Binocular Rivalry and Perception of ambiguous objects

Question 1

What is perception?

Answer 1

Interpretation of sensory information to interpret and understand the information

Question 2

What is the concept of the ‘Grandmother cell’?

[Lettvin]

(3 marks)

Answer 2

• Theory that one neuron is highly active when it sees the ‘grandmother’ and is not active at other times
• Supported by scans from inferior temporal cortex of monkeys that fire selectively to faces
• This alongside the ‘Halle berry neurons’ show that individual neurons can be V1 selective

Question 3

What is the distributed representation theory?

(1 mark)

Answer 3

• Specific stimulus coded by its unique pattern of activity across a group of neurons

Question 4

What is the binding problem?

(1 mark)

Answer 4

How the different parts of an image broken down into parts in the brain are able to then be perceived as one whole seamless image

Question 5

What is the combination porblem?

(1 mark)

Answer 5

Problem of how objects, background and abstract or emotional features are combined into a single experience

Question 6

Explain superposition and catastrophe with an example.

(2 marks)

Answer 6

• When looking at a blue square and yellow circle, what neural mehcanisms ensure that the square is perceived as blue and the circle yellow ad not vice versa?

Question 7

Outline the path of the primary visual pathway.

(3 marks)

Answer 7

• Light
• Retina
• Contralateral optic nerve
• Optic chiasm
• LGN
• Visual cortex

Question 8

What are the two visual streams?

(2 marks)

Answer 8

Dorsal stream - movement

Ventral stream - object recognition

Question 9

What is the geometry of stereopsis?

(2 marks)

Answer 9

• Processed in visual cortex in binocular cells having receptive fields in horizontal positions in the two eyes
• When staring at an object the 2 eyes converge so that the object appears at the centre of the retina in both eyes

Question 10

What happens in terms of fibres in the geometry of stereopsis?

(2 marks)

Answer 10

• ½ the fibres syau on teh same side and the other half cross over
• The difference in angle of a point from 2 eyes known as binocular disparity causing 3D image

Question 11

What is the binocular disparity equation as seen on the slide?

Answer 11

δ=θ_L - θ_R

Question 12

Why can depth only be seen with a stereoscope in random dot stereogram?

Answer 12

It contains no monocular features

Question 13

What happens to our perception in binocular rivalry?

Answer 13

• Fluctuating perception despite the physically unchanging stimulus
• Stochastic alterations in dominance and suppresion of left and right eye stimulus - the ‘stronger’ stimulus has longer periods of dominance

Question 14

What is binocular rivalry?

(2 marks)

Answer 14

Two dissimilar images are presented simultaneously to each eye and perception alternates between them

Question 15

What is eye rivalry?

Answer 15

• Competition between retinal inputs when dissimliar molecular stimuli are presented to corresponding retianl locations of the two eye

Question 16

How are alteration rates affected in binocular rivalry?

(3 marks)

Answer 16

• Alteration rates can’t be stopped, nor voluntarily controlled
• Alteration rates can increae over time (modulatory perception)?
• Rate of alteration can be modified by perception (which image is shown for longer?)

Question 17

Is reduced visual sensitivity during suppression selective?

Answer 17

• It is general and non-selectie for stimulus attributes

Question 18

What do binocular neurons in V1 show?

(2 marks)

Answer 18

• Exhibit interocular suppresion that is selective for stimulus conditions in which binocular rivalry is experienced.
• Show a moncular response to a neuron - with rating of same orientation - see that response is bigger in rivalry expected high response in particular orientation

Question 19

What are teh highest visual areas in the human brain?

(1 mark)

Answer 19

• FFA - Fusifrom face area - high response to faces
• PPA - Parahippocampal place area - shows high response to scenes

Question 20

In rivalry between a face and a house, which area is more domiant the FFA or PPA?

(1 mark)

Answer 20

• FFA peaks in activity when the face is shown and is more dominant
• PPA peaks in activity when the house is shown and is therefore more dominant

Question 21

If a grating is stronger than the other what does this mean?

Answer 21

• Suggests that the grating has a higher contrast stimuli than its competitor and therefore shows stronger perceptual competition as seen by faster rivalry alterations

Question 22

Give an argument in favour of stimulus rivalry.

Answer 22

• Monocular rivalry can be experienced with the stimuli superimposed in one eye
• Under certain conditions rapid switching of stimuli between the eyes goes unnotices it is one particular stimulus that is dominant for several seconds

Question 23

How is activity affected in V1 when a high contrast image is perceived vs a low contrast image?

(1 mark)

Answer 23

• Increases when higher contrast pattern perceived and decreases when lower contrast pattern is perceived
• (firing can also be increased by physical alteration of images)