Lecture 8- Cortical processing of vision

Question 1

What are the characteristics of M ganglion cells?

Answer 1

• M (parasol) ganglion cells - magni= large -large receptive fields -subserve motion detection, flicker and analysis of gross features -not good at telling what it is we are seeing

Question 2

What are the characteristics of P ganglion cells?

Answer 2

-P (midget) ganglion cells -parvi= small -more numerous -visual acuity and colour vision -tells us what it is we are seeing more

Question 3

What is the visual pathway like?

Answer 3

1. Retina 2. Optic nerve 3. LGN 4. Optic radiation 5. Visual cortex

Question 4

Where do the LGN neurons project to in the V1?

Answer 4

• project to the primary visual cortex V1 -area 17 -occipital lobe around the calcarine fissure

Question 5

What is the retinotopic organization of the visual system?

Answer 5

• neighbouring cells within the retina project to neighbouring cells in the LGN and visual cortex
• central part of vision= as far back in the occipital lobe as you can get

Question 6

What is layer 4 for in the cortex?

Answer 6

-always the input area

Question 7

What are the inputs into the V1?

Answer 7

• segregation of M and P pathways
• M cells terminate in layer 4Ca
• P cells terminate mainly in layer 4Cb

Question 8

What are the outputs of V1?

Answer 8

• layer 3 and IVb (4B) and other cortical areas
• layer 5: superior colliculus
• layer 6: LGN

Question 9

How much of the cortex is involved in vision?

Answer 9

• 40%
• the cortical visual system is composed of multiple visual areas with different functions

Question 10

What are the two parallel visual streams?

Answer 10

1. Dorsal pathway (WHERE) 2. Ventral pathway (WHAT)

Question 11

What is the dorsal pathway about?

Answer 11

• where
• mid temporal lobe is important for detecting where an object is
• get info from M ganglion and M LGN cells then via V1 4Ca layer to MT (medial temporal lobe)

Question 12

What is the ventral pathway about?

Answer 12

• what -inferior temporal lobe (IT) is the centre for object recognition
• visual processing through V1, V2,V4 and IT
• anterior and posterior subdivisions of the inferior temporal lobe
• get info from P ganglion, P LGN cells then from V1 via the 4Cb layer

Question 13

What are the two subdivisions of inferior temporal lobe? (IT)

Answer 13

-anterior and posterior -these have to do with object recognition, different aspects of it

Question 14

What is apperceptive agnosia?

Answer 14

• damage to posterior inferior temporal lobe (this is closer to V1 so less complex function)
• lesion in regions important for integrating visual information into sensory representations of entire objects
• ability to match an object is impaired
• can’t copy it
• can’t send the info from seeing to copying it
• cannot see object parts as a unified whole
• unable to construct sensory representation of visual stimuli
• part of ventral (what) pathway

Question 15

What is associative agnosia?

Answer 15

• lesion in anterior inferior temporal lobe (further away from V1 so more complex function)
• can match or copy objects but cannot identify objects
• can copy but cannot tell you what it is
• cannot interpret, understand or assign meaning to objects
• sensory representation is created normally but cannot be associated with meaning, function or utility
• part of ventral (what) pathway

Question 16

What do neurons in V4 respond to?

Answer 16

-relatively insensitive to simple stimuli (e.g. orientation, colour) -they get information from the downstream areas -vast majority have large receptive fields -as the visual pathway goes further then neurons respond to ever more complicated stimuli

Question 17

What do V4 neurons encode?

Answer 17

-encode complex features -e.g. some respond to curved patterns of a particular colour -some neurons encode specific information about objects e.g. faces, hands

Question 18

What do some neurons in the IT area respond to?

Answer 18

-to faces -some neurons respond to front of the face -other neurons respond best to the side of the face

Question 19

What is object constancy?

Answer 19

-the IT neurons are attuned to seeing faces but it does not matter which face, the subtle differences do not matter -will recognise an object as a face even when different colour, age etc.

Question 20

How is the inferior temporal lobe organised?

Answer 20

-columns -arranged in columns of neurons representing the same or similar stimulus properties (side of a face next to front of the face)

Question 21

How is the primary visual cortex organised?

Answer 21

-organised in columns of neurons that represent the same stimulus feature (e.g. orientation or direction of motion)

Question 22

What are the patches in the inferior temporal lobe?

Answer 22

-inferior temporal lobe contains patches where each patch can be stimulated by the same object -for face recognition, 5 regions that are linked by horizontal connections. Each region encodes a different aspect about faces.

Question 23

What is object recognition associated with?

Answer 23

-with visual categorization, visual memory and emotion

Question 24

What are the inputs and outputs in and from inferior temporal lobe?

Answer 24

• information from inferior temporal cortex must go into hippocampal cortex= so you can remember it, also perirhinal
• amygdala and entorhinal cortex= emotion
• prefrontal cortex= working memory

Question 25

What is visual memory?

Answer 25

-visual experience influences the processing of incoming visual information -neurons in the inferior temporal lobe can be modified by experience -neural activity changes when sees something that has experienced before -experience is important

Question 26

How does vision and short term memory work?

Answer 26

-neurons in prefrontal cortex and inferior temporal cortex continuously fire even after the visual image has been removed. This continual firing is thought to be important for maintaining short term memories. -involves the prefrontal cortex -how to get it to short memory -show object, then delay and must pick it= in delay= the neurons continue to fire that they saw the red dot, still active -but only if trained to see it -if have visual expreience then it changes the funtcion of the neurons in IT= inferior temporal lobe area

Question 27

What areas are involved in the dorsal stream (the where pathway)?

Answer 27

-where pathway -V1, V3, MT, parietal lobe -links with motor system

Question 28

Where does the MT (middle temporal lobe) receive input from?

Answer 28

-it is an area specialised for processing object motion -received retinotopic information from a number of cortical areas including V2 and V3 -received input from cells in layer IVB of the primary visual cortex (IVB= this is where the M ganglion plus LGN info is processed)

Question 29

What was the video about?

Answer 29

-blind man walking and correctly avoiding obstacles

Question 30

What is blindsight?

Answer 30

-when blind people can avoid obstacles and “see” but can’t

Question 31

What is the explanation for blindsight?

Answer 31

-there is a connection from the LGN to the MT area bypassing the V1, so that connection remains even after the V1 is gone -proven that the MT cells still respond to visual stimuli after V1 destruction

Question 32

What does this show?

Answer 32

-