Lecture 7 - Receptive Fields and Central Representation

Question 1

What are the 7 steps of the perceptual process?

Answer 1

1. Stimulus in the environment
2. Stimulus hits the receptors
3. Receptor processes
4. Neural processing
5. Perception
6. Recognition
7. Action

Question 2

What is transduction?

Answer 2

Converting environmental energy into electrical signals or nerve impulses

Question 3

What is transmission?

Answer 3

When signals are sent from receptors to sensory neurons and from sensory neurons to the brain.

Question 4

What is processing?

Answer 4

It occurs as a result of the interactions among neurons.

Question 5

What is the receptive field of a neuron?

Answer 5

The receptive field of a neuron is the area on the receptor surface (the retina for vision, the skin for touch) that, when stimulated, affects the firing of that neuron.

Question 6

Describe the receptive fields of ganglion cells (2).

Answer 6

Signals from photoreceptors travel through the retina and reach the retinal ganglion cells.
The axons of the ganglion cells leave the retina as fibres of the optic nerve.

Question 7

What did Kuffler discover with center-surround receptive fields?

Answer 7

Kuffler measured ganglion cell receptive fields in the cat and reported a property of these receptive fields that Hartline had not observed in the frog.
In the cat, the ganglion cells have center-surround receptive fields that are arranged like concentric circles, in a center surround organization.

Question 8

Who studied receptive fields?

Answer 8

Hubel and Wiesel

Question 9

What is centre-surround antagonism?

Answer 9

Excitatory and inhibitory inputs cancel each other out.
ON-centre cells are maximally responsive when entire centre is stimulated without any stimulation of surround.
OFF-centre cells are maximally stimulated when the entire surround is stimulated without any stimulation centre.
Stimulation of both centre and surround reduce firing rate.

Question 10

What is lateral inhibition in centre-surround antagonism?

Answer 10

• Photoreceptors in the centre if the receptive field transmit excitatory signals to the ganglion cells.
• Photoreceptors in the surrounding receptive field transmit excitatory signals to intermediate neurons (A and C) (amacrine and horizontal cells).
• Intermediate neurons receiving input from the surrounding receptive field send inhibitory signals to the ganglion cell (B)

Question 11

Why are the receptive fields (RFs) of retinal ganglion cells (RGCs) so important? (3)

Answer 11

• All visual information sent to the brain from the eye is encoded in the responses (e.g., firing rate) of RGCs
• Their RFs extract, capture and enhance features in our vision
• The RFs of retinal ganglion cells are fundamental for understanding our perception of colour, luminance contrasts and edges

Question 12

Explain the main concept of the RGC Receptive fields

Answer 12

A spatially opponent (centre-surround) receptive field can encode:
*Differences in luminance
*The position of edges
*Differences in colour
*But they can’t encode orientation! (a stimulus presented across the receptive field will result in the same response no matter the orientation)

Question 13

What is the Lateral Geniculate Nucleus (LGN) in the visual system?

Answer 13

• Receives input from retinal ganglion cells regarding contralateral visual field
• Relays visual information from retina to primary visual cortex
• Also receives input from primary visual cortex and rest of the brain, including regions involved in eye movement

Question 14

What are the characteristics of a ganglion cell’s receptive field?

Answer 14

Center-surround receptive field.
Responds best to small spots, but will respond to other stimuli.

Question 15

What are the characteristics of a lateral geniculate’s receptive field?

Answer 15

Center-surround receptive fields very similar to the receptive field of a ganglion cell.

Question 16

What are the characteristics of a simple cortical’s receptive field?

Answer 16

Excitatory and inhibitory areas are arranged side by side.
Responds best to bars of a particular orientation.

Question 17

What are the characteristics of a complex cortical’s receptive field?

Answer 17

Responds best to movement of a correctly orientated bar across the receptive field.
Many cells respond best to a particular direction of movement.

Question 18

What are the characteristics of an End-stopped cortical’s receptive field?

Answer 18

Responds to corner’s, angles, or bars of a particular length moving in a particular direction.

Question 19

How are complex cells similar/dissimilar to simple cells?

Answer 19

Similar: respond to bars of a light of a particular orientation.
Dissimilar: Respond to movement of bars of light in specific direction.

Question 20

What do end-stopped cells respond/not-respond to?

Answer 20

Respond to:
- moving lines of specific length
- moving corners or angles.
No response to:
- stimuli that are too long/large.

Question 21

What is a horopter?

Answer 21

A curved line or surface that represents the points in space that stimulate corresponding points on the retina of each eye.

Question 22

Explain the study on the physiology of binocular depth perception

Answer 22

• DeAngelis et al.
• Monkey trained to indicate depth from disparate images.
• Disparity-selective neurons activated by this process.
• Experimenter used microstimulation to activate different disparity-selective neurons.
• Monkey shifted judgement to the artificially stimulated disparity.

Question 23

What is the pathway from the retina to the cortex?

Answer 23

Signals from the retina travel through the optic nerve to the:
- Lateral geniculate nucleus (LGN)
- Primary visual cortex in the occipital lobe (striate cortex)
- Secondary visual association cortex
- Then through two pathways to the temporal lobe and parietal lobe.

Question 24

Explain dorsal and ventral visual systems

Answer 24

Ungerleider and Mishkin (1982) - distinguished between ventral and dorsal pathways projecting from the primary visual cortex to the inferior temporal cortex and the posterior parietal cortex.
*These pathways, they suggested, are involved in object identification (‘what’) and object location (‘where’).