stimulus localisation

Question 1

what is stimulus localisation?

Answer 1

⇒ where is change happening?

Question 2

types of object localisation in visual system

Answer 2

• orienting reflex
  
  • orientation of the head and eyes to focus salient stimulus on the fovea
• When novel stimulus appears animals tend to turn their heads and eyes in a position suitable for inspection of this stimulus

Question 3

types of object localisation in visual system

Answer 3

• orienting reflex
• smooth persuit
• prediction of motion
• saccadic movements during object inspection

Question 4

what is orienting reflex

Answer 4

• orientation of the head and eyes to focus salient stimulus on the fovea
• When novel stimulus appears animals tend to turn their heads and eyes in a position suitable for inspection of this stimulus
• not an innate response = develops with age

Question 5

what are saccadic movements during object inspection

Answer 5

moving eyes round to move fovea to get a more accurate representation of something

Question 6

important areas in stimulus localisation and motion processing

Answer 6

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

Question 7

parvocellular or magnocellular cells used more in stim localisation?

Answer 7

magnocellular cells

Question 8

role of superior colliculis

Answer 8

• input from ganglion cells, auditary system and integrates information
• main function: regulation of saccadic movements

Question 9

what structure is responsible for regulation of saccadic movements

Answer 9

superior colliculus

Question 10

role of different layers of somatosensory cortex

Answer 10

Different layers receive input from different brain areas: Retina, Somatosensory cortext (S1), visual cortex (V1) etc.

Question 11

retinotopic maps

Answer 11

organisation of neurones where neighboring cells in retina feed information to neighboring places in target structures (LGN, SC, cortex)

Question 12

what is direction selectivity?

Answer 12

• neurones show different responses to different directions of motion
• shown by cells in primary visual cortex (v1)

Question 13

morphology of direction-selective cells

Answer 13

• highly asymmetric
• preferred direction can be guessed from the morphology

Question 14

why/how do ganglion cells respond to motion?

Answer 14

• excitatory input from bipolar cell
• inhibitory input from amacrine cell
  -> In preferred direction excitation is larger and Inhibition is smaller and delayed
  -> In null direction, the excitation is smaller and delayed and inhibition is larger

Question 15

how is direction selectivity determined

Answer 15

• ratio between inhibitory and excitatory inputs is what defines direction selectivity
• when the stimulus moves in the preferred direction the excitatory input (blue) is much larger than the inhibitory input. When the stimulus moves in the null direction, the inhibitory input dominates.