PY 262 Sensation &
Perception
Introduction to the senses
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George Berkeley (1710) “A Treatise Concerning
the Principles of Human Knowledge”
• “If a tree falls in the woods,
and there’s no one around to
hear it… does it make a
sound?”
• Is there “objective” reality or
only “subjective” perspective?
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Do we all see the same color,
shape, size?
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• Some species sense
energies that humans
cannot:
– Bees see ultraviolet lights
– Rattlesnakes sense
infrared energy
– Dogs and cats can sense
sounds with higher
frequencies
– Birds, turtles, and
amphibians use magnetic
fields to navigate
– Elephants can hear very
low-frequency sounds,
which are used to
communicate
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Which view is real?
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46
44
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North
1st
Qtr
3rd
Qtr
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Which view is real? They both are.
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46
44
42
North
1st
Qtr
3rd
Qtr
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What is Real?
http://www.youtube.com/watch?v=Dseb1Y1GBx8
( @ 0:00 to 2:00, then 3:34 to 7:40 )
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From The Matrix:
Morpheus says to Neo….
“If you’re talking about what you
can feel, what you can smell,
what you can taste and see, then
real is simply electrical signals
interpreted by your brain. This is
the world that you know.”
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Is the “Matrix” simply science
fictions?
• http://www.cbsnews.com/video/watch/?id=
5228109n
• Recognizing the “Brain Power” of
sensation, perception and thought
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Wilhelm Wundt (1879):
Our PERCEPTION is
constructed from the
combinations of our
SENSATIONS
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Copyright © 2002 Wadsworth Group. Wadsworth is an imprint of the
Wadsworth Group, a division of Thomson Learning
What is this object?
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Can you “reverse frame?”
1. Cube floating over
dark circles? (hint,
first see how the
white lines connect;
seeing “white box”)
2. Cube seen through
(or behind) holes or
perforations? (hint,
seeing “black box”)
3. Cube pointed “up” or
“down?”
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Wilhelm Wundt (1879) had
some things WRONG!
Our PERCEPTION is NOT
constructed from JUST the
combinations of our
SENSATIONS, but
involves “interpretations” of
the mind
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Sensation
-the reception of stimulus energy by the nervous system
-conversion or transformation
Perception
-interpretation of the barrage of stimulus events
-a conscious sensory experience
Recognition
-ability to categorize objects, to give them meaning
Action
-motor activity
-the outcome of the perceptual process
-ultimately changes perception
Knowledge
-memories, information-processing, reasoning, problem solving, etc
-important for determining perception, recognition and action
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Knowledge
Sensation & Perception
Perception
Processing

•Action
Transduction
Central
Nervous
System
(CNS)
Stimulus 
on Receptors
•Recognition
External World:
“environment”
•Environmental

Attended
Stimulus
Stimuli
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Synaptogenesis
• Form in large numbers quickly in early infancy
• “Use it or lose it” processes
• Synaptic pruning – over-produced number of
synapses are reduced over time & experience
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The importance of experience
(Greenough & Black, 1992)
• Experience-Expectant Plasticity –
typical brain development occurs as a
result of general species-typical
experience
– Vision is processed in the occipital lobe
– Occipital lobe development is atypical when
lacking typical visual experience
• Infants’ vision is progressively more impaired the
longer it takes to remove a cataract
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The importance of experience
(Greenough & Black, 1992)
• Experience-Dependent Plasticity –
Unique neural connections occur from an
individual’s personal experiences
– How we recognize what is familiar to us
(mom’s face; home telephone number)
– Relative sophistication of CNS connections as
a function of experience
• Musician’s finger tips have a larger region of the
Somatosensory cortex processing touch than do
non-musicians
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Brain plasticity is the norm not the exception – the
example of “selective rearing”
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SENSATION &
PERCEPTION
Nervous
System
Activity
Environmental
Stimuli
Stimulus Environment question: What information do we
use from the environment to create perceptions?
Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
Sensation & Perception question: How does the brain
mediate perception & action, and extract the gestalt (the “big
picture”) interpretation?
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SENSATION &
PERCEPTION
Nervous
System
Activity
Environmental
Stimuli
Stimulus Environment question: Psychophysics
Stimulus-Physiological question: Neurophysiology
Sensation & Perception question: Psychophysiology
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The Dawn of Psychophysics
• Fechner (1801–1887) invented
“psychophysics,” thought to be the true
founder of experimental psychology
– Pioneering work relating changes in the
physical world to changes in our
psychological (perceptual/subjective)
experiences
Psychophysics: The science of
defining quantitative relationships
between physical and
psychological (subjective) events
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The Dawn of Psychophysics
(cont’d)
• Two-point threshold: The minimum
distance at which two stimuli (e.g., two
simultaneous touches) can be
distinguished
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The Dawn of Psychophysics
(cont’d)
• Just Noticeable Difference (JND)
– The smallest detectable difference between
two stimuli
– The minimum change in a stimulus that can
be correctly judged as different from a
reference stimulus
– Also known as “difference threshold”
– Weber’s Law – JND is proportional to the
magnitude change of the physical stimuli
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The Dawn of Psychophysics
(cont’d)
• Absolute threshold: Minimum amount of
stimulation necessary for a person to detect
a stimulus 50% of the time
• “Common” examples of Absolute Threshold:
–
–
–
–
–
–
Vision: Stars at night
Hearing: A ticking clock at 20 feet
Vestibular: Tilt of less than ½-minute on a clock
Taste: A teaspoon of sugar in 2 gallons of water
A drop of perfume in a 3-room apartment
The wing of a fly falling on your check from 3-inches
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The Dawn of Psychophysics
(cont’d)
• Fechner’s (Weber-Fechner) Law
– A principle describing the relationship
between stimulus magnitude and resulting
sensation magnitude
– The magnitude of subjective sensation
increases proportionally to the logarithm of
the stimulus intensity
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(Loudness)
Fechner’s Law
(Sound Pressure Level (Decibels dB))
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Perceived magnitude: understanding response
expansion vs. response compression
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
The Structure of a Neuron
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Stimulus-Physiological
question: How are the
properties of objects
represented by the activity
of neurons?
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
- synapses involve
an electrical to
chemical to
electrical process
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
Crossing the Synapse
Vesicles contain
neurotransmitters
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Neural Communication
Whether a neuron
fires depends upon
the inputs it gets from
multiple sources.
Some connections are
excitatory (systematic
neural activation) and
others are inhibitory
(systematic neural
quieting).
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
Neurons have a resting potential of
about –70mv
outside – positively charged
Sodium (Na+) ions, negatively
charged Chloride (Cl-) ions
inside – positively charged
Potassium (K+) ions.
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The physics & chemistry of membrane permeability:
Ionic “current” is created by the change in positive and
negative charges
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
Excitation causes Na+
ion channels to open –
cell becomes less
negatively charged =
DEPOLARIZATION
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
inhibition causes chloride ion
channels to open – cell becomes
more negatively charged =
HYPERPOLARIZATION
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How does a neuron propagates an electrical signal down the axon?
[Alan] Hodgkin – [Andrew] Huxley cycle
Sodium (Na+) in = depolarization; Potassium (K+) out = hyperpolarization
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Centre-Surround Receptive Field In the Lateral
Geniculate Nucleus: neurons act together as a group
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Stimulus-Physiological question: How are the properties
of objects represented by the activity of neurons?
Physiological-Perception question: This is your brain
during perception
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SENSATION &
PERCEPTION
Nervous
System
Activity
Environmental
Stimuli
Stimulus Environment question: Psychophysics
Stimulus-Physiological question: Neurophysiology
Sensation & Perception question: Psychophysiology
42
Herman Grid
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"Throwing cast nets"
Circles appear to expand.
opyright A.Kitaoka 2004 (February 12, 2004)
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"Rotating snakes"
cular snakes appear to rotate 'spontaneously'.
pyright A.Kitaoka 2003 (September 2, 2003)
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Explanation (PDF file)
"Dongururin"*
Rotation of donguri (acorns). "Gururin" means rotation.
Rings of donguri appear to rotate.
Copyright A.Kitaoka 2003 (July 3, 2003)
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"Light of chrysanthemums"
center of a flower appears to be bright.
pyright Aiyoshi Kitaoka 2005 (April 5)
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From The Matrix:
Morpheus says to Neo….
“If you’re talking about what you
can feel, what you can smell,
what you can taste and see, then
real is simply electrical signals
interpreted by your brain. This is
the world that you know.”
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