Alex- Seeing- Part 2

Question 1

Gain control

Answer 1

Neurones adapt their sensitivity to the environment over time and space as have to deal with big dynamic ranges. Establish baseline and signal changes around this. E.g. light and dark, pheromones, wealth. Webster et al: blurry seems sharp among sharp, see imprint after looking.

Question 2

Canonical/universal computation

Answer 2

Cajal: how all the neurones in the brain operate using same gain control. When stain brain, diff places have same layers so function related to shape. Brain has columns with layers which differ in thickness. Called hypercolumns, blobs, interblolbs in visual . Limited number of universal computations

Question 3

Why use Vision as a model system

Answer 3

Human brain project tried to make computations of 3D brain, big budget but failed- should use vision as window to brain, visual stim cheap and easy, big visual neain so can record, access brain consciously, 11 years of data

Question 4

Contrast - path of info - retina

Answer 4

Retina-lgn- Cortex. Retina turns luminance patterns (how much light) into contrast (how much light changes across space). Expressed as decimal or % but becomes saturated. Lgn has contrast not L, currency of early vis system, seen by mante. Input from eyes still together so has contrast & eye of origin but not orient or spat feq

Question 5

Cortex

Answer 5

V1/striate: info from lgn in retinotopic- middle of vis field and v2 and v3 periphery. Hubel and Wiesel show nuerone preference. Cortical neurones have wide visual fields. Test gain control by showing blurred in middle of diff and match to a scale of diff contrasts. If measure neurones in isolation, more sensitive but with mask in environ respdices response- in animals

Question 6

Retinal gain control and cortical

Answer 6

Short range, untuned (no orientation), direction, does depend on eye as independent. Cortical gain control: long range, has tuning and complex like facial expression

Question 7

Issues W gain control

Answer 7

Seen in epilepsy, autism, shizo, parkinsons and normal aging
Indicator of nueral dysfunction but abnormal gain control may be cause of some diseases

Question 8

Schizo

Answer 8

Ps have diff contrast stim so abnormal gain control so neurones fire when shouldn’t- may be a cause?

Question 9

Epilepsy

Answer 9

Pokemon used strobing lights, undocked seasides in photosensitive epilepsy. Neurones aren’t being desensitised. Ps W idiopathic gen ep showed flickering contrast and found had reduced gain control-Wade

Question 10

Ageing

Answer 10

Moving pattern across screen and say l or r, when young cant tell as suppressing neurones on periphery so as you make patch bigger, get worse at detecting motion due to long range gain control – tadin . found older people dont show this effect, they are better at big disks- due to loss of neurons at periphery

Question 11

Parkinson’s

Answer 11

Tremor, rigidity, a kinesia, postural instability (trap). A fork of genetic- G2019S in North Africa on lrrk2 gene. When inserted to fruit flies, get Parkinson’s. Neurones of flies more sensitive so more gain control and faster- could id disorder accurately. Did humans and found less responsive

Question 12

Tutorial - measuring blind spot

Answer 12

When shine light into eye, can see shadows of blood vessels called the purkinje tree. Retina is 15 degrees horizontally into nasal retina. To find visual angle a due =degrees (ATAN(x/y)) in excel. Brain takes out blinking, sac adds (rem). Motion induced blindness: vision active so edits out moving to stop them looking blurred