extrastriate cortex, dorsal stream, ventral stream, visual areas 2, 3, 4, 5, MT and IT, V2 and V3 inputs and projections, motion perception, global stimulus, motion aftereffect, V4 inputs and projections, visual agnosia, synaesthesia, grandmother cells, visual integration, binocular rivalry, bottom-up visual attention, top-down visual attention

1. Extrastriate cortex
Dr Gauri Sr Shrestha
MMC, IOM, TU

2. Learning objectives
• Overview the extrastriate cortex.
• Understand the extrastriate cortex inputs and projections.
• Elaborate dorsal and ventral processing streams.
• Understand visual integration and attention associated with
the extrastriate cortex.
• Define the types of visual agnosia.

3. The Extrastriate cortex
• Attributes to analysis of specific visual stimuli and have a
degree of functional specificity relating to particular stimulus
attributes
• e.g., color, form, movement, texture, binocular disparity etc
• Human have around 20 cortical visual associated areas
• V1 and extrastriate cortices together occupy ~ 30–40% of the
cortex.
• V1 ~ 12 – 18 %
• Retinotopic organisation is cruder than that in V1
• No distinguished by Line of Gennari

4. Visual
processin
g in the
nervous
system

5. The Extrastriate Cortex
• Extrastriate Cortex Areas
Include:
• Visual area 2 (V2)
Dorsal stream
• Visual area 3 (V3)
• Visual Area 5 (V5)
• Middle Temporal (MT) cortex
Ventral stream
• Visual area 4 (V4)
• Inferotemporal (IT) cortex
AIT
PI

6. Processing Streams
Stream Function Input Origin
Passes
through
Destination Pathway
Dorsal
(parietal)
Spatial
location,
motion
perception
M and K
channels
V1
V2, V3,
MT (V5)
Parietal
cortex
Where
(Magno)
Ventral
(temporal)
Object
recognition
P, M,
and K
channels
V1 V2, V4
Temporal
cortex
What
(Parvo)

7. V2 inputs and projections
• V2 Inputs
• from the same V1 layers and is segregated
according to two pathways:
• (a)CO blobs to thin stripes
• (b)Interblob areas to pale and thick stripes
• V2 projections
• The neurons in the thin and pale
stripes project to V4
• Associated with a ventral stream for form
processing, color, and object recognition.
• The thick stripes project to V5, a dorsal
stream area
• associated with motion processing
• Some thick stripe neurons project to the SC
for controlling saccadic eye movement.
https://entokey.com/the-extrastriate-cortex/

8. V3 inputs and projections
(for supplementary reading)
• V3 is a narrow area of the cortex in front of V2.
• Its precise location and function are controversial.
• V3 dorsal and ventral halves represent the lower and upper
visual quadrants, respectively
• Dorsal half: direction of movement, stereopsis
• Ventral half: color, orientation

9. V5/ MT inputs and projections (the
Dorsal stream)
• V5/ MT inputs
• input from direction-selective cells in V1
• Input from the cells located in thick stripes in V2.
• V5 neurones are sélective for:
• orientation of elongated contours
• direction of movement
• binocular disparity
• wide-field motion contrast.
• V5 has connections with frontal eye fields important in generating smooth
pursuit movements
• V5 also receives inputs from the pulvinar and koniocellular LGN cells that
bypass V1.

10. Motion Perception and V5
• In addition to the direction Selectivity to
individual grating movement, certain
cells in V5 respond best to the complex
grating (of Global motion perception)
and manifest coherence thresholds
• Global Stimulus
• Stimulus composed of two components
• Appears as a single object moving in an
intermediate direction
• the ability to perceive the overall,
coherent motion of a visual scene
Global
Stimulus
Random dot kinematogram
showing coherence
thresholds

11. Motion Aftereffects (MAEs)
• Illusions of motion that occurs in the
absence of motion
• Due to the adaptation of direction-
specific motion detectors
• View an example of MAE
• V5 is active while the individual is
experiencing the aftereffect even
though the object is stationary

13. V4 inputs and projections (the ventral
stream)
• Receptive fields of V4 neurons are substantially larger than
those of V2 and V3 neurons
• V4 Inputs
• receives direct inputs from V1, V2 (thin stripes and pale stripes), and V3
(ventral half).
• Receives V1 inputs from P, M, and K channels arising from layer 3 CO
blobs and interblob regions.
• V4 projections
• projects to inferotemporal areas involved in detailed object form
analysis (object recognition)
• Cells in V4 are principally concerned with color sensitivity

14. IT inputs (the ventral stream)
• Cells have large, complex receptive fields selective for particular
combinations of orientation, size, texture, and color.
• IT Input
• receives input from V2, V4, and the prefrontal cortex
• is involved in perception and recognition of objects
• can display invariance to stimulus size, rotation, and visual
field location.
• can detect sophisticated forms (circles, squares, ovals)
• Fusiform face area (FFA)- recognizes faces not other objects
• Parahippocampal area (PPA)- recognizes objects and places
https://entokey.com/the-extrastriate-cortex/

15. Overview of the extrastriate cortex
Stream
Extrastriate
area
Function
V2
Thin dark stripes: color processing
Thick dark stripes: orientation selectivity and
binocular disparity
Pale stripes: form processing and object recognition
Dorsal
V5/MT
V3
Parietal areas
Direction of movement, binocular disparity
Dorsal V3: direction of movement
Ventral V3: color, orientation
Visuospatial perception and movement planning
Ventral
V4
Inferotempor
al areas (IT)
Color sensitivity, object recognition
Complex receptive field properties, e.g., form
perception and face recognition

16. FIGURE | Left: A typical hierarchical, feedforward model,
where information processing starts at the retina, proceeds
to the LGN, then to V1,V2, V4, and IT.
https://www.researchgate.net/publication/267872860_Why_vision_is_not_both_hierarchical_and_feedforward
https://www.frontiersin.org/articles/10.3389/fncom.2014.00135/full

17. Additional inputs to extrastriate cortex
• Some extrastriate cortical areas (e.g., area MT) receive
substantial direct input from dorsal thalamic nuclei
(the lateral geniculate nucleus (LGN) and the pulvinar).
• Laminae of the LGN (K layers) and regions of pulvinar which
project to the extrastriate cortices receive direct input from
the superficial layers of the superior colliculus (SC).

18. What happens with a lesion in the
cortex ?
• Striate Cortex
• Simple blind spots (scotomas)
• Extrastriate Cortex
• Ventral Processing Stream
• Visual Agnosia – inability to recognize objects**
• Dorsal Processing Stream (superior temporal lobe)
• Visual Neglect – patient ignores area of visual field

19. Visual agnosia
• Form and pattern
▫ Object agnosia inability to recognize real objects
▫ Agnosia for drawing inability to recognize drawing objects
▫ Prosopagnosia inability to recognize faces
• Color
▫ Color agnosia inability to associate colors with objects
▫ Color anomia inability to name colors
▫ Achromatopsia inability to distinguish hues
• Depth and movements
▫ Visual spatial agnosia inability to perceive stereoscopic vision and
topographical relations
▫ Akinetopsia inability to perceive motion
Prosopagnosia

20. Synaesthesia
• Cortical modularity is
abnormally linked to
each other such that
stimulation of one sense
results in the activation
of another
• e.g.,
• Presentation
perception
• 5 green
• 2 red
On left, the the image of a number
matrix as the non-synaesthete sees it;
on right, a color-coded representation of
how a synaesthete might see it

21. Grandmother cells (GC)
• GC is a hypothetical neuron that represents a complex but
specific concept or object
• Remembrance of visualized objects result in a pattern of
activity that is similar to that elicited by actually viewing the
object.
• It activates when a person "sees, hears, or sensibly
discriminates“ a specific entity, such as their grandmother.
• Visual signal is continuously processed until it reaches a
high-level cortical cell whose activity results in visual
consciousness

22. Visual
integration
• Information from various
cortical areas must be
integrated for our perception
• Example: Viewing a moving
red car
• Motion and position
information from dorsal
stream must be integrated
with color and form sense
from the ventral stream
• The integration occurs in the
Prefrontal cortex

23. Binocular rivalry
• the presentation of mutually
incongruent images to the left
and the right eye, which typically
results in the perceptual
alternation of the two stimuli
instead of their perceptual
fusion.
• occurs when two eyes view
different images at the same
time presented to corresponding
retinal locations of the two eyes.
Figure. Experimental design and stimuli.
Following a practice session, subjects
viewed a composite of red circular and
green radial gratings through a pair of
red–green anaglyphic glasses. They
perceived a stochastic alternation in
percept between the two monocular
images (binocular rivalry).
https://www.frontiersin.org/journals/neuroscience/articles/10.3389/

24. Binocular rivalry
• An observer is
presented with two
different images to the
two eyes. During
binocular rivalry, the
observer experiences
alternating perceptions
in a temporally
stochastic fashion,
rather than a constant
mixture of the two
images.
https://link.springer.com/article/10.1007/s41745-017-

25. Bottom-Up Visual
Attention
• Lower visual area cells respond to
physical characteristics
• Higher cells reflect two equally
plausible perception we observe
• Examples: Ambiguous figures:
Bistable percepts in
• Necker Cube
• Rubin’s Face-Vase
• Bottom-Up Visual Attention
• Observer does not ‘choose’ the
perception

26. Top-Down Visual Attention
• We perform better on certain tasks when we are attentive to
the demand of those tasks
• Subject chooses which object in the cell’s receptive field to
focus visual attention on
• Cortical cells reflect this conscious choice of attention
• Since this choice comes from higher areas in the brain, it is
referred to Top-Down Visual Attention

27. Can vision be trained?
Visual training-
associated
attention may
improve visual
skills
Visual
performance of
adult can be
improved with
practice-
perceptual
learning but not
resolution task.
Learning certain
task can be
selective other
generalizable
Continue
exposure to
subliminal
stimuli can
influence
behavior.

28. Thank you