金光閃閃瑞氣千條 視覺系統 - national tsing hua...
TRANSCRIPT
金光閃閃瑞氣千條 - 視覺系統
焦傳金
國立清華大學生命科學系
Are they still or moving?
http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html
The squares marked A and B are the same shade of gray
The original image plus two stripes.
By joining the squares marked A and B
with two vertical stripes of the same
shade of gray, it becomes apparent
that both squares are the same.
Take home messages
1. Your retina is NOT like your digital camera.
2. What your eye see is NOT exactly what you actually see.
Our retina is “inversed”, and we have a “blind spot”
視蛋白（o p s i n）與視黃醛（retinal，非常類似維生素A）
視色素一旦吸收了光線，新增加的能量就會改變視黃醛的形狀
視色素一旦吸收了光線，引發一連串的分子事件，造成錐細胞的興奮
To see the back of human eye
Ophthalmoscope
Fundus of human eye
Find your blind spot and beyond
What if the backgrounds on both sides are different?
What if we reverse the green and the yellow background?
What if it is more than a spot?
Finally, what if it is not a plain background?
What your eye see is not exactly what you
actually see
Contrast between an object and its background
Nobel Laureate 1967
Lateral inhibition
On-center, off-surround cells
Responds to light in the center and inhibited by light in
the surround. Inhibited by a dark spot in the center and
excited by dark in the surround
Your retina is NOT like your digital camera
Orientation columns
in the visual cortex of
the monkey
The primary visual cortex
is organized into
functional modules
9x12 mm
Pinwheel-like area
Using optical imaging the form of the orientation columns
in the cortex for all possible orientations takes on the
shape of small pinwheels
Parallel pathways convey information from the retina to parietal
and temporal cortices
Motion and color are processed in different brain areas
Monocular cues create far-field depth perception
Occlusion (4,5)
Linear perspective (6/7, 8/9)
Size perspective (1,2)
Familiar size (2,3)
Optic flow: the full-field motion that results
from the observer’s own movement
Neural basis of stereoscopic vision
Binocular disparity
Cells are binocular and receive input from corresponding
visual fields.
movie
Random dot stereograms separate stereopsis from object vision
See this pair through a
stereoscope, or by training
the eyes to focus outside
the image plane
Ocular disparity, rather
than the form
Cells in V2 respond to both illusory and actual contours
Illusory contour
Cells in V4 respond to form, many inferior temporal neurons
also respond to color
A “Circle” selective cell A “pink” color selective cell
Recognition of faces and other complex forms depend upon the
inferior temporal cortex
A “face” selective cell
Size constancy
Figure-ground recognition
Young lady & old lady
Color blind
1. What do color blind people see?
2. Can your slides been seen by color blind people?
In its most severe forms, color
blindness is caused by the absence of
one of the cone visual pigments.
Shown here, the spectral sensitivities
of the cone pigments in color normal
trichromats are compared with those
of a color blind person. Also compare
the spectrum as it appears to a color
normal person with the illustration of
how it might look to a red-green color
blind person.
1 2
3 4
1 2
3 4
1 2
3 4
2008/3/28
The difficulties with certain
colors can be illustrated on a
color wheel. For a severely red-
green color blind person there
are only two hues, the ones a
color normal person sees as
yellow and blue. Intermediate
colors, the ones seen as blueish-
green and magenta, appear gray.
Clear graphics are very important and often the source of the most difficulty;
here are two examples showing the difference between good and bad use of
color. The Trick is to keep brightness differences large and to avoid color
combinations that do not contrast well.
A comparison of the two color wheels shows which color combinations would be
difficult to see. Graphics cause the most problems, but the colors can be eco-
nomically illustrated as text examples, below. The right-hand column illustrates
how the left hand column might look to a color blind person.
Some examples of color combinations that are easily seen by a color blind person
are shown below. These are illustrated as text examples but these principles are
most important to keep in mind when preparing drawings, graphs, and figures.
