Sensation and
Perception
Sensory input and Psychophysics
Sensation and Perception
What do you hear?
 What do you see?
 What do you taste?
 What do you smell?
 What do you feel? (not emotion)
 What conclusions can you draw from
these answers?
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Sensation
Starts with a stimulus (any aspect of
change in our environment to which
we respond)
 Can be measured in size, duration,
intensity and wavelength
 Occurs anytime a stimulus activates a
receptor

Sensory Receptor
Living cell that responds to certain
type of energy
 Often located in sense organs

Specialized structure that collects
energy particularly well… (eye, ear,
etc)
 Detect physical changes in energy
such as heat, light, sound, and
physical pressure

Eye- notes changes in light
Ear- notes changes in sound
Skin- notes changes in heat
and pressure
Perception
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Organization of sensory information into a
meaningful experience
Comes from a combination of sensations
and past experiences
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Translating the stimulus into the language of
the nervous system (neural impulse)
comprehending the basic components of
the stimulus, size, shape, color
Organizing the components into an
understandable explanation
Psychophysics
The interaction between the physical
world (stimuli) and the psychological
world (internal experience)
 What is the relationship between color
and wavelength?
 How does changing a light’s intensity
affect your perception of it’s
brightness?

Threshold
How much energy is required for
someone to hear a sound, or see a
light?
 How much of a scent must be in a
room for someone to smell it?
 How much pressure must be put on
the skin for someone to feel it?
 Is it the same for everyone?

How strong must a stimulus
be in order for detection?
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Threshold- dividing line
Not exact
Absolute threshold- point at which a very
weak stimulus can be detected 50% of the
time
Difference threshold- smallest change a
person can detect 50% of the time.
(JND) just noticeable difference
Absolute threshold for 5 senses

Vision- seeing a candle flame 30 miles
away on a clear night
Absolute threshold

Hearing- watch ticking 20 feet away
Absolute Threshold
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Tasting- 1 teaspoon of sugar
dissolved in 2 gallons of water
Absolute threshold

Smell- 1 drop of perfume in a 3 room
house
Absolute threshold
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Touch- feeling a bee’s wings falling a
distance of 1 centimeter onto your
cheek
Weber’s Law- related to the Just Noticeable Difference
(also known as the difference threshold), which is the minimum
difference in stimulation that a person can detect 50 percent of the
time.
The larger the magnitude of the
stimulus, the larger the JND
 25 watt light bulb / 50 watt light bulb
very different
 175 watt light bulb / 200 watt light bulb
hard to notice

Weber’s Law
The JND increases in direct
proportion to the intensity of the
stimulus.
 Often not true when stimuli approach
extreme values.
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Sensory adaptation
Our senses are tuned to change and
respond to increases and decreases
in stimuli, or new events rather than
constant stimulation.
 We adapt to change/deviation in
stimulation
 Movie theater
 Clothes on body

Signal Detection theory- how
good are you at recognizing stimuli?
Study of people’s tendencies to make
correct judgments in detecting the
presence of stimuli
 Recognizing stimuli against a
competing background of stimuli
 Individuals vary based on situation
 Radar operator
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Signal Detection theory
Pre-attentive process- getting info
automatically and simultaneously
when presented with stimuli
 Attentive process- paying attention to
only one of the stimuli at a time when
presented with multiple stimuli
 All tasks require attention, but some
require more than others.
 P.212-213
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