Measuring the blind spot

Question 1

The blind spot

Answer 1

• Optic disk is the part of the retina where the optic nerve leaves the eye
• There are no photoreceptors here so they don’t register any light falling on this region
• At the blind spot blood vessels leave the retina here

Question 2

Seeing your blood vessels

Answer 2

• Shine your phone torch into eye from side
• Can see shadows of retinal blood vessels
• Called purkinje tree

Question 3

Where on retina is the blindspot?

Answer 3

• 15 degress horizontal into nasal retina
• Fill blind spot when both eyes are open by using the other eye
• When one eye is closed the brain makes up something to fill the blind spot

Question 4

Degrees of visual angle

Answer 4

• Objects far away look smaller
• Rule of thumb = thumb is 2 degrees away at arms length
• Human nature to look proportionate

Question 5

What else is the brain making up?

Answer 5

• Blinding –> never notice lights going out when you blink (spend 5-10% of life blinking) - brain edits blinks out + fills the gaps
• Saccades –> rapid eye movement when you move your eyes across the world - never aware of this
• Attentional blindness –> focused on one aspect of brain doesn’t process everything thats happening

Question 6

Motion induced blindness

Answer 6

• Motion stimulus captures visual input making you unable to see whats behind the motion
• Suggests visual system has multiple parts to it (motion, colour) and attending to 1 part makes you blind to the other pathway
• May be active process deliberately editing out the edges of moving things + behind image gets caught up in this process
• Behind image fades our because the photoreceptors adapt