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Chapter 5

Chapter 5 Notes .doc

Course Code
PSYC 100
Daniel Levitin

of 13
Chapter 5: Sensation and Perception
How Do We Sense Our Worlds?
way we experience the world is divided into two sections:
sensation: the organs’ responses to external stimuli and the transmission of these
responses to the brain
light, air vibrations, odor
is an elementary experience such as colour or motion without the more
complex perceptual experience of what is being seen or what is moving
perception: the processing, organization, and interpretation of sensory signals, it
results in an internal representation of stimulus
often based on prior experiences which shape our expectations about new
sensory experiences
unlikely to see a blue applep-shaped object as a real apple because you
know apples are not blue
our perception of the world does not work like a camera/tape recorder, what
we sense is the result of brain processes that actively construct perceptual
experiences > allow us to adopt to our environments detail
Stimuli Must Be Coded to Be Understood by the Brain
sensory coding: our sensory organs’ translation of stimuli’s physical properties
into neural impulses
brain cannot process raw stimuli > must be translated into chemical and
electrical signals that the brain can interpret
sensory coding begins with transduction: a process by which sensory
receptors produce neural impulses when they receive physical or chemical
to function properly, our brains need qualitative and quantitative information about
qualitative: knowing whether traffic light is green or yellow, difference
between salty and sweet
quantitative: coded by the speed of a particular neuron’s firing
a brighter light
Psychphysics Related to Stimulus Response
psychophysics: examines our psychological experiences of physical stimuli
how much change is required before we notice that change
Sensory Thresholds
absolute threshold: the minimum intensity of stimulation that must occur before
you experience a sensation
the absolute threshold for hearing is the faintest sound a person can detect
50% of the time
difference threshold: the just noticeable difference between two stimuli > the
minimum amount of change required for a person to detect a difference
the minimum change in volume required for you to detect a difference
the difference threshold increases as stimulus becomes more intense
Weber’s Law: states that the just noticeable difference between 2 stimuli is based
on a proportion of the original stimulus rather than on a fixed amount difference
I / I 1/10 = 0.1 you can detect a single candle when you have 10
Signal Detection Theory
since people might convince themselves that a stimulus was presented due to
signal detection theory (SDT): a theory perception based on the idea that the
detection of a faint stimulus requires a judgement - is is not an all-or-nothing
any trial in which participants judge whether an event occurs can have 1 of 4
hit: if signal is presented and observer detects it
miss: if participant fails to detect a signal
false alarm: if participant “detects” a signal that was not presented
correct rejection: if signal is not presented and observer does not detect it
response bias: refers to a participant’s tendency to report detecting the signal in
an ambiguous trial
people’s expectations often influence the extent to which they are bias
Sensory Adaptations
sensory systems are tuned to detect environmental changes
sensory adaptations: a decrease in sensitivity to a constant level of stimulation
researchers have noticed that if stimulation is presented continuously, the
responses of the sensory systems that detect it tend to diminish over time
those who live near the airport become less aware of the airplane noises
over time
What Are the Basic Sensory Processes?
only the neurons in the sensory organs respond directly to events in the world > the
neurons in the brain do not respond to events in the world, they only respond to input
from other neurons
In Taste, Taste Buds Detect Chemicals
gustation: our sense of taste
taste buds: sensory receptors that transduce taste information (mostly on the
tongue) - individual has from 500 to 10 000 taste buds
every taste experience is composed of a mixture of 5 basic qualities: sweet,
sour, salty, bitter, umami (yummy)
entire taste experience occurs in mouth and brain
taste relies heavily on sense of smell, texture
the same food can taste different to people because of the sensation
associated with that food
cultural experiences influence taste preference
what mothers ate during pregnancy effected children’s tastes
In Smell, the Nasal Cavity Gathers Odorants
olfaction: sense of smell
has the most direct route to the brain but may be the least understood
olfactory epithelium: a thin layer of tissue embedded with smell receptors >
receptors transmit information to the olfactory bulb
olfactory bulb: the brain centre for smell (below the frontal lobes)
part of the brain (prefrontal cortex: involved with emotion and memory > smell can
evoke feelings and memories
women have better sense of smell than men
impaired sense of smell is associated with increased risk of mental decline and
In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain
haptic sense: sense of touch
conveys sensations of temperature, pressure, pain, and a sense of where limbs are
in space
anything that makes contact with our skin provides tactile stimulation which gives
rise to an integrated experience of touch
pain receptors are found throughout the body, not just the skin
pain is part of a warning system that stops you from continuing activities that may
harm you
most experiences of pain result when damage to the skin activated haptic
nerve fibers that convey pain are thinner than those for temperature and pressure
> are found in all body tissues that sense pain: skin, muscles, membranes around
bones and joints, organs etc
two types of pain (two kinds of nerve fibers):
fast fibers: sharp immediate pain
fast pain leads us to recoil from harmful objects > is protective
slow fibers: chronic, dull, steady pain