L8 - Stimulus Location and Processing of Motion

Question 1

What are the 4 examples of object localisation in the visual system?

Answer 1

Orienting reflex
Smooth pursuit
Prediction of motion during prey capture
Saccadic movements during object inspection

Question 2

What is the orienting reflex?

Answer 2

Orientation of the head and eyes to focus salient stimulus on the fovea
When a novel stimulus appears animals turn their heads and eyes to allow inspection of stimulus

Question 3

What is smooth pursuit?

Answer 3

Following moving object

Question 4

What is prediction of motion during prey capture?

Answer 4

Motion anticipation

Question 5

What is saccadic movement during object inspection?

Answer 5

Eyes move all the time

Some parts of the object are observed more than others

Question 6

Ablation of what leads to disappearance of orienting reflex?

Answer 6

Optic tectum

Superior colliculus in lower vertebrates

Question 7

Why do we need motion anticipation?

Answer 7

1. 1 photon absorbed by 1 opsin
2. 800 transducin molecules
3. 800 PDE enzymes
4. 4800 cGMP converted to GMP
5. 200 cGMP sensitive ion channels close
6. Causes hyperpolarisation and decrease in glutamate release
   This process takes 60 ms

Question 8

What areas are involved in stimulus localisation and motion processing?

Answer 8

Retina - orientation selective ganglion cells and motion anticipation
Dorsal stream in the cortex
Superior and inferior colliculus

Question 9

What does the superior colliculus receive input from?

Answer 9

Ganglion cells
Auditory system
Somatosensory system

Question 10

Where does the superior colliculus integrate information from?

Answer 10

Different sensory modalities

Question 11

What is the function of the superior colliculus?

Answer 11

Regulation of saccadic movements

Question 12

What do lesions of the superior colliculus lead to?

Answer 12

Disappearance of orienting reflex

Question 13

What are retinotopic maps in the retina?

Answer 13

Organisation where neighbouring neurons in the retina feed information to neighbouring places in target structures
- Lateral geniculate nucleus, superior colliculus and visual cortex

Question 14

How are eye saccades regulated?

Answer 14

Via command neurons

Question 15

Where are command neurons found?

Answer 15

Deeper layers in superior colliculus contain neurons that spike before the saccadic movements

Question 16

How are the deep layers of superior colliculus neurons organised?

Answer 16

Organised in maps (similar to retinotopic maps)
Send projections to layers regulating eye movements
Maps of the retina and superior colliculus are aligned

Question 17

What is the foveation hypothesis?

Answer 17

Interaction between maps initiates orienting reflex

Question 18

Whys is the foveation hypothesis wrong?

Answer 18

Interaction between maps seems to be indirect

Question 19

Along what pathway does processing of motion in higher areas occur?

Answer 19

Dorsal stream

Question 20

Dorsal stream pathway

Answer 20

1. Magnocellular ganglion cell
2. LGN Magn
3. V1 cortical area
4. V2 cortical area
5. V3 cortical area
6. Middle temporal visual area
7. Parietal cortical area - parietal pathway (where)

Question 21

Along the dorsal stream pathway the neurons are?

Answer 21

Motion sensitive

Have retinotopic organisation

Question 22

Why we need motion perception example

Answer 22

A patient following a stroke had difficulty perceiving certain forms of motion
Object recognition and colour perception were intact
She couldn’t see coffee flowing into the cup - didn’t perceive fluid rising
- Coffee often spilt

Question 23

Motion detection and direction selectivity

Answer 23

Movement of a bar in a particular direction causes a much bigger response than a bar moving in the other direction

Question 24

What is preference direction?

Answer 24

Direction that produces the biggest response

Question 25

What is null direction?

Answer 25

Direction that produces the smallest response

Question 26

Where is direction selectivity in the retina?

Answer 26

Typical On/OFF cells

Responds to movements in some directions but not others

Question 27

What is the morphology of direction selectivity cells?

Answer 27

Highly asymmetric – only have neurons in one direction

Preferred direction can be guessed from the morphology

Question 28

Retinal ganglion cell inhibitory input?

Answer 28

Amacrine cells

Question 29

Retinal ganglion cell excitatory input?

Answer 29

Bipolar cells

Question 30

Direction selective cells receive input from?

Answer 30

Excitation from bipolar cells

Inhibition from amacrine cells

Question 31

Direction selective On-OFF cell movement in preferred direction?

Answer 31

Excitation is larger

Inhibition is smaller and delayed

Question 32

Direction selective On-OFF cell movement in null direction?

Answer 32

Excitation is smaller and delayed

Inhibition is larger

Question 33

What is the flash lag illusion?

Answer 33

If yellow light is flashed on a blue cell while the cell is moving to the right we perceive it as only the left half of the cell turning yellow
The whole cell actually turns yellow

Question 34

How does the retina predict the location of moving objects?

Answer 34

In a flashed object
- Spike rate reaches greater Hz
- Response is delayed 
In moving object 
- Spike rate reaches lower Hz
- Response is not delayed