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BHS 140.2 – Vision Science II
Notetaker: Elisabeth Anderson
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Date: 4/23/2013, 2nd hour
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Disorders of the Ventral Pathway: Prosopagnosia
o There is not just one face area in the brain, but three key areas
 They are extensively interconnected with one another
 They also extensively interact with other regions of the brain
 Not that difficult to have a disruption with all the interconnections
 Disruptions can be acquired or congenital
o People with disruptions will have a problem with face perception
o Can be difficult to interact with people you don’t know, but with people you know well you will
be able to recognize them by voice and other attributes
o First case study reported in 1956
 Man woke up from being unconscious and could see his family’s faces but couldn’t
recognize them
 Results from post V1 damage
 This man could see his face well enough to shave, but couldn’t recognize his own face
o MRIs on top of pg. 26
 The top row of MRIs are from patients with congenitally acquired prosopagnosia
 Bottom row are matched controls
 The pathways that the axons travel in that are important for facial recognition are the
inferior frontal occipital fasciculus (IFOF, not responsible for knowing this one) and
inferior longitudinal fasciculus (ILF) (shown in images)
 Clinicians were able to calculate the volume of white matter in each tract
 Patients with prosopagnosia had less volume of white matter in the important tracts than
in the controls
 Severity of symptoms correlated with volume of axonal white matter
 Patients 2,4, and 6 appear significantly different in the thickness shown in the image, but
remember the total volume of axonal white matter was measured, not just the thickness in
the image
 The ILF runs along the lateral walls of the inferior and posterior lateral ventricles in the
temporal lobe
 The temporal lobe is an important part of the ventral pathway
o Brain image in middle of pg. 26
 Green represents axons of ILF that connect the temporal lobe with the occipital lobe
 The red (squiggly lines) represents the u-shaped loops coming from the right cerebral
hemisphere, not part of ILF
o Amish farmer could not distinguish his family members by their faces but he could distinguish his
sheep by their faces
 This indicates that processing centers for human faces and animal faces must be in
different places
Turning Point Questions
o Q: Which of the following will produce the weakest response from a “face” neuron?
 A: Random collection of facial features
o Q: Which of the following is an example of endogenous attention?
 A: Searching for a face in the crowd
o Q: What does visual agnosia mean?
 A: Inability to recognize objects
o Q: The ability of patient DF to correctly make a motor movement of a visual target indicates that
which pathway remains intact?
 A: Dorsal
Dorsal Pathway
o There may be up to a dozen pathways, and there are extensive interconnections between all the
pathways
o Not just ventral and dorsal pathways
o Dorsal stream is responsible for the visual guidance of actions
 Reaching, grabbing, directing eye movements
o Part of visually guiding an action is knowing where objects are
o Dorsal pathway is not just a “where” pathway though, it is much more
BHS 140.2 – Vision Science II
Notetaker: Elisabeth Anderson
o
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Date: 4/23/2013, 2nd hour
Page2
Memorize and be responsible for dorsal pathway from top to bottom:
 Retina
 LGN
 V1
 V3A/V5
 Posterior Parietal Lobe (inferior lobule)
o Area that is specialized for motion V5/MT is on the border between the occipital lobe and the
parietal lobe not far from the temporal lobe
o Posterior parietal lobe is where the dorsal pathway ends
o Post central sulcus divides the anterior part of parietal lobe from posterior part of parietal lobe
 Posterior portion of parietal lobe is posterior to sulcus
o Posterior portion of parietal lobe has a superior lobule and inferior lobule
 Superior and inferior parietal lobules are separated by intraparietal sulcus
 Inferior lobule of posterior parietal cortex is where dorsal pathway comes to an end
Characteristics of Dorsal Pathway Neurons
o Receives visual information and transform it into the control of action
o The dorsal pathway needs input about object’s location size and shape
 Input sent to dorsal pathway is from ventral pathway, but not in the same amount of
detail that ventral processing can accomplish
o Output of dorsal pathway is sent to motor cortex, basal ganglia, and brainstem
o Dorsal pathway has no conscious perception or long term memory
o Dorsal pathway has neurons with large receptive fields
o Every neuron in the pathway is directionally sensitive to motion
 Each neuron responds best to their preferred direction
o Area MT/V5 is where most of the directional sensitivity is most prominent
o Area MT was discovered in monkeys in the posterior part of medial temporal gyrus
o In humans area MT is located in the ascending limb of the inferior temporal gyrus
o Online Tutorial
 In area MT the cells are arranged in columns just like in V1
 Each column responds to one part of the visual field
 Each neuron in a column responds to only one preferred direction of motion
 Know that each part of the visual scene has a column of neurons in MT associated with it
with specific directional neurons responding to it
 Area MST, just lateral to area MT is divided into MST lateral (MSTl) and MST dorsal
(MSTd)
 MSTl has small receptive fields
 MSTl responds to object motion along with MT
 MSTd neurons have huge receptive fields that cover almost the whole visual
scene
 MSTd neurons respond to motion in the whole visual scene
 Self-motion and optic flow occur all over the retinal image
 MSTd is responsible for encoding optic flow which signals self-motion
 A microelectrode is inserted into area MT of a monkey recording impulses per second
traveling down a neuron in a specific receptive field
 Neuron really responds to upward motion in that receptive field
 While recording they trained the monkey to change their attention to a different stimulus
 When the monkey was not paying attention to the upward motion stimulus the
response is not increased
 When the monkey attends to the stimulus that is moving upward the response is
increased
 If you want neurons in MT to respond to the preferred stimulus motion they
have to attend to that stimulus
Disorders of Dorsal Pathway
o Problems with dorsal pathway make visually guided movements problematical
o In 1909 Balint described a patient with bilateral strokes in parietal lobe
BHS 140.2 – Vision Science II
Notetaker: Elisabeth Anderson
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Date: 4/23/2013, 2nd hour
Page3
Balint syndrome symptoms
 Patient could not grasp an object with their eyes open
o This is referred to as Optic Ataxia
o Patient could do the task with their eyes closed
o Shows that it was not a problem with motor neurons
o Able to close eyes and touch ears when instructed
o Can’t put together visual guidance and motor activity
 Simultagnosia
o Inability to perceive things simultaneously
o Posterior parietal lobe is somehow involved in selective attention
process
o Problem is that subjects spotlight of attention is so narrow they can
only focus on one stimulus at a time
 Patients cannot generate voluntary saccadic eye movement
o Have to turn their head if they want to look in a different direction