the VF.
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18. Where Pathway…
• It is a visual process which is involved in:
 Recognizing location of objects in visual space
 Guidance of actions to manipulate them
 Perception and interpretation of spatial relationships, accurate
body image
 Learning of tasks involving body coordination in space
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19. Where Pathway…
• Detecting and analyzing movements.
• Neurons within the dorsal stream respond selectively to spatial
aspects of stimuli, such as the direction and speed of stimulus
motion.
• These neurons also respond when a person visually tracks a
moving target.
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20. Disorders of Where Pathway
▪Spatial disorders due to damage to the posterior parietal cortex:
⁎ Optic ataxia
⁎ Akinetopsia
⁎ Apraxia
⁎ Simultanagnosia
⁎ Hemispatial neglect
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21. Disorders of Where…
• Optic ataxia: the patient can't use visuospatial information to
guide arm movements (mis-reaching).
• Akinetopsia (motion blindness): an inability to perceive motion,
despite stationary objects remaining more or less visible.
• Apraxia: inability to produce movement in the absence of
muscular disorders.
• Simultanagnosia: the patient can only describe single objects
without the ability to perceive it as a component of a set of details
or objects in a context (e.g percieve forest as a single tree)
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22. Disorders of Where…
• Hemispatial neglect: Inability to be aware of things in one
FOV while perceiving them in the other.
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Fig. 1. Clock picture drawn by a patient with neglect syndrome

23. Comparison of What & Where pathway
What pathway Where Pathway
Also called ventral stream Also called dorsal (how) stream
Originates in primary visual cortex Originates in primary visual cortex
Extends along the ventral surface Extends along the dorsal surface
Leads into the temporal cortex Leads into parietal cortex
Recognition/identification of objects Visually guided behavior
Neurons respond to visual features needed
for object identification
Neurons respond to spatial stimuli
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24. What and Where pathway… 24
Red - face matching
Green - location matching
Yellow - both tasks.
Fig. 2. Diagrammatic representation of what and where areas in the occipital brain

25. References
1. Vaughan & Asbury. General Ophthalmology: 19th ed, 2018
2. Kaufman, Paul L. Adler’s Physiology of The Eye: 11th ed, 2011
3. https://en.wikipedia.org/wiki/Two-streams_hypothesis (Accessed 22/01/2020)
4. http://www.richardsonthebrain.com/visual-pathways (Accessed 22/01/2020)
5. Dr. Leslie G. Ungerleider, Dr. Luiz Pessoa (2008): What and where
pathways, (scholarpedia.org)
6. Goodale, M. (1994). Separate neural pathways for the visual analysis of
object shape in perception and prehension. Current Biology, 604-610
7. https://ghr.nlm.nih.gov/condition/achromatopsia (Accessed 22/01/2020)
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26. .
THANK YOU
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