Stimulus Recognition:

Question 1

Remember photoreceptors are stimulated by light, this sends signals to bipolar cells then to ganglion cells. Ganglion cells then send signals to the LGN

What does LGN stand for, how many layers of cells does it have?

Answer 1

This is the lateral Geniculate nuclues

It has 6 layers of cells

Question 2

How many layers of the LGN receive inputs from the magnocellular and parvocellular ganglion cells ? And what is meant by the LGN receiving monocular inputs?

Answer 2

2 layers of the LGN receive input from the magnocellular cells - these are the inner layers of the LGN

The outer 4 layers receive input from parvocellular ganglion cells

The LGN layers has monocular inputs. Thus each LAYER receives input from a single eye!

The outer most layer receives contralateral input, then the next one receive ipsilateral, then the next in receives contralateral.

Question 3

What type of neurones is the LGN? And what kind of connections are made between ganglion cells and LGN neurones? And what is special about the receptive fields on LGN’s in comparison to Ganglion neurones?

Answer 3

Interneurones

1:1 connections are made.

And the receptive fields on the LGN’s are similar to those on ganglion cells

Question 4

What do parvocellular and magnocellular ganglion cells do?

Answer 4

Parvocellular ganglion cells detect space

Magnocellular detect motion

Question 5

Where does information from the LGN go?

Answer 5

The the visual cortex or the V1 cortex

Question 6

Information from the visual cortex travels to other parts of the brain via which two streams and to which two place?

Answer 6

Information either goes along the ventral pathway to the inferior temporal lobe or it goes via the dorsal stream via the posterior parietal CORTEX (not lobe).

Question 7

How much synaptic input in the LGN comes from the cortex? What does this mean? And how many interneurones are in the LGN?

Answer 7

60% of synaptic input in the LGN comes from the cortex

This means the cortex tightly regulates the LGN

There are also many interneurones in the LGN

Question 8

Information which travels from parvocellular ganglion cells travels through the ventral stream. Describe the route:

Answer 8

Parvocellular ganglion cells send signals to the LGN, then to the V1 cortex, then via the ventral stream this info is sent to the V2 cortex, then V4(to process colour)

then it helps us to understand what we are seeing by going to the INFERIOR temporal lobe

Question 9

Information which travels from magnocellular ganglion cells travels through the dorsal stream. Describe the route:

Answer 9

The Magnocellular cells send info to the LGN, the the V1 cortex. Via the dorsal stream info is then sent to the v2 and v3 cortex before movement is processed.

Question 10

What must we do before we use neurones which respond to object recognition in tests?

Answer 10

Firstly find single neurones which specifically respond to presentation of specific objects

Stimulate these neurones - and observe perception from these neurones
Everything pre synaptic to these neurones need to be studied in detail.

You must understand how activation of these neurones cause behavioural changes and look at how one neurone (jennifer anniston neurones) and populations of neurones work

Question 11

What are the key principles of object recognition by the brain?

Answer 11

We have orientation invariance - we can easily recognise objects in orientations we dont usually experience

We also see scale invariance = we recognise objects independently of size.

We can also recognise objects which dont have typical features - e.g. recognise lego.

Question 12

What is the hierarchal model of object recognition? As in what are the steps in object recognition?

Answer 12

Firstly we have detection of edges

Then we have detection of a combination of edges and contours

Then there is detection of the object parts - e.g. the face (this detection is deeper in the brain)

Even later we have neurones which respond to specific objects from a single specific point of view.

We then have view invariant object detection - this helps us to view a particular person for instance

You then categorise this - identify humans and animals

Question 13

What is the issue with damage in the cortex and how do we study this?

Answer 13

Lesions in the inferior temporal cortex (not lobe) for instance decrease the ability of a person to recognise objects

We can study this through electrophysiology

Question 14

Whats important to note about modelling the brain?

Answer 14

You dont tend to look at the entire brain, you tend to focus on certain parts of it with imaginig

Question 15

Along the ventral stream, what happens to receptive fields?

Answer 15

The receptive field size on neurones increases as you go along the ventral stream.

Question 16

What are two features of the cortical structure in ref to the visual cortex?

Answer 16

There is layers of neurones in the cortex

There is also columns and blobs (detect colour) in the cortex - the column detect ocular dominance, orientation and direction

Question 17

How many layers does the v1 cortex have? (note this is not asking about the layering of the LGN neurones! Its talking about the visual cortex)

And how do the neurones in each layer differ?

How do the inputs differ?

Answer 17

There are 6 layers in the visual cortex

They differ in the neurotransmitters they release. And different layers have different properties.

Different layers receive different inputs either from the dorsal or ventral pathways.

Question 18

What is the different columnar organisation in the cortex?

Answer 18

There are ocular dominance columns
Orientations (direction) columns
And blobs (which detect colour)

Question 19

How to find ocular dominance columns in the visual cortex?

Answer 19

You can either:

Inject radioactive proline into one eye:
This diffuses into the LGN and then into the visual cortex
In the cortex you then see stripes where there are lots of proline and stripes where there isnt. This tells you where the columns are.

OR
Inject radioactive glucose in the cortex and stimulate on eye
This again shows stripes in the cortex which correspond to where the ocular columns are
This is because glucose is consumed by firing neurones in the visual cortex. These firing neurones are where the ocular dominance neurones are.

Question 20

Why are stripes seen in the ocular dominance experiements?

Answer 20

Remember one eye is used
And the cortex has contralateral then ipsilateral inputs

Thus all contralateral or ipsilateral inputs are highlighted

Question 21

What do oreintation columns tell you?

Answer 21

The orientation of an object

Important to note neurones close to each other have different orientation selectivities

One neurone may be selective to one particular orientation of an object. If you move to the next neurone it detects the object in a slightly different orientation and so on.

Question 22

Blob columns?

Answer 22

Found shape

They receive input from parvocellular cells from the LGN. These discriminate between different colours

Question 23

Hypercolumns?

Answer 23

• this is just your oreintation columns , ocular dominance columns and then blobs

Question 24

What is the orientation test which helps us to distinguish which neurones in the v1 cortex respond to certain orientations of light?

Answer 24

Cat test - hubel and weasel test

Gently insert electrodes into cats brain and monitor visual area of brain

Different neurones light show a response to different orientations of light. These flashcards will refer to the orientation of the objects are bars as these are straight

Individual oreintations columns in the v1 respond to a single orientation of an object in sight

Question 25

What are simple cells? What is special about their receptive fields?

Answer 25

Simple cells are found in layers 4 and 6 of the visual cortex and respond to orientation again

Their receptive fields are elongated and in one long line. These respond to the same orientation of an object

This is because they receive a large input from LGNs.

However these tend to detect orientation in the CENTRE of their receptive fields

Question 26

What are complex cells? Where are they found? How do they differ from simple cells?

Answer 26

These are found in the v1 cortex

These detect object orientation away from the centre of their receptive fields . Whereas simple only detect orientation in the centre of their receptive fields.

But this is usually in one orientation, changing the orientation of the bar means the cells stop responding

Question 27

Where are simple and complex cells found?

Answer 27

Layers 2,3,5 of the visual cortex

Question 28

What make up complex cells?

Answer 28

Complex cells receive multiple inputs from simple cells

Yet they respond to objects like bars in slightly different orientations. Collectively these simple cells help complex cells to identify objects like bars in a range of different positions

Question 29

What a hypercomplex cells? And what happens when objects are shone half way in and out of the receptive field?

Answer 29

These are called end stopped complex cells

They respond to certain orientations of objects but if the objects slightly go out of the receptive field due to change in orientation then you see some of the object in normal orientations and then not the rest

Question 30

After the v1 cortex where does information go?

Answer 30

Layers 2 and 3 of the v1 send info from the v1 to other cortical regions

Layers 5 and 6 send info to deeper structures

Remember layer 3 is for object locations and 4 is for colour

Question 31

How do receptive fields change downstream (After) v1?

Answer 31

They increase in size

So v1 receptive fields are smaller than v2

Question 32

What are neurones in the temporal cortex sensitive to? And what happens if you change the properties of these things these neurones are sensitive to?

Answer 32

This cortex is sensitive to faces

If you remove some properties (such as facial features) from the face, faces become harder to detect

Question 33

What are grandmother cells? Why are they related to jennifer aniston?

Answer 33

These are cells in the temporal cortex and detect facial features

They are also called jennifer anniston neurones

This is because patients who had parts of their brain removed to stop epileptic seizure had their facial recognition abilities tested . Jennifers annistons face was used to see if the individuals were correctly identifying faces

Electrodes were inserted in their brains to see if Jennifer Anniston face was being detected adequately. At different orientations and sizes

Question 34

Whats wrong with the hierarchal model of v1 ect?

Answer 34

This model is poor at explaining scale and orientation invariance

And doesnt take into account feedback from other higher cortical regions