Unformatted text preview: 4/12/2021 Sensation and Perception | Introduction to Psychology Introduction to Psychology
Module 5: Sensation and Perception Sensation and Perception … 1/20 4/12/2021 Sensation and Perception | Introduction to Psychology What you’ll learn to do: di erentiate between
sensation and perception Sensation and perception are two separate processes that are very
closely related. Sensation is input about the physical world obtained by
our sensory receptors, and perception is the process by which the brain
selects, organizes, and interprets these sensations. In other words,
senses are the physiological basis of perception. Perception of the same
senses may vary from one person to another because each person’s
brain interprets stimuli di erently based on that individual’s learning,
memory, emotions, and expectations. LEARNING OBJECTIVES De ne sensation and explain its connection to the concepts of absolute threshold, di erence threshold, and
subliminal messages
Discuss the roles attention, motivation, and sensory
adaptation play in perception … 2/20 4/12/2021 Sensation and Perception | Introduction to Psychology Sensation
What does it mean to sense something? Sensory receptors are specialized neurons that respond to speci c types of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. For
example, light that enters the eye causes chemical changes in cells that
line the back of the eye. These cells relay messages, in the form of action potentials (as you learned when studying biopsychology), to the
central nervous system. The conversion from sensory stimulus energy to
action potential is known as transduction.
You have probably known since elementary school that we have ve
senses: vision, hearing (audition), smell (olfaction), taste (gustation), and
touch (somatosensation). It turns out that this notion of ve senses is
oversimpli ed. We also have sensory systems that provide information
about balance (the vestibular sense), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature
(thermoception).
The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Absolute threshold refers to the minimum amount of stimulus energy that must be
present for the stimulus to be detected
50% of the time. Another way to think
about this is by asking how dim can a
light be or how soft can a sound be and
still be detected half of the time. The
sensitivity of our sensory receptors can
be quite amazing. It has been estimated
that on a clear night, the most sensitive
sensory cells in the back of the eye can
Figure 1. The absolute
threshold for detecting light
is greater than you probably
imagined—the human eye detect a candle ame 30 miles away
(Okawa & Sampath, 2007). Under quiet
conditions, the hair cells (the receptor … 3/20 4/12/2021 Sensation and Perception | Introduction to Psychology can see a candle on a clear
night up to 30 miles away! cells of the inner ear) can detect the tick
of a clock 20 feet away (Galanter, 1962). It is also possible for us to get messages that are presented below the
threshold for conscious awareness—these are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the
brain: this is an absolute threshold. A message below that threshold is
said to be subliminal: we receive it, but we are not consciously aware of
it. Therefore, the message is sensed, but for whatever reason, it has not
been selected for processing in working or short-term memory. Over the
years there has been a great deal of speculation about the use of subliminal messages in advertising, rock music, and self-help audio programs. Research evidence shows that in laboratory settings, people can
process and respond to information outside of awareness. But this does
not mean that we obey these messages like zombies; in fact, hidden
messages have little e ect on behavior outside the laboratory (KunstWilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin,
Legrain, & Gobancé, 2009; Loersch, Durso, & Petty, 2013). DIG DEEPER: UNCONSCIOUS PERCEPTION These days, most scienti c
research on unconscious
processes is aimed at showing that people do not need
consciousness for certain
psychological processes or
behaviors. One such example is attitude formation. The
most basic process of attitude formation is through
mere exposure (Zajonc,
1968). Merely perceiving a
stimulus repeatedly, such as
a brand on a billboard one Figure 2. Priming can be used
to improve intellectual test
performance.
Research
subjects primed with the
stereotype of a professor – a
sort of intellectual role model –
outperformed those primed
with
an
anti-intellectual
stereotype. [Photo: Jeremy
Wilburn] passes every day or a song … 4/20 4/12/2021 Sensation and Perception | Introduction to Psychology that is played on the radio frequently, renders it more positive.
Interestingly, mere exposure does not require conscious
awareness of the object of an attitude. In fact, mere-exposure
e ects occur even when novel stimuli are presented sublimi- nally for extremely brief durations (e.g., Kunst-Wilson & Zajonc,
1980). Intriguingly, in such subliminal mere-exposure experiments, participants indicate a preference for, or a positive attitude towards, stimuli they do not consciously remember being
exposed to.Another example of modern research on unconscious processes is research on priming. Priming generally relies on supraliminal stimuli, which means that the messaging
may occur out of awareness, but it is still perceived, unlike
subliminal messaging. Supraliminal messages are be perceived by the conscious mind. For example, in one study,
shoppers listened to either French or German music (the
supraliminal messaging) while buying wine, and sales originating from either country were higher when music from that
same country was played overhead.[1]In a well-known experiment by a research team led by the American psychologist
John Bargh (Bargh, Chen, & Burrows, 1996), half the participants were primed with the stereotype of the elderly by doing
a language task (they had to make sentences on the basis of
lists of words). These lists contained words commonly associated with the elderly (e.g., “old,” “bingo,” “walking stick,” “Florida”). The remaining participants received a language task in
which the critical words were replaced by words not related to
the elderly. After participants had nished they were told the
experiment was over, but they were secretly monitored to see
how long they took to walk to the nearest elevator. The primed
participants took signi cantly longer. That is, after being exposed to words typically associated with being old, they behaved in line with the stereotype of old people: being
slow.Such priming e ects have been shown in other domains
as well. For example, Dijksterhuis and van Knippenberg (1998)
demonstrated that priming can improve intellectual performance. They asked their participants to answer 42 general
knowledge questions taken from the game Trivial Pursuit. Under normal conditions, participants answered about 50% of the
questions correctly. However, participants primed with the … 5/20 4/12/2021 Sensation and Perception | Introduction to Psychology stereotype of professors—who are by most people seen as intelligent—managed to answer 60% of the questions correctly.
Conversely, performance of participants primed with the
“dumb” stereotype of hooligans dropped to 40%. Both of
these studies have had di cult times replicating, so it is worth
noting that the conclusions reached may not be as powerful as
originally reported. Absolute thresholds are generally measured under incredibly controlled
conditions in situations that are optimal for sensitivity. Sometimes, we
are more interested in how much di erence in stimuli is required to detect a di erence between them. This is known as the just noticeable
di erence (jnd) or di erence threshold. Unlike the absolute threshold, the di erence threshold changes depending on the stimulus intensity.
As an example, imagine yourself in a very dark movie theater. If an audience member were to receive a text message on her cell phone which
caused her screen to light up, chances are that many people would notice the change in illumination in the theater. However, if the same thing
happened in a brightly lit arena during a basketball game, very few people would notice. The cell phone brightness does not change, but its
ability to be detected as a change in illumination varies dramatically between the two contexts. Ernst Weber proposed this theory of change in
di erence threshold in the 1830s, and it has become known as Weber’s
law: The di erence threshold is a constant fraction of the original stimu- lus, as the example illustrates. It is the idea that bigger stimuli require
larger di erences to be noticed. For example, it will be much harder for
your friend to reliably tell the di erence between 10 and 11 lbs. (or 5 versus 5.5 kg) than it is for 1 and 2 lbs. TRY IT … 6/20 4/12/2021 Sensation and Perception | Introduction to Psychology ________ refers to the minimum amount of
stimulus energy required to be detected 50% of
the time.
Absolute threshold
Difference threshold
Just noticeable difference
Transduction
Check Answer ________ involves the conversion of sensory
stimulus energy into neural impulses.
Inattentional blindness
Difference threshold
Sensory adaptation
Transduction
Check Answer … 7/20 4/12/2021 Sensation and Perception | Introduction to Psychology Please generate a novel example of how just
noticeable difference can change as a function of
stimulus intensity.
Write your essay response here Check Answer THINK IT OVER Think about a time when you failed to notice something
around you because your attention was focused elsewhere. If
someone pointed it out, were you surprised that you hadn’t
noticed it right away? Perception
While our sensory receptors are constantly collecting information from
the environment, it is ultimately how we interpret that information that
a ects how we interact with the world. Perception refers to the way sensory information is organized, interpreted, and consciously experienced.
Perception involves both bottom-up and top-down processing. Bottomup processing refers to the fact that perceptions are built from sensory input. On the other hand, how we interpret those sensations is in u- … 8/20 4/12/2021 Sensation and Perception | Introduction to Psychology enced by our available knowledge, our experiences, and our thoughts.
This is called top-down processing.
Look at the shape in Figure 3 below. Seen alone, your brain engages in
bottom-up processing. There are two thick vertical lines and three thin
horizontal lines. There is no context to give it a speci c meaning, so
there is no top-down processing involved. Figure 3. What is
this image? Without
any context, you
must use bottomup processing. Now, look at the same shape in two di erent contexts. Surrounded by
sequential letters, your brain expects the shape to be a letter and to
complete the sequence. In that context, you perceive the lines to form
the shape of the letter “B.” Figure 4.
With top-down
processing, you use context to
give meaning to this image. Surrounded by numbers, the same shape now looks like the number
“13.” … 9/20 4/12/2021 Sensation and Perception | Introduction to Psychology Figure 5. With top-down processing, you
use context to give meaning to this
image. When given a context, your perception is driven by your cognitive expectations. Now you are processing the shape in a top-down fashion.
One way to think of this concept is that sensation is a physical process,
whereas perception is psychological. For example, upon walking into a
kitchen and smelling the scent of baking cinnamon rolls, the sensation is
the scent receptors detecting the odor of cinnamon, but the perception
may be “Mmm, this smells like the bread Grandma used to bake when
the family gathered for holidays.”
Although our perceptions are built from sensations, not all sensations result in perception. In fact, we often don’t perceive stimuli that remain relatively constant over prolonged periods of time. This is known as sensory adaptation. Imagine entering a classroom with an old analog clock. Upon rst entering the room, you can hear the ticking of the clock; as
you begin to engage in conversation with classmates or listen to your
professor greet the class, you are no longer aware of the ticking. The
clock is still ticking, and that information is still a ecting sensory receptors of the auditory system. The fact that you no longer perceive the
sound demonstrates sensory adaptation and shows that while closely
associated, sensation and perception are di erent. TRY IT … 10/20 4/12/2021 Sensation and Perception | Introduction to Psychology Decreased sensitivity to an unchanging stimulus
is known as ________.
difference threshold
inattentional blindness
transduction
sensory adaptation
Check Answer ________ occurs when sensory information is
organized, interpreted, and consciously
experienced.
sensory adaptation
sensation
perception
transduction
Check Answer Attention and Perception … 11/20 4/12/2021 Sensation and Perception | Introduction to Psychology There is another factor that a ects sensation and perception: attention.
Attention plays a signi cant role in determining what is sensed versus
what is perceived. Imagine you are at a party full of music, chatter, and
laughter. You get involved in an interesting conversation with a friend,
and you tune out all the background noise. If someone interrupted you
to ask what song had just nished playing, you would probably be unable to answer that question. WATCH IT See for yourself how inattentional blindness works by watching this selective attention test from Simons and Chabris
(1999): selective attention t…
t… One of the most interesting demonstrations of how important attention is
in determining our perception of the environment occurred in a famous
study conducted by Daniel Simons and Christopher Chabris (1999). In
this study, participants watched a video of people dressed in black and
white passing basketballs. Participants were asked to count the number
of times the team in white passed the ball. During the video, a person … 12/20 4/12/2021 Sensation and Perception | Introduction to Psychology dressed in a black gorilla costume walks among the two teams. You
would think that someone would notice the gorilla, right? Nearly half of
the people who watched the video didn’t notice the gorilla at all, despite
the fact that he was clearly visible for nine seconds. Because participants were so focused on the number of times the white team was passing the ball, they completely tuned out other visual information. Failure
to notice something that is completely visible because of a lack of attention is called inattentional blindness.
In a similar experiment, researchers tested inattentional blindness by
asking participants to observe images moving across a computer
screen. They were instructed to focus on either white or black objects,
disregarding the other color. When a red cross passed across the
screen, about one third of subjects did not notice it (Most, Simons,
Scholl, & Chabris, 2000). LINK TO LEARNING Read more on inattentional blindness at the Noba Project
website. Motivations,
Expectations, and
Perception
Motivation can also a ect perception. Have you ever been expecting a really important phone
call and, while taking a shower,
you think you hear the phone
ringing, only to discover that it is
not? If so, then you have experienced how motivation to detect a Figure 6. Nearly one third of
participants in a study did not notice
that a red cross passed on the
screen because their attention was
focused on the black or white
gures. (credit: Cory Zanker) meaningful stimulus can shift our
ability to discriminate between a true sensory stimulus and background … 13/20 4/12/2021 Sensation and Perception | Introduction to Psychology noise. The ability to identify a stimulus when it is embedded in a distracting background is called signal detection theory. This might also explain
why a mother is awakened by a quiet murmur from her baby but not by
other sounds that occur while she is asleep. Signal detection theory has
practical applications, such as increasing air tra c controller accuracy.
Controllers need to be able to detect planes among many signals (blips)
that appear on the radar screen and follow those planes as they move
through the sky. In fact, the original work of the researcher who developed signal detection theory was focused on improving the sensitivity of
air tra c controllers to plane blips (Swets, 1964).
Our perceptions can also be a ected by our beliefs, values, prejudices,
expectations, and life experiences. As you will see later in this module,
individuals who are deprived of the experience of binocular vision during
critical periods of development have trouble perceiving depth (Fawcett,
Wang, & Birch, 2005). The shared experiences of people within a given
cultural context can have pronounced e ects on perception. For example, Marshall Segall, Donald Campbell, and Melville Herskovits (1963)
published the results of a multinational study in which they demonstrated that individuals from Western cultures were more prone to experience certain types of visual illusions than individuals from non-Western
cultures, and vice versa. One such illusion that Westerners were more
likely to experience was the Müller-Lyer illusion: the lines appear to be
di erent lengths, but they are actually the same length. Figure 7. In the Müller-Lyer illusion, lines appear to be di erent lengths
although they are identical. (a) Arrows at the ends of lines may make the line
on the right appear longer, although the lines are the same length. (b) When … 14/20 4/12/2021 Sensation and Perception | Introduction to Psychology applied to a three-dimensional image, the line on the right again may
appear longer although both black lines are the same length. These perceptual di erences were consistent with di erences in the
types of environmental features experienced on a regular basis by people in a given cultural context. People in Western cultures, for example,
have a perceptual context of buildings with straight lines, what Segall’s
study called a carpentered world (Segall et al., 1966). In contrast, people
from certain non-Western cultures with an uncarpentered view, such as
the Zulu of South Africa, whose villages are made up of round huts arranged in circles, are less susceptible to this illusion (Segall et al., 1999).
It is not just vision that is a ected by cultural factors. Indeed, research
has demonstrated that the ability to identify an odor, and rate its pleasantness and its intensity, varies cross-culturally (Ayabe-Kanamura, Saito,
Distel, Martínez-Gómez, & Hudson, 1998).
Children described as thrill seekers are more likely to show taste preferences for intense sour avors (Liem, Westerbeek, Wolterink, Kok, & de
Graaf, 2004), which suggests that basic aspects of personality might affect perception. Furthermore, individuals who hold positive attitudes toward reduced-fat foods are more likely to rate foods labeled as reduced
fat as tasting better than people who have less positive attitudes about
these products (Aaron, Mela, & Evans, 1994). WATCH IT Review the di erences between sensation and perception in
this CrashCourse Psychology video: … 15/20 4/12/2021 Sensation and Perception | Introduction to Psychology Sensation and Perception: Crash Course Ps…
Ps… TRY IT Failure to notice something that is completely
visible because of a lack of attention is called
________.
sensory adaptation
transduction
difference threshold
inattentional blindness
Check Answer … 16/20 4/12/2021 Sensation and Perception | Int...
View
Full Document
