Psychology 1000 Chapter 5 Notes (Sensation and Perception)
Sensation is a stimuli-detection based process where sensory organs respond to and translate
stimuli to our brain via nerve impulses.
Perception is the act of processing the nerve impulses and giving them meaning.
o Perception is part is a decision
Psychophysics studies the relationship between physical stimulus and psychological response.
o Fechner was the ‘father’ of psychophysics.
Absolute threshold refers to the intensity where a certain stimuli can be perceived properly
50% of the time; lower the threshold, higher the sensitivity; the lower limit of perceived stimuli.
o Vision: candle flame at 50km
o Hearing: tick of a watch at 6m
o Taste: Tsp. of C H O in 8L of H O
6 12 6 2
o Smell: 1 drop of perfume in a 6 room apartment
o Touch: Wing of a fly falling on a cheek from 1cm
There is a range of uncertainty that people have when reacting to stimuli and that range is called
an individual’s decision criterion.
The difference threshold is the smallest difference between two ranges of stimuli that people
can detect 50% of the time, also called the just noticeable difference.
o There is no 1 to 1 relationship for JNDs.
o Ernst Weber discovered that there is a degree to of lawfulness in the range of sensitivity;
Weber’s Law states that the difference is α magnitude of the stimuli with which the
comparison is being made.
Weber’s Law breaks down at the extremes of stimuli, however.
The size of the difference threshold relative to the physical intensity of the test
Example: If I= 50db and a JND is reported at 55 db.
o I=50, ΔI=5
What’s a JND at 100db?
o 10 ΔI=100, ΔI=10
A JND will occur at 110db or 90db.
JND= +/- new test
Value of JND is not constant
Smaller the Weber Constant, the ‘better; it is.
No ratio is greater than 1:
o Vision (brightness): 1/60
o Kinesthesis (weight): 1/50
o Pain (thermal): 1/30
o Audition (medium pitch; moderate volume): 1/10
o Pressure (skin) : 1/7 o Smell (India Rubber): ¼
o Taste (salt): 1/3
Fechner’s Law: Sensation increases with the logarithm of intensity
o compared to
Steven’s Power Law:
o More predictable across a variety of sensations.
Subliminal stimuli refer to stimuli that are so brief that it cannot be perceived; lower than that
of the absolute threshold.
o Behaviour, to an extent, can affect behaviour and attitudes without an individual’s
o James Vickery (1957) claimed there was 50% increase in popcorn sales after the use of
subliminal messaging during movies.
There was no increase.
However, it got the public and scientists concerned about the usage of
In general, there is no evidence that subliminal messaging influences consumer
o Bruce and Valentine (1986) priming
Shown subjects pictures of Elvis and Kissinger (subliminally), then a picture of
Time increases by 100ms (the ability to recognize Nixon) if Kissinger was shown
instead of Elvis.
o Fitzsimons et al (2008)
30ms exposure to pictures on different sides of the screen.
Before the picture was shown; a logo was flashed; either the Apple or
Creativity task given to subject after; “Creative ways to use a brick”
o Individuals given the Apple logo gave more creative responses
compared to the individual’s given the IBM logo.
All sensory systems:
o Contain accessory structures
o All transduct; record stimuli into nerve impulses
o All code; they determine the frequency of firing
o All interact with the physiological and psychological impulses
They clean up sensory information
o The rods in your retina are sensitive to changes in light intensity; dark and light, but
have no colour sensing.
o The cones in your retina are sensitive to colour and work the best in bright light. o The fovea, the centre of your retina, contains only cones, whereas the rest of your
retina contains rods and no cones.
Image acuity increases as the closer the image is to the fovea.
o Rods and cones send messages to your brain via layers of nerves; connected to the
cones and rods are bipolar cells and horizontal cells. Bipolar cells are connected
Ganglion cells, and connected to both the ganglion and bipolar cells are Amacrine cells.
Rods and cones translate light into nerve impulses via proteins called
photopigments; they change the rate of NT release at the synapse between the
rods/cones and the bipolar cells.
Horizontal cells cause lateral inhibition:
Whenever you stimulate an adjacent channel, the frequency of firing
Creation of receptive fields
o Lateral inhibition can explain phantom spots
o There are two theories to how people perceive colour:
The trichromatic theory states that there are three types of colour receptors in
the retina and each conform to certain wavelengths; blue, red and green.
However, several facts did not fit the theory; yellow is a combination of
red and green, yet red-green colour blind people were able to
distinguish yellow. As well, afterimages tend to disprove the
trichromatic color theory
The opponent-process theory states that each of the three cones is responsible
for two different wavelengths; one being red/green, blue/yellow and
Dual-process theory combines both theories; while cones are sensitive to
different wavelengths of colour.
o From the retina, the nerve impulses are sent to the visual relay centre in the thalamus,
which gets redirected to other parts, mainly the primary visual cortex in the occipital
lobe. The information is then routed to a cortical region called the vis