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Chapter 4.1

PSY100H1 Chapter 4.1: Module 4.1

Course Code
Michael Inzlicht

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Chapter 4: Sensation and Perception, Module 4.1
Module 4.1 Sensation and Perception at a Glance
- In 1985, 18-yr old Ray Belknap shot himself to death and his friend James Vance tried to do the same
thing but survived
o Vae later said that his atios ere iflueed  suliial essages foud i the hea
metal music of the band Judas Priest
o The sued the ad ad proseutors laied that he plaed akards, the sog Better 
You, Better tha Me otaied the phrase do it
o It took the work of two Canadian psychologists to demonstrate that these allegations were
- Sensation and perception are different, yet integrated processes
o To get this point, look at the Necker cube in fig. 4.1 (page 132)
o After looking at it for a couple of seconds, the perspective changed
The cube seemingly flipped in orientation
o Although the cube remains constant on the page and in the way that it is reflected in the eye, it
can be perceived in different ways
o The switching of perspectives is a perceptual phenomenon taking place in the brain
Sensing the World around Us
- The world outside our body is full of stimuli (songs, colors, pictures, etc)
- The body has developed specializes processes for sensing and perceiving the world around us
- The process of detecting and then translating the complexity of the world into meaningful experiences
occurs in two stages
o 1) Sensation: the process of detecting external events by sense organs and turning those stimuli
into neural signals
At this leel, the soud of soeoe’s oie is just oise
The sight of a persons is merely a combo of color and motion
o 2) Perception: attending to, organizing, and interpreting stimuli that we sense
Its recognizing that sound as a human voice
Understanding that certain colors and motion make up an image of a person
Its interpreting the raw info
- The raw sensations detected by the sensory organs are turned into info that the brain can process
through transduction
o Transduction: specialized receptors transform the physical energy of the outside world into
neural impulses
o The neural impulses travel to the brain and influence the activity of different brain structures,
which gives rise to our internal representation of the world
- The sensory receptors involved in transduction are different for different senses
o Transduction of light happens when it reaches the receptors at the back of the eye
Light sensitive chemicals in the retina then convert this energy into nerve impulses that
travel to different brain areas where they are perceived
o Transduction of sound happens in a structure called the cochlea
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Where sound energy is converted into neural impulses that travel to the hearing-centers
of the brain
- All of our senses use the same mechanism for transmitting information in the brain: the action
o Thus, the brain is constantly bombarded by neural impulses, but is still able to separate different
sensory signals (sight, sound, touch, smell, and taste)
o It does this by sending different sensory signals to different parts of the brain
o Thus, it is not the original sensory input that is most important for generating our perceptions;
rather, it is the brain area that processes this info
We see because visual info is sent to the occipital lobe which generates our experience
of vision
We hear because auditory info is sent to temporal lobes which generate a hearing
This idea that the different sense are separated in the brain was proposed by German
dude named Muller
It is called the doctrine of specific nerve energies
- Doctrine of specific nerve energies: different senses are separated in the brain
o This requires that distinct pathways connect sensory organs to the appropriate brain
Interestingly, these pathays aren’t that distint in the deeloping rain
Studies show that infants have a number of overlapping sensations
Ex. Spoken language elicits activity in hearing and vision area
This effect does not disappear until age three
As kids age, the pathways in the brain become more distinguished
Therefore, perception is a skill that our brain learn through experience
- Experience also impacts how we adapt to sensory stimuli in our everyday lives:
o Generally, our sensory receptors are most responsive upon initial exposure to a stimulus
Ex. When you exit a dark movie theatre after a long time, the light you encounter seems
This feeling occurs since our sensory receptors and brain areas related to perception
are really sensitive to change
Change in the environment provides new info for the brain, and processing new
info is important for survival
Evolutionarily, it makes sense
Our brains evolved to be highly selective to signals of danger
The orienting response describes how fast we shift our attention to stimuli that
signal a change in our sensory world
o Flip side of this is that we allocate less attention to stimuli that remain the same over time
These unchanging stimuli elicit less activity in the nervous system and are perceived as
being less intense over time
The sound of traffic will seem less intense after a few mins than it did when you
first heard it
This process is called sensory adaptation
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Sensory adaptation: the reduction of activity in sensory receptors with
repeated exposure to a stimulus
This helps us adjust to our surroundings and shift our focus to other events that may be
A cool example of this happens in our everyday lives
If you watch TV for 5-10 mins, but instead of following the plot, count how
many times the camera angle changes
Directors change the angles every few seconds in order to prevent you from
experiencing sensory adaptation and making it difficult for you to look away
Whether this overexposure to changing stimuli is having a permanent effect on
developing brain (kids) is an ongoing debate in research
Stimulus Thresholds
- How loud does someone have to whisper for you to hear them?
- Fechner coined the term psychophysics
o Psychophysics: field of study that explores how physical energy such as light and sound and
their intensity relate to psychological experience
- A popular approach was to measure the minimum amount of a stimulus needed for detection, and the
degree to which a stimulus must change in strength for the change to be perceptible
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