COLOR THEORY, STEREOPSIS, READING, HEARING, TOUCH, MOVEMENT

<< HUMAN INPUT-OUTPUT CHANNELS, VISUAL PERCEPTION

COGNITIVE PROCESS: ATTENTION, MEMORY, REVISED MEMORY MODEL >>

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Another illusion created by our expectations compensating an image is the

proofreading illusion. Example is shown below

The quick brown

fox jumps over the

the lazy dog.

The way that objects are composed together will affect the way we perceive them, and

we do not perceive geometric shapes exactly as they are drawn. For example, we tend

to magnify horizontal lines and reduce vertical. So a square needs to be slightly

increased in height to appear square and line will appear thicker if horizontal rather

than vertical.

Optical illusions also affect page symmetry. We tend to see the center of a page as

being a little above the actual center so if a page is arranged symmetrically around

the actual center, we will see it as too low down. In graphic design this is known as

the optical center.

These are just a few examples of how the visual system compensates, and sometime

overcompensates, to allow us to perceive the world around us.

Lecture

Lecture 8. Human Input-Output Channels

Part II

Learning Goals

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.

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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 yellow-

green.

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 over-

stimulation. 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 red-

purple 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 στερεοs, solid or firm, and οψιs,

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 'αsλουs (haplous) and διsλουs (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 -s-

has 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 οsτικοs,

meaning "thing seen", from the future οψσοµαι of οραω, (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 three-

dimensional 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 three-

dimensional 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 textbook, 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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