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GWU / Psychology / PSYC 3122 / How would you describe the anatomy of retina?

How would you describe the anatomy of retina?

How would you describe the anatomy of retina?

Description

School: George Washington University
Department: Psychology
Course: Cognitive Neuroscience
Professor: Shomstein
Term: Fall 2016
Tags:
Cost: 50
Name: Cognitive Neuroscience Exam 2 Study Guide
Description: Material on Exam 2: Visual System Attention Emotions
Uploaded: 04/03/2018
25 Pages 40 Views 5 Unlocks
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Cognitive Neuroscience Exam 2 Study Guide 


How would you describe the anatomy of retina?



The Visual System 

Visual Agnosia  

∙ Patients have problems in perception (not sensation)

∙ Video Example:  

o When the patient was looking at the tea bag he was able to recognize  and “see the string” but not the tea bag  

o Once he touched the tea bag he was able to figure out what it was

o Somewhere in the reconstruction process of the visual stimulus,  something went wrong If you want to learn more check out What is physiological therapy?

Visual Perception: Light  

∙ Light = range of electromagnetic radiation (particles and waves) o Particles are photons  

o Waves of various lengths  

∙ We have sensory receptors sensitive to the physical stimulus  o Short vs medium vs long waves  


What does fovea see?



∙ Light bounces off surfaces, it is the reflection of light that is collected by our  eyes  If you want to learn more check out Who is giovanni pietro bellori?
Don't forget about the age old question of What is the role of the rna polymerase?

The Eye 

Retina 

∙ The retina is all the way in the back of the eye  

o So all the physical stimuli may get warped on its journey to the retina  (poor design?)

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∙ Retina Anatomy:  

o Synapse in the middle layer of the retina  

o Synapses on the retinal ganglion cells  

o Receives info via synapase  

o Axons of retinal ganglion cells form the optic nerve  

∙ Contains sensory receptors that absorb photons of different wavelengths  ∙ The point of conversion of physical stimuli to neural signal at rods and cones  ∙ Photoreceptors (photopigment molecules):


Where si the nasal side of the eye located?



o Rods: low levels of stimulation (night vision) - 120 million  

 Sensitive to a wide range of wavelength  

 Do not code for color, don’t differentiate  

 When it’s dark, you rely on rods  

 Example of looking at constellations  

o Cones: intense light, day vision - 6 million  

 Only responds to intense light, used during the day time  

 Red, green, blue

 Have a higher threshold  

o Rods and Cones are all the way in the back of the eye pointing away  from the source of light (lens) Don't forget about the age old question of What are the variables used in the analysis?

Optical Tract: Blind Spot 

∙ Distribution of rods and cones on retina is the “cause” of the blind spot o Where optic nerve leaves the eye there are no rods and cones  ∙ Fovea “sees” only central 2 degrees (side of thumb at arm's length)  

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o At Fovea, the amount of cones

spike, while the amount of rods

goes down  

 Cones needed for acuity  

o Most rods are in the peripheral

vision  

 Rods don’t have such great acuity  

∙ Our field of view is 80 degrees to the right and to the left If you want to learn more check out What is the scope of hemisphere specialization?

o Information form one eye picks up slack for the other  

From Eye to the Brain  

∙ Each eye receives information from different side of space

∙ Left side of the brain receives information from the right visual field  ∙ Right side of the brain receives information from the left side of the brain  ∙ Stimuli in the left visual field is processed in the right primary visual cortex.  

o This stimuli is taken in on the nasal side of the left eye and the  temporal side of the right eye (the right side of each eye)

∙ Stimuli in the right visual field is We also discuss several other topics like What are the different schemes observed in saltworks at chaux?

processed in the left primary visual

cortex

o This stimuli is taken in on the  

temporal side of the left eye and

the nasal side of the right eye (the

left side of each eye)

∙ Each eye receives information from a

different side of space  

∙ Nasal side of the eye = ipsilateral (same)

side  

o This side of the eye is taking in stimuli from the same side its on  3

∙ Temporal side of the eye= contralateral (opposite) side

o This side of the eye is taking in stimuli from the opposite side its on  ∙ Temporal information foes not have to cross (decussate)

∙ Nasal part crosses the midline at the optic chiasm  

∙ Temporal part remains on the same side

∙ 90% of axons go to the LGN and 10% go to the superior colliculus  

o this 10% of the visual nerve is larger than the whole auditiory nerve  combined  

∙ Pathway:

o The optic nerve leaves the eye, two sections (functionally different),  some decussates (splinters/crosses midline)

 Part of the info goes to the left hemisphere and other parts goes  to the right

o All of the info synapses at the thalamus at the lateral geniculate  nucleus (relay station)

∙ Info then goes to the primary visual cortex (on calcarine sulcus in occipital  lobe) by optical radiation  

Lateral Geniculate Nucleus (LGN)  

∙ Retinotopic = nearby cells have nearby receptive fields

o Nearby locations in space are represented by nearby neurons/cells  o The LGN consists of 6 layers with retinotopic organization  

∙ Cells respond to bars of light stimulus  

o The receptive field of these cells have on-center/off-surround  system

 If the stimulus is on the on-center of the cell, then the cell is  active

 If the stimulus is on the off-surround of the cell, then the cell is  inhibited

 If the stimulus is on both on-center and off-surround there is no  change

∙ LGN Neurons have a very small visual field

o Top 4 layers: larger cells, Parvo (slow)

 Receives information from cones  

 color!

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o Bottom 2 layers: Mango (fast)

 Receives information from rods

∙ Ipsilateral vs Contralateral  

o Same vs opposite retina  

o Layers of LGN receive info from different retina  

Visual Cortex 

∙ V1, Area 17  

∙ Retinotopically organized  

o Organized according to cortical modules – a group of neurons with  nearly identical receptive fields  

 About 1 mm of physical cortex  

 Of all the neurons ½ the dedicated to processing information  from the left eye and ½ from the right  

 Also have color blobs that sort colors/input from rods (no  

processing)

∙ Maintain Mango/Parvo distinction

o Mango= rods, parvo= cones  

o ~4 million neurons  

∙ RF = 0.5 of visual angle  

o Many to one convergence of LGN to

V1

 Many LGN cells to one V1 cell  

o All of the LGN cells need to be

activated and sending input to their

V1 cell in order for a response to

occur  

 Only a vertical line can do this

( hitting all 3 on centers in the

LGN cells)

o LGN cells are PHYSICALLY hooked up to their respective V1 cell  ∙ V1 cells see color and orientation

Visual Cortex 

∙ If you damage V1 on the left side, they are blind to information on the right  side (as if you don’t) have eyes  

o Cortical blindness

o More Specifically: If you have lesions on the superior and inferior banks of the calcarine fissure, this result in cortical blindless  

Cortical Visual Areas  

∙ Orientation is so important because all visual stimuli is made out of  orientation (small lines next to lines next to lines....)

∙ Optimal stimulus more complex as you continue along the route o V1 -> V2 -> V3 ->  

 As you go onto V3 and V4 you get curvature  

 V1 = line  

 V3= curve  

 Complex preferences increase as you go on and on

o Increasing receptive field as you keep going  

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∙ Several cells specific for one particular curve  

o If all of those cells died (which is unlikely), you will be blind to that  curve  

∙ Bidirectional Connectivity  

∙ Receptive Field: 0.5 in V1 to 40 in TE

Imaging : Retinotopic Mapping  

∙ Looking at fMRI we can map out V1, V2, V3… etc  

∙ There are so many areas because there is a hierarchy

o Retina : points of light, very small  

o LGN: on/off cells, bit larger RF

o V1: Larger receptive fields, orientation selectivity  

o V2, V3, V4: Even Larger receptive fields, gets increasingly specific   edges, T-junctions, curvature  

∙ Analytical; divide and conquer  

o Different parts of visual field are responded to differently in a system of highly organized cells  

Segregation of Duties; Parallel Pathways  

∙ Rods -> LGN Mango Cells -> V1

o Movement and contrast sensitive  

o Color and location insensitive  

 Larger receptive fields  

 Low acuity  

∙ Cones -> LGN Parvo Cells -> V1

o Color and orientation selective  

o Contrast insensitive  

V4 Selectivity: Color  

∙ Receives information from color blobs in V1

∙ Only fire action potential if the light has different color (not black and white) ∙ In imaging studies…  

o Show colored blocks to subjects in fMRI

∙ Damage to V4 results in cortical color blindness (not eye related, cones are  likely fine)

Color Blindness  

∙ Eye related color blindness results from issues with cones

o This is more likely in males  

∙ Achromatopsia = cortical color blindness resulting from damage to V4 o To evaluate, do a test of reflectance (brightness) versus Hue (color)  Reflectance stays the same but color will change  

 Color change X axis and on y axis reflectance stays the same   Show two blocks separated by hue, patient won’t see a  

difference

 Show blocks separated by reflectance and the patient will be  able to tell a difference (greyscale)

Motion and Speed (Region MT) 

∙ En route to parietal cortex

∙ Sensitive to which way the visual stimulus is moving and at what speed  o Activation of the MT neurons influences the perceived direction of  motion  

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∙ Damage to MT will result in movement dysfunction  

o Akinetopsia= loss of motion  

Constraints on Perception  

∙ Complexity builds up as a result of many to one convergence to a single cell ∙ Is perception constrained by an architecture based on concurrent processing  pathways?

o Is information is really being built up from step to step  

o There is a functional consequence to this “divide and conquer  approach”

 Many different areas needed to process one stimuli  

Faces/Objects and Reaching/Grasping  

∙ The Primary visual cortect segregates into two streams from the occipital  lobe, The WHAT and WHERE pathways

∙ The WHERE Pathway

o Parietal Lobe - Dorsal Stream

 Where information is and how to reach for it

o VIP, 7a - Reaching and grasping  

∙ The WHAT Pathway

o Temporal lobe - Ventral Stream  

o Identification  

o FFA (Fusiform Face Area) = Processes faces  

o LOC and IT - Objects ‘

∙ These two streams are independent  

o Constrains how information is processed in the visual stream  

Spatial Versus Object Perception  

∙ Those with damage to both sides of V1 (primary visual cortex) are cortically  blind

∙ Weiskrantz (Blindsight)

o Threw a rubber ball at patients, and even though the patients were  blind, they tried to swat away the ball when it was thrown  

 They were reacting because 10% of the visual nerve goes  

straight to the parietal lobe which deals with the what and  

where pathways  

 Even though these patients were cortically blind, they could  sense the ball coming at them

o This phenomenon is Blindsight

∙ Another experiment by Weiskrantz; He ask blind patients to look at a screen,  he projected an image on the screen and sounded a beep at the same time.  Asked them to look at the screen  

o Plotted a graph of where the light was and where the patients looked  o When the target was close to the fixation point, the patients were  actually more accurate (@ 5 degrees) and got more inaccurate as the  target went farther from the fixation point

Empirical Evidence for Two Streams (What and Where) 

∙ Ungerleider and Mishkin performed this experiment  

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∙ Hypothesized that What and Where are computed independently  ∙ Trained monkeys on two tasks involving revealing food wells; the Landmark  task and object task  

o Object tasks: learned that food would be under a particular shape o Landmark Task: learned that food would be in a particular area  ∙ Lesioned parietal or temporal cortex and then retested  

o Lesioned temporal -> cannot perform object task, but perform  perfectly well on landmark task  

o Lesioned parietal -> cannot perform landmark task, but perform  perfectly well on object task  

o This shows…

 The two pathways are separate, independence of the two  

processes  

 Double dissociation  

Summary of Anatomical Segregation of Streams  

∙ “Where” Pathway

o Dorsal stream  

o Parietal lobe  

∙ Primary Visual Cortex

o Occipital lobe  

∙ “What” Pathway

o Ventral stream

o Temporal lobe  

∙ Object Discrimination Task performed poorly when Temporal Lobe  waslesioned  

∙ Landmark Task performed poorly when Parietal lobe was lesioned

 Properties of The “What” Pathway  

∙ The “What” Stream is in the the temporal  

o Encompass fovea info on right or left fields  

∙ Temporal Association Cortex

∙ Present many pictures while recording from a single cell  

∙ Simplify the stimulus as much as possible  

∙ Stimuli found to be selectively excite cells in inferior temporal cortex ∙ Neurons may have preferences for complex visual features  

o Orientation (in V1) combines to make further meaning  

∙ Building blocks of vision that neurons have preference for  

o Convergence from many neurons to one neuron  

∙ If you were able to record from every single cell in the temporal lobe, you  would be able to see all the building blocks of vision  

∙ Columns of related shape-selective cells may exist in inferior temporal cortex, similar to orientation columns in primary visual cortex

Properties of the “Where” Pathway  

∙ Perception for Action vs for Identification  

∙ Patient DF:  

o Had carbon monoxide poisoning but survived

o Had damage in occipital cortex damage (bilateral) and temporal  8

 Lesion is diffuse  

o She is now severely agnosic in regards to the visual images  

 She has no abilities for object recognition, but she can reach out  and grab items perfectly fine  

o When given a What/Where task…

 Orientation matching is impaired  

 Given a piece of paper to inset into a slot, unable to orient

the paper to fit in the slot  

 Action preserved  

 Can perform the action of moving her arm to insert the  

paper

 Memory is intact  

o She cannot recognize the object until it is given to her to interact with  o Other tasks- irregular novel shapes  

Different Types of Agnosia  

∙ Apperceptive

o Right hemisphere, posterior lesions  

o Low levels

o Areas V2, V3 are damaged  

o Lacking parts of cortex that combine the multiple orientations derived  from V1

 Occipito-temporal vision areas are impaired

o Failure to recognize objects due to functional impairments in the  perception process  

∙ Integrative

o Right/Left hemisphere, more anterior lesions  

o Intermediate levels  

o Patients are presented a homogenous display, (all right side up Ts  except for one) and a heterogenous display (One T is upside down and  the rest are in many different ways), goal is to locate the upside down  T

 For a Control Group with no brain damage, it takes them longer to find the upside down T in the heterogenous display

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 You actually have to search through each T to see which is

upside down  

 In a homogenous display it’s easy to group all of the right  

side up Ts  

 For Patient HJA, they are able to process both at about an equal  amount of time

 They are lacking the part of the cortex that fuses the  

features together  

∙ Associative

o Left hemisphere, more anterior lesions  

o High level

o Cannot match visual representation with a correct label  

o By looking at the way they color in overlapping images, it is clear that  the patients can differentiate the separate items  

 Poor info processing

∙ Bedside Task for Agnosia Patients  

o Copying down an image (two squares and a circle)

o Apperceptive Patients will dray just squigly lines  

o Integrative Patients will probably draw the outline of the shape,  lacking the understanding that there are 3 different options  

∙ SAMPLE QUESTION: When you show each agnosic patient  

an item, they all will say they don’t know what it is, but all

for different reasons. Why does each patient say this?

o Answer: Apperceptive agnosic patients cannot perceive the item due to impairments in V2 and V3. Integrative agnosic cannot see the object as a whole. Associative agnosic patients cannot associate a name with  the object

Patient CK 

∙ A man who was hit by a truck, resulted in Integrative agnosia 10

∙ Task 1: read and write a sentence  

o He cannot read, the letters are just blobs

o When asked to copy the sentence as it was typed out, he copies down  the literal font

 He doesn’t process that these are letters/words, just shapes

o when the sentence is read to him he was able to write it in his own  handwriting

∙ Task 2: Asked him to draw England and a Guitar  

o He is able to draw it but if he is presented with the photo that he just  drew he was unable to recognize the object  

o

Faces vs Objects; What is so Special about Faces 

∙ There is a strong dissociation between object and face processing  

∙ Patient CK, who has integrative agnosia and couldn’t recognize objects, was  able to recognize faces

∙ Indicates that neurons had different preferences for faces

o Different pathways  

∙ Faces are…

o Important socially  

o Consistent (almost every face has two eyes, a nose a mouth…)

Tanaka and Farah, 1993 

∙ Experiment that showed that Subjects more accurate at identifying whole  faces rather than parts of a face

o The computation that is happening on a face is much different from the computation on an object  

∙ This part/whole difference did not hold for other kinds of stimuli 11

o Scrambled faces, inverted faces, houses  

∙ Concluded that faces are represented holistically

o Parts not represented on their own, only in the context of the whole  face  

∙ Holistic Effect:

o Faces are hard to perceive upside down (inversion)

o The holistic effect disappears

Why are Faces Represented Holistically  

∙ View 1: “Special”

o Area of the brain devoted specifically to recognizing faces, so not  processed like other objects (FFA)

o Faces are evolutionarily important to primates (social cues)

o Fusiform Face area shows both generality and specificity

o The Fusiform Gyrus is instrumental in facial processing  

∙ View 2: “Expertise”

o Faces are different from other objects, subordinate level  

 Subtle perceptual differences

o We never look at a face and say “oh look, a face!”  

 We refer to the face by the person’s name  

o We are all “face experts”  

 Fine distinctions among many faces

o Faces are represented holistically just like experts represent their  objects of object expertise  

∙ Bird and car experts show activity in the Fusiform Face Area when they are  asked to make judgments about their area of expertise

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o But this is a learned trait  

∙ Prosopagnosia (inability to recognize faces) patients have also been reported  to have difficulty distinguishing between individual types of dogs  

o Study done in a patient who was previously a dog expert

o Perhaps FFA is not face specific, maybe it has to do with ones area of  expertise  

∙ Furthermore, these patients can tell that a face is a face (just not who’s face) Modularity- Two Sides of a Debate  

∙ Focus on: Stimulus Type  

o View #1 holds that the FFA is a face processing module

o The area is involved selectively in recognizing faces, its purpose is to  recognize faces

o This module evolved as a unit, because of the evolutionary advantage  of recognizing faces efficiently.  

o Modules: Extremely efficient  

 Processing is fast and mandatory  

 Domain specific  

 ONLY activated by faces

 Information is encapsulated  

 Fixed neural architecture  

 Neurons in the FFA

∙ Focus on: Process

o View 2 holds that the “face area” is not an area devoted to specific  domain (faces), but an area that is especially involved in a certain kind  of process- in this case holistic recognition

o The fact that the area is especially involved in face recognition as an  emergent property of neural processes carried out there

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o Is the brain a dynamic system that is engaged for the processes  involved?

o There are so many different stimulus types that is so hard to engineer  a system that is so efficient and specific for each stimulus  

o Neurons are not activated by a specific stimulus but by a process

∙ Debate: Are neuron preferences built around Stimulus or  

Process?

∙ Is the localization of function specific to stimulus or  

process?

Kanwisher (1997) 

∙ First paper that demonstrated FFA activity linked with facial recognition  

∙ Past investigations suggest that fusiform gyrus (right temporal lobe) is  selective for face perception  

o Cases of patients with damage to the right temporal cortex with FFA,  were specifically impaired with face processing  

o Prosopagnosia patients could recognize all objects but no faces

o Whatever the neurons are doing in the right side of the brain, is not  bilateral

 There is no damage on the left side, so why isn’t it helping to  pick up the slack?

∙ Alternate Interpretations  

o Low-level feature extraction

o Attention

o “Subordonate-level” visual recognition  

 meaning all faces have noses and mouths, all houses have doors and windows  

o Animate vs objects

∙ Conclusions:  

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o Fusiform gyrus (temporal lobe) is selective for face perception.  Alternative interpretations can be debunked

 FFA is selective ONLY for faces

 Faces are processed holistically

Attention 

∙ Attention is Selection for Processing

o Circa 1890 – William James on Attention

 “Every one knows what attention is. It is the taking possession  by the mind, in clear and vivid form, of one out of what seem  

several simultaneously possible objects or trains of thought.”

o Circa 1993 – Alan Allport on Attention

 “There can be no simple theory of attention, any more than  

there can be a simple theory of thought.”

o What determines whether information is selected??? How and What ∙ ATTENTION=SELECTION

Attention- How? 

∙ Two ways to selectively orient

o they are both independent but they operate simultaneously

o we need both

o operate in parallel

o independent neuromechanisms  

∙ Top-down (goal-directed)  

o Temporo-parietal junction (TPJ) superior parietal lobe (SPL)

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o Attentive, you are paying attention to what is being said, for example,  in class

o Only top: miss abrupt sound, like a fire alarm, and burn

∙ Bottom-up (stimulus driven)  

o Temporo-parietal junction (TPJ)

o Involuntary, like when something salient in the environment catches  your attention,  

 example: a clap

 You were not sitting there listening to it

o We are adaptive to abrupt changes in the environment because they  could signal danger

o Only bottom: distracted by every little sound

Attention- What 

∙ What are the units of attention? What is it that we select?

o Space, Features, Objects, Time, Modalities  

∙ Spatial Orienting- the gist of an image can be gathered very quickly, but to recognize details and their location, you need attention

o The detail is what you need attention for

∙ Neurophysiological data- found in a single cell study,  

o receptive field of a V4 neuron, the effective stimulus for the V4 neuron  is a vertical blue bar, just this causes activation of the neuron

o Now, there's something else in the horizontal field, the horizontal white field, without the blue bar, it does not change the receptive field of the  neuron

o When attending the ineffective stimulus, the neuron is not activated as strongly because it is not the direct preference, overall profile of the  response is reduced

o There is competition for the resource, the response of this neuron 16

 when there is competition, it reduces the strength of the  

response, mutual inhibition

o Physical stimuli are exactly the same, what is inside the receptive field  is exactly the same

o Attention resolves competition by “shrink wrapping” the receptive field

Spatial Orienting Posner Cueing Task 

∙ Used in human literature to demonstrate the spatial nature of attentional  selection

o Measured signal response through EEG

o Does the brain response differ as a function of what you are paying  attention to?

∙ Participant presented with a fixation point and a cue (an arrow pointing to the left, right or in both directions)

o Then a square is presented and the participant has to press a button  when they see a square is there  

o Your task is to simply react as fast as possible to the square (the  target) on the screen  

o However, the cue direction really effects the response time, even  though the cue has nothing to do with the task  

 Valid Cue Trial- when the target and the cue match (cue points  to the left, square in left)

 Invalid Cue Trial - when the target and the cue don’t match  (cue points to the left, square in right)

 Neural Cue Trial- bidirectional arrow cue  

∙ Reaction time is much longer when there is an invalid trial, as compared to a  faster response with a valid cue trial  

o When attention is shifted towards where the target already is  o There is more activation on a valid trial  

o Activation is reduced on an invalid trial  

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∙ ERP Variant of the Posner Cueing Task:

∙ Attention and eye gaze are not coupled  

∙ Participant stares at fixation point but their attention is either to the  left vs right  

o The two responses are to exactly the same physical stimulus  and the only difference is where the participants attention is  

 Selection matters!

Failures to Select in Space  

∙ Change blindness  

o Blindness exists for changes in modalities other than vision  

∙ Example: Switching the photo in class where only one aspect of the picture is  different  

o “Spot the difference” Challenges  

∙ We have capacity limitation, there is too much information going on, so  spatial selection is limited  

∙ Experiment: Simons and Levin  

o Example of Change Blindness; “The Switcheroo”

o On Stanford Campus, one experimenter approached a campus visitor  on street with a map asking to find a building that requires several  steps of explanation, a door would be carried in between them and in  the shuffle the asker would be switched  

 30% of the time, the direction giver didn’t notice  

∙ Conditions for Failure  

o Increase in information in the same modality  

o Extent of crosstalk between representation  

o Can be sensory when there is too much input  

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 Party setting  

o Can be motor when there is too much output  

 Operator

∙ Practice and experience can reduce interference  

Object Based Orientation  

∙ Experiment:  

o Subjects presented line through a rectangle  

 Rectangle is either small or large, open to the left or open to the  right  

 Line is tilted to the left or right, dotted or dashed  

o Asked to describe either the both line aspects or both rectangle  aspects, or one aspect of line and one of rectangle  

o Reaction time much faster when they only needed to describe one  object

∙ Experiment: O’Craven Face vs House Stimulus superimposed on each other,  one image moves  

o Fusiform Face Area (FFA) has a preference for faces stimulus  o Parahippocampal Place Area (PPA) has a preference for house stimulus  

∙ One of the two stimuli (house or face) was still and the other was in motion, o if you are paying attention to static face, and they say pay attention to  object in motion, then PPA will be rescued  

Attention: Selecting Modality  

∙ Experiment: Shomstein and Yantis  

∙ Subjects are hearing a stream of letters through headphones, and seeing  different letters and numbers on screen

o Both a visual and auditory streams

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∙ Participant ask to pay attention to either one or the other  

o Sometimes asked to switch from one to another

∙ Changes tracked in Brain with fMRI

∙ 4 Conditions:  

o Pay attention to auditory stimulus, hold vision

o Pay attention to visual stimulus, hold audition \

o Stop attending to the visual stimuli and start attending to auditory  stimulus, a shift to audition  

o Stop attending to the auditory stimuli and start attending to visual  stimulus, a shift to vision  

∙ When asked to pay attention to pay attention to Auditory Stream, auditory  activation was greater than activation in Visual Cortex

o Bilateral Activation in Superior Temporal Gyrus (STG)

o Attention to auditory stimuli is strikingly low  

∙ When asked to pay attention to visual Stream, visual activation greater than  in auditory Cortex

o Fusiform Gyrus (FG)

o Attention to visual stimuli is strikingly low

∙ By subtraction logic, we can see which parts of the brian should be activated  for auditory stimuli and not visual and visa versa

∙ Highlights the dangers of driving and talking on the phone (distracted driver  accidents)

Attention: Resolves Competition for Resources  

∙ Kastner Experiments

∙ Hypothesized that fMRI signals would be smaller during the simultaneous  conditions rather than during the sequential presentations due to competition for resources (mutual suppression)

∙ Experiment 1:  

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o Sequential condition- stimulus presented sequentially in 1 of 4 possible locations

 Resulted in greater signal change  

 Brain activity is overall higher in this condition, as there is no  competition  

o Simultaneous condition - stimulus presented together in all four  conditions  

 Resulted in signal change being suppressed

 Many neurons are converging into a single one, thus increasing  the receptive field  

 Competition for resources (mutual suppression)

o Suppression of activation is greater as we go up the extrastriate  regions since receptive fields are larger in V4 and TEO

∙ Experiment 2:  

o 2x2 design  

 Still have Sequential and Simultaneous (SEQ vs SIM) conditions  but now participants are either looking at the fixation point or  

not (ATT vs UNATT)

 Four blocks of visual stimulation  

o Signal at V4 and TEO is significantly greater during directed attention o Stronger reduction of suppression seen in V4 and IT

∙ Attention resolves competition for resources

∙ Multiple stimuli in the visual field interact in a mutually suppressive way.

∙ Spatially directed attention enhances processing of stimuli in the attended  location by counteracting suppression induced by nearby stimuli

∙ Modulation of suppression at several extrastriate stages may be due to a  mechanism by which attention filters irrelevant information.  

Neglect Patients  

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∙ Patients with neglect completely ignore one side of the visual field, yet they  can see everything, they just don’t select that information

o Don’t shave left side of face, don’t eat from left half of

tray  

o They don’t understand that there is anything wrong with

them

∙ When presented with the Posner Task  

o When the target appears as Ipsilesional stimulus

 Targets appear on same side as the “good” side

o Target appears as Contralesional stimulus

 Appears on “bad side”  

o At Valid trial of contralesional stimulus side, patient performs just fine!

 They can see stimulus on the left (“bad” side) when attention is  pushed towards that direction  

 If you draw their attention to the left they will “see” the stimulus ∙ Not a sensory disorder, but an issue with attention  

Extent Of Effect 

∙ Neglect is not unique to visual modality

o Other Sensory modalities include…

 Auditory  

 Olfactory  

 Tactile  

∙ Neglect is about selection processes so it extends to more than vision, it can  effect even internal selection  

∙ Mental imagery

o Internal selection, your thoughts  

o Piazza del Duomo (Bisiach and Luzzatti Study)

 Everybody from Milan knows the arrangement of buildings in  this famous Piazza  

 In this study, the patient was asked to describe all the buildings  in the Piazza (there was no picture present, it was all from  

memory)

 The patients didn’t describe any of the buildings on the  

right side

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 Even when the patient was asked to pretend they were  

facing in different directions, they just didn’t name any of  

the buildings on the right  

 They could name all the buildings when facing different  

ways (in different trials), but they couldn’t name them all  

in the same trial due to the fact that they didn’t select for  

buildings in the right  

∙ Affects Output: Not surprisingly  

Vision and Eye Movements  

∙ Behrmann Experiment:  

o Presented an image with many random letters

o Patients asked to indicate number of As in the display, while tracking  eye movement  

o Control patients had a pretty typical distribution of where on the screen they looked  

o Patients with neglect only looked at the right side of the image (eyes  fifnt even go towards the left)

Spatial Neglect vs Object Centered Neglect  

∙ Spatial Neglect:

o Right IPL/TPJ are damages  

o Copying Task - patients ignore the left side of the image and only copy the right  

∙ Object Centered Neglect:  

o Superior Temporal Gyrus is damaged  

o Copying Task- patients only dry the right side of each object  o Break in the Circle Task: Patients asked to circle the circles that were  full, and draw an X through the circles without breaks  

 When the break in the circle was on the right they put the X

∙ This is a double dissociation; these two types of neglect have nothing to do  with eachother  

o Two separate things  

Emotion  

∙ Very difficult to study because it is very hard to define  

∙ There are 6 Universal Emotions;

o Happy, Angry, Disgusted, Surprised, Sad, Scared  

o You can ask people about these emotions and change/ vary how much  a person emotes  

∙ Participants asked to look at emotion images and rank on a scale how strong  the face’s emotion is  

o Patient SM; asked to look at these emotion images and rank   Ranks afraid emotion very low in comparison to the ranking of  the control  

 This patient had damage to the Amygdala  

∙ The emotions we experience are all for the purpose of decision making,  which, from an evolutionary perspective, aid in our ability at survival  

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Techniques for Studying Emotion  

∙ Mood Induction  

o Reward and Punishment  

o Present emotionally evocative stimuli  

∙ Measure  

o Direct Assessment (ask)

o Indirect  

 Let people choose response  

 Measure physiological response  

 Pulse, sweat on palms  

 SCR/GSR (Galvanic skin response)

 Sweat

 ERP  

 Blood: Cortisol (stress hormone)

 Quantified as change from baseline for each individual  

Neural System in Emotion  

∙ Distributed circuits with different areas all contributing to one response  ∙ Papez Circuit and the Limbic System  

o Hypothalamus  

o Anterior Thalamus  

o Cingulate  

o Hippocampus  

o MacLean  

 Amygdala  

 Orbitofrontal  

 Basal Ganglia  

 Dopamine isn’t only important for movement, but for  

exhibiting a particular types of emotion

Orbitofrontal 

∙ Affected Phineas Gage  

∙ Decision making  

o processing , evaluating, filtering social and emotional information  ∙ Social Decision Making- Making a decision that is appropriate for a  particular social context  

o Lhermitte utilization behavior  

∙ Damage is accompanied by  

o Diminished Social awareness  

o Apathy  

o Lack of concern for social rules (acquired sociopathy)

∙ Same in animals  

o Lose status/ incur aggression and leave group

Emotional Decision Making  

∙ Somatic Marker  

o Gut feeling  

o Body reaction to making decisions

 wm is too busy, emotions merely restrict possibilities  

∙ Demasion worked with patients with OF lesions  

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o Showed them hideous pictures of things like severed limbs, horrifically  graphic and emotionally charged stimuli as well as flat pictures with no meaning behind it like a chair  

o Flat Skin Conductance Responses for patients with OF lesion   Control response had peaks for the emotional stimulus   For control; the second peak wasn’t as high as the first  because the participant could have been desensitized the  first time

 OF patients will say the image is horrible but won’t show any  physical response  

∙ Experiment: Gambling! Participants placed sat in front of  Pile A and Pile B with winning and losing cards

o Pile A has larger amounts (Most you can win is $100, most you can lose is $1250) and Pile B (Winning Cards is at most $50, Losing Cards is at  Most $100)

o Control Subject gets nervous (sweats) when selecting from pile A o PAtients select from pile A way more than the control   Response to the losing card is the same in OF patient and  control  

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