Psychology 100 Chapter 5 Notes
Sensation, Perception and Attention
Story about Helen Keller – explaining that perception is the only bridge we
have to the world.
How Do We Sense Our Worlds?
•Sensory organs gain information by converting forms of physical energy
into signals that our brain can understand.
•This system has been evolved, to solve adaptive problems.
•Each animal is sensitive to different types of physical energy, because
each faced different adaptive problems.
oEx. Animals that hunt at night, have poor vision by excellent
Stimuli Must Be Coded to Be Understood by the Brain
•Sensory coding – the way our sensory organs translate stimuli’s
physical properties into neural impulses – different features of the
environment are coded by different patterns of neural activity.
•Receptors are specialized neurons in the sense organs that pass
impulses to connection neurons when they receive physical or chemical
stimulation. – This is called transduction.
oAfter transduction in the receptors, connection neurons in the
sense organs transmit information to the brain, in form of
•Most sensory information first goes to the thalamus (structure in
middle of brain)
oNeurons in the thalamus then send info to the cortex where
incoming neural impulses are interpreted as the five senses.
•Sensations refer to the transduced message that is carried by nerve
•Sensory coding – two categories
oQuantitative - intensity, brightness, and loudness (often
indexed by the neural firing frequency – higher the firing
frequency – the brighter, louder etc. the stimulus. – more
intense stimuli need to recruit more neurons.
oQualitative – color and taste – possible because different sensory
receptors respond to different qualities of stimulus. – Involves
coarse coding > sensory qualities are coded by only a few
receptors, each of which respond to a broad of range of stimuli.
Psychophysics Relates Stimulus to Response
•Psychophysics - the study of physical properties and how we sense or
•Absolute Threshold - How much of a physical energy source needs to be
presented before our sensory organs detect it. – The minimum
oEx. Faintest sound a person can hear.
•Difference Threshold – just notable difference between two stimuli. –
The difference threshold increases at something is very noticeable.
•Principle of Weber’s law – the size of a just noticeable difference is
based on a relative proportion of difference rather than a fixed amount
oEx. Getting 6/10 on a test, or 96/100 (both four points separate,
but mean different things) – the percentage is the important
thing, not that absolute size of difference.
•An absolute threshold is not concrete, because of variable human
•Signal-detection theory – detecting a stimulus requires making a
judgment about its presence or absence, bias on a subjective
interpretation of ambiguous information.
oEx. Task of radiologist – has to make judgment calls, on whether
someone has cancer. > Draws from previous health, age and
family history etc. factors also motivation and attention of
•Signal-detection is based on a series of trials – some stimulus is
presented, some it isn’t.
oOne of four outcomes – hit (correct) miss (failure to detect true
signal) false alarm (detects a stimulus that wasn’t even there)
correct rejection (chooses correctly that the stimulus wasn’t
oThe observer’s sensitivity is computed by comparing the hit rate,
with the false-alarm rate.
•Response bias refers to the participant’s tendency to report the
stimulus on ambiguous trials.
•Your response to a stimuli changes over time. – Sensory adaptation
oEx. When construction starts, when you’re in a quiet place, you
can notice it, overtime it starts to fade into the background.
•When certain aspects in our environment change, it is important for us
to realize it, however it is less important for us to keep responding to
unchanging stimuli. – But when continuous stimuli stop, there is also a
What Are the Basic Sensory Processes?
•No neurons beyond the sensory organs respond directly to events in the
•A neuron in the brain doesn’t respond to the outside world, but
responds to its input from other neurons.
In Gustation (sense of taste), Taste Buds Are Chemical Detectors
•Sense of taste’s job – keep poison out of our bodies, while allowing good
•Stimuli for taste – chemical substances from food that dissolve in
•Taste receptors are part of the taste bud - some people have 500,
where others have 10,000
oEach taste bud has about 50 receptor cells. Microvilli – hair like
structures at the tip of each taste bud, (come into direct contact
with saliva) - when stimulated they send electrical signals to a
brainstem region, called the medulla and from there to the
thalamus and cortex, which ultimately produces the experience
•Primary four flavors - salty, sweet, sour and bitter. – Different taste
buds are spread throughout the whole mouth uniformly.
•Textures affect sensory experience, as to extent to which food causes
discomfort. The entire taste experience occurs in your brain, not your
•Supertasters are people who experience intense taste. – 6 x as many
taste buds as normal tasters.
In Smell (olfaction), The Nasal Cavity Gathers Particles of Odor
•Most direct route to the brain.
•We smell when odorous particles pass into our nose and the upper and
back portions of the nasal cavity. – There they come into contact with
the olfactory epithelium > thin layer of tissue embedded with olfactory
receptors – the particles dissolve in the solution that surrounds the
epithelium and causes a reaction that triggers chemical receptors.
•These nerve impulses convey information to the olfactory bulb (the
brain center for smell, just below the frontal lobe)
•Smell signals go directly to other brain areas, initially bypassing the
thalamus. –Regions in the prefrontal cortex process information about
whether the smell is pleasant, or aversive, the intensity of small is
processed in the amygdala.