金光閃閃瑞氣千條 視覺系統 - national tsing hua...

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

movie

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

缺少紅色感光細胞

（紅綠色盲）

2008/3/28

http://www.vischeck.com/

缺少綠色感光細胞

（紅綠色盲）

2008/3/28

http://www.vischeck.com/

缺少藍色感光細胞

（黃藍色盲）

2008/3/28

http://www.vischeck.com/

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.