UVC100Summer16_Class2

agenda 5.19.16
• how eye and brain work together to create vision
• the active, constructed nature of vision
• the psychology of habit and how art can make a difference

In general in this course, we are interested not
in the “nature” of vision, but in its culture; in
other words, how humans have developed
languages of visual communication given
our status as sighted creatures.

So this session is a bit
of a departure.
Today we study the eye, the brain and
the dynamic process of visual
perception, to understand how our
perception works.

Most people assume that vision works as pictured in the diagram below.
Put in words: our vision is just what our eye sees and reports to the brain.

(please note: this
diagram is WRONG)

why is the eye/camera analogy wrong?
There is no “image,” or picture of any
sort in the eye.
In the eye, light admitted through the pupil and focused
through the lens differentially stimulates the neuron-rich
tissue at the back of the eye (the retina), sending chemical
signals to the brain (specifically to the visual cortex), where
those signals must be processed and interpreted to create
our visual field.

“the eye is [not] like a camera”
The analogy holds up to a point.
The point at which it no longer holds
is the retina.
Please note: this diagram is TRUE up to a
point and then becomes FALSE.

what happens in the retina?
Light is converted into electrical impulses in the retinal
photoreceptors via a light-sensitive protein called rhodopsin.
Transduction is the process by which electrical impulses are
converted to chemical form. This occurs differently in rods and
cones.
The signaling mechanism is sophisticated. It optimizes the
information transmitted from the retina by using “lateral inhibition” to
reduce the signal in certain areas (thus boosting the rest).

cones vs. rods
• cones: large range of intensities, color vision, work quickly,
very sensitive to small changes, concentrated in center
• rods: evolutionarily more recent, but outnumber cones 20
to only work in very low light, evenly distributed across the
retina

• these electrical signals are
transmitted via the optic nerve to
the primary visual cortex

what happens in the visual
cortex?
This is where matters get really complicated!
There is evidence that there are THREE separate systems
that process these signals.

animal + human evidence for 3
discrete processing systems
“Although the visual processing mechanisms are not yet completely
understood, recent findings from anatomical and physiological
studies in monkeys suggest that visual signals are fed into at least
three separate processing systems. One system appears to
process information mainly about shape; a second, mainly about
color; and a third, movement, location, and spatial organization.”
Human psychological studies support the findings obtained through
animal research. These studies show that the perception of
movement, depth, perspective, the relative size of objects, the
relative movement of objects, shading, and gradations in texture all
depend primarily on contrasts in light intensity rather than on color.”
SOURCE: http://www.brainfacts.org/sensing-thinking-behaving/senses-and-
perception/articles/2012/vision-processing-information/

3 separate systems
This helps us to understand why black and white drawings
appear every bit as convincing in the illusion they produce of
objects in space as colored ones.

in the third system
(depth/location/movement)
• “About 60 years ago, scientists discovered that each vision cell’s
receptive field is activated when light hits a tiny region in the center
of the field and inhibited when light hits the area surrounding the
center. If light covers the entire receptive field, the cell responds
weakly.”
• Another way to put this is: “the visual process begins by
comparing the amount of light striking any small region of
the retina with the amount of surrounding light.”
• This is known as “lateral inhibition,” in which all but the very
strongest signals are filtered out by the retina before even
reaching the brain. (Creates strong edges around objects,
allowing us to perceive space.)
http://www.brainfacts.org/sensing-thinking-behaving/senses-and-
perception/articles/2012/vision-processing-information/

The raw data entering the third system has to do with
differences in light intensity. These signals are
enhanced by the retina through the process of lateral
inhibition and are subsequently interpreted by the visual
cortex to produce our field of vision, which we
experience as continuous and compelling rather than as
a series of approximations of distance, size and depth
via contrasts between light and shadow.

John Singleton COPLEY
Mrs. Ezekiel Goldthwaite
1771
oil on canvas
50 1/8 x 40 1/8 inches
The human visual system
functions by looking for “edges”—
areas of high contrast between
light and shadow. This perceptual
tendency is exploited by artists
wanting to create convincing
three-dimensional illusions in
their two-dimensional art.

summary 1
The brain constructs your field of vision from electrico-
chemical impulses sent by your eyes.
The eye collects data on:
• shape
• color
• position/location/movement
These elements seem to be processed via discrete mechanisms
in the visual cortex and coordinated into a coherent visual field.

• Our ability to, judge distance, move through space, avoid
obstacles,—these are all INFERENCES drawn from
information about contrasts between light intensity rather
than actual visual data—even though we perceive them
as properties of our vision.
• The brain can adjust for relative brightness/darkness;
provide motion stabilization; even reverse the visual field if
trained to do so.
• This is ANOTHER REASON why the eye/camera idea is
completely misleading.
summary 2

M.C. Escher
Drawing
Hands 1948
lithograph
11 1/8 x 13 1/8
inches
visual puzzles and optical illusions exploit
the ambiguities in these systems

agenda part 2
• what is perception?
• neuroscientific answer
• now, more of a psychological answer
• particular focus on what happens when perception becomes
too routine/habitualized/patterned
• art as the antidote to habitualized perception
• Paul Valery
• Viktor Shlovsky

“To see is to
forget the name
of the thing one
sees.”
—Paul Valery

Viktor Shklovsky
born 1893 in St.
Petersburg, Russia
died 1984 in Moscow,
USSR
literary critic and novelist

I. If we start to examine the general laws of perception,
we see that as perception becomes habitual, it
becomes automatic.
Thus, for example, all of our habits retreat into the area
of the unconsciously automatic; if one remembers the
sensations of holding a pen or of speaking in a foreign
language for the first time and compares that with his
feeling at performing the action for the ten thousandth
time, he will agree with us.

II. Such habituation explains the principles by which, in
ordinary speech, we leave phrases unfinished and
words half expressed. In this process, ideally realized in
algebra, things are replaced by symbols. Complete
words are not expressed in rapid speech; their initial
sounds are barely perceived. Alexander Pogodin offers
the example of a boy considering the sentence "The
Swiss mountains are beautiful" in the form of a series of
letters: T, S, m, a, b.

III. This characteristic of thought not only suggests the
method of algebra, but even prompts the choice of
symbols (letters, especially initial letters). By this
"algebraic" method of thought we apprehend objects
only as shapes with imprecise extensions; we do not
see them in their entirety but rather recognize them by
their main characteristics. We see the object as though
it were enveloped in a sack. We know what it is by its
configuration, but we see only its silhouette.

things are replaced by symbols...
the example of a boy considering
the sentence "The Swiss
mountains are beautiful" in the
form of a series of letters: T, S, m,
a, b.

"This characteristic of thought not
only suggests the method of
algebra, but even prompts the
choice of symbols (letters,
especially initial letters)."

"the object as though
enveloped in a sack..."
...we apprehend objects
only as shapes with
imprecise extensions; we
do not see them in their
entirety but rather
recognize them by their
main characteristics. We
see the object as though it
were enveloped in a sack.
We know what it is by its
configuration, but we see
only its silhouette.

Tolstoy cleans his office
“I was cleaning and, meandering about, approached the
divan and couldn't remember whether or not I had dusted it.
Since these movements are habitual and unconscious I
could not remember and felt that it was impossible to
remember - so that if I had dusted it and forgot - that is, had
acted unconsciously, then it was the same as if I had not. If
some conscious person had been watching, then the fact
could be established. If, however, no one was looking, or
looking on unconsciously, if the whole complex lives of many
people go on unconsciously, then such lives are as if they
had never been.”

habit devours...
“Habitualization devours work, clothes, furniture, one's wife,
and the fear of war... ...art exists that one may recover the
sensation of life; it exists to make one feel things, to make
the stone stony.
The purpose of art is to impart the sensation of things as
they are perceived and not as they are known. The technique
of art is to make objects "unfamiliar," to make forms difficult,
to increase the difficulty and length of perception because
the process of perception is an aesthetic end in itself and
must be prolonged. Art is a way of experiencing the
artfulness of an object: the object is not important...”

"After we see an object several times, we begin to recognize
it. The object is in front of us and we know about it, but we do
not see it—hence we cannot say anything significant about it.
Art removes objects from the automatism of perception in
several ways."
 defamiliarization

UVC100Summer16_Class2

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UVC100Summer16_Class2