Chapter 1: Foundations
Chapter 1
Foundations
Note to Instructors: This section provides a broad overview of the main points of the
chapter.
World, Brain, and Mind (p. 2)
The field of Sensation and Perception is interdisciplinary. Content in this book is drawn from
psychology, cognitive neuroscience, physics, chemistry, neurology, neuropsychology, and
computer science.
Many of these fields obtain knowledge through experiments with humans or animals as
experimental subjects. Experimental work on living creatures is carefully monitored to conform
to ethical principles by government agencies and local institutional review boards.
The Perceptual Process (p. 3)
When we interact with the world via our sensory systems, we are reacting to some distal
stimulus. We can only do so, however, if the object being perceived gives rise to some proximal
stimulus—a physical phenomenon generated by the external object that interacts with our
,Chapter 1: Foundations
sensory receptors. An object (e.g., a friend, the distal stimulus) may reflect light absorbed by our
retinas, speak to us, generating pressure waves in the air that vibrate our eardrums, and shake our
hand, pressing against the mechanoreceptors of our skin. They may be wearing perfume, the
molecules of which waft through the air and activate our nasal epithelium. The light, pressure
waves, physical pressure, or molecules of perfume are the proximal stimuli, which either directly
(e.g., in photoreceptors of the eye) or indirectly (e.g., inner hair cells of the cochlea) evoke neural
signals in neurons, the electrically active cells of the nervous system. This process is illustrated
in Figure 1.1 (p. 4).
Information generated by the sensory receptors is referred to as bottom-up information. Our
perception of a stimulus depends also on top-down information, which includes the experiencer’s
knowledge, expectations, and prior history.
Three Main Types of Questions (p. 5)
These steps of the perceptual process (see previous section) guide three types of questions asked
by perceptual researchers. First, how does the proximal stimulus—light, pressure waves, and
airborne molecules—convey information about the distal stimulus? Second, how is that
information represented in the nervous system? In other words, how is the proximal stimulus
transduced at the sensory receptors, and how does peripheral and central nervous system activity
represent features of the stimulus—what are the neural codes? Third, how do these events relate
to someone’s experience of a stimulus? This latter category—the relationship of subjective
experience to variations in the distal stimulus—is the main question underlying psychophysics.
,Chapter 1: Foundations
How Many Senses Are There? (p. 5)
Traditionally, five senses have been described: vision, audition, olfaction, gustation, and
somatosensation. In reality, there are a host of sensory systems, including pain, proprioception,
thermoreception, balance, and—in some organisms—magnetosensation. The dividing lines are
not always clear (e.g., several subdivisions of somatosensation have been described). Table 1.1
(p. 6) provides a guide.
Evolution and Perception (p. 7)
The sensory systems of organisms have been shaped by natural selection. Researchers sometimes
choose animals for study that have particularly highly developed sensory abilities, such as the
auditory system of echolocating bats or nocturnally hunting owls.
Exploring Perception by Studying Behavior: Psychophysics (p. 8)
Beginning with the pioneering work of Gustav Fechner (author of The Elements of
Psychophysics, 1860), researchers began studying subjective experiences. Rather than use
introspective methods, psychophysicists strive for objectivity by requiring simple, well-defined
responses from subjects (e.g., binary responses like “stronger” vs. “weaker” or “stimulus
present” vs. “stimulus absent”). By measuring these responses while systematically varying the
stimulus (e.g., wavelength of light, concentration of an odorant, and weight of lifted objects),
, Chapter 1: Foundations
psychophysicists can explore relationships between variations in the physical stimulus and
people’s subjective perceptual experiences.
Using this method, psychophysicists might quantify perceptual experience in a variety of ways.
For example, they might determine the minimum intensity of a stimulus required for detection
(i.e., measurement of detection thresholds), the minimum difference in intensity (or other
parameter) of a stimulus required for it to be discriminable from another stimulus (i.e.,
measurement of difference thresholds), or determine the subjective intensity of a stimulus
relative to its physical intensity (i.e., measurement of perceptual scaling).
Absolute Threshold (p. 9)
Detection thresholds can be assessed using a variety of methods.
In the method of adjustment, the subject is given control of stimulus intensity—for example,
turning a volume knob down to the point that the subject no longer hears an auditory stimulus.
Several such trials must be averaged, as thresholds vary from trial to trial using any method.
In the method of constant stimuli, a subject reports whether a stimulus is detected over several
trials. Stimuli are prepared in advance to include a number of perithreshold intensities that are
randomly presented, and the intensity of each stimulus is presented on multiple trials. The
psychometric function that results (see Figure 1.2b, p. 10, for an example) is typically sigmoidal
rather than stair-step, indicating that there is no true absolute detection threshold—it is not the
Chapter 1
Foundations
Note to Instructors: This section provides a broad overview of the main points of the
chapter.
World, Brain, and Mind (p. 2)
The field of Sensation and Perception is interdisciplinary. Content in this book is drawn from
psychology, cognitive neuroscience, physics, chemistry, neurology, neuropsychology, and
computer science.
Many of these fields obtain knowledge through experiments with humans or animals as
experimental subjects. Experimental work on living creatures is carefully monitored to conform
to ethical principles by government agencies and local institutional review boards.
The Perceptual Process (p. 3)
When we interact with the world via our sensory systems, we are reacting to some distal
stimulus. We can only do so, however, if the object being perceived gives rise to some proximal
stimulus—a physical phenomenon generated by the external object that interacts with our
,Chapter 1: Foundations
sensory receptors. An object (e.g., a friend, the distal stimulus) may reflect light absorbed by our
retinas, speak to us, generating pressure waves in the air that vibrate our eardrums, and shake our
hand, pressing against the mechanoreceptors of our skin. They may be wearing perfume, the
molecules of which waft through the air and activate our nasal epithelium. The light, pressure
waves, physical pressure, or molecules of perfume are the proximal stimuli, which either directly
(e.g., in photoreceptors of the eye) or indirectly (e.g., inner hair cells of the cochlea) evoke neural
signals in neurons, the electrically active cells of the nervous system. This process is illustrated
in Figure 1.1 (p. 4).
Information generated by the sensory receptors is referred to as bottom-up information. Our
perception of a stimulus depends also on top-down information, which includes the experiencer’s
knowledge, expectations, and prior history.
Three Main Types of Questions (p. 5)
These steps of the perceptual process (see previous section) guide three types of questions asked
by perceptual researchers. First, how does the proximal stimulus—light, pressure waves, and
airborne molecules—convey information about the distal stimulus? Second, how is that
information represented in the nervous system? In other words, how is the proximal stimulus
transduced at the sensory receptors, and how does peripheral and central nervous system activity
represent features of the stimulus—what are the neural codes? Third, how do these events relate
to someone’s experience of a stimulus? This latter category—the relationship of subjective
experience to variations in the distal stimulus—is the main question underlying psychophysics.
,Chapter 1: Foundations
How Many Senses Are There? (p. 5)
Traditionally, five senses have been described: vision, audition, olfaction, gustation, and
somatosensation. In reality, there are a host of sensory systems, including pain, proprioception,
thermoreception, balance, and—in some organisms—magnetosensation. The dividing lines are
not always clear (e.g., several subdivisions of somatosensation have been described). Table 1.1
(p. 6) provides a guide.
Evolution and Perception (p. 7)
The sensory systems of organisms have been shaped by natural selection. Researchers sometimes
choose animals for study that have particularly highly developed sensory abilities, such as the
auditory system of echolocating bats or nocturnally hunting owls.
Exploring Perception by Studying Behavior: Psychophysics (p. 8)
Beginning with the pioneering work of Gustav Fechner (author of The Elements of
Psychophysics, 1860), researchers began studying subjective experiences. Rather than use
introspective methods, psychophysicists strive for objectivity by requiring simple, well-defined
responses from subjects (e.g., binary responses like “stronger” vs. “weaker” or “stimulus
present” vs. “stimulus absent”). By measuring these responses while systematically varying the
stimulus (e.g., wavelength of light, concentration of an odorant, and weight of lifted objects),
, Chapter 1: Foundations
psychophysicists can explore relationships between variations in the physical stimulus and
people’s subjective perceptual experiences.
Using this method, psychophysicists might quantify perceptual experience in a variety of ways.
For example, they might determine the minimum intensity of a stimulus required for detection
(i.e., measurement of detection thresholds), the minimum difference in intensity (or other
parameter) of a stimulus required for it to be discriminable from another stimulus (i.e.,
measurement of difference thresholds), or determine the subjective intensity of a stimulus
relative to its physical intensity (i.e., measurement of perceptual scaling).
Absolute Threshold (p. 9)
Detection thresholds can be assessed using a variety of methods.
In the method of adjustment, the subject is given control of stimulus intensity—for example,
turning a volume knob down to the point that the subject no longer hears an auditory stimulus.
Several such trials must be averaged, as thresholds vary from trial to trial using any method.
In the method of constant stimuli, a subject reports whether a stimulus is detected over several
trials. Stimuli are prepared in advance to include a number of perithreshold intensities that are
randomly presented, and the intensity of each stimulus is presented on multiple trials. The
psychometric function that results (see Figure 1.2b, p. 10, for an example) is typically sigmoidal
rather than stair-step, indicating that there is no true absolute detection threshold—it is not the
