Lecture 3 - basic vision

Question 1

Vision

Answer 1

-Makes up a third of the cortex

Question 2

Face on moon: example of Pareidolia

Answer 2

• Region on moon detected using face recognition techniques
• Left hemisphere of brain = fusiform gyrus detects accuracy of how face like object is
• Right fusiform gyrus then uses info from left to conclude whether image is a face
• Pareidolia = idea that brain detects and recognises faces and patterns when it shouldn’t be recognised

Question 3

Brains can be easily tricked

Answer 3

• Face on moon issues occur due to the way eye processes info and relays to the brain
• It doesn’t always capture high resolution version of reality
• There is not enough receptors to process high definition
• Energy required to process all info all the time would be too large

Question 4

Consequences of energy saving processes

Answer 4

• Very sensitive to sudden changes and movement
• Very poor at detecting slow changes
• High resolution for black and white
• Low resolution for colour
• Good at comparing things side by side
• Poor at making absolute judgements or comparisons at different times
• Appearance of things can change over time
• Past events change what we perceive
• Surrounding context affects what we perceive

Question 5

Solution of energy saving processes

Answer 5

• Compression
• Only transmit important info
• Don’t transmit things humans don’t need to react to
• Changes are more important than stuff that stays the same
• Changes across space = edges
• Changes over time = new objects, things that move
• Some kinds of information more important than others
• To save energy brain performs optimisation = leads to visual illusions

Question 6

Encoding changes over time

Answer 6

• When looking at white square, the red, green, blue receptors equally active. But when looking at just red = just red photoreceptors active
• Over time these red receptors inhibit their activity (temporal inhibitors) because cell active for too long
• After this, when go to look back at white, the red photoreceptor still inhibited = mixture of green and blue photoreceptors gives you an after effect

Question 7

Encoding changes over space

Answer 7

• Context also affects perception
• When brain looking at solid red bar, realises not all red photoreceptors need to be active so turns off some
• When there is a boundary between 2 colours they will all remain active
• The consequence of spatial inhibition means only cells looking at borders of objects remain active and neighbouring ones are inhibited

Question 8

What happens when balance of inhibition and excitation goes wrong

Answer 8

• Visual stress
• Migraine
• Epilepsy