WANDELL Brian COLOR VISION April 23 2012

title: how wavelength becomes color

hiroshi is in his lab  (and is here)

Dennis Baylor  (my old neighbor) is here
Andrea is here  (another vision researcher)

intro by Paul Skokowski

Monday, 4:15P  in Humanities Center...

color... an advantage... he shows a picture of red berries amidst crowded leaves.

rather than assign color to a light patch... it is really assigning color to an OBJECT
he shows Adelson illusion... great illusion
coffee table  with a "white" patch beneath it  and "dark" patch under the light.

assigning an experience to OBJECTS!  (not to a patch of light)...

"i don't know a lot abt color experience" 
  he'll talk abt the front end... hard to talk abt the back end (others will need to do that)

sl = slide

brief intro to retina

retinal thickness is 400 microns thick

distance from retina to lens is 17 mm  (f  2.4 to ? big number)

GCL = gangl cell layer
then INL = inner nuclear layer  then ONL  outer nuclear layer  then
OS = outer segments...

he shows fovea...  GCL  thins way down

fovea means PIT...

foveal cone width is about 1-2 microns
1 million optic nerve fibers

retina has  5 * 10**6 cones

out in periphery  a cone might have to share  50  rgcs  ret gang cells

but  in  fovea  each cone might go to only 3 rt gang cells

fovea is very special (? in primates)

small region where its entirely cones right at fovea...

(rods total = 100M)

sl  gorgeous pic of rods and cones...

image formed at the inner segment... its a waveguid... it stays inside

lubert stryer figured it out.. how to  transition from  photopigment to electricity.

opsin could sit  there for 300 years... v stable  except when it absorbs light..

william rushton  (was at cambridge for yrs0.. pic of alligator...

rhodopsin  (visual purple)  in regenerated state... it is purple

after exposure to light the pigment become clear...

he shows cartoon  of Newton's prism experiment... (with 2 prisms)

violet  abt 400 nano... reds and oranges around 700...

SPD = spectral power distribution...  power on y axis and  ave length on x axis...

Newton's color  circle:  intro in his book Opticks in 1704...  (opposites make white... wrong!)

John Mollen historical review...

1708  color industry was born...  mix 3 pigments to make any color...  from the Hague in 1708..

superposition of light...  MIX  blue light + yellow light  and get two separ. peaks...

color matching experiment...
compare mix of RGB primaries  with  a test light...
make them look the same... look the same....

T  the test light can be ANY spectral power  and you can match it with 3 lights  (RGB)

METAMERISM  (spectra are totally different!)

he shows  4 difft  SPDs  quite difft but they all look the same;  spd = spectral power distribution.

color blind = 6% of men and 2% of women  (only 2  types of cones)

even 3 sharp peaks will match a contin spd...

the color matching expt is LINEAR

he shows  ADDING  A  and B  will also produce a match...

rhs   is just difft quants of RGB  and lhs is  pastel  blue and purple
in difft quants...  then add them together and they STILL MATCH!

this was known in 1930s...

see schnapf and baylor in 1986...
single cone photocurrent measurment  (he sucks ONE toad cone in a micropipette)

julie and brian nunn moved him (Denis) into primates...

picoamp current with a flash of light  (in ONE cone)

this particular cell  does not CARE  abt  the wavelength.. ONLY the intensity...
principle of univariance!! (so called by Wm Rushton)

3 types of cones in the eye  (go down 5 orders of magnitude in sensitivity)

L= red;  M = green;  S =blue

ALL THAT MATTERS is the L,M,S cones... they must match for the person to call the mixes the same...

Julie  Schnapf... was there when BW = Brian Wandell visited Denis's lab...

lubert stryer showed genetics and  and alter of  photocascades etc.

3 types of receptors... first guy was Thomas Young  1802...  philos  transactions  of royal soc...

what newton got WRONG... some wavelenths can NOT be cancelled by other wavelengths (as newton claimed)

grassman...  great genius... invented linear algebra...

Koenig and Dieterici  (he finds it on google books)  1892.. they  FOUND the exact wavelengths of  cones!!!

look at Heidi  Hofer  J neurosci  in 2005  she can actually SEE the cones  and their 3 colors... see the acual mosaic!

330 microns = 1 degree
foveolar ede...  cone diameter is 3 to 4 microns..

i ask abt  relat rarity of blue cones...  A  short wavelength is DISPERSED MORE than long wavelenth
in the exact propotion to their  spacing in the retina!!!  (rest of the cns follows that pattern)

****
Here' what i'm not telling u that u really want to know...  (abt qualia)

color appearance and context.... he shows they are hugely different
he shows  a giant  yellow X on a gray bkgrnd and a giant gray x on a yellow bkgrnd  with identical  wavelength mix!!!
he brings them together and boom.. they are identical!

noted by  De La Hire  in 1694 and 1730...

Bart Anderon and Jon Winawer  in Nature  2005...

bw shows 2 rows of chess pieces

black on white at top  and
white on black at bottom  ... but identical  intensities!!!

he overlaps the black  king and the white king and they match!!!

Ewell Herring....cannot  ever find  something that looks both  yellow and blue

bw  there is no such thing as primary colors!

Herring.. opponent color  (bw believes this is true)

after images...  discoverd in the cns later!

L and M are only 8 base pair difference....

we HAD the short and long  cones  and then the M  are prob a recent innovation...

genetic tweak

semir zeki...record from v4...  bw DOES think that u cud record from say v4 neurons and say... S is experiencing red37 or blue 53.

steve palmer   and david hilbert will be at this same workshop in a week....

norm hardy asks abt wiring  of retina to brain

bw  quotes  dave  brainerd?  abt  ret gang cell  ...  how long it takes it to figure which cones are connected to it..

quote from  newton... "for the rays are not colored" (in response to a Q from Paul S)

bw ... color  is the experience u ascribe to firings of certain neurons...