Visual processing

Question 1

What is a receptive field?

Answer 1

Area of retina where light changes the activity of a neuron (bipolar or ganglion cell).

Question 2

What forms the centre of a bipolar cell’s receptive field?

Answer 2

Direct input from photoreceptors.

Question 3

What forms the surround of a bipolar cell’s receptive field?

Answer 3

Indirect input via horizontal cells.

Question 4

Why does the surround have the opposite effect to the centre?

Answer 4

Horizontal cell inhibition → enhances contrast detection.

Question 5

In darkness, what do photoreceptors release?

Answer 5

More glutamate.

Question 6

How does an ON-centre bipolar cell respond to light in the centre?

Answer 6

Photoreceptor hyperpolarises → glutamate ↓ → ON bipolar depolarises → ganglion firing ↑.

Question 7

How does an ON-centre bipolar cell respond to light in the surround?

Answer 7

Photoreceptor hyperpolarises → horizontal cell inhibition removed → ON bipolar hyperpolarises → ganglion firing ↓.

Question 8

How does an OFF-centre bipolar cell respond to light in the centre?

Answer 8

Photoreceptor hyperpolarises → glutamate ↓ → OFF bipolar hyperpolarises → ganglion firing ↓.

Question 9

How does an OFF-centre bipolar cell respond to light in the surround?

Answer 9

Photoreceptor hyperpolarises → horizontal cell effect → OFF bipolar depolarises → ganglion firing ↑.

Question 10

What do centre–surround receptive fields specialize in detecting?

Answer 10

Edges and contrast, not absolute brightness.

Question 11

Why do we perceive objects mainly through contrast?

Answer 11

Visual system compares object to background, not raw light intensity.

Question 12

What layers of LGN receive rod (magno) input?

Answer 12

Layers 1–2 (magnocellular).

Question 13

What layers of LGN receive cone (parvo) input?

Answer 13

Layers 3–6 (parvocellular).

Question 14

Do the eyes mix before cortex?

Answer 14

No — left/right eye input remains separate in the LGN.

Question 15

Where does LGN project in V1?

Answer 15

Layer 4C of primary visual cortex.

Question 16

Which V1 sublayer receives magnocellular input?

Answer 16

4Cα.

Question 17

Which V1 sublayer receives parvocellular input?

Answer 17

4Cβ.

Question 18

What are ocular dominance columns?

Answer 18

Alternating columns responding to the left or right eye.

Question 19

What are orientation columns?

Answer 19

Columns of neurons tuned to a specific orientation of a bar or edge.

Question 20

What do simple cells in V1 detect?

Answer 20

Orientation + position, responding to bars/edges in exact locations.

Question 21

How do complex cells differ from simple cells?

Answer 21

Same orientation tuning but position-invariant; respond best to moving edges.

Question 22

What does area MT (V5) process?

Answer 22

Object motion.

Question 23

What does area MST process?

Answer 23

Linear, radial, and circular optic flow (self-motion).

Question 24

What does V4 process?

Answer 24

Colour and shape (orientation + colour-selective).

Question 25

What does the inferior temporal (IT) cortex process?

Answer 25

Complex shapes and faces.

Question 26

What is the dorsal visual stream specialised for?

Answer 26

“Where” pathway → motion, spatial processing (MT/MST).

Question 27

What is the ventral visual stream specialised for?

Answer 27

“What” pathway → object identity, colour, faces (V4, IT).