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Chapter 1: What Is Vision Science The Thinking Eye, The Seeing Brain by James T. Enns

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Title: Chapter 1: What Is Vision Science The Thinking Eye, The Seeing Brain by James T. Enns


1
Chapter 1 What Is Vision Science?The
Thinking Eye, The Seeing Brain by James T. Enns
2
What vision is not
  • Folk Psychology and Commonsense intuitions are
    wrong
  • Four Myths
  • The myth that seeing provides a faithful record
    of the world in front of us eye as a camera
  • The myth that seeing occurs automatically and
    without any thoughtful activity on our part
    passivity of sense
  • The myth that our eyes are responsible for our
    sight windows of the soul
  • The myth that we can think without using our
    senses immutability of soul

3
Slogans
eye as a camera
  • immutability of soul

passivity of sense
  • windows of the soul

4
Figure 1.1. The myth of vision as a faithful
record
       Concentric circles or continuous
spiral?        The pattern of light is of
concentric circles        Human vision sees a
continuous spiral
5
Figure 1.2. Vision as a useful construction of
the mind
       Which two tabletops have identical
dimensions on the page?        Tabletops A and B
are identical in size on the page except for
rotation.        Human vision sees tabletops B
and C as similar because of a three-dimensional
interpretation of the world that is built into
our brains and through which we see.
6
The Myth of seeing as a faithful record
  • Tables (a) and (b) are invariant in 3D spatial
    Manifold
  • Fraser Spiral is really a series of concentric
    circles that we see as a continuous spiral. Why
    is that?

7
The Myth of vision as a passive process
  • The Grand illusion of complete perception
  • (1) Vision is not rich in detail
  • the size of a thumbnail at arms length gets
    processed
  • (2) Attention is limited the law of ONEs
  • vision sees one object, one event, one location
  • These two factors are illustrated by
  • Impossible triangle
  • Escher drawings

8
Brains construct a well-behaved 3-D world so we
cannot experience a world that is not. Here we
see an ordinary triangle and building with normal
corners and angles instead of the shocking
reality. Why? (p. 9)
Go to http//www.michaelbach.de/ot/cog_imposs1/in
dex.html
9
The Myth of the Seeing Eye
False perception only occurs when the images
recorded by the eyes are sent to the brain.
  • Software becomes hardware
  • the eye of frogs and rabbits perform a
    sophisticated analysis of visual motion, an
    analysis that occurs in only the higher levels of
    the brain in monkeys and humans.

10
The Myth of Imageless thought
  • sensory imagination is active
  • Answer the following
  • When you approach the front door or the main
    entrance, how many windows are visible
  • helicopter approach, floating air-car approach
  • eye movements mimic the real situation
  • Where are your hands?
  • Experiments show that physically similar images
    increase response time for similar questions.
  • Do some dogs have tails? and Do some cats have
    tails? trigger faster response than a pair with
    dissimilar physical characteristics. Why?

11
The Myth of objective vision
  • Necker cube
  • Brains see random variation between limited
    alternatives (see next slide)
  • Geometrically, many views are possible
  • humans only see two possibilities
  • selection of view is random

12
Figure 1.5. Subjective perceptions are not
necessarily arbitrary perceptions
       Brains see two instead of all of these
interpretations? Why not?        Humans bring
shared assumptions to the vision project, (1)
that objects are generally convex, (2) that
straight lines in a picture represent straight
edges in an object, and (3) that three-edge
junctions are generally right-angled corners.
13
Figure 1.4. Subjective perceptions are not
necessarily arbitrary perceptions
       A perceptually ambiguous wire
cube        How many different interpretations
can you see?
Go to
http//mindbluff.com/necker.htm
14
vision myths
  • myth vision as passive
  • what is vision for?
  • survival not to reproduce
  • intersubjective, objective, arbitrary
  • tables, Necker cubes
  • faithful reproduction less important than fast
    response

15
Measurement in Vision Science
  • light measured in nanometers (nm)
  • 1nm1billionth meter
  • eyes sense from 360nm to 780nm on the infinite
    scale of wavelength nothing.
  • light is whatever energy falls in that range -
    light by definition, is anthromorphized.
  • 1st feature of light
  • wavelength480blue, 540green, 565yellow,590red

nanometer (nan'?-me't?r)
16
The Spectrum of Visible Light The visible part of
the spectrum may be further subdivided according
to color, with red at the long wavelength end and
violet at the short wavelength end, as
illustrated (schematically) in the following
figure.
How Roy G. Bv Lost a Vowel The sequence of colors
red, orange, yellow, green, blue, and violet may
be remembered by memorizing the name of that fine
fellow "ROY G. BV". This was originally "ROY G.
BIV", because it used to be common to call the
region between blue and violet "indigo". In
modern usage, indigo is not usually distinguished
as a separate color in the visible spectrum thus
Roy no longer has any vowels in his last name.
17
The notation "eV" stands for electron-volts, a
common unit of energy measure in atomic physics.
Each color has its energy. A graphical
representation of the electromagnetic spectrum is
shown in the figure below.
Thus we see that visible light and gamma rays
and microwaves are really the same things. They
are all electromagnetic radiation they just
differ in their wavelengths.
18
measurement
  • 2nd feature of light
  • intensity or amount, photon catch the number of
    photons that actually make contact with light
    sensitive receptors in the eye
  • candelaintensity of light emitted from a candle
    onto a square meter at one meter, 1/1000 watt
    bulb with a peak wavelength of 555 nm.
  • Lightnessthe degree of surface reflectance (24),
  • brightnessthe intensity of the source of light

19
measurement
  • Visions various jobs
  • determine the combination of brightness and
    lightness that generates the total photon catch
    at the eye
  • is it a black paper illuminated by bright light,
    or white paper under dim light?
  • Both pieces of paper may reflect similar amounts
    of light to the eye but usually the black
    reflects more so why arent we fooled into seeing
    it as white?
  • Space
  • candela is defined in terms of space
  • the angle formed by rays extending from the lens
    to the object equals the angles formed by rays
    extending from the lens to the retina.
  • visual angle is measured in degrees, minutes,
    seconds (see next)

20
Figure 1.6 The 2-D image size (on the retina) is
a function of S. Visual sizes and distances are
measured in terms of degrees of visual angle
(hunk of an arc) for convenience
21
measurement
  • time
  • the amount of light shining on the eye depends on
    how long the eyes sits still.
  • a single cycle of neural activity in response to
    a signal takes between 1-10 milliseconds, 1
    millisecond1/1000 second. Between the retina and
    the cerebral cortex, there are 4 cycles, or 40 ms
    of a lapse time. the minimum time for a motor
    response is 200ms, a fifth of a second.
  • neurons can track pulsating light only up to 60
    cycles, 8 ms on and 8 ms off. Individual movie
    frames change every 30 ms (33 cycles per second)
    and we cant see them.
  • Eyeblink duration is around 100 ms.

22
measurement
  • cones vision under bright illumination
  • Cone time constant100ms, 1,000 photons can be
    presented in a brief period (say, 1000 photons
    within a 1 ms period) or over a long period (such
    as 200 photons in each of five 20 ms period) for
    the same visual effect. The cones cannot tell the
    difference.
  • Rod time constant400 ms, meaning the photon
    catch extends over a longer time interval working
    like a slow shutter speed on a camera (well,
    cameras once had shutters that had a click that
    digital cameras artificially reproduce even
    though there is nothing to click any more.)

23
measurement
  • limitations
  • space constants of the eye are limited by the
    size of, and interaction among, cones and rods.
  • constant, the point at which the eye cannot
    distinguish whether the number of photons were
    concentrated in a small region of the retina or
    were distributed over a large region
  • space and time constants are limited by the size
    and interaction among cones an rods
  • the closer to the center the eye, the smaller the
    constant (the eye can see more in daylight)
    (27).

24
behavior
  • psychophysical function
  • measurement of a stimulus that is too weak,
  • measurement of a stimulus that is too strong,
  • measurement of the threshold halfway between too
    weak and too strong

25
Figure 1.7. The visual threshold
       How much of a stimulus is needed for
detection?        When a stimulus can be seen
50 of the time, it is said to be at the
threshold of the visual system.
26
Figure 1.8. Visual discrimination and
identification
       It is always possible to trade response
accuracy for response speed.        Tasks A and
B are therefore equally difficult increased
accuracy in Task A has only come about through a
reduction in response speed.        Task C is
easier than either Task A or B it is performed
faster than Task A at the same level of accuracy,
and it is performed faster and more accurately
than Task B.
27
  • THE END

28
Visual mapping of the idea and brain
  • Close your right eye and fix your gaze on the dot
    at the center of figure 2.3b.
  • hold the book about 6 inches from your face.
  • Follow the rest of the directions.
  • Perform the second experiment
  • Perform the third experiment

29
Analysis
  • We do not see the gap in the bars or the hole in
    the center donut. The bars become continuous and
    the donut becomes a solid disk.
  • These experiments illustrate that the brain can
    generate experience in a location of space even
    when no sensory input takes place

30
Thought experiment
  • If the bar was plaid, would the filled in segment
    be plaid?
  • what would this suggest about first person
    reports that the person sees the bar to be
    solid?
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