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Sensation & Perception
Chapter 4
Transduction
• Transduction: Transformation of one form of
energy into another – especially the transformation
of stimulus information into nerve impulses
• Receptors: Specialized neurons that are activated by
stimulation and transduce (convert) it into a nerve
impulse
• Sensory pathway: Bundles of neurons that carry
information from the sense organs to the brain
Sensation and Perception
• Sensation: An early stage of perception in which
neurons in a receptor create an internal pattern of
nerve impulses that represent the conditions that
stimulated it – either inside or outside the body
• Perception: A process that makes sensory patterns
meaningful and more elaborate
• Stimulation  Transduction  Sensation  Perception
Sensory Adaptation
• Sensory adaptation: Loss of responsiveness in
receptor cells after stimulation has remained
unchanged for a while
• Examples???
Thresholds
• Absolute threshold: Amount of stimulation
necessary for a stimulus to be detected (50% of
time)
• Difference threshold: Smallest amount by which a
stimulus can be changed and the difference be
detected (also called just noticeable difference –
JND)
Looking at the JND
• Weber’s law: The JND increases with the magnitude of the
stimulus.
– The JND is large when the stimulus intensity is high, and small
when the stimulus intensity is low
• TV (volume high – turn down a lot, volume low – turn down little)
• Groceries (50 pound bag, add 1 lb., 25 pound bag, add .5 lb)
• Steven’s power law:
– Used for wider array of stimuli (shock, temperature)
– Fills in gaps left by Weber and Fechner
Signal Detection Theory
• Signal detection theory: Perceptual judgment as
combination of sensation and decision-making processes
– based on each individual’s sensitivity and response criterion
– Explanation example: holiday weekend on the interstate
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False Alarm (brakes and no cop)
Hit (brakes and cop)
Miss (no brakes and cop)
Correct Rejection (no brakes and no cop)
– Lowers response criterion and raises hit rates
• Flawed merchandise off the assembly line, TSA putting weapons in bags
– Cocktail Party Effect: when you hear your name across
a room you will involuntarily switch attention to it
Subliminal Persuasion
• Studies have found that words flashed subliminally
on a screen can “prime” a person’s later responses.
– scary faces activate amygdala.
• No controlled research has ever shown that
subliminal messages delivered to a mass audience
can influence people’s buying habits.
The Anatomy of Visual Sensation
• Cornea  Pupil  Retina  Rods/Cones  Bipolar
Cells  Ganglion Cells (Optic Nerve)
The Anatomy of Visual Sensation
• Photoreceptors: Light-sensitive cells in the retina that
convert light energy to neural impulses
• Rods: sensitive to dim light but not colors
• Cones: sensitive to colors but not dim light
• Dark adaptation: increased visual sensitivity that
develops when it gets dark
•
http://www.youtube.com/watch?v=x6Ua5d3wlA0 (6:32)
• Fovea: area of sharpest vision on the retina
• Optic nerve: Bundle of neurons that carries visual
information from the retina to the brain
• Blind spot: Where the optic nerve exits the eye; there
are no photoreceptors (money in bank demo)
Color Blindness & Afterimages
• Color blindness: Vision
disorder that prevents an
individual from discriminating
certain colors
– Red –green most common
• Afterimages: Sensations that
linger after the stimulus is
removed
– Flag activity
How the Visual System Creates Color
• Visual cortex: Part of the brain – the occipital cortex –
where visual sensations are processed
• Brightness: Sensation caused by the intensity of light waves
• Color: Psychological sensation derived from the
wavelength of visible light – color, itself, is not a property
of the external world
• Electromagnetic spectrum: Entire range of electromagnetic
energy, including radio waves, X-rays, microwaves, and
visible light
• Visible spectrum: Tiny part of the electromagnetic
spectrum to which our eyes are sensitive
How the Visual System Creates Brightness
Wavelength
Intensity
(amplitude)
Color
Brightness
Sensing Colors
• Trichromatic Theory: Idea that colors are sensed by
three different types of cones sensitive to light in the
red, blue and green wavelengths.
– Explains the earliest stage of color sensation.
• Opponent-process Theory: Idea that cells in the
visual system process colors in complimentary pairs,
such as red or green or as yellow blue.
– Explains color sensation from the bipolar cells onward in
the visual system.
Hearing: How Sound Waves Become Auditory
Sensations
Pinna  Ear Canal  Tympanic Membrane  Middle Ear
Bones  Oval Window  Cochlea (Basilar Membrane) 
Auditory Nerve
Tympanic membrane:
The eardrum
Hearing: How Sound Waves Become Auditory
Sensations
Cochlea: Where
sound waves are
transduced
Hearing: How Sound Waves Become Auditory
Sensations
Cochlea
Basilar membrane:
Thin strip of tissue with
hairs sensitive to
vibrations
Hearing: How Sound Waves Become Auditory
Sensations
Auditory nerve:
Neural pathway
connecting the ear
and the brain
Deafness
• Conduction deafness: Results from damage to
structures of the middle or inner ear
– Disruption in converting sound into nerve energy
• Nerve deafness: Linked to a deficit in the
body’s ability to transmit impulses from the
cochlea to the brain
– Usually involves the auditory nerve or higher
auditory processing centers, but can be from life
damage
– Most born deaf have this
Hearing: The Physics of Sound
• Loudness: produced by the amplitude of a sound
wave
- Amplitude: Physical strength of a wave
High Amplitude
Low Amplitude
Hearing: The Physics of Sound
• Pitch: produced by the frequency of a sound wave
– Frequency: Number of cycles completed by a wave in a
given amount of time
Low Frequency
High Frequency
How Sound Waves Become Auditory Sensations
• Pitch:
– Place Theory: different places on the basilar membrane
send neural codes for different pitches
– Frequency Theory: neurons have different firing rates
for different sound wave frequencies
• Timbre: Quality of a sound wave that derives from
the wave’s complexity
• Auditory cortex: Portion of the temporal lobe that
processes sounds
Position and Movement
• Vestibular sense: Sense of body orientation with
respect to gravity
• http://www.youtube.com/watch?v=x6Ua5d3wlA0 (7:21)
• Kinesthetic sense: Sense of body position and
movement of body parts relative to each other
Smell
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Olfaction: Sense of smell
Chemical sense, just like taste
Olfactory bulbs: Brain sites of olfactory processing
Pheromones: Chemical signals released by
organisms to communicate with other members of
the species
Smell
Taste
• Gustation: The sense of taste
• Chemical sense
Taste buds: Receptors
for taste (primarily on
the upper side of the
tongue)
The Skin Senses and Pain
• Gate-control Theory: An explanation for pain
control that proposes we have a neural “gate” that
can, under some circumstances, block incoming pain
signals.
• Placebos: Substances that appear to be drugs but
are not
• Placebo effect: A response to a placebo caused by
subjects’ belief that they are taking real drugs
What is the Relationship Between Perception
and Sensation?
Perception brings meaning
to sensation, so perception
produces an interpretation of
the external world, not a
perfect representation of it
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The Machinery of Perceptual Processing
Percept: Meaningful product of a perception
Selective attention: Focused awareness of only a
limited amount of all you are capable of
experiencing
Feature detectors: Cells in the cortex that specialize
in extracting certain features of a stimulus
Binding problem: A major unsolved mystery in
cognitive psychology, concerning the physical
processes used by the brain to combine many
aspects of sensation to a single percept
Bottom-Up and Top-Down Processing
• Bottom-up processing: Analysis that begins with the sense
receptors and works up to the brain’s integration of sensory
information; focuses on characteristics of stimuli, not
internal concepts
• http://www.youtube.com/watch?v=x6Ua5d3wlA0 (50
seconds)
• Top-down processing: Analysis guided by higher-level
mental processes - emphasizes perceiver's expectations,
memories, and other cognitive factors
• http://www.youtube.com/watch?v=x6Ua5d3wlA0 (1:44)
Perceptual Constancies
• Perceptual constancy: Ability to recognize the same
object under different conditions, such as changes in
illumination, distance, or location
• Shape, color, size
Perceptual Ambiguity and Distortion
• Illusions: Distortion of a stimulus
pattern, shared by others in the same
perceptual environment
– More likely when:
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stimulus is unclear
info is missing
elements combined in unusual ways
familiar patterns aren’t apparent
• Ambiguous figures: Images that are
capable of more than one interpretation
The Gestalt Approach
• Gestalt psychology: View that much of perception
is shaped by innate factors built into the brain
– Nature view: programmed to find patterns
– The whole pattern is greater than the sum of its parts.
• Figure: Part of a pattern that commands attention
• Ground: Part of a pattern that does not command
attention; the background
The Gestalt Approach
• Subjective contours: Boundaries that are perceived
but do not appear in the stimulus pattern
• Closure: Tendency to fill in gaps in figures and see
incomplete figures as complete
The Gestalt Laws of Perceptual Grouping
Proximity
Similarity
Closure
Continuity
Common Fate
Prägnanz
Law of Prägnanz
A
BIRD
IN THE
THE HAND
Binocular Cues – two eye depth cues
• Binocular Convergence: lines of vision from each
eye converge at different angles on objects at
different distances
• Retinal Disparity: difference in perspectives of the
2 eyes (greater disparity for nearby objects –
provides us with depth information)
Monocular Cues – one eye depth cues
• Monocular Cues:
– Linear Perspective: parallel lines appear to meet in the
distance
Monocular Cues – one eye depth cues
• Monocular Cues:
– Relative Motion: objects closer to you move faster than
those further away from you
Monocular Cues – one eye depth cues
• Monocular Cues:
– Relative Size: two objects the
same size; if one appears larger
then it’s closer to us
Monocular Cues – one eye depth cues
• Monocular Cues:
– Interposition: hidden objects are more distant than those
objects that hide them
Monocular Cues – one eye depth cues
• Monocular Cues:
– Texture Gradient: as object gets further away from us,
the texture gets smoother
Theoretical Explanations for Perception
• Learning-based inference: View that perception is
primarily shaped by learning, rather than innate
factors (nurture); opposite of Gestalt
• Context, expectation and perceptual set
• Perceptual set: Readiness to detect a particular
stimulus in a given context
Muller-Lyer Illusion
• When 2 objects make the same size image on the
retina, and we judge one to be farther away than the
other, we assume that the more distant one is larger.