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Lesson#8
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HUMAN INPUT-OUTPUT CHANNELS-2
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As the aim of this lecture is to introduce you the study of
Human Computer
Interaction, so that after studying this you will be able to:
. Understand role of
color theory in design
. Discuss hearing
perception
. Discuss haptic
perception
. Understand movement
8.1 Color Theory
Color theory encompasses a multitude of definitions, concepts
and design
applications. All the information would fill several
encyclopedias. As an introduction,
here are a few basic concepts.
The quick brown
fox jumps over the
the lazy dog.
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The Color Wheel
A color circle, based on red, yellow and blue, is traditional in
the field of art. Sir Isaac
Newton developed the first circular diagram of colors in 1666.
Since then scientists
and artists have studied and designed numerous variations of
this concept. Differences
of opinion about the validity of one format over another
continue to provoke debate.
In reality, any color circle or color wheel, which presents a
logically arranged
sequence of pure hues, has merit.
Primary Colors
In traditional color theory, these are the 3 pigment colors that
cannot be mixed or
formed by any combination of other colors. All other colors are
derived from these 3
hues
PRIMARY COLORS
Red, yellow and blue
Secondary Colors
These are the colors formed by mixing the primary colors.
SECONDARY COLORS
Green, orange and purple
Tertiary colors
These are the colors formed by mixing one primary and one
secondary color.
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TERTIARY COLORS
Yellow-orange, red-orange, red-purple, blue-purple, blue-green
and yellowgreen.
Color Harmony
Harmony can be defined as a pleasing arrangement of parts,
whether it be music,
poetry, color, or even an ice cream sundae.
In visual experiences, harmony is something that is pleasing to
the eye. It engages the
viewer and it creates an inner sense of order, a balance in the
visual experience. When
something is not harmonious, it's either boring or chaotic. At
one extreme is a visual
experience that is so bland that the viewer is not engaged. The
human brain will reject
under-stimulating information. At the other extreme is a visual
experience that is so
overdone, so chaotic that the viewer can't stand to look at it.
The human brain rejects
what it cannot organize, what it cannot understand? The visual
task requires that we
present a logical structure. Color harmony delivers visual
interest and a sense of
order.
In summary, extreme unity leads to under-stimulation, extreme
complexity leads to overstimulation.
Harmony is a dynamic equilibrium.
Some Formulas for Color Harmony
There are many theories for harmony. The following illustrations
and descriptions
present some basic formulas.
Analogous colors
Analogous colors are any three colors, which are side by side on
a 12 part color
wheel, such as yellow-green, yellow, and yellow-orange. Usually
one of the three
colors predominates.
A color scheme based on analogous colors
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Complementary colors
Complementary colors are any two colors, which are directly
opposite each other,
such as red and green and red-purple and yellow-green. In the
illustration above, there
are several variations of yellow-green in the leaves and several
variations of redpurple
in the orchid. These opposing colors create maximum contrast and
maximum
stability.
A color scheme based on complementary colors
Natural harmony
Nature provides a perfect departure point for color harmony. In
the illustration above,
red yellow and green create a harmonious design, regardless of
whether this
combination fits into a technical formula for color harmony.
A color scheme based on nature
.
Color Context
How color behaves in relation to other colors and shapes is a
complex area of color
theory. Compare the contrast effects of different color
backgrounds for the same red
square.
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Red appears more brilliant against a black background and
somewhat duller against
the white background. In contrast with orange, the red appears
lifeless; in contrast
with blue-green, it exhibits brilliance. Notice that the red
square appears larger on
black than on other background colors.
Different readings of the same color
As we age, the color of lens in eye changes. It becomes yellow
and absorb shorter
wavelengths so the colors with shorter wavelength will not be
visible as we aged. So,
do not use blue for text or small objects. As we age, the fluid
between lens and retina
absorbs more light due to which eye perceive lower level of
brightness. Therefore
older people need brighter colors.
Different wavelengths of light focused at different distances
behind eye’s lens this
require constant refocusing which causes fatigue. So, be careful
about color
combinations. Pure (saturated) colors require more focusing then
less pure. Therefore
do not use saturated colors in User interface unless you really
need something to stand
out (danger sign).
Guidelines
. Opponent colors go
well together (red & green) or (yellow & blue)
. Pick non-adjacent
colors on the hue circle
. Size of detectable
changes in color varies. For example, it is hard to detect
changes in reds, purples, & greens and easier to detect changes
in yellows &
blue-greens
. Older users need
higher brightness levels to distinguish colors
. Hard to focus on
edges created by color alone, therefore, use both brightness
& color differences
. Avoid red & green
in the periphery due to lack of RG cones there, as yellows
& blues work in periphery
. Avoid pure blue for
text, lines, & small shapes.
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. Blue makes a fine
background color
. Avoid adjacent
colors that differ only in blue
. Avoid single-color
distinctions but mixtures of colors should differ in 2 or 3
colorse.g., 2 colors shouldn’t differ only by amount of red
Accurate color discrimination is at -+60 degree of straight head
position.
Limit of color awareness is -+90 degree of straight head
position
.
8.2 Stereopsis
Introduction
3D vision, binocular vision and stereopsis all mean the same
thing: That remarkable
power of the visual sense to give an immediate perception of
depth on the basis of the
difference in points of view of the two eyes. It exists in those
animals with
overlapping optical fields, acting as a range finder for objects
within reach. There are
many clues to depth, but stereopsis is the most reliable and
overrides all others. The
sensation can be excited by presenting a different, properly
prepared, view to each
eye. The pair of views is called a stereopair or stereogram, and
many different ways
have been devised to present them to the eye. The appearance of
depth in miniature
views has fascinated the public since the 1840's, and still
appears now and then at the
present time. There was a brief, but strong, revival in the
1990's with the invention of
the autostereogram. Stereopsis also has technical applications,
having been used in
aerial photograph interpretation and the study of earth
movements, where it makes
small or slow changes visible.
The word stereopsis was coined from the Greek
s,
solid or firm, and s,
look or appearance. Since terms derived from Greek are often
used in this field, it
may be useful to have a brief discussion. Single and double
vision are called haplopia
and diplopia, respectively, from '
s (haplous) and
s (diplous), which
mean "single" and "double". Haplopia is the happy case; with
diplopia we are seeing
double. The use of a Greek term removes the connotations that
may attach to a
common English word, and sounds much more scientific. Note that
the "opia" part of
these words refers to "appearance", and does not come from a
word for "eye". The -shas
been dropped for euphony. Otherwise, the closest Greek to "opia"
means a cheese
from milk curdled with fig juice. "Ops", for that matter is more
usually associated
with cooked meat or evenings. In fact, words like "optic" come
from s,
meaning "thing seen", from the future
μ of
,
(horao) "to see", not from a
reference to the eye. The Latin oculus does mean "eye" and is
used in many technical
terms, like binocular, which combines Greek and Latin.
Stereopsis
-
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Stereopsis is the direct sensing of the distance of
an object by comparing the images received by the
two eyes. This is possible only when the eyes of a
creature look in the same direction, and have
overlapping fields. The placing of the two eyes
this way gives up the opportunity of a wide field
of view obtained with eyes on the sides of the
head. Predators find it best to have eyes in front,
prey to have them on the sides. Stereopsis yields benefits for
close work, such as
fighting for cats and hand work for humans. Note that normal
binocular vision is
single, so that the two images have been fused by the brain.
There is no evidence that
the image resulting from the many simple eyes of an insect is
not also fused in a
similar way.
Visual perception makes use of a large number of distance clues
to create its threedimensional
picture from the two-dimensional retinal images. Strong clues
are the
apparent sizes of objects of known size, overlapping and
parallax, shadows and
perspective. Weaker clues are atmospheric perspective (haze and
scattering), speed of
movement, and observed detail. The strongest clue of all,
however, is stereopsis,
which overrides all other evidence save touch itself. The
convergence of the optic
axes of the two eyes, and their distance accommodation, when
fixated on an object,
do not seem to be strong clues, though some have believed them
to be. Although we
have two eyes, we usually have only one visual world, which is a
remarkable and
important fact calling for explanation. Stereopsis gives a
reliable distance clue as far
away as 450 metres, Helmholtz estimated. The fineness of the
comparison that must
be made by the visual system is remarkable.
The interpretation of retinal images to produce stereopsis is
entirely mental, and must
be learned. When the images on the eyes are consistent with the
observation of a
single object, the two flat images fuse to form a vivid
three-dimensional image. With
practice, fusion can be achieved with two pictures side by side
and the eyes
voluntarily diverged so that each eye sees its picture straight
ahead, though
accommodated for the actual distance. Both the original pictures
remain in view, but a
third, fused, image appears before them when the concentration
is diverted to it that
appears strikingly solid. The brain regards this fused image as
the real one, the others
as mere ghosts. This skill is called free fusion, and requires
considerable practice to
acquire. In free fusion, both the convergence of the eyes, and
their distance
accommodation, are inconsistent with the actual location of the
image, and must be
overridden by stereopsis. It shows, incidentally, that
convergence of the optic axes is
not a strong depth clue. By the use of a stereoscope, one can
achieve fusion without
diverging the eyes, or focusing on a close object with the eyes
so diverged, so no
practice or skill is required. A stereoscope mainly changes the
directions in which the
two images are seen so that they can both be fixated by normally
converged eyes. The
two images are called a stereo pair.
When the images on the retinas are too different to be views of
the same object,
rivalry occurs, and either one image is favoured and the other
suppressed, or a
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patchwork of parts of the two images is seen. When everything
corresponds except
the illumination or colour, the fused image exhibits lustre.
The fundamentals of stereopsis were discovered by Charles
Wheatstone in 1836,
when stereopairs had to be created by drawing (this could be
aided with the camera
obscura, but was very difficult except for stick images). The
methods of descriptive
geometry can be used to create stereopairs. He designed the
mirror stereoscope, which
directs the view of the images into the eyes with plane mirrors
and reflection at about
45[. David Brewster invented the prism stereoscope, which used
prisms to deviate
the light, which made a more compact and convenient apparatus.
Lenses can also be
used to decrease the viewing distance and make fixation easier.
Photograpy was the
natural way to create stereopairs. A stereopair can also be
drawn in two colours with
the views superimposed. When this anaglyph is viewed through
coloured filters that
present one image to each eye, fusion is easy. A similar method
is to project the two
images in orthogonal polarizations, and to view them through
polarizing filters. Both
of these methods have been used to project 3D films and
transparencies before an
audience. A small fraction of people, perhaps 4%, have defective
stereopsis.
The pattern above demonstrates the stereoscopic wallpaper
illusion, which was first
discovered by H. Meyer in 1842, and also noted by Brewster. When
viewed with the
eyes parallel, a strong stereoscopic effect is seen. The green
fleurs-de-lis are farthest
away, the blue discs closest, and the red crosses at an
intermediate distance. This is an
autosterogram, a single figure that gives stereoscopic images to
the two eyes. Since
the figures in a line are identical, when the eyes are turned
for free fusion, two
different figures are assumed to be parallactic views of the
same object. The eye finds
it preferable to fuse the images rather than report double
vision. It is easier to fuse this
autostereogram than a normal stereopair, so it is good practice
for developing the
useful skill of free fusion.
The mind does not have to recognize the object in a stereopair
for fusion to occur. The
pattern can be random, but the stereopair must represent the
same random pattern as
seen from the different positions of the eyes (Julesz, 1960).
Even more strikingly, a
single apparently random pattern can be fused
autostereographically to give a threedimensional
image. No image is seen until fusion occurs. Each point on the
image
must be capable of interpretation as two different points of a
stereopair. These
random-dot autostereograms were widely enjoyed in the 1980's. An
autostereogram
requires free fusion, which must be learned in order to
appreciate them. Many people
found this difficult, so the autostereograms were usually
presented as a kind of puzzle.
Psychologists have argued about stereopsis for many years, but
most of their musings
are not worth repeating. A widely held theory was that the two
retinas were somehow
mapped point-by-point, and differing image positions with
respect to this reference
frame was interpreted stereoptically. It seems more likely to me
that the images are
compared by the visual sense for differences, than by their
absolute locations on the
retina. In the past, psychologists have preferred mechanical
explanations, where the
brain and retina are created with built-in specializations and
functions, spatially
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localized, rather than regarding the organs as canvases, which
the cognitive powers
organize as necessary.
I have not discussed the broad and interesting field of optical
illusions here, since they
tell us nothing definite about the inner workings of the visual
sense, only give
examples of its operation, and also because the 'reasons' for
them are controversial,
and the arguments are not especially enlightening. Illusions are
discussed at length in
another article on this website. The oldest and most widely
known illusion is the
horizon illusion, in which the moon appears larger on the
horizon than at the zenith.
This illusion was known and discussed in antiquity, and is still
the subject of much
study. Its explanation is not known. For the application of the
visual sense to
investigation and appreciation of the world around us,
Minnaert's book is outstanding.
8.3 Reading
So far we have concentrated on the perception of images in
general. However, the
perception and processing of text is a special case that is
important to interface design,
which inevitably requires some textual display.
There are several stages in the reading process. First the
visual pattern of the word on
the page is perceived. It is then decoded with reference to an
internal representation of
language. The final stages of language processing include
syntactic and semantic
analysis and operate on phrases or sentences.
We are most interested with the first two stages of this process
and how they
influence interface design. During reading, the eye makes jerky
movement called
saccades followed by fixations. Perception occurs during the
fixation periods, which
account for approximately 94% of the time elapsed. The eye moves
backwards over
the text as well as forwards, in what are known as regressions.
If the text is complex
there will be more regressions.
8.4 Hearing
The sense of hearing is often considered secondary to sight, but
we tend to
underestimate the amount of information that we receive through
our ears.
The human ear
Hearing begins with vibrations in the air or sound waves. The
ear receives these
vibrations and transmits them, through various stages, to the
auditory nerves. The ear
comprises three sections commonly known as the outer ear, middle
ear and inner ear.
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The outer ear is the visible part of the ear. It has two parts:
the pinna, which is the
structure that is attached to the sides of the head, and the
auditory canal, along which
sound waves are passed to the middle ear. The outer ear serves
two purposes. First, it
protects the sensitive middle ear from damage. The auditory
canal contains wax,
which prevents dust, dirt and over-inquisitive insects reaching
the middle ear. It also
maintains the middle ear at a constant temperature. Secondly,
the pinna and auditory
canal serve to amplify some sounds.
The middle ear is a small cavity connected to the outer ear by
the tympanic
membrane, or eardrum, and to the inner ear by the cochlea.
Within the cavity are the
ossicles, the smallest bones in the body. Sound waves pass along
the auditory canal
and vibrate the ear drum which in turn vibrates the ossicles,
which transmit the
vibrations to the cochlea, and so into the inner ear.
The waves are passed into the liquid-filled cochlea in the inner
ear. Within the
cochlea are delicate hair cells or cilia that bend because of
the vibrations in the
cochlean liquid and release a chemical transmitter, which causes
impulses in the
auditory nerve.
Processing sound
Sound has a number of characteristics, which we can
differentiate.
Pitch
Pitch is the frequency of the sound. A low frequency produces a
low pitch, a high
frequency, a high pitch.
Loudness
Loudness is proportional to the amplitude of the sound; the
frequency remains
constant.
Timber
Timber related to the type of the sound
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Sounds may have the same pitch and loudness but be made by
different instruments
and so vary in timber.
Sound characteristics
Audible range is 20 Hz to 15 KHz. Human ear can distinguish
between changes less
than 1.5 Hz but less accurate at higher frequencies. Different
frequencies trigger
neuron activity causing nerve impulses. Auditory system filters
sounds e.g., Cocktail
Party Effect
8.5 Touch
The third sense is touch or haptic perception. Although this
sense is oftern viewed as
less important than sight or hearing, imagine life without it.
Touch provides us with
vital information about our environment. It tells us when we
touch something hot or
cold, and can therefore act as a warning. It also provides us
with feedback when we
attempt to lfit and object.
Haptic perception involves sensors in the skin as well as the
hand and arm. The
movement that accompanies hands-on exploration involves
different types of
mechanoreceptors in the skin (involving deformation,
thermoreception, and vibration
of the skin), as well as receptors in the muscles, tendons, and
joints involved in
movement of the object (Verry, 1998). These different receptors
contribute to a neural
synthesis that interprets position, movement, and mechanical
skin inputs. Druyan
(1997) argues that this combination of kinesthetics and sensory
perception creates
particularly strong neural pathways in the brain.
Haptics vs. Visual
For the science learner, kinesthetics allows the individual to
explore concepts related
to location, range, speed, acceleration, tension, and friction.
Haptics enables the
learner to identify hardness, density, size, outline, shape,
texture, oiliness, wetness,
and dampness (involving both temperature and pressure
sensations) (Druyan, 1997;
Schiffman, 1976).
When haptics is compared to vision in the perception of objects,
vision typically is
superior with a number of important exceptions. Visual
perception is rapid and more
wholistic—allowing the learner to take in a great deal of
information at one time.
Alternatively, haptics involves sensory exploration over time
and space. If you give a
student an object to observe and feel, the student can make much
more rapid
observations than if you only gave the student the object to
feel without the benefit of
sight. But of interest to science educators is the question of
determining what a haptic
experience adds to a visual experience. Researchers have shown
that haptics is
superior to vision in helping a learner detect properties of
texture (roughness/
smoothness, hardness/ softness, wetness/ dryness, stickiness,
and slipperiness) as well
as mircrospatial properties of pattern, compliance, elasticity,
viscocity, and
temperature (Lederman, 1983; Zangaladze, et al., 1999). Vision
dominates when the
goal is the perception of macrogeometry (shape) but haptics is
superior in the
perception of microgeometry (texture) (Sathian et al., 1997;
Verry, 1998). Haptics and
vision together are superior to either alone for many learning
contexts.
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While vision provides information about an object geometric
feature, touch is
unparalleled in its ability to extract information about
materials. For a surgeon trying
to decide where to begin excising a patch of cancerous tissue,
it might be helpful to
feel the texture and compliance, and not just rely on the shape.
Haptic Learning
Haptic learning plays an important role in a number of different
learning
environments. Students with visual impairments depend on haptics
for learning
through the use of Braille as well as other strategies.
8.6 Movement
Before leaving this section on the human’s input-output
channels, we need to consider
motor control and how the way we move affects our interaction
with computers. A
simple action such as hitting a button in response to a question
involves a number of
processing stages. The stimulus is received through the sensory
receptors and
transmitted to the brain. The question is processed and a valid
response generated.
The brain then tells the appropriate muscles to respond. Each of
these stages takes
time, which can be roughly divided into reaction time and
movement time.
Movement time is dependent largely on the physical
characteristics of the subjects:
their age and fitness, for example. Reaction time varies
according to the sensory
channel through which the stimulus is received. A person can
react to an auditory
signal in approximately 150ms, to a visual signal in 200ms and
to pain in 700ms.
Movement perception
Assume that while you are staring at the bird, a
racing car zooms by. The image of the car will
travel across your retina as indicated by the
dotted line with the arrow. This image
movement will cause you to say that the car
moves from your right to your left.
Now suppose you were looking at the car and
followed its movement as it passes in front of
you.
This time you are following the car by moving
your eyes from right to left.
Just as before, your percept is that of the car moving from
right to left.
This is true even though the image remains on the fovea during
the motion of the car
and your eyes.
Third illustration shows that another way to follow the racing
car is to keep the eyes
steady and to move just the head. This causes the image to
project to exactly the same
retinal location at each instant (assuming you move your head at
precisely the correct
angular velocity) as the car moves from right to left.
Once again, the percept is of the car moving from right to left.
This percept will be the
same as the two previous illustrations. How the brain
distinguishes these different
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ways of following moving objects is the subject of much
research. One more thing,
although I have presented three distinct ways of following
moving objects, these
illustrations are gross simplifications. In point of fact, when
we follow moving objects
we use various combinations of head and eye movements.
The illustrations that, undoubtedly you have been looking at
demonstrate that motion
perception is very complex. Recall that we perceive motion if we
hold our heads and
eyes still as a moving object passes in front of us. If we
decide to hold our heads still
and let our eyes follow the object
we still see it move. Finally, we could even decide
to hold our eyes steady and move only our head to
follow an object. The interesting thing is all three
modes of viewing a moving object result in about
the same perception.
So far we have been concerned with perceiving
real movement. By real movement I mean that the
physical stimulus is actually moving and we
perceive it as moving. It is possible to perceive
motion when the stimulus is not moving. An
example is the motion after effect (MAE)
demonstration that was loaned to me by Dr. Ben
Bauer, Trent University.
Here is a demonstration you can observe for
yourself. If you have the opportunity to view a
waterfall, (e.g.. Niagara Falls) look at the falling
water for about a minute and then allow your gaze
to fall on any stationary object. A building would
be excellent. If you do this, the texture of the
building, perhaps even the windows will appear to
move up. Waterfalls usually are not readily
available. However, you can easily build your
own MAE apparatus. Take a round paper plate.
Draw a dozen or so heavy lines radiating out from the middle of
the plate. Then with a
pin attach the plate through its center to the eraser end of a
pencil. Now spin the plate
at a moderate speed. Don't spin it so fast that the lines become
an indistinct blur. After
viewing the spinning plate for about a minute stop it and
continue to look at the
radiating lines. What do you suppose you will see? If you see
what most people notice
the radiating lines, which are actually stationary, will appear
to rotate in the direction
opposite to that which you spun the plate originally. If that is
way you saw you
witnessed the MAE. It is useful to try this demonstration with
the paper plate because
it will convince you that there are no special tricks involved
with the MAE demo I
mentioned above.
The phenomenon of Motion After Effects (MAE) has been studied
intensively by
visual scientists for many years. One explanation of how the MAE
works is the
following. The visual system has motion detectors that, like
most neurons, undergo
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spontaneous activity. You normally do not see motion when there
is none because
the spontaneous activity is in balance. However, when you viewed
the downward
motion of the black bars you adapted the motion detectors for
motion in the
downward direction. When the real motion stopped, the
spontaneous activity was no
longer in balance, the upward spontaneous activity being
slightly stronger and thus
the black bars appear to drift upward. The adaptation effect
lasts for a short time,
the motion detection system quickly becomes balanced again and
the apparent
movement stops.
Another example of motion being seen, when there is no physical
motion, is the phi
phenomenon. To those unacquainted with the field of vision
research this
phenomenon is probably unknown. However, all of you have seen
it. The simplest
demonstration of the phi phenomenon is to have two illuminated
spots of light about 6
to 8 inches apart. When these lights alternately go on and off
one usually sees a single
spot of light moving back and forth.
This principle is used in many movie marquees where one sees a
pattern of lights
moving around the display. In fact, there is no physical motion,
only a series of lights
going on and off. Then, of course there are the movies. Movies
are a series of single
frames presented in rapid succession. No one would doubt the
perception of
movement seen in the cinema. Yet, if you analyze the strips of
film that yield these
images all you would see is a series of frames each with a
slightly different image.
When they are rapidly projected on to the viewing screen motion
is seen.
A similar technique is used with cartoons. The illustrator
actually draws a series of
pictures. When they are rapidly presented to the viewer motion
of the cartoon
characters is seen.
There are two other instances when movement is perceived. Have
you ever sat in a
train or bus station patiently waiting to get moving? Then all
of a sudden, low and
behold there you go. Or are you? You feel no vibration,
something feels wrong. Then
you notice that it is the vehicle (train or bus) right next to
you that is moving and it
just felt as if you were moving. This is called induced motion.
Finally, (and this is an experiment you can try at home) view a
small very dim light in
an otherwise completely dark room. Make sure that the light is
in a fixed position and
not moving. After sometime in the dark, the small light will
appear to move somewhat
randomly. This is called autokinetic movement.
Here is another little experiment you can try. Look around your
surroundings freely
moving your eyes. As you move your eyes around are the
stationary objects moving?
Probably not. Now look at some object and with your finger
rapidly press against
your eyeball by pushing on your eyelid. (Don't push directly
against the white (sclera)
area). As you force your eye to move you will probably notice
that whatever you are
looking at starts to jump around. So you can see that it makes a
difference whether
you move your eyes normally or cause them to move in an unusual
manner.
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Electrophysiologists are scientists who insert tiny electrode
into the brain of
experimental subjects. They have discovered that there are
cortical neurons which are
specialized for movement. In fact, these neurons often are so
specialized that they will
respond best when the motion is in a specific direction. E.
Bruce Goldstein presents a
neural model in his , which shows how the early retinal
neural processing
could occur which results in a signal being sent to the brain
which say that movement
has occurred in a specific direction.
How to use MAE
Fixate the red square in the center of the diagram as the black
bars move down.
When the black bars stop moving down, continue to fixate the red
square and pay
attention to the black bars. What if anything do the black bars
appear to be doing? If
they do not appear to do anything, try running the demonstration
again by clicking on
the refresh icon at the top of your screen. If the black bars
appeared to be drifting
upwards you witnessed the motion after effect. If you have a
slow computer, a 486
machine or older, this demo may not work very well and you won't
experience the
MAE. |
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