stimulus localisation

Question 1

Give some examples of object localisation in the visual system

Answer 1

¥ Orienting reflex (orientation of the head and eyes to focus salient stimulus on the fovea)
¥ Smooth pursuit (following moving object)
¥ Prediction of motion during prey capture (motion anticipation)
¥ Saccadic movements during object inspection

Question 2

What are saccadic movements?

Answer 2

When inspecting an object we look at all angles and try to get as much information as possible

Question 3

Explain saccadic movements during object inspection

Answer 3

During natural scene perception, we move our eyes about three times each second via rapid eye movements (saccades) so that the object of interest is centered on the high-resolution fovea

Question 4

What leads to disappearance of orienting reflex?

Answer 4

Ablation of optic tectum (superior colliculus in lower vertebrae)

Question 5

Where does the orienting reflex originate?

Answer 5

Optic tectum (superior colliculus)

Question 6

What is the function of the orienting reflex?

Answer 6

Alerts us to changes in our sensory environment

Question 7

State the areas involved in stimulus localisation and motion processing

Answer 7

¥ Retina (orientation selective ganglion cells, motion anticipation)
¥ Dorsal stream in the cortex
¥ Superior and inferior colliculus

Question 8

Whats the main function of the superior colliculus?

Answer 8

Regulation of saccadic movements

Question 9

What is a consequences of a lesion of the superior colliculus?

Answer 9

Leads to disappearances of the orienting reflex

Question 10

How are command neurons organisaed? What is their function?

Answer 10

Into maps, similar to retinotopic maps and send projections to layers, regulating eye movements

Question 11

What does the foveation hypothesis state?

Answer 11

that retinotopic and topographic maps align and this is a basis for orientation reflex.
That interaction between these maps initiates orientating reflex

Question 12

Explain the dorsal stream

Answer 12

Dorsal stream starts with V1 cortex – then v2, v3, major temporal area and then parietal area – where pathway
Interaction between where and what pathway

Question 13

Which neurons are responsible for detection of motion?

Answer 13

Neurons in both V1 and MT cortex – some are responsible

They are able to discriminate between motion in different directions

Question 14

Where is direction selectivity evident?

Answer 14

In the retina – mostly in typical ON/OFF cells

Question 15

What is the morphology of DS cells?

Answer 15

Highly asymmetric – preferred direction can be guessed

Question 16

Describe how you can record activity from individual cells in retina?

Answer 16

Good thing about retina is ganglion cells are on the top – can do sharp electrode recording and patch clamp

Question 17

Where to excitatory inputs come from?

Answer 17

Bipolar cells

Question 18

Where to inhibitory inputs come from?

Answer 18

Amacrine cells

Question 19

Describe how you can discriminate in a ganglion cells between inhibitory and excitatory inputs

Answer 19

Record form ganglion cell and hold membrane potential – can discriminate between excitatory and inhibitory inputs.
i.e put membrane potential on the reversal potential for Gaba receptors then can record ampa currents. Visa versa

Question 20

What defines direction selectivity?

Answer 20

the ratio between inhibitory and excitatory inputs

Question 21

Describe what happens when stimulus moves in preferred direction?
.

Answer 21

stimulus moves in the preferred direction the excitatory input is much larger than the inhibitory input

Question 22

What happens when the stimulus moves in null direction?

Answer 22

When the stimulus moves in thenul direction, the inhibitory input dominates.
There is not enough to pass threshold therefore doesn’t spike

Question 23

What are retinal ganglion cells?

Answer 23

Neurons sending signals along the optic nerve

Question 24

What is the spiking difference of a moving or flash object in a ganglion cell?

Answer 24

When you flash object – spiking kicks in a little bit later
Moving object- spiking rate starts earlier
Ganglion cells start spiking earlier based on position of receptive field