Practical 2003 Cones and brightness perception

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Practical 2003 ? Cones and brightness
perception 1. A plane of equal brightness for
a range of colors is assessed applying flicker
fusion photometry. 2. Keywords Cones, color,
spectral sensitivity, brightness perception,
retina   3. Abstract A new method combines
flicker fusion photometry and the determination
of the loci of 16 equally bright colors in cone
space using geometry. Each student determines
her/his plane of equal brightness. I doing so
(s)he will also learn the Relative contributions
of the three cone types.   4. Required
Elementary knowledge on the visual system of
primates.   5. Literature Teufel HJ Wehrhahn C
(2000) Evidence for the contribution of S-cones
to the detection of flicker brightness and
red-green. Journal of the Optical Society of
America A, 17(6) 994-1006.   Textbooks Rodieck
RW The first steps in Seeing. Sinauer Assoc.
Sunderland, Mass. USA Dudel/Menzel/Schmidt
Neurowissenschaft, 2. Auflage, Chapters on Retina
(Kirschfeld) and Central Visual Systems
(Hoffmann Wehrhahn). p. 385-428.
Personel Barbara Dillenburger (T.
07071.601541, barbara.dillenburger_at_tuebingen.mpg.d
e) Christian Wehrhahn (T. 07071.601522,
christian.wehrhahn_at_tuebingen.mpg.de)
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Vision, neurophysiology and physiologically
plausible models

• motion perception
• Hyperacuity
• color vision
• contextual vision

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From Hubel 1988
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Eye and schematic view of the retina in humans
From Hubel 1988
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invaginating bipolars ? on flat bipolars ? off DG
? diffuse (parasol) ganglion cell
From Baylor, 1995
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h
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Cones count photons and generate electrical
signals depending on the number of quanta. Cone
signals are called cone excitations S, M and L
or receptoral mechanisms. The amplitude of
the cone response also depends on recent
history The longer and stronger a cone is
illuminated, the less sensitive is its signal to
current light flux changes. Its gain
decreases. The instantaneous effect of light
stimuli in photopic (i.e. daylight) vision is
completely described by the three cone
excitations. Each triplet forms a point in 3-D
space of cone excitations (SML-space).
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Spectral sensitivity of human cones
Wavelength discrimination in human observers.
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Some details about cone anatomy and the
processing of cone signals in retina and LGN.
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invaginating bipolars ? on flat bipolars ? off
Heinz Wässle
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Analog VLSI retina chip
1mm
Delbruck Kramer 2003
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4 pixels
30mm
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closest view of part of the pixel these
transistors are not minimum size because this is
an analog design
yellow areas are transistor channels green -
two ends of transistor red - transistor gates
blue is metal squares - contacts between
layers.
1mm
Delbruck Kramer 2003
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invaginating bipolars ? on flat bipolars ? off
Heinz Wässle
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• 2. Combination of cone signals into 3
• postreceptoral mechanisms.
• These code
• achromatic contrast cbr cL cM
• (ii) blue-yellow contrast (cS - cbr), and
• (iii) red-green contrast (cL- cM).
• For example L-cone contrast between a target
• and its surround is defined as
• cL (Ltarget Lsurround)/ Lsurround

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Heinz Wässle
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Heinz Wässle
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Combination of cone signals in retinal ganglion
cells L - and M cone contrasts are added in
thea achromatic ganglion cells On center
(cLcM), Off center (cLcM)
L - and M - cone
contrasts are subtracted in the chromatic
ganglion cells Redon cL-cM Redoff
-(cL-cM) Greenon cM-cL Greenoff
-(cM-cL) --------------- The achromatic contrast
(cLcM) is subtracted from Scone contrast Blue
on cs-(cLcM) (Blue off)
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Parasol cells or Magnocellular (MC)-cells code
achromatic contrast
Martin 1998
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The red-greenmechanism
Midget ganglion or Parvocellular (PC)-cells code
red-green contrast
Martin 1998
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Small bi-stratified or Koniocellular (K-) cells
code blue-yellow contrast
Martin 1998
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The axons of retinal ganglion cells leave the
eyes through the blind spot and form the
optic nerve. After partial crossing over
the axons enter the lateral geniculate nucleus
(LGN).
From Hubel 1988
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From Hubel 1988
Lateral geniculate nucleus of a macaque monkey
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Funktional differences between ganglion
cell classes (1) Extent of RF und
coverage. (2) Achromatic contrast
sensitivity is low in chromatic gcs. (3)
Temporal properties achromatic gcs respond
phasic, chromatic gcs respond tonic, i.e.
fast and slow Characterisation of the pathway
that transmits the brightness signal requires
inactivation of the chromatic pathway. We
provide a stimulus that is fast enough to impair
temporal modulation of the chromatic
signals Brightness modulation of a light spot
with 15 Hz is transmitted by achromatic gcs, but
not (or almost not) by chromatic gcs. We
construct colors, that are equally bright, but
differ in their chromatic composition. We can
thus find differences in the perception of color
stimuli depending only on wavelength.
Flicker fusion photometry (FP)
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Methods Color monitor PC. Calibration in cone
excitations We measure the spectral distribution
of the three monitor guns (R,G,B) and integrate
about spectral sensitivities of the cone
types. Background white with luminance of 40
cd/m2. Colored squares of 2 side length
alternate with the background white. Frequency
15 Hz. VP manipulate the gain of one of the
monitor guns (R, G, B) until perceived flicker is
minimal.
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The values assessed are transformed into cone
excitations and plotted in SML-space. We find a
plane in SML-space fitting the points. Use
implicite equation for a plane aLL aMM aSS
1 Obtain 3 coefficients aL, aM, and aS, the
relative contributions of L-, M- and S-cones to
the perception of brightness. These coefficients
are specific for each observer.
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