Cat 1

Visual Perception and Sensation

	This Essay is about visual perception.  It will
show that people who don't have sight problems all receive
the same sensations, whereas there can be differences in the
way that we perceive these sensations.
	The reason that visual sensation is the same in
most people is because it is a physiological/biological
process.  Visual sensation involves light waves, EMR
(Electrical Magnetic Radiation) being collected by our rods
and cones on our retina after being focused by our lens. 
The EMR is then transduced into ECI (ElectroChemical
Energy) and transmitted via the optic nerve to our visual
cortex (located at the rear of our brain) where perception
occurs.
	Perception is the complex process of selecting,
organizing and interpreting the data gathered by the
sensory organs.  It starts to occur somewhere along the
optic nerve.  The point where sensation stops and
perception starts has not been defined. Perception can also
be different in different people as thoughts and feelings
affect the way we perceive the world through past
experience.  For example, if two people are walking down
a street and a dog starts running towards them, one person
may perceive the dog as going to attack them because they
have had bad experiences with dogs in the past.  This may
be the opposite with the other person who has had good
experiences with dogs and also knows this dog.  They may
perceive the dog as just being friendly and won’t be scared. 
Both of these people received the same stimulus of the
dog, but both had different perceptions because of previous
thoughts and feelings through prior experience.
	There are three different categories of visual
principles.  The Gestalt principles, perceptual constancy
and also depth cues.  Depth perception allows us to
perceive depth using either monocular (one eye) or
binocular (both eyes) depth cues.  Gestalt principles
suggest that we perceive objects in their simplest form,
allowing us to recognize that objects are separate, and
perceptual constancies allow us to perceive that objects
stay constant under different conditions, ie they don’t
change shape when viewed from different angles or in
different situations.
	An example of a perceptual constancy is
brightness constancy.  This occurs when an object appears
to maintain it’s level of brightness relative to it’s
surroundings despite changes in the amount of light being
cast on the retina.  Consider being in a movie theatre
before the lights are turned down looking into the back of a
persons jumper. When the lights are then turned down you
don’t perceive the sweater to have changed in colour.  This
is because all of the other objects have become dull as well. 
It is important to realize that brightness constancy doesn’t
occur when the surrounding environment doesn’t change
brightness.  In this case consider being at the release of a
new car, the stage and surrounding area are dark.  When
spot lights are put onto the car, the surrounding area
remains dark.  You would not maintain brightness
constancy on the car because of the surrounding area still
being dark.
	An example of a Gestalt principle is similarity. 
Similarity is based on the idea that objects or patterns that
have similar features such as size, shape, brightness or
colour tend to be grouped together.  “For instance, picture
two bands marching side by side.  If their uniforms are
different colours, the bands will be seen as two separate
groups, not as one large group” (Coon, Page 132).  Note
(See Appendix No. 1) that the I’s and 0’s form columns
and not rows in the picture, as they get grouped into their
own kind through likeness.  They are organized like this
through the perception principle of similarity.
	Another example of a Gestalt principle is
closure.  Closure is the process of mentally completing an
object when it is visually incomplete.  An example of
closure can be seen in the Stanmore Cycles logo (Shown in
Appendix No. 3).  There are a few lines that are placed in
between the writing, two curved semi circular lines and
three squiggly lines.  By themselves you may not perceive
these lines to mean anything, but when you also read that it
is for a cycle store it is easy to perceive the lines to be a
person riding a bike.
	Visual factors psychologically affect how we
perceive things from any stimuli that we sense.
	One of these psychological factors is perceptual
set.  It is often referred to as expectancy.  This is because
we can't deal with all of the information that is bombarded
on us so we ignore some pieces of data by psychologically
filling in the gaps with what we expect to see.
	Two fellow class mates and I conducted an
experiment to test the effects of perceptual set.  44 people
from different age groups were asked to read the following
sentence out loud," Row row row your boat gently down
the stream, merrily merrily merrily merrily life is but _
dream" (The "a" is missing from this well known rhyme). 
The results showed that only 6 of the test subjects
responded correctly, while the others all relied on their
previous experience and knowledge once prompted by the
written composition.  We came to the conclusion that most
of the time what one expects to see is generally what they
do see due to their expectations coming from prior
experience and knowledge.  This is backed up by another
experiment that was done by Jerome Bruner and Leigh
Minturn.  In their experiment they used an ambiguous
figure which could either be seen as ‘13’ or ‘B’ (See
Appendix 2).  They also used two series of figures, a series
of letters (L, M, Y, A,) and a series of numbers (16, 17,
10, 12).  One group was shown the ambiguous figure for
8- thousandths of a second after being shown the series of
letters.  A second group was shown the same ambiguous
figure after being shown the series of numbers for the same
exposure time.  “The task given to the observers was to
identify what they saw and to draw it” (Grivas, page 128). 
The group that saw the letters first had results showing that
92% of them saw the ambiguous figure as being a ‘B’.  The
other group that were shown the numbers first had results
showing that 83% of them saw the ambiguous figure as
being ‘13’.  “In this instance, context is akin to previous
experience which is gained immediately prior to observing
the stimulus.” (Grivas, Page 128)
	One other psychological factor is attention. 
"Attention is the process by which an individual focuses
awareness on certain contents of consciousness, while
ignoring others." (Grivas, Page 123).  We tend to focus on
changes in stimulus while we ignore stimulus that stays the
same.  For example, if you were at a horse race in an area
restricted for jockey's (mostly small people) and a tall
person was to go into that area you would likely focus
your attention on that person because the stimulus has
changed its uniqueness.
	“Our visual perception is not always as accurate
as we would like to believe” (Grivas Page 131).  Our eyes
can play tricks on us because of perceptual principles and
factors.  This is called fallibility of perception.  These
intentionally manipulate/change the organizational cues
creating a visual perception of something that’s not real.
	Take the moon illusion for example.  When the
moon is close to the horizon it appears to be larger than
when “it is at its zenith (its highest point)” (Grivas, page
134).
	One theory about the moon illusion is that when
the moon is on the horizon you have got things to compare
it against, thus giving depth cues to show that the moon is
a long way away.  By using the principle of size constancy
you unconsciously reason that the moon must be larger. 
This is not the case though when the moon is at its zenith. 
There are no depth cues available around the moon.  This
makes you perceive that the moon is closer, hence
appearing to be a smaller object.
	In conclusion, visual perception is the process
by which we become aware of and interpret visual
sensations about the world around us.  There are many
different factors that influence our perceptions, such as the
cues from the stimulus, the surroundings, the experiences
we have derived from the past, the inherited abilities we
were born with, and finally the many different motives,
needs, and desires at the moment of the perception. 
Impirical research has been used to show and prove most
of these theories.  Discussion continues into different forms
of fallibility of these theories that result in visual illusions
and hallucinations. But one thing that is for certain, sight is
a gift, blessed to all who see.  Those that understand the
complexity of sight often cherish it greater than those who
don’t.

Bibliography

Books

	Grivas: John Grivas, Ross Down and Linda Carter
“Introduction to Psychology”.  Published by Macmillan
Education Australia.  1996


	Coon: Denis Coon “Introduction to Psychology,
Exploration and Application” Published by West
Publishing Company.  1995


	Larry S. Skurnik and Fran George “Psychology for
Everyman”.  Published by Penguin Books Ltd.  1975


	Desmond Morris “Bodywatching, A Field Guide to
the Human Species”.  Published by Grafton Books.  1987


	Judith Kinner and Marjory Martin “Nature Of
Biology(Book two)” Published by Jacaranda Wiley Ltd. 
1993

Experiments

	1997, Expectancies - “Row Row Row Your Boat”
Class experiment by three people including myself


	1951, Previous Experience - “The Effect Of
Contex On Perceptual Set” By Jerome Bruner and Leigh
Minturn