Schacter
Gilbert
Wegner
PSYCHOLOGY
Chapter 4
Sensation and
Perception
Slides prepared by:
Melissa S. Terlecki, Cabrini College
Schacter
Gilbert
Wegner
PSYCHOLOGY
4.1
The Doorway to
Psychology
Figure 4.1: Synesthesia (p. 90)
Questions
 What
role does the brain play in
what we see and hear?
Sensation

Synesthesia: the perceptual experience of one
sense that is evoked by another sense.


psychological and neurobiological evidence.
Sensation: simple awareness due to the
stimulation of a sense organ.
 Perception: the organization, identification,
and interpretation of a sensation in order to
form a mental representation.
 Transduction: when sensors in the body
covert physical signals from the environment
into neural signals sent to the nervous system.
Culture and Community: Our
Brain Interpret Messages…

Cultural differences (Japanese and
American participants) in relative versus
absolute tasks of sensation and
perception.

experiment in line drawing.
Psychophysics
Scientific investigation requires objective
measures, but behavior must be
operationalized; quantify perception.
 Psychophysics: methods that measure
the strength of a stimulus and the
observer’s sensitivity to that stimulus.


experiments involving making judgments.
Questions
 Why
is the perception of any event
unique to yourself?
Measuring Thresholds

Absolute threshold: the minimal intensity
needed to just barely detect a stimulus.




threshold: a boundary.
difference between “sensing” and “not sensing”.
detection on 50% of experimental trials.
Just noticeable difference (JND): the
minimal change in a stimulus that can just
barely be detected.
 Weber’s Law: the just noticeable difference of
a stimulus is a constant proportion despite
variations in intensity.
Table 4.1: Approximate Sensory
Thresholds (p. 92)
Signal Detection

Sensing is gradual, not all-or-none.
 Noise: all other stimuli coming from the
internal and external environment.


can compete and interfere.
Signal detection theory: an observation that
the response to a stimulus depends both on a
person’s sensitivity to the stimulus in the
presence of noise and on a person’s response
criterion.

errors: hits, misses, false alarms, and correct
rejections.
Questions
 How
accurate and complete are our
perceptions of the world?
Cluttered Environments (p. 93)
Sensory Adaptation

Sensory adaptation: sensitivity to
prolonged stimulations tends to decline
over time as an organism adapts to
current conditions.

stimulus doesn’t change.
Questions
 What
conditions have you already
adapted to today?

sounds?

smells?
The Real World: Multitasking

Selective attention impairs multitasking
when sudden reaction is required.
driving and multitaksing: reaction time
experiments.
 more impaired for complex or novel tasks.

Schacter
Gilbert
Wegner
PSYCHOLOGY
4.2
Vision: More Than
Meets the Eye
Vision

Visual acuity: the
ability to see fine
detail.

smallest font
readable from 20
feet away in
humans (20/20 is
perfect).
The Snellen Eye Chart, p. 96
Sensing Light

Visible light is the portion of the
electromagnetic spectrum that we can
see.

light waves vary in wavelength.

length (hue), amplitude (brightness), number of
wavelengths (purity).
Table 4.2: Properties of Light
Waves (p. 96)
Figure 4.2: Electromagnetic
Spectrum (p. 97)
The Human Eye

Parts of the eye include the cornea,
pupil, iris, and retina.


retina: light-sensitive tissue lining the back
of the eye that houses the receptors for
detecting light.
Accommodation: the process by which
the eye maintains a clear image on the
retina.
myopia: nearsightedness.
 hyperopia: farsightedness.

Figure 4.3: Anatomy of the
Human Eye (p. 97)
Figure 4.4: Accommodation
(p. 98)
Questions
 How
do eyeglasses actually correct
vision?
Phototransduction in the
Retina

Two types of photoreceptors in the retina.



Fovea: an area of the retina where vision is the clearest
and there are no rods at all.



cones: detect color, operate under normal daylight conditions,
and allow us to focus on fine detail.
rods: become active only under low-light conditions for night
vision.
Peripheral vision: lower acuity.
Layers of retina include rod and cone layers, but also
bipolar and retinal ganglion cells (RGCs).
Blind spot: an area of the retina that contains neither
rods nor cones and therefore has no mechanism to
sense light, connects with the optic nerve.
Figure 4.5: Close-up of the
Retina (p. 99)
Figure 4.6: Blind Spot
Demonstration (p. 100)
Receptive Fields

Receptive field: the region of the
sensory surface that, when stimulated,
causes a change in the firing rate of that
neuron.
on-center cell: receptive field with a central
excitatory zone surrounded by an inhibitory
zone.
 off-center cell: receptive field with a central
inhibitory zone surrounded by an excitatory
zone.

Figure 4.7: RGC Receptive
Fields Viewed End-on (p. 100)
Perceiving Color

Visible spectrum; most sensitive to red (long),
green (medium), and blue (short) wavelengths.



additive color mixing: increasing light to create
color.
subtractive color mixing: removing light from the
mix.
Color deficiency/color blindness: one or
more cone types is missing.

Color afterimage: staring too long at one color can
cause sensory adaptation, a type of color
deficiency.
Figure 4.8: Seeing in Color
(p. 101)
Figure 4.9: Color Mixing (p. 101)
Figure 4.10: Color Afterimage
(p. 102)
The Visual Brain

Outside of the eye, visual information
travels to the lateral geniculate nucleus
(LGN) in the thalamus to area V1 in the
occipital cortex.

area V1: the part of the occipital lobe that
contains the primary visual cortex.

perceiving shapes, location, orientation, and
edges.
Figure 4.11: Visual Pathway
from Eye Through Brain (p. 103)
Figure 4.12: Single Neuron
Feature Detectors (p. 103)
Representing Objects and Faces
in the Brain
Modular view: specialized brain areas,
or modules, detect and represent objects
and faces.
 Distributed representation: pattern of
activity across multiple brain regions that
identifies any viewed object (including
faces).
 Visual-Form agnosia: the inability to
recognize objects by sight.

Questions
 How
do we recognize our friends,
even when they’re hidden behind
sunglasses?
Principles of Perceptual
Organization
Perceptual constancy: a perceptual
principle stating that even as aspects of
sensory signals change, perception
remains constant.
 Gestalt perceptual grouping rules:
simplicity, closure, continuity, similarity,
proximity, common fate.
 Figure versus ground perception.


size, movement, edge assignment.
Figure 4.13: Perceptual
Grouping Rules (p. 105)
Figure 4.14: Ambiguous Edges
(p. 106)
Perceiving Depth and Size
The visual world exists in length, width,
and depth dimensions, but the retina only
processes 2 dimensions (length and
width) and thus must rely on depth cues.
 Monocular depth cues: aspects of a
scene that yield information about depth
when viewed with only one eye.


linear perspective, texture gradient,
interposition, relative height
Figure 4.15: Familiar Size and
Relative Size (p. 106)
Figure 4.16: Pictorial Depth
Cues (p. 107)
Perceiving Depth and Size
Binocular disparity: the difference in the
retinal images of the two eyes that
provides information about depth.
 Illusions in depth perception


Ames room.
Figure 4.17: Binocular Disparity
(p. 108)
Figure 4.18: The Amazing Ames
Room (p. 109)
Questions
 What
does the Ames room tell us
about how the brain can be fooled?
Perceiving Motion

The visual system encodes information
regarding space and time.


MT region of temporal lobe.
Motion perception subject to illusions.
waterfall illusion, phi phenomenon.
 apparent motion: the perception of
movement as a result of alternating signals
appearing in rapid succession in different
locations.

Questions
 How
can flashing lights on a casino
sign give the impression of
movement?
Schacter
Gilbert
Wegner
PSYCHOLOGY
4.3
Audition: More Than
Meets the Ear
Sensing Sound

Sound waves: changes in air pressure
unfolding over time.





described by frequency, amplitude, complexity.
pitch: how high or low a sound is.
loudness: a sound’s intensity.
timbre: a listener’s experience of sound quality or
resonance.
Pure tone: a simple sound wave that first
increases air pressure then creates a relative
vacuum.
Table 4.3: Properties of Sound
Waves (p. 111)
Questions
 Why
does one note sound so
different on a flute and a trumpet?
The Human Ear

The human ear is divided into 3 parts:
outer ear (pinna, auditory canal,
eardrum), middle ear (ossicles), and the
inner ear (cochlea).

cochlea: a fluid filled tube that is the organ
of auditory transduction.
basilar membrane: undulates when vibrations
from the ossicles reach the cochlear fluid.
 hair cells: specialized auditory receptor neurons
embedded in the basilar membrane.

Figure 4.19: Anatomy of the
Human Ear (p. 112)
Questions
 How
do hair cells in the ear enable
us to hear?
Figure 4.20: Auditory
Transduction (p. 113)
Perceiving Pitch

Area A1: a portion of the temporal lobe that
contains the primary auditory cortex.



topographic organization.
processes simple tones.
Two methods for encoding sound-wave
frequency:


place code: the cochlea encodes different
frequencies at different locations along the basilar
membrane.
temporal code: the cochlea registers low
frequencies via the firing rate of action potentials
entering the auditory nerve.
Figure 4.21: Primary Auditory
Cortex (p. 113)
Questions
 How
does the frequency of a sound
wave relate to what we hear?
Localizing Sound Sources

Loudness and timing differences allow
us to localize sound (stereophonic
hearing).
Schacter
Gilbert
Wegner
PSYCHOLOGY
4.4
The Body Senses: More
Than Skin Deep
The Body Senses
Somatosenses: the body senses.
 Haptic perception: active exploration of
the environment by touching and
grasping objects with our hands.

Touch
Four types of receptors located under
the skin’s surface enable us to sense
pressure, texture, pattern, and vibration.
 Thermoreceptors sense cold and warmth
and respond when skin temperature
changes.

Figure 4.22: Touch Receptors
(p. 115)
Questions
 Why
might discriminating spatial
detail be important for fingertips and
lips?
Pain

Tissue damage is transduced by pain receptors.




A-delta fibers: transmit initial sharp pain.
C-fibers: transmit longer-lasting, duller pain.
Referred pain: the feeling of pain when sensory
information from internal and external areas converge
on the same nerve cells in the spinal cord.
Gate-control theory: a theory of pain perception
based on the idea that signals arriving from pain
receptors in the body can be stopped or gated by
interneurons in the spinal cord via feedback from 2
directions.


bottom-up control.
top-down control.
Questions
 Why
does rubbing an injured area
sometimes help alleviate pain?
Self-amputation (p. 117)
Body Position, Movement, and
Balance
Sensory receptors in the muscles,
tendons, and joints provide information
related to position, movement, and
balance.
 Vestibular system: the 3 fluid filled
semicircular canals and adjacent organs
located next to the cochlea in each inner
ear.


detects movement of the fluid when the
head moves or accelerates.
Questions
 Why
is it so hard to stand on one
foot with your eyes closed?
Schacter
Gilbert
Wegner
PSYCHOLOGY
4.4
The Chemical Senses:
Adding Flavor
Smell (Olfaction)

Smell sensed through odorant molecules.


pheromones: biochemical odorants emitted by
other members of a species that can affect an
animal’s behavior or physiology.
Olfactory epithelium contains olfactory
receptor neurons (ORNs): receptor cells that
initiate the sense of smell.
 Olfactory bulb: a brain structure located
above the nasal cavity beneath the frontal
lobes; collects axons from ORNs.
Figure 4.23: Anatomy of Smell
(p. 119)
Questions
 How
many scents can humans
smell?
Figure 4.24: Smell and Social
Behavior (p. 120)
Taste (Gustation)

The tongue is covered with thousands of
papillae which contain hundreds of taste
buds (the organ of taste transduction).


Microvilli: taste receptor tips that react with
tastant molecules in food.
Taste system contains taste receptors
that detect 5 sensations: salt, sour, bitter,
sweet, and umami.
Figure 4.25: A Taste Bud
(p. 121)
Questions
 Why
is the sense of taste an
evolutionary advantage?
Where Do You Stand:
Perception and Persuasion

Subliminal advertising at movie theaters.

Mixed evidence of effectiveness.
Sensory branding used today;
associations made with pleasant
sensations.
 Ethics in (mis)leading perceptions?
