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Module 1.6a

Transduction

1.6-1 Which three steps are basic to all of our sensory systems?
1.6-1 Which thr ee steps ar e basic to all of our sensory systems? TEACH 1.6-1
Our sensory systems perform the amazing feat of transduction : They convert outside Active Learning

energy into a form our brain can use. Vision processes light energy. Hearing processes sound (15 minutes) Understanding the three
waves. All of our senses
steps of transduction is important
• receive sensory stimulation, often using specialized receptor cells,
• transform that stimulation into neural impulses, and because these steps apply to all of the
• deliver the neural information to our brain. senses covered in Unit 1. To ensure
Transduction is rather like translation — in this case, of a physical energy such as light that students understand these steps,
waves into the brain’s electrochemical language. Psychophysics studies the relation- have them engage in a Drawing for
ships between the physical energy we can detect and its effects on our psychological Understanding activity. Ask them
experiences. transduction conversion of one
Later in this module, we’ll focus on specific sensory systems. How do we see? Hear? form of energy into another. In to draw, with no words included, a
Feel pain? Taste? Smell? Keep our balance? In each case, a sensory system receives, trans- sensation, the transforming of picture that illustrates the principle of
physical energy, such as sights,
forms, and delivers the information to our brain. And our senses work together. sounds, and smells, into neural transduction in an analogous applica-
Let’s first explore some strengths and weaknesses in our ability to detect and interpret impulses the brain can interpret.
stimuli in the vast sea of energy around us. psychophysics the study tion outside the senses or the brain.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
of relationships between the Share and compare drawings to clear
Thresholds physical characteristics of stimuli, up any misunderstandings. Tell stu-
such as their intensity, and our
psychological experience of them. dents to look out for these three steps
and
absolute thresholds
1.6-2 How do absolute thresholds and difference thresholds differ?
1.6-2
How do
How do
absolute thresholds
How do

fer?
dif
difference thresholds

absolute threshold the as you move through the unit.
Copyright © Bedford, Freeman & Worth Publishers.
minimum stimulus energy
At this moment, each of us is being struck by X-rays and radio waves, ultraviolet and infra- needed to detect a particular
red light, and sound waves of very high and very low frequencies. To all of these we are blind stimulus 50 percent of the time.
and deaf. In contrast, other animals with differing needs detect a world that lies beyond our signal detection theory a
experience. Migrating birds stay on course aided by an internal magnetic compass. Bats and theory predicting how and PRACTICE
dolphins locate their prey using sonar, bouncing echoing sound off objects. Bees navigate when we detect the presence
on cloudy days by detecting invisible (to us) polarized light. of a faint stimulus ( signal ) Research Methods & Design
amid background stimulation
Our senses open the shades just a crack, allowing us a restricted awareness of this vast ( noise ); assumes there is no
sea of energy. But for our needs, this is enough. single absolute threshold and (SP 2)
that detection depends partly (20 minutes) Students should be
Absolute Thresholds on a person’s experience,
expectations, motivation, and able to identify the best research
To some kinds of stimuli we are exquisitely sensitive. Standing atop a mountain on an alertness. method to use for a specific
utterly dark, clear night, most of us could see a candle flame atop another mountain 30 miles
(nearly 50 kilometers) away. We could feel the wing of a bee falling on our cheek. We could research question. Have them,
smell a single drop of perfume in a three-room apartment ( Galanter, 1962 ). in small groups, come up with a
German scientist and philosopher Gustav Fechner (1801–1887) studied the edge of SPOTLIGHT ON: research question appropriate

.

our awareness of these faint stimuli, which he called an absolute threshold To test your Gustav Fechner
absolute threshold for sounds, a hearing specialist would send tones, at varying levels, into for each of the basic methods.
each of your ears and record whether you could hear each tone ( Figure 1.6-2 ). The test For example, what is the average

results would show the point where, for any sound frequency, half the time you could detect absolute threshold for sound for
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the sound and half the time you could not. That 50-50 point would define your absolute AP Science Practice
threshold. Research students in this class (descriptive)?
Detecting a weak stimulus, or signal (such as a hearing-test tone), depends not only on Depending on their research Does age predict absolute thresh-
its strength but also on our psychological state — our experience, expectations, motivation, question, signal detection theorists old (correlational)? Does being in
and alertness. Signal detection theory predicts when we will detect weak signals (mea- might use non-experimental or
sured as our ratio of “hits” to “false alarms”). Signal detection theorists seek to understand experimental methods. Could a loud versus quiet environment
you identify the difference? These
why people respond differently to the same stimuli, and why the same person’s reactions methods are described in Unit 0 . affect absolute threshold (experi-
vary as circumstances change.
mental)? This task is likely to be dif-
Sensation: Basic Concepts Module 1.6a 117 ficult for students, but it will provide
a thorough review of the research
methods they will be expected to
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TEACH 1.6-2
03_myersAPpsychology4e_28116_ch01_002_163.indd 117 that are very similar. The participant 15/12/23 9:24 AM know for the AP exam.
Enrichment responds “yes” if the stimuli are perceived
or if a difference exists, or “no” if nothing is
Explain to students that Gustav Fechner perceived or different. TEACH 1.6-2
(1801–1887) developed the following three • Method of adjustment. Adjust a comparison
methods of experimental measurement used stimulus until it appears identical to the Teaching Tip
to study sensory phenomenon: Students may wonder why anyone
standard stimulus. Every error is recorded, cares about signal detection theory.
• Method of limits. Begin with a minimal and after many trials the average error is Inform them that research in this area
stimulus and increase it until the participant computed. It, too, provides a measure of is especially important to fields where
can perceive it. This method helps determine just noticeable difference. attention to detail amid environmental
the absolute threshold. distractions is paramount, such as
• Method of right and wrong cases. Present air traffic control, security screening,
identical stimuli repeatedly—either single law enforcement, and even ordinary
stimuli at the threshold or pairs of stimuli driving.
Sensation: Basic Concepts Module 1.6a 117
03_HammerTE4e_47547_ch01_2a_163_4pp.indd 117 07/02/24 5:26 PM