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Chapter 4

PSYA01 Chapter 4: PSYAO1 Chapter4: Chapter Four


Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens
Chapter
4

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Psychology Notes
Psychology Lecture Number:
Date: October 18, 2015 6
Chapter Four
Sensation and Perception
Module 4.1
oProcess of detecting and then translating the complexity of the world into meaningful
experiences occurs in two stages
First step is SENSATION: The process of detecting external events by sense
organs and turning those stimuli in to neural signals
Second step is PERCEPTION: attending to, organizing and interpreting stimuli
that we sense
oThe idea that different senses are separated in the brain was first proposed in 1826 by
Johannes Muller a germane psychologist
oSENSORY ADAPTATION: Reduction of activity in sensory receptors with repeated
exposure to stimulus
oExample of television and how directors change the camera angle frequently to
prevent from experiencing sensory adaptation
Stimulus Thresholds
oPSYCOPHYSICS: The field of study that explores how physical energy such as light
and sound and their intensity relate to psychological experience
oScientist was interested I the basc nature of perceptual behavior and saught to
better understand perception
oABSOLUTE THRESHOLD: Minimum amount of energy or quantity of a stimulus
required for it to be reliably detected at least 50% of the time it is presented
oExample of experiment where you are asked to listen to various spoken words,
but some of the words volumes are altered by the experimenter. So the volume at
which you can detect the words 50 % of the time is known as absolute threshold
oDIFFERENCE THRESHOLD: Smallest difference between stimuli that can be
detected at least 50% of the time
French fries and salt example: if you add a pinch of salt to a plate of fries that
already has a pinch of salt, you may be able to taste the extra pinch added (detect

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the difference) but if u add a pinch of salt to a plate that has 5 pinches of salt
already, you won’t be able to detect the difference.
Signal detection
oSIGNAL DETECTION THEORY: states weather a stimulus is perceived depends both
on sensory experience as well as judgment made by the subject
Theory makes us examine two processes
a) SENSORY PROCESS: what you sense, so in a basic stimulus experiment, the
sensory process would be weather the experimenter presents faint stimulus or no
stimulus
b) DECISSION PROCESS: Experimenter is asked whether stimulus was actually
presented
oOther factors also influence how sensitive a person is to various sensory stimuli including
emotional factors, motivations, psychological and nervous system arousal level
Perceiving the World Around us
oGasalt principle of perception: So in 1910, Max Wertheimer was riding the bus home and
it appeared as though the buildings out the window were moving backwards
Researched this illusion and discovered that each individual movement of pictures
created the perception of movement (Moving picture book )
“Whole is greater than the sum of its parts.”
“Figure Ground Principle”: When figures in our environment tend to stick out
and stand out against a background. For example: when you’re talking to
someone in a party, their voice is the figure amongst the background noise of
other people at the party
“Proximity and Similarity principle”: Grouping people based on similar visual
appearances. For example, if I ask you to group the following objects: (* * # * # #
#) into groups, you would probably place the asterisks and the pound signs into
distinct groups.
“Common fate” - elements that move together tend to be grouped together. For
example, when you see geese flying south for the winter, they often appear to be
in a "V" shape.
“Continuity principle”: refers to perceptual rule that lines and other objects tend
to be continuous , rather than abruptly changing direction
“Closure” - we tend to complete a form when it has gaps.
All these principles describe that WE create our own organized perceptions out of
the different sensory inputs that we experience
Attention and Perception

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oDIVIDED ATTENTION: Paying attention to more than one stimulus or task at the same
time
Dividing attention affects performance
Should not be on twitter and listen to your professor at the same time, haha haha
ha
oSELECTIVE ATTENTION: Focusing on one selective task or event at a time
People with selective attention often miss the obvious, research says
oINATTENTION BLINDNESS: Failure to notice clearly visible events or objects
because attention is directed elsewhere
In a study, students were asked to count the number of passes between people
with white t-shirts only although people with black t-shirts were also present and
passing the ball to each other. Because they were so focused on counting the
passes, they did not even see a person walk in with a gorilla suit and thump his
chest right in the middle of the passing. Example of inattention blindness.
Module 4.2
oThe visual system works on sensing and perceiving light waves. Light waves vary in their
length and amplitude:
oWave 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)
oWave amplitude (this is the size/height of the wave) - affects brightness perception.
oStructure of The EYE:
Cornea - the round, transparent area that allows light to pass into the eye.
Sclera: White outer surface of the eye
Lens - the transparent structure that focuses light onto the retina.
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.
Pupil - opening at the center of the iris which controls the amount of light
entering the eye. Dilates and Constricts.
Iris: round muscle that adjusts the size of the pupil, also gives eye their
characteristic colour
Rods & Cones – Two main general type of photoreceptors. Many more rods
(approximately 120 million) than cones (approx 6.4 million).
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.
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