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Chapter 4

PSYC 1001 Chapter Notes - Chapter 4: Color Vision, Peripheral Vision, Wavelength


Department
Psychology
Course Code
PSYC 1001
Professor
Bruce Tsuji
Chapter
4

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Sensation & Perception - When we smell a fragrant flower, are we experiencing a
sensation or a perception? In everyday language, the terms "sensation" and
"perception' are often used interchangeably.
However, as you will soon see, they are very distinct, yet complementary processes. In
this section, we will discuss some concepts central to the study of sensation and
perception and then move on to discuss vision and the perception of pain (it is not
possible in the scope of these notes to discuss all the senses).
I. Sensations and Perceptions
Sensations can be defined as the passive process of bringing information from the
outside world into the body and to the brain. The process is passive in the sense
that we do not have to be consciously engaging in a "sensing" process.Perception can
be defined as the active process of selecting, organizing, and interpreting the
information brought to the brain by the senses.
A) HOW THEY WORK TOGETHER:
1) Sensation occurs:
a) sensory organs absorb energy from a physical stimulus in the environment.
b) sensory receptors convert this energy into neural impulses and send them to the
brain.
2) Perception follows:
a) the brain organizes the information and translates it into something meaningful.
B) But what does "meaningful" mean? How do we know what information is important
and should be focused on?
1) Selective Attention - process of discriminating between what is important & is
irrelevant (Seems redundant: selective-attention?), and is influenced by motivation.
For example - students in class should focus on what the teachers are saying and the
overheads being presented. Students walking by the classroom may focus on people in
the room, who is the teacher, etc., and not the same thing the students in the class.
2) Perceptual Expectancy - how we perceive the world is a function of our past
experiences, culture, and biological makeup.For example, as an American, when I look
at a highway, I expect to see cars, trucks, etc, NOT airplanes. But someone from a
different country with different experiences and history may not have any idea what to
expect and thus be surprised when they see cars go driving by.
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Another example - you may look at a painting and not really understand the message
the artist is trying to convey. But, if someone tells you about it, you might begin to see
things in the painting that you were unable to see before.
ALL OF THIS IS CALLED Psychophysics
C) Psychophysics can be defined as, the study of how physical stimuli are
translated into psychological experience.
In order to measure these events, psychologists use THRESHOLDS.
1) Threshold - a dividing line between what has detectable energy and what does not.
For example - many classrooms have automatic light sensors. When people have not
been in a room for a while, the lights go out. However, once someone walks into the
room, the lights go back on. For this to happen, the sensor has a threshold for motion
that must be crossed before it turns the lights back on. So, dust floating in the room
should not make the lights go on, but a person walking in should.
2) Difference Threshold - the minimum amount of stimulus intensity change needed to
produce a noticeable change.
the greater the intensity (ex., weight) of a stimulus, the greater the change needed to
produce a noticeable change.
For example, when you pick up a 5 lb weight, and then a 10 pound weight, you can feel
a big difference between the two. However, when you pick up 100 lbs, and then 105 lbs,
it is much more difficult to feel the difference.
3) Signal-Detection Theory - detection of a stimulus involves some decision making
process as well as a sensory process. Additionally, both sensory and decision making
processes are influenced by many more factors than just intensity.
a) Noise - how much outside interference exists.
b) Criterion - the level of assurance that you decide must be met before you take action.
Involves higher mental processes. You set criterion based on expectations and
consequences of inaccuracy.
For example - at a party, you order a pizza...you need to pay attention so that you will
be able to detect the appropriate signal (doorbell), especially since there is a lot of noise
at the party. But when you first order the pizza, you know it won't be there in 2 minutes,
so you don't really pay attention for the doorbell. As the time for the pizza to arrive
approaches, however, your criterion changes...you become more focused on the
doorbell and less on extraneous noise.
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II. SIGHT/VISION
A) the visual system works on sensing and perceiving light waves. Light waves vary in
their length and amplitude:
a) wave length (also referred to as frequency, since the longer a wave, the less
often/quickly it occurs) - affects color perception (ex., red=approx 700, yellow approx
600)
b) wave amplitude (this is the size/height of the wave) - affects brightness perception.
B) Structure of The EYE:
1) Cornea - the round, transparent area that allows light to pass into the eye.
2) Lens - the transparent structure that focuses light onto the retina.
3) Retina - inner membrane of the eye that receives information about light using rods
and cones. The functioning of the retina is similar to the spinal cord - both act as a
highway for information to travel on.
4) Pupil - opening at the center of the iris which controls the amount of light entering the
eye. Dilates and Constricts.
5) Rods & Cones - many more rods (approximately 120 million) than cones (approx 6.4
million).
a) cones - visual receptor cells that are important in daylight vision and color vision.
the cones work well in daylight, but not in dim lighting. This is why it is more difficult to
see colors in low light.
most are located in the center of the retina...called the FOVEA, which is a tiny spot in
the center of the retina that contains ONLY cones...visual acuity is best here.
SO...when you need to focus on something you attempt to bring the image into the
fovea.
b) rods - visual receptor cells that are important for night vision and peripheral vision.
the rods are better for night vision because they are much more sensitive than cones.
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