Sensation ane Perceptions

90 Pages·2011·15.75 MB·English

Sensation and Perception
OUTLINE OF RESOURCES
Introducing Sensation and Perception
Podcast/Lecture/Discussion Topic: Person Perception (p. 305) NEW
Basic Principles of Sensation and Perception
Lecture/Discussion Topics: S ensation Versus Perception (p. 306)
Top-Down Processing (p. 307)
Sensory Processing Disorder (p. 308) NEW
“Thin-Slicing” (p. 309)
Classroom Exercises: A Scale to Assess Sensory-Processing Sensitivity (p. 308)
Human Senses Demonstration Kits (p. 309)
Classroom Exercises/Student Projects: The Wundt-Jastrow Illusion (p. 306)
Worth Video Anthology: The Man Who Cannot Recognize Faces
Thresholds
Lecture/Discussion Topics: G ustav Fechner and Psychophysics (p. 310)
Subliminal Smells (p. 311)
Subliminal Persuasion (p. 311)
Applying Weber’s Law (p. 312)
Student Projects: T he Variability of the Absolute Threshold (p. 310)
Understanding Weber’s Law (p. 312)
Sensory Adaptation
Student Project: Sensory Adaptation (p. 312)
Classroom Exercise: Eye Movements (p. 313)
Classroom Exercise/Lecture Break: Sensory Adaptation in the Marketplace (p. 313) NEW
Perceptual Set
Classroom Exercises: Discovering Personal Bias (p. 313)
Perceptual Set (p. 314)
Perceptual Set and Gender Stereotypes (p. 316)
Classroom Exercise/Lecture Break: The Role of Experience in Visual Perception (p. 315) NEW
Context Effects (see also Brightness Contrast, p. 328)
Lecture/Discussion Topic: Context and Perception (p. 317)
Vision
Classroom Exercise/Student Project: P hysiology of the Eye—A CD-ROM for Teaching Sensation and
Perception (p. 318)
Worth Video Anthology: Vision: How We See* NEW
The Eye and the Stimulus Input
Classroom Exercise: The Hermann Grid (p. 318)
Student Project: Locating the Retinal Blood Vessels (p. 318)
Student Projects/Classroom Exercises: Rods, Cones, and Color Vision (p. 318) NEW
Locating the Blind Spot (p. 319)
* Titles in the Worth Video Anthology are not described within the core resource unit. They are listed, with
running times, in the Lecture Guides and described in detail in their Faculty Guide, which is available at
www.worthpublishers.com/mediaroom.
303
304 Sensation and Perception
Visual Information Processing
Classroom Exercise/Student Project: Movement Aftereffects (p. 319)
Lecture/Discussion Topic: Blindsight (p. 320)
Worth Video Anthology: Visual Information Processing: Elementary Concepts*
Color Vision
Classroom Exercises: The Color Vision Screening Inventory and Color Blindness (p. 320)
Subjective Colors (p. 320)
PsychSim 5: Colorful World (p. 320)
Visual Organization
Lecture/Discussion Topics: O bject Recognition (p. 322)
Visual Agnosia (p. 323)
Autostereograms (p. 326)
Auditory Organization (p. 328)
Classroom Exercises: Visual Illusions and Principles (p. 321)
Visual Organization (p. 324)
An Auditory Analogue of the Visual Reversible Figure (p. 324)
The Ganzfeld (p. 325)
Binocular Vision (p. 325)
Brightness Contrast (p. 326)
Variation in the Size of the Retinal Image (p. 327)
Perceived Distance and Perceived Size (p. 327)
Binocular Disparity and Size Constancy (p. 328)
Classroom Exercise/Lecture Break: Identifying Cues to Depth and Distance (p. 326) NEW
Classroom Exercises/Student Projects: B inocular Vision Versus Monocular Vision (p. 325)
Perceived Lunar Size (p. 328)
Student Projects: P laying Cards and Illusions (p. 323)
Instant Object Recognition (p. 323)
Visual Capture (for entire section on vision) (p. 329)
PsychSim 5: Visual Illusions (p. 321)
Worth Video Anthology: Depth Cues* NEW
Müller-Lyer Illusion* NEW
A Variety of Visual Illusions* (also appropriate for the section on the size-distance
relationship)
The Visual Cliff*
Visual Interpretation
Lecture/Discussion Topic: Cases of Restored Vision (p. 329)
Classroom Exercise: Displacement Glasses (p. 330)
Feature Film: At First Sight (p. 330)
Worth Video Anthology: Seeing the World Upside Down*
Hearing
Lecture/Discussion Topics: R ecognizing Our Own Voice (p. 331)
Hearing Loss (p. 331)
A Quiet World—Living with Hearing Loss (p. 331)
Classroom Exercise: Locating Sounds (p. 331)
PsychSim 5: The Auditory System (p. 331)
Worth Video Anthology: Hearing: From Vibration to Sound NEW
The Other Senses
Touch
Lecture/Discussion Topics: T he Amazing Capabilities of Touch (p. 331)
The Remarkable Case of Ian Waterman (p. 333) UPDATED
Classroom Exercises: Two-Point Thresholds (p. 332)
Touch Localization (p. 333)
Sensation and Perception 305
Classroom Exercise/Student Project: Warm Plus Cold Equals Hot (p. 332)
Worth Video Anthology: Losing One’s Touch: Living Without Proprioception*
Pain
Lecture/Discussion Topics: C ultural Differences in Pain (p. 335)
Pain Control (p. 336)
Lecture/Discussion Topic/Critical Thinking Break: “Amputating” a Phantom Limb (p. 335) UPDATED
Classroom Exercise: The Revised Reducer–Augmenter Scale (p. 334)
Worth Video Anthology: P hantom Limb Sensations*
Pickpockets, Placebos, and Pain: The Role of Expectations*
Coping With Pain*
Taste
Lecture/Discussion Topics: T aste Preferences (p. 339)
Taste Preferences—Leaarned and Genetic (p. 340)
Synesthesia (p. 340) UPDATED
Classroom Exercises: Taste: The Basic Taste Sensations (p. 338)
Genetic Effects in Taste (p. 338)
Classroom Exercise/Student Project: Taste (p. 340)
Student Project: Mapping Your Tongue (p. 339)
Worth Video Anthology: “ Supertasters”*
The “Red Hot” Chili-Eating Contest: Sensitivity to Taste*
Synesthesia: The Man Who Tastes Words*
Smell
Lecture/Discussion Topics: A nosmia (p. 341)
Odor and Sex Identification (p. 343)
Pheromones (p. 343)
Fragrance Effects (p. 344)
Classroom Exercise: Identifying Odors (p. 342)
Body Position and Movement
Classroom Exercises: Nystagmus (p. 345)
Vision and Balance (p. 346)
Extrasensory Perception
Lecture/Discussion Topic: Belief in ESP (p. 346)
Classroom Exercises: Belief in ESP Scale (p. 346)
ESP Tricks (p. 347)
Student Project: The Psychic Challenge (p. 347)
Student Project/Classroom Exercise: Testing for ESP (p. 350)
RESOURCES issues and phenomena. The podcasts are produced from
its weekly episode. They are available as free down-
Introducing Sensation and Perception loads from iTunes, as well as directly from their website
(www.radiolab.org); they vary in length from about 6
Podcast/Leccture/Discussion Topic: Person Perception
minutes to more than an hour (depending on the topic
As an extension of the text chapter’s opening descrip- and purpose of the episode). They are well produced
tion of Heather Seller’s problem with recognizing faces, (lots of sound effects, music, suspense); you and your
have students listen to RadioLab’s podcast “Strangers students will enjoy listening to them as well as learning
in the Mirror.” Radiolab is a biweekly radio program from them.
produced by WNYC and heard across the country on In the “Strangers in the Mirror” episode (www.
public broadcasting stations. The episodes, hosted by radiolab.org/blogs/radiolab-blog/2010/jun/15/strangers-
Jad Abumrad and Robert Krulwich, are witty, insight- in-the-mirror), which was recorded at the annual World
ful, and focused on understanding and informing the Science Festival in New York City, we listen in on a
public about interesting (even intriguing) scientific conversation among Robert Krulwich and two famous
306 Sensation and Perception
individuals who suffer from face blindness, the inability a meaningful configuration. For the top figure, K. M.
to recognize familiar faces. One is Oliver Sacks, the Dallenbach states that the picture “appears when first
famous neuroscientist and prolific author. The other is scrutinized as an amorphous blotch without meaning
Chuck Close, a painter made popular by his unusual or organization. Clearly, one is receiving stimulation,
style of painting faces. This episode was broadcast June but it is a meaningless array of black, white, and gray.”
15, 2010, and is 26:25 minutes long. Another psychologist likens the experience to what
A related reading can be found at Cecilia Burman’s William James described as a baby’s first perceptual
prosopagnosia website: What it’s like to have face experience, that is, “one great, blooming, buzzing
blindness (www.prosopagnosia.com/main/stones/index. confusion.”
asp). On this web page, Cecilia attempts to show people Bloomquist argues that in viewing puzzle pictures
what it is like to be face blind with an analogy to distin- we readily come to appreciate that perception is an
guishing among stones. This is a very clever, concrete active process. We struggle to impose some organiza-
example of how difficult it can be to recognize individ- tion upon the meaningless array we are sensing. We
uals, especially when the viewing context changes. may even gen erate hypotheses about the figures, then
Another Radiolab episode related to prosopagnosia/ test them by searching the picture for features that are
face blindness is “Do I Know You?” (www.radiolab. congruent with those hypotheses. After a few minutes
org/blogs/radiolab-blog/2010/mar/08/do-i-know-you/) of unsuccessful inspection, we are likely to experience
in which the hosts discuss interviews with Dr. Carol some degree of frustration.
Berman and Dr. V. S. Ramachandran to understand a The subject of the picture is a Dalmatian dog. Why
rare delusional disorder called capgras. In this disorder, is it difficult to see? First, it is not a complete figure.
the person can process and recognize faces, but suffers Dallenbach suggests that even when asked to see a dog,
a disturbing “disconnection” between knowledge of the we may adopt a set to perceive an entire figure, not part
face’s familiarity (e.g., “That person looks just like my of one. A related explanation is that the contours are
mother . . .”) and associating that face to the presence insufficient to readily differentiate figure from ground.
of the actual person (e.g., “. . . but that person is NOT Both figure and ground are made up of irregular spots
my mother”). This leaves the sufferer to experience of black and white.
the perception that the person (s)he is literally seeing The bottom figure, which is known as a Fraser
is merely an “imposter” of the familiar person. This spiral, is provided by Stanley Coren and his colleagues
experience seems to be limited to visual processing. as another example of the distinction between sensation
This episode was broadcast March 8, 2010, and is 9:43 and perception. Although the figure appears to form a
minutes long. spiral, it is actually a set of concentric circles. Instruct
Another related reading is an article by Abumrad students to place one figure on any line composing the
and Krulwich on National Public Radio’s website: spiral. Then have them place a finger from the other
www.npr.org/templates/story/story.php?storyId= hand beside it and begin tracing the circle while holding
124745692. their first finger in place. Eventually, they will return to
Still another is Hoffman, K. (2003, Sept. 23). the first finger confirming the figure to be a circle.
“Victims of capgras syndrome often cannot recognize
Bloomquist, D. W. (1985). Teaching sensation and per-
their own image.” Philadephia Post-Gazette. www.post-
ception: Its ambiguous and subliminal aspects. In A. M.
gazette.com/ pg/03266/224822.stm. (This newspaper
Rogers and C. J. Sheirer (Eds.), The G. Stanley Hall lec-
article describes the problem of “mirror self-misidentifi- ture series: Volume 5 (pp. 157–203). Washington, DC:
cation” that capgras sufferers often experience.) American Psychological Association.
Coren, S., Ward, L. M., & Enns, J. T. (2003). Sensation
Basic Principles of Sensation and Perception and perception (6th ed.). New York: Wiley.
Lecture/Discussion Topic: Sensation Versus Perception Dallenbach, K. M. (1951). A puzzle-picture with a
new principle of concealment. American Journal of
Sensation refers to how our sensory receptors and ner-
Psychology, 64, 431–433.
vous system receive and represent stimulus energies
from our environment. Perception refers to how we Goldstein, E. B. (2010). Sensation and perception (8th
organize and interpret sensory information. Sensation ed.). Pacific Grove, CA: Wadsworth.
provides the raw information that perception constructs
into our experiences. Classroom Exercise/Student Project: The Wundt-
Douglas Bloomquist suggests using a “puzzle Jastrow Illusion
picture” to illustrate the complex nature of perception David Pick suggests use of the Wundt-Jastrow illu-
as opposed to sensation. Distribute a copy of Handout sion to highlight the distinction between sensation and
1 to each student. Most will not immediately perceive perception. This compelling and reliable illusion is
Sensation and Perception 307
easy to demonstrate and is a wonderful opener to class Pick suggests making the illusion the basis for
discussion of perception. At the bottom of this column a project in which students attempt to discover its
is the template for constructing the illusion. Enl arge it underlying explanation. He suggests that they begin
approximately 300 percent, using an 11” x 17” sheet by searching the literature. It is variously referred to
of paper and then trace two copies onto posterboard. as the Wundt-Jastrow illusion, the Jastrow illusion, the
Cut out the two segments for presentation in class. ring segment illusion, and the concentric arc illusion.
Initially, present them side by side, curving in the same Pick notes that J. O. Robinson’s work contains the most
direction, and ask if one appears larger. This is truly a extensive discussion of the illusion but offers no final
dramatic illusion with the segment on the inside curve explanation of it. Students might also formulate their
appearing undeniably larger. Reverse the position of own hypotheses and design appropriate experimental
the two segments, and your class will be astonished to tests to be presented in class.
find that the apparently smaller segment now appears
Pick, D. (1992, August). The Wundt-Jastrow illusion as
to be the larger. Then place one over the other to con- demonstration of the discrepancy between sensation and
vince your audience that they are indeed the same. perception. Paper presented at the Annual Convention of
Finally, present the segments curving away from each the American Psychological Association, Washington,
other and they will also appear equivalent. Emphasize DC.
that while the same sensation is produced by the two
stimuli, under certain conditions the perception of them Lecture/Discussion Topic: Top-Down Processing
is very different. By the late nineteenth century, when Christopher Green passed along the following sentences
psychology was emerging as a discipline, perceptual that you might present in class to introduce top-down
illusions such as this one had already begun to fascinate processing when discussing differences between sensa-
scientists. Illusions mislead us by playing on the ways tion and perception.
we organize and interpret our sensations. Understanding
Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it
illusions can sometimes provide valuable clues to the deosn’t mttaer in waht oredr the ltteers in a wrod are, the
ordinary mechanisms of perception. olny iprmoetnt tihng is taht the frist and lsat ltteer be at
the rghit pclae. The rset can be a total mses and you can
sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn
mnid deos not raed ervey lteter by istlef, but the wrod as
a wlohe.
Our experience and expectations enable us to
immediately perceive the scrambled letters as meaning-
ful words and sentences.
The notion that higher-level processes guide our
perceptions can be traced all the way back to Herman
von Helmholtz’s proposed likelihood principle: We will
perceive the object that is most likely to be the cause of
our sensory stimulation. That is, if a number of differ-
ent objects could have caused a specific pattern of light
and dark on the retina, we will perceive the object that
is most likely to occur in that particular situation. For
example, in one study participants were shown a kitch-
en scene and then briefly flashing pictures of a drum,
mailbox, and loaf of bread. Most correctly identified
the loaf of bread (which, of course, is appropriate to the
kitchen scene) but not the mailbox or drum.
A contemporary extension of the likelihood prin-
ciple is Richard Gregory’s suggestion that perception
is governed by hypothesis testing. He states, “We may
think of sensory stimulation as providing data for
hypotheses concerning the state of the external world.”
We may hypothesize that a dimly lit object across the
room is a small table but in looking more closely in the
corner find the hypothesis is incorrect. On the basis of
new data gathered, we revise the hypothesis: the “table”
is actually a chest of drawers. In summary, we do not
perceive in an automatic, nonthinking way. Rather, as
308 Sensation and Perception
Goldstein concludes, “Our perceptions are determined ity, Journal of Personality and Social Psychology, 73,
by a combination of automatic processes that begin 345–368.
with properties of the stimulus, and individualistic Zeff, T., & Aron, E. N. (2004). The highly sensitive per-
processes that depend on a person’s past experiences, son’s survival guide: Essential skills for living well in
knowledge, and expectations.” an overstimulating world. Oakland, CA: New Harbinger
Publications
Goldstein, E. B. (2010). Sensation and perception (8th
ed.). Pacific Grove, CA: Wadsworth.
Lecture/Discussion Topic: Sensory Processing Disorder
Green, C. (2003, September 17). FW: Wrkos for me.
The condition known as sensory processing disorder
Message posted to [email protected].
(SPD), a disorder involving difficulties in sensory
Classroom Exercise: A Scale to Assess Sensory- processing, has been generating a lot of attention
Processing Sensitivity lately. The condition was first described 40 years
ago by Dr. Jean Ayres, an occupational therapist, as
Elaine Aron designed Handout 2 to measure individual
a “sensory integration disorder.” Today, it is recog-
differences in sensory processing sensitivity. To score,
nized primarily among occupational therapists and a
students should simply add up the numbers they gave
handful of psychologists and psychiatrists; it is not
in response to the 27 items. Total scores can range
officially recognized in any standard medical refer-
from 27 to 189, with higher scores reflecting greater
ence manuals (e.g., the World Health Organization’s
sensitivity. Aron cautions, “No psychological test is so
International Statistical Classification of Diseases and
accurate that an individual should base his or her life on
Related Health Problems or the American Psychiatric
it. We psychologists try to develop good questions, then
Association’s Diagnostic and Statistical Manual of
decide on the cut off based on the average response.”
Mental Disorders). SPD is associated with a wide range
In her book, The Highly Sensitive Person: How to
of behavioral, language, neurological, and psychiatric
Thrive When the World Overwhelms You, Aron sug-
symptoms and is thought to be related to autism spec-
gests that high sensitivity is an innate trait found in as
trum disorder and other disorders in which sensory
many as one out of every five people. It is as common
processing is disrupted (e.g., disorders involving ves-
in men as it is in women. Aron claims that high sen-
tibular, motor, peripheral nervous system, or central
sitivity has sometimes been confused with shyness or
nervous system problems). Some researchers organize
introversion. However, these are quite different person-
the symptoms of SPD in three categories of dysfunc-
ality dimensions. In fact, she estimates that 30 percent
tion: Type I, Sensory Modulation Disorder (over- or
of highly sensitive persons are extraverts. Very likely, a
under-responding to sensory information, or increased
culture that prefers confident, bold extraverts is one that
or decreased sensation seeking); Type II, sensory-based
views sensitivity as a weakness and confuses it with
motor disorder (disorganized motor output which may
timidity.
include poor posture and motor planning); and Type III,
Highly sensitive persons only appear inhibited
sensory discrimination disorder (a “catch all” category
because they are more aware of all the possibilities in
thought to reflect a general difficulty in integrating
a situation. They naturally process information from
sensory information evidenced by inattention, distract-
the environment more carefully and study it thoroughly
ibility, and inability to remain on task).
before acting. Highly sensitive people possess a more
SPD is diagnosed primarily in children. Several
sensitive nervous system and thus are more aware of
different types of therapeutic assistance are available
subtleties in their surroundings, an advantage in many
and recommended for individuals with SPD. Most of
situations. Indeed, many are intellectually gifted, unusu-
these are described and assessed in the occupational
ally creative and productive workers, and attentive and
therapy research literature. You can obtain more infor-
thoughtful in close relationships. However, highly sen-
mation about this disorder from the SPD Foundation
sitive persons are also more easily overwhelmed when
(www.spdfoundation.net), an advocacy group that
in a highly stimulating environment. They become
provides support for families of children diagnosed
exhausted when bombarded by multiple stimuli, and
with SPD, a clearinghouse for information about SPD,
they need more down time to recover. In short, high
research, and resources/referrals for funding and treat-
sensitivity, concludes Aron, is neither a flaw nor a
ment.
reason to brag. Rather, it is a trait that highly sensitive
Within psychology, there is considerable debate
persons must learn to use wisely.
whether SPD is a real disorder. In fact, the committee
Aron, E. N. (1999). The highly sensitive person: How assembling the DSM-5 is currently evaluating whether
to thrive when the world overwhelms you. New York:
SPD should be included in the new DSM edition (see
Random House.
www.dsm5.org/proposedrevision/Pages/Conditions-
Aron, E. N., & Aron, A. (1997). Sensory-processing Proposed-by-Outside-Sources.aspx). The controversy
sensitivity and its relation to introversion and emotional- over the existence of SPD has also been documented
Sensation and Perception 309
in Time (“The Next Attention Deficit Disorder?” www. had to immediately assess whether that person was
time.com/time/magazine/article/0,9171,1689216,00. friend or foe. Those who read the person’s expression
html) and the New York Times (“The Disorder is accurately were more likely to survive and reproduce,
Sensory; the Diagnosis, Elusive” www.nytimes. which helps explain why people today can read in a
com/2007/06/05/health/psychology/05sens.html). A glance facial expressions of fear, anger, sadness, or
very nice brief video (3 minutes) about SPD and the pleasure.
controversy can be found at http://abclocal.go.com/wls/ Nalini Abady and Robert Rosenthal discovered the
video?id=7570702. speed of our perceptions within the classroom setting.
Sensory processing disorder is clearly a topic rel- They videotaped 13 Harvard University graduate stu-
evant to any discussion of human sensation and percep- dents teaching undergraduate courses. Research partici-
tion. However, it is also relevant to discussions about pants observed three 10-second slices of each teacher’s
what constitutes a psychological disorder and how psy- behavior from the beginning, middle, and end of a class
chological scientists and practitioners weigh evidence and then rated the teacher’s confidence, activeness,
in defining and recognizing specific disorders. You may warmth, and so on. The ratings based on watching only
also want to use the topic to discuss the evolving nature 30 seconds of behavior very accurately predicted aver-
of scientific knowledge and the impact this has on the age student ratings of teachers at the end of the semes-
maintenance of the most widely used mental health ref- ter. In fact, even thinner slices—three 2-second clips—
erence, the Diagnostic and Statistical Manual of Mental gave ratings that still correlated +.72 with end-of-course
Disorders. For more information, see evaluations. Thus, instant first impressions predicted
lasting impressions.
Bar-Shalita, T., Vatine, J-J., Seltzer, Z., & Parush,
In other studies, research participants hear people
S. (2009). Psychophysical correlates in chil-
recite the alphabet and accurately perceive their social
dren with sensory modulation disorder (SMD).
assertiveness. They also watch 90 seconds of people
Physiology and Behavior. 98(5), 631–639.
walking and talking and accurately predict how others
Miller, L. J., Nielsen, D. M., Schoen, S. A., &
evaluate them. After a quick glance at someone’s photo,
Brett-Green, B. A. (2009). Perspectives on sen-
people have a pretty good sense of the person’s extra-
sory processing disorder: A call for translational
version and agreeableness.
research, Frontiers in Integrative Neuroscience. 3,
More recently, Ambady and her graduate student
1–12.
Nicholas Rule reported that observers can accurately
spot a man’s sexual orientation at levels greater than
Classroom Exercise: Human Senses Demonstration Kits
chance with a less than half-second glance at his face.
Carolina Biological Supply Company (www.carolina.
Using photographs from online personal ads for homo-
com) provides two demonstration kits for the human
sexual and heterosexual men, the researchers asked
senses. Materials and suggested activities illustrate prin-
their research participants to choose whether the men
ciples of vision, touch, taste, and smell. Each kit pro-
were likely to be gay or straight. Results indicated that
vides supplies for up to 30 students. Lab-Aids Human
participants accurately picked sexual orientation about
Senses Experiment Kit (Item #694505) retails for
70 percent of the time within one-tenth of a second.
$102.50; Human Senses Biokit (Item #694506) costs
Ambady suggests that the human ability to recognize
$77.95. A complete description of each can be found at
sexual orientation may be tied to the evolutionary drive
the Carolina website. To order and obtain more infor-
to find a mate.
mation you can also call Customer Service at
For more on the strengths and weaknesses of our
800-334-5551.
social perceptions, see Myers’ Intuition: Its Powers and
Perils (Yale University Press) and Malcolm Gladwell’s
Lecture/Discussion Topic: “Thin-Slicing”
Blink: The Power of Thinking Without Thinking (Little,
We all speedily and efficiently transform sensations
Brown).
into perceptions. Even microslices of people’s appear-
Ambady, N., & Rosenthal, R. (1993). Half a minute:
ance and behavior tell us something. For example, John
Predicting teacher evaluations from thin slices of non-
Bargh’s research indicates that we always interpret an
verbal behavior and physical attractiveness. Journal of
object or a face, even if we see it for only 200 milli-
Personality and Social Psychology, 64, 431–441.
seconds. “We’re finding that everything is evaluated as
Azar, B. (1998, September). Split-second evaluations
good or bad within a quarter of a second of seeing it,”
shape our moods. APA Monitor, 13.
argues Bargh. In an eyeblink, we find ourselves loving
or hating a new roommate, an abstract painting, or a Rule, N., & Ambady, N. (2008). Brief exposures: Male
sexual orientation is accurately perceived at 50 ms.
relative’s new car.
Journal of Experimental Social Psychology, 44, 1100–
These instantaneous perceptions make biological
1105.
sense. When encountering a stranger in the forest, one
310 Sensation and Perception
Thresholds ticipant can perceive it. To determine a just noticeable
difference, the researcher presents a standard stimulus
Lecture/Discussion Topic: Gustav Fechner and
and a comparison stimulus and increases the difference
Psychophysics
between them by small steps until the participant says it
In pioneering the study of the relationship between
is perceptible.
physical energy and psychological experience, Gustav
In the method of right and wrong cases, the experi-
Fechner (1801–1887) was actually attempting to pro-
menter presents identical stimuli repeatedly—either
mote his belief that every person, animal, and plant
single stimuli at the threshold or pairs of stimuli that
in the universe is composed of both matter and soul.
are very similar. The participant responds “Yes” (if she
Although trained in medicine, Fechner soon turned his
perceives it, or the two are different) or “No” (if she
attention to physics and mathematics and held a pro-
does not perceive it or the two are not different). The
fessorship at the University of Leipzig. As part of his
responses yield averages and these tell how likely it is
research, he discovered that after staring at the sun for
that at any given stimulus level or difference between
a period of time, he would see an afterimage (blue, the
stimuli, the paticipant will perceive the stimulus or the
complement of yellow). He began to devote all his time
difference.
to this psychological research. Although his findings
In the method of adjustment, the researcher or par-
were well-received, the work led him to suffer photo-
ticipant adjusts a comparison stimulus until it appears
phobia and emotional collapse. Virtually blind, he spent
identical to the standard stimulus. Of course, there is
a long period in a darkened room where, Morton Hunt
always a small margin of error. Every error is recorded
reports, “he was tormented by pain, emotional distress,
and after many trials, the average error is computed. It,
intolerable boredom, and severe digestive problems.”
too, provides a measure of just noticeable difference.
He eventually began to improve and to see again with-
In recognizing Fechner’s contributions, the great
out pain. As he emerged from his room he walked into
historian of psychology Edwin G. Boring writes,
a garden where the flowers appeared brighter, more
“Fechner, because of what he did and the time at which
beautiful, and more intensely colored than ever before.
he did it, set experimental quantitative psychology
This led him to write a book about the mental life of
off upon the course which it has followed. One may
plants, and for the rest of his life he sought to pro-
call him the ‘founder’ of experimental psychology, or
mote his theory that consciousness and matter coexist
one may assign that title to Wundt. It does not matter.
throughout the world. Hunt describes how this mystical
Fechner had a fertile idea which grew and brought forth
notion led Fechner to his historic work in experimental
fruit abundantly.”
psychology.
Hunt, M. (2007). The story of psychology. New York:
Lying in bed on the morning of October 22, 1850,
Doubleday.
wondering how to prove that mind and body are two
aspects of a fundamental unity, Fechner had a sudden
Student Project: The Variability of the Absolute
insight. He thought that if somehow he could show a
Threshold
consistent mathematical relationship between the force
of stimuli and the intensity of the sensations they pro- An absolute threshold is defined as the minimum
duce, he would have established the identity of body amount of stimulation a person needs for a particular
and mind. Fechner asked the important question: Is stimulus to be detected 50 percent of the time. Students
there a consistent mathematical relationship between can experience the variability of the absolute thresh-
the magnitude of a stimulus and the magnitude of old for sound by placing a kitchen timer on a table in
the sensation it creates? Although he could measure an otherwise quiet room. They should move away so
stimulus intensity directly, Fechner thought he faced an that they can no longer hear the ticking, then gradu-
enormous problem in measuring sensations. They are ally move toward the timer until they begin to hear the
subjective. Finally, he realized he could do so indirectly sound. This is their “momentary” threshold. If they
by using sensitivity as the guide. He could determine remain where they are, they will notice that occasion-
the smallest increase in stimulus strength that would be ally they won’t be able to hear the sound and will need
just barely noticeable to the research participant. “Just to step forward to reach threshold. At other times the
barely noticeable” meant the same thing at any level. sound will get louder and they will be able to step
That measurement of sensation could be compared with back. This changing sensitivity indicates that the “abso-
the increase in stimulus necessary to produce the lute threshold” is any thing but absolute. Our
awareness. sensitivity changes from moment to moment and from
The three methods of experimental measurement measurement to measurement. As long ago as 1888,
used by Fechner continue to be used in psychophysical Joseph Jastrow speculated that lapses of attention, slight
research. In the method of limits, the researcher begins fatigue, and other psychological changes could cause
with a minimal stimulus and increases it until the par- fluctuations in the absolute threshold.
Sensation and Perception 311
Coren, S., Ward, L., & Enns, J. T. (2003). Sensation and Lecture/Discussion Topic: Subliminal Persuasion
perception (6th ed.). New York: Wiley.
Anthony Pratkanis notes that at various times a claim
regarding subliminal persuasion has been made and,
Lecture/Discussion Topic: Subliminal Smells
although it has been unsubstantiated or validly criti-
You may want to expand your discussion of sub-
cized on methodological grounds, the original claim has
liminal stimulation to cover research on the impact
gained acceptance in lay audiences. To understand this
of subliminal odors. Wen Li and her research team at
acceptance, Pratkanis did a content analysis of
Northwestern University reported that subliminal scents
popular-press articles on subliminal persuasion pub-
can affect how much we like someone. “We evalu-
lished between 1955 and 1987. He identified five fac-
ate people every day and make judgments about who
tors that contribute to their effect on the public’s beliefs
we like or don’t like,” claims Li. “We may think our
regarding subliminal influence. His analysis, first
judgments are based only on various conscious bits of
reported in 1990, remains instructive today.
information, but our senses also may provide subliminal
First, popular accounts of subliminal influence
perceptual information that affects our behavior.”
appeal to the “pop” psychology of the day. Many
To assess whether subliminal smells affect social
Americans believe in a powerful unconscious capable
preferences, research participants sniffed three different
of performing amazing feats. Subliminal influence is
scents: lemon (good), sweat (bad), and ethereal (neu-
portrayed in the media and by proponents as a means of
tral). The odors were delivered just below detection lev-
directly communicating to this unconscious.
els. (Research participants were told that an odor would
Second, popular accounts link subliminal influ-
be present in 75 percent of the trials.) Most people
ence to the issue of the day. Subliminal influence
proved unaware of the barely perceptible odors.
first emerged as a national concern after the Korean
After sniffing from each of the bottles, the research
war when brainwashing and hypnotic suggestion cap-
participants were shown a face with a neutral expres-
tured the nation’s imagin ation in films such as The
sion. They were asked to evaluate it using ratings that
Manchurian Candidate. In the post-Watergate years,
ranged from extremely likable to extremely unlikable.
Americans felt that their leaders were involved in devi-
Odor significantly affected likability ratings for those
ous conspiracies of the type dramatized in Network.
participants who lacked conscious awareness of the
Wilson Bryan Key, author of Subliminal Seduction,
smells. People who discerned that the minimal smell
capitalized on the idea that big business and big gov-
was present were not affected by the scents. “The study
ernment were conspiring to get us. Today’s producers
suggests that people conscious of the barely noticeable
of subliminal tapes link their products to the growing
scents were able to discount that sensory information
interest in human potentials and self-enhancement.
and just evaluate the faces,” observed Li. “It only was
Third, those advertisers accused of using sublimi-
when smell sneaked in without being noticed that judg-
nal persuasion to manipulate the public are subjected to
ments about likability were biased.”
what can be termed “the witch test.” During the Middle
“When sensory input is insufficient to provoke a
Ages, a woman accused of witchcraft would be bound
conscious olfactory experience, subliminal processing
and thrown into a pond. If she floated, she was a witch.
prevails and biases perception,” Ken Paller added. “But
Only if she drowned was her innocence affirmed. How
as the awareness of a scent increases, greater executive
do we know that advertisers use subliminals and that
control in the brain is engaged to counteract uncon-
they work? According to writers such as Key, advertis-
scious olfaction.”
ers would not spend so much money on them if they
The acute sensitivity of human olfaction tends to
did not work. The fact that subliminal messages can-
be underappreciated. “In general, people tend to be dis-
not be readily identified demonstrates the advertiser’s
missive of human olfaction and discount the role smell
craftiness. The protestations of the accused are merely
plays in our everyday life,” concluded Jay Gottfried.
signs of guilt. The only way advertisers could prove
“Our study offers direct evidence that human social
their innocence is by going out of business. In contrast,
behavior is under the influence of miniscule amounts
the motives of the proponents of subliminal seduction
of odor, at concentrations too low to be consciously
who frequently profit by the sale of more books and
perceived, indicating that the human sense of smell is
tapes are rarely questioned.
much keener than commonly thought.”
Fourth, many of the popular articles fail to report
Li, W., Moallem, I., Paller, K.A., & Gottfried, J. A. scientific evidence that is critical of claims for sublimi-
(2007). Subliminal smells can guide social preferences. nal persua sion. If negative information is given, it is
Psychological Science, 18, 1044–1049. often presented at the end of the article, giving the read-
Northwestern University (2007, December 8). Subliminal er the impression that, at best, the claims for subliminal
Smells Bias Perception About A Person’s Likeability. effectiveness are somewhat controversial.
ScienceDaily. Retrieved August 4, 2008 from www.
sciencedaily.com/releases/2007/12/071206163437.htm.
312 Sensation and Perception
Finally, belief in subliminal persuasion may serve a think it best to sell the sweater first. Having spent a
need for many individuals. We live in an age of persua- lot on a suit, the customer might be reluctant to spend
sion. The average American is likely to see over 6 mil- more on a sweater. However, sales motivation analysts
lion ads in a lifetime, yet he or she knows little or noth- suggest the opposite. Sell the suit first because the addi-
ing about the persuasion process. Subliminal persuasion tional cost of the sweater will not be so readily noticed.
is presented as an irrational force outside the control If the man has just paid $300 for a suit, an additional
of the message recipie nt. In this way, it takes on a $75 for a sweater will not seem excessive. The same
supernatural “the devil made me do it” quality capable applies to other accessories, such as a shirt or shoes. As
of explaining why Americans engage in irrational con- a rule, people will almost always pay more for acces-
sumer behavior. “Why did I buy this worthless product sories if they buy them after rather than before a more
at such a high price?” Subliminal sorcery! expensive purchase.
The same principle holds for the purchase of acces-
Pratkanis, A. (1990, August). Subliminal sorcery then
sories on a new car. After paying $32,000 for the car,
and now: Who is seducing whom? Paper presented at the
the customer will hardly notice $700 for a sound system
98th Annual Convention of the American Psychological
to go with it. The trick, of course, is to mention these
Association, Boston, MA.
accessories indepen dently so that each addition will
seem negligible in comparison to the much larger com-
Student Project: Understanding Weber’s Law
mitment already made.
Stanley Coren and his associates suggest a simple dem-
onstration of Weber’s law for the perception of heavi- Cialdini, R. B. (2009). Influence: Science and practice
(5th ed.). Needham Heights, MA: Allyn and Bacon.
ness. Students need three quarters, two envelopes, and
a pair of shoes. Have them place one quarter in one
Sensory Adaptation
envelope and the remaining two quarters in the other.
Lifting each envelope, they can easily determine which Student Project: Sensory Adaptation
is heavier. Now have them put each envelope in a shoe.
Adaptation to the taste of one substance can affect
When they lift the shoes, one at a time, the weight
the taste of another, either decreasing or increasing
difference will be imperceptible. Weber’s principle:
our sensitivity to it. This phenomenon has sometimes
Difference thresholds grow with the magnitude of the
been called “cross-adaptation.” After drinking tea with
stimulus.
lemon, for example, a grapefruit will not taste sour.
Students can also try a more precise weight dis-
After eating a sweet roll, on the other hand, grapefruit
crimination task to demonstrate Weber’s law. Art Kohn
juice may taste extremely sour.
and Max Brill describe how students can prepare an
The variability in the taste of ordinary tap water
ascending scale of weights by inserting increasing num-
following adaptation to various substances will surprise
bers of BBs from a pop gun, or other similar items, into
many students. Have them mix a strong solution of
small containers (like the old 35-mm film canisters).
water and salt and hold it in their mouth for a time; it
The weights must differ by exactly equal increments
will gradually taste less salty. If they then take a glass
and should be noted on the bottom of each canister.
of fresh water, it will taste bitter or sour. Conversely, if
Volunteers can then be asked to arrange the canisters
they first take a mouthful of diluted vinegar or strong,
from lightest to heaviest. Diffic ulty in discrimination
caffeinated coffee, the glass of water will taste sweet.
will increase as the canisters get heavier.
(A way to make anything taste sweet is to eat miracle
Coren, S., Ward, L., & Enns, J. T. (2003). Sensation and fruit first.)
perception (6th ed.). New York: Wiley. Dani Raap brings the familiar fruity-smelling
magic markers to class to demonstrate adaptation to
Kohn, A., & Brill, M. (1981). An introductory labora-
odor. Give each student a marker to sniff and rate his
tory demonstration produced entirely by undergraduates.
Teaching of Psychology, 8(3), 133–138. or her perception of the intensity of the aroma from
1 to 20. Have students repeat quick successive sniffs
Lecture/Discussion Topic: Applying Weber’s Law and each time again rate the strength of the odor. Raap
indicates that the aroma completely disappears by the
Weber’s law can be applied to many situations. For
fourth or fifth sniff. After a few minutes of discussion
example, a $10-per-hour worker may require a 50-cent
and no sniffing, each student should pair up with a part-
pay raise to notice the difference; a $20-per-hour work-
ner. After sniffing to adaptation, have students quickly
er may need to receive a $1 raise to notice.
change markers and whiff. In a class of 30, Raap
Robert Cialdini illustrates the principle for sales.
reports that 3 experienced cross-adaptation (smelled
Assume that a man wants to buy a suit and a sweater. If
nothing); the remaining students easily smelled the new
you were the salesperson, which should you show him
stimulus. Many of them actually experienced facilita-
first to get him to spend the most money? You might
tion (heightened intensity) of the new smell.