Task 4

Question 1

Processig from R to VC

• Responding of Single Fibres in Optic nerve
• Centersurround organization

Answer 1

 each optic nerve fibre monitors a small area of retina  all of them together take in information about what is happening over the entire retina
Centre-surround organization: area in “centre” of receptive field responds differently to light than area in “surround

Question 2

Excitatory- centre, inhibitory- surround receptive field

Answer 2

o Excitatory area: presenting spot of light to centre increases firing
o Inhibitory area: stimulation of surround causes decrease in firing

Question 3

Inhibitory centre, excitatory surround receptive field

- center surround antagonism

Answer 3

(figure b)
when centre stimulated => inhibition  when surround stimulated => excitation
• Centre-surround antagonism: neurons respond best to specific patterns of illumination
 when spot of light large enough to cover also inhibitory area, stimulation of inhibitory surround counteracts centre’s excitatory response  decrease in neuron’s firing rate  particular area has to be exactly illuminated du make neuron respond best

Question 4

Superior Colliculus

Answer 4

receives some signals from eye; plays important role in controlling eye movements

Question 5

Neurons in Visual Cortex

- Simple cortical cells

Answer 5

cells with receptive fields that have excitatory & inhibitory areas which are arranged side by side rather than in centre-surround configuration; respond to small spots of light or stationary stimuli
 layout of excitatory & inhibitory areas tells us to which stimuli cell would respond best (e.g. vertical bars but could be directed in any direction)

Question 6

Orienttion tuning curve

Answer 6

indicates relationship between orientation & firing of a neuron;
 determined by measuring responses of a simple cortical cell to bars with different orientations
• many cortical neurons respond best to moving bar-like stimuli with specific orientations:

Question 7

Complex cells

Answer 7

o respond best to bars of particular orientation
o BUT most of them respond only when a correctly oriented bar of light moves across the entire receptive field
o many complex cells respond best to a particular direction of movement

Question 8

End- stopped cells

Answer 8

fire to moving lines of specific length or to moving corners or angles
 Because simple, complex, & end-stopped cells fire in response to specific features of the stimulus they are called feature detectors
 Neurons respond to some patterns of light and not to others
 As we travel farther from the retina, neurons fire to more complex stimuli

Question 9

Selective Adaption

Answer 9

• Adaptation causes two physiological effects:
1. neuron’s firing rate decreases
2. neuron fires less when that stimulus is immediately presented again
 adaptation selectively affects only some orientations, just as neurons selectively respond to only some orientations
 near match between orientation selectivity of neurons & perceptual effect of selective adaptation supports the idea that orientation detectors play a role in perception
• psychophysical experiment: presenting the same stimulus again & again  neurons decrease contrast sensitivity
• when they are fatigued they need higher threshold to fire
• orientation tuning curve

Question 10

Sensory Code

Specificity Coding

Answer 10

o Specificity coding: a particular object is represented by the firing of a neuron that responds only to that object & to no other objects
 firing of single neurons as key to understand sensory coding
–>WRONG NOW

Question 11

Spase Coding

Answer 11

a particular object is represented by pattern of firing of only a small group of neurons, with the majority of neurons remaining silent
o a particular neuron can respond to more than one stimulus

(Small)

Question 12

Distributed coding

Answer 12

representation of a particular object by the pattern of firing of a large number of neurons
 Firing of neuron groups as key for sensory encoding

Question 13

A) Exploration of Spatial Organization

Answer 13

the way stimuli at specific locations in environment are represented by activity at specific locations in nervous system

Question 14

Electronic map on v1

Retinotopic map

Answer 14

electronic map of the retina on the cortex, showing that locations on cortex correspond to locations on retina;
 two points that are close together on an object & on the retina will activate neurons that are close together in the brain

Question 15

Cortical magnification

Answer 15

apportioning of a large area on the cortex to the small fovea;
map on cortex is distorted: more space allotted to locations near fovea than to locations in peripheral retina;
 signals from the fovea account for 8 - 10 % of the retinotopic map on the cortex
o fMRI experiment: stimulation of small area near fovea activated a greater area on cortex (red) than stimulation of larger area in periphery (blue)
o Consequences when looking at a scene: information about part of the scene you are looking at takes up a larger space on cortex than an area of equal size that is off to the side
 more space on cortex translates into better detail vision rather than larger size
 what we perceive doesn’t exactly match the “picture” in the brain

Question 16

Location Column

Answer 16

striate cortex is organized into location columns perpendicular (vertical) to cortex surface  all neurons within a location column have their receptive fields at same location on retina

Question 17

Orientation Column

Answer 17

cortex is organized into orientation columns  each column contains cells that respond best to a particular orientation;
 adjacent orientation columns have cells with slightly different preferred orientations

Question 18

One location column many orientation column

Hypercolumn

Answer 18

 one location column serves one location on the retina (all neurons in the column have their receptive fields at about the same place on retina) & contains neurons that respond to all possible orientations
: a location column with all of its orientation columns;
 receives information about all possible orientations that fall within a small area of retina  well suited for processing information from a small area in the visual field

Question 19

Tiling

Answer 19

when working together, columns cover the entire visual field;
 visual field is served by adjacent (often overlapping) location columns
 any scene is represented by activity in many location columns  a scene is represented in striate cortex by an amazingly complex pattern of firing

Question 20

B) Streams

What/Ventral Pathway

Answer 20

pathway leading from striate cortex to temporal lobe; responsible for determining an object’s identity
responsible for identity looks at colour and shapes
provides information about how to direct action with regard to stimulus;
 goes beyond “where” to involve a physical interaction with the object

Question 21

Where/Dorsal Pathway

Answer 21

pathway leading from striate cortex to parietal lobe (Memory, language); responsible for determining an object’s location, spatial perception
considering shape and motion
for taking action, e.g. picking up an object, which also involves knowing object´s location

Question 22

Stereopsis

Answer 22

coordination of both eyes, seeing depths with both eyes (for both pathways)
• properties of ventral & dorsal streams are established by two different types of ganglion cells in the retina, which transmit signals to different layers of the LGN  cortical ventral & dorsal streams can actually be traced back to retina & LGN
• the pathways are not totally separated, but have connections between them

Question 23

Feedback signals

Answer 23

signals flow not only “up” the pathway toward parietal/temporal lobes, but “back” as well;
 one of the mechanisms behind top-down processing; provides information from higher centres that can influence the signals flowing into the system

Question 24

Patient D.F.

Answer 24

o D.F. suffered damage to her ventral pathway  was not able to match orientation of a card in her hand to different orientations of a slot; BUT she could “mail” the card through the slot;
 performed poorly in static orientation-matching task but did well as soon as action was involved
o D.F.’s behaviour shows that there is one mechanism for judging orientation & another for coordinating vision & action
 ventral stream is damaged
o Patients with damage to dorsal streams can judge visual orientation, but can’t accomplish tasks that combine vision & action
 other description of dorsal pathway is how/action pathway, because it determines how a person carries out an action
 perception & action are served by different mechanisms

Question 25

C)Modulatity

Answer 25

a structure that is specialized to process information about a particular type of stimulus;
 Since neurons that respond to similar stimuli are often grouped together in one area of the brain
• There is good evidence that specific areas in temporal lobe respond best to particular types of stimuli

Question 26

Fusiform Face area

Answer 26

): located in fusiform gyrus on underside of the brain directly below IT cortex; specialized to respond to faces

Question 27

Prosopagnosia

Answer 27

difficulty recognizing faces of familiar people; caused by damage to temporal lobe

Question 28

Parahippocampal place area

Answer 28

are activated by pictures depicting indoor & outdoor scenes;
 information about spatial layout seems to be important for this
–>houses, plain, sink

Question 29

Extrastriate Body Area

Answer 29

area activated by pictures of bodies & parts of bodies (but not by faces)
 even though stimuli like faces & buildings activate specific brain areas, these stimuli also activate other brain areas as well

Question 30

LGN

Answer 30

six-layered structure in thalamus/midbrain; receives input from retinal ganglion cells & has input & output connections to visual cortex;
• LGN neurons have concentric receptive fields, which respond well to spots & gratings (same as ganglion cells do that provide their input)
• LGN is relay station between retina & cortex
 There are more feedback connections from visual cortex to LGN than from LGN to cortex
 FILTERING; REGULATES INFORMATION AND ORGANIZE IT; TOPOGRAPICAL MAPPING

Question 31

LGN magnocellular layer

Answer 31

: two bottommost layers, contain physically larger neurons; receive input from M ganglion cells; respond to large, fast-moving objects

Question 32

LGNParvocellular layer

Answer 32

: top four layers, contain physically smaller neurons; receive input from P ganglion cells; responsible for processing details of stationary targets
–>Visual sytsem spilts inout from image into different types of information

Question 33

LGN Koniocellular cell

Answer 33

: top four layers, contain physically smaller neurons; receive input from P ganglion cells; responsible for processing details of stationary targets, V1

Question 34

Mapping visual world

Left/right LGN

Answer 34

1. Left LGN receives projections from left retina side of both eyes  right LGN receives projections from right side of both retinas

Question 35

LGN Layer 1,4,6

Layer 2,3,5

Answer 35

2. Each LGN layer receives input from one or the other eye:
   o Layers 1,4,6 (from bottom to top) of LGN receive input from the other side (contralateral) eye
   o Layers 2,3,5 receive input from same side (ipsilateral) eye
   o Koniocellular layers fall in space between magno & parvo layers

Question 36

LGN Topographical mapping/Retinotopic

Answer 36

orderly mapping of the world in LGN & visual cortex -> each layer contains highly organised map of a complete half of the visual field
 Basis for knowing where things are in space

Question 37

Striate Cortex/Primary Vc, V1

Answer 37

area of cerebral cortex that receives direct inputs from LGN, as well as feedback from other brain areas
• Consists of six major layers, some of which have sublayers MOST TO LEVEL 4
• Has a systematic topographical mapping of the visual field
• Performs major & complex transformation of visual information

Question 38

Features

Answer 38

a) Topography but bigger- more cells than LGN
b) Cortical magnification: amount of cortical area devoted to a specific region in the visual field (fovea has more space than periphery space) that is why we have visual acuity
c) 3 different receptors with different fields- simple, complex, as subdiffision of endstop cell

Question 39

Columns

Answer 39

vertical arrangement of neurons; neurons with single column tend to have similar receptive fields & similar orientation preferences

Question 40

Hypercolumns

Answer 40

a 1-mm block of striate cortex containing two sets of columns, each covering every possible orientation (0-180°)
 one set prefers input from left eye, the other set prefers input from right eye
 Not all hypercolumns see world at same level of detail, due to cortical magnification

Question 41

Blobs

Answer 41

: section of visual cortex where groups of neurons

Question 42

E-Reader “Seperate visual pathways for perception and action!

Answer 42

Dissociation between prehension(where pathway) and apprehension(what pathway):
• Visual agnosia: patients with visual agnosia after brain damage in e.g. occipitotemporal region are often unable to recognize/describe common objects, faces, pictures, abstract designs
• Optic ataxia: patients suffering from optic ataxia after damage to posterior parietal region are unable to reach accurately towards visual targets that they have no difficulty recognizing
• damage to parietal lobe can impair ability use information about size, shape & orientation of an object to control hand & fingers during a grasping movement, even though this same information can still be used to identify & describe the objects
• after parietal damage, spatial information may still be processed quite well for some purposes, but not for others
• singe dissociation: one thing works without the other (you can see what it is but cannot grab it) function a (What) and function b (where) if function a is intact but in function b there is a lesion there is a single dissociation
• double: dorsal: two patient 1 has working what pathway but impaired where pathway and patient 2 rhe other pathway- then you can compare them and if the disease
• Case: after carbon monoxide poisoning patient D.F. prehension developed a profound visual-form agnosia: inability to recognize size, shape & orientation of visual objects;
RW. Apprehension
o diffuse brain damage BUT most damage in cortical visual areas was evident in areas 18 & 19, with area 17 (V1) apparently remaining largely intact
o despite agnosia, D.F. showed strikingly accurate guidance of hand & finger movements directed at the very same objects
 visual projection system to the parietal cortex provides action-relevant information about structural characteristics & orientation of objects, and not just about their position
 projections to temporal lobe may furnish our visual perceptual experience  seems to be damaged in D.F.