Sensation and Perception - Book Summary
Summary of the book Sensation and Perception by Wolfe et al., fifth edition.
Written by Vivianne Streefkerk, Utrecht University, 2019-2020.
Inhoudsopgave
Sensation and Perception.............................................................................................................................. 4
Chapter 1 - Introduction......................................................................................................................................4
Sensation and Perception...............................................................................................................................4
Thresholds and the Dawn of Psychophysics...................................................................................................4
Sensory Neuroscience and the Biology of Perception....................................................................................6
Development over the Life Span....................................................................................................................9
Sensation and Perception............................................................................................................................ 10
Chapter 2 – The First Steps in Vision: From Light to Neural Signals.................................................................10
A Little Light Physics......................................................................................................................................10
Eyes That Capture Light................................................................................................................................10
Dark and Light Adaptation............................................................................................................................12
Retinal Information Processing.....................................................................................................................13
Sensation and Perception............................................................................................................................ 16
Chapter 3 – Spatial Vision: From Spots to Stripes.............................................................................................16
Visual Acuity: Oh Say, Can You See?.............................................................................................................16
Retinal Ganglion Cells and Stripes................................................................................................................17
The Lateral Geniculate Nucleus....................................................................................................................17
The Striate Cortex.........................................................................................................................................18
Receptive Fields in the Striate Cortex...........................................................................................................19
Columns and Hypercolumns.........................................................................................................................20
Selective Adaptation: The Psychologist’s Electrode.....................................................................................21
Development of Vision.................................................................................................................................22
Sensation and Perception............................................................................................................................ 22
Chapter 4 – Perceiving and Recognizing Objects..............................................................................................22
From Simple Lines and Edges to Properties of Objects................................................................................22
What and Where Pathways..........................................................................................................................22
The Problems of Perceiving and Recognizing Objects..................................................................................23
Mid-level Vision............................................................................................................................................23
Object Recognition.......................................................................................................................................26
Sensation and Perception............................................................................................................................ 28
Chapter 5 – The Perception of Colour...............................................................................................................28
Basic Principles of Colour Perception...........................................................................................................28
Step 1: Colour Detection...............................................................................................................................28
Step 2: Colour Discrimination.......................................................................................................................28
, Step 3: Colour Appearance...........................................................................................................................29
Individual Differences in Colour Perception.................................................................................................30
From the Colour of Lights to a World of Colour...........................................................................................30
What is Colour Vision Good For?..................................................................................................................31
Sensation and Perception............................................................................................................................ 32
Chapter 6 – Space Perception and Binocular Vision..........................................................................................32
Monocular Cues to Three-Dimensional Space.............................................................................................32
Triangulation Cues to Three-Dimensional Space..........................................................................................33
Binocular Vision and Stereopsis....................................................................................................................33
Combining Depth Cues.................................................................................................................................34
Development of Binocular Vision and Stereopsis........................................................................................35
Sensation and Perception............................................................................................................................ 36
Chapter 7 – Attention and Scene Perception....................................................................................................36
Selection in Space.........................................................................................................................................36
Visual Search.................................................................................................................................................36
Attending in Time: RSVP and the Attentional Blink......................................................................................37
The Physiological Basis of Attention.............................................................................................................37
Disorders of Visual Attention........................................................................................................................38
Perceiving and Understanding Scenes..........................................................................................................38
Sensation and Perception............................................................................................................................ 40
Chapter 8 – Visual Motion Perception..............................................................................................................40
Motion Aftereffects......................................................................................................................................40
Computation of Visual Motion.....................................................................................................................40
Using Motion Information............................................................................................................................41
Eye Movements............................................................................................................................................41
Development of Motion Perception.............................................................................................................42
Sensation and Perception............................................................................................................................ 43
Chapter 9 – Hearing: Physiology and Psychoacoustics.....................................................................................43
What Is Sound?.............................................................................................................................................43
Basic Structure of the Mammalian Auditory System...................................................................................43
Basic Operating Characteristics of the Auditory System..............................................................................47
Hearing Loss..................................................................................................................................................48
Sensation and Perception............................................................................................................................ 49
Chapter 10 – Hearing in the Environment.........................................................................................................49
Sound Localization........................................................................................................................................49
Complex Sounds...........................................................................................................................................50
Auditory Scene Analysis................................................................................................................................50
Continuity and Restoration Effects...............................................................................................................51
Auditory Attention........................................................................................................................................51
Sensation and Perception............................................................................................................................ 52
Chapter 12 – Vestibular Sensation....................................................................................................................52
Vestibular Contributions...............................................................................................................................52
Evolutionary Development and Vestibular Sensation..................................................................................52
Modalities and Qualities of Spatial Orientation...........................................................................................52
The Vestibular Periphery..............................................................................................................................53
Spatial Orientation Perception.....................................................................................................................54
Sensory Integration.......................................................................................................................................55
Active Sensing...............................................................................................................................................55
Reflexive Vestibular Responses....................................................................................................................55
2
, Spatial Orientation Cortex............................................................................................................................56
When the Vestibular System Goes Bad........................................................................................................56
Sensation and Perception............................................................................................................................ 57
Chapter 13 – Touch...........................................................................................................................................57
Touch Physiology..........................................................................................................................................57
Sensation and Perception............................................................................................................................ 59
Chapter 15 – Taste............................................................................................................................................59
Taste versus Flavour.....................................................................................................................................59
Anatomy and Physiology of the Gustatory System......................................................................................59
The Four Basic Tastes?..................................................................................................................................60
Are There More Than Four Basic Tastes? Does It Matter?...........................................................................61
Genetic Variation in Bitter............................................................................................................................61
How Do Taste and Flavour Contribute to the Regulation of Nutrients........................................................62
The Nature of Taste Qualities.......................................................................................................................62
3
, Sensation and Perception
Chapter 1 - Introduction
Sensation and Perception
Sensation is the ability to detect a stimulus and, perhaps, to turn that detection into a
private experience.
Perception is the act of giving meaning and/or purpose to a detected sensation.
Method 1: Thresholds
o Measuring the sensitivity of our senses
Method 2: Scaling – measuring a private experience
o Are your sensory experiences the same as those of someone else?
Those experiences are called qualia: private conscious experiences of
sensation or perception (philosophy).
Method 3: Signal Detection Theory – measuring difficult decisions
o Perceptual decisions made by an expert, with real consequences.
Method 4: Sensory Neuroscience
o The ways in which sensory receptors and nerves undergird your perceptual
experience.
Method 5: Neuroimaging – an image of the mind
o Modern brain imaging techniques enable us to see traces of an experience as it
takes place in the brain.
Thresholds and the Dawn of Psychophysics
Gustav Fechner (1801-1887)
o The true founder of experimental psychology (Wilhelm Wundt started later).
o Interested in the relationship between mind and matter, which placed him in the
middle of the dualism / materialism debate.
Dualism is the idea that the mind has an existence separate from the
material world of the body.
Materialism is the idea that the only thing that exists is matter, and that all
things, including mind and consciousness, are the results of interactions
between bits of matter. The mind is what the brain does.
o He proposed to split the difference by imagining that the mind/consciousness is
present in all of nature. This is called panpsychism, the idea that the mind exists as a
property of all matter.
o After a 3-year mental breakdown (big mood) he recovered and on October 22 nd,
1850 he had a specific insight; to describe the relation between sensation (mind)
and the energy (matter) that gave rise to that sensation.
He called his methods and theory psychophysics.
Fechner was inspired by Ernst Weber (1795-1878) who was interested in touch.
o Weber tested the accuracy of our sense of touch by measuring the smallest distance
between two points that was required for a person to feel touch on two points
instead of one. Fechner called this two-point touch threshold.
o Weber tested the ability of a person to detect the difference between two weights
and found this depended greatly on the weight of the standard. He called the
difference required for detecting a change in weight the just noticeable
difference/JND/difference threshold.
4
, JNDs change in a systematic way; for virtually every measure, a constant
ratio between the change and the standard could describe the threshold of
detectable change quite well.
Fechner called these ratios Weber fractions and gave a mathematical
formula. Weber’s law states that the size of the detectable difference (ΔI) is
a constant proportion (K) of the level of the stimulus (I).
Fechner extended Weber’s law to create Fechner’s law: S=k log R , where
S is the psychological sensation and R the physical stimulus level; a principle
describing the relationship between stimulus and resulting sensation.
o An absolute threshold is the minimum amount of stimulation necessary for a person
to detect a stimulus 50% of the time.
Psychophysical Methods
o The method of constant stimuli is a psychophysical method in which many stimuli,
ranging from rarely to almost always perceivable, are presented one at a time,
multiple times. Participants respond to each presentation, saying whether they
perceive the stimulus or not.
Subtle perceptual judgments and thus threshold judgments, and other
factors, are variable. One measure is never enough.
o The method of limits is a psychophysical method in which the particular dimension
of a stimulus, or the difference between two stimuli, is varied incrementally until the
participant responds differently.
o The method of adjustment is a
method of limits in which the
participant controls the change in
stimulus. Not a commonly used
method.
Scaling Methods
o Magnitude estimation is a
psychophysical method in which
the participant assigns values
according to perceived magnitudes
of the stimuli.
The relationship between
stimulus intensity and
sensation is described by Steven’s power law: S=a I b which states that the
sensation S is related to the stimulus intensity I by an exponent n.
o A variant of the scaling method can show that different individuals can live in
different sensory worlds, even if they are exposed to the same stimuli; this method
is called cross-modality matching. Here, an observer adjusts a stimulus of one sort
to match the perceived magnitude of a stimulus of a completely different sort.
o An individual who experiences the most intense taste sensations is called a
supertaster. They also experience intense oral burn and touch sensations.
Signal Detection Theory
o The signal detection theory is a psychophysical theory that quantifies the response
of an observer to the presentation of a signal in
the presence of noise. Measures obtained from a
series of presentations are sensitivity (d’) and
criterion of the observer.
A criterion, in reference to signal
detection theory, is an internal threshold
that is set by the observer. If the internal
response is above criterion, the observer
5
, gives a positive response (I hear that), if below criterion, the observer gives a
negative response (I hear nothing).
The sensitivity, in reference to signal detection theory, is a value that
defines the ease with which an
observer can tell the difference
between the presence and absence of
a stimulus or the difference between
stimulus 1 and stimulus 2.
For a fixed value of d’, changing the
criterion changes the hits and false
alarms in predictable ways. If you plot
false alarms on the x-axis of a graph
against hits on the y-axis for different criterion values, you get a curve
known as a receiver operating characteristic (ROC) curve.
Fourier Analysis
o Joseph Fourier (1768-1830) developed analyses that help scientists to better
describe how complex sounds/motions/images can be decomposed into a set of
simpler components.
A sine wave is one of the simplest sounds (in hearing, a pure tone). The time
taken for one complete cycle of a sine wave, a wavelength, to pass a point,
is the period of the sine wave. The height of the wave is its amplitude. The
phase of the wave is its position relative to a fixed marker.
All sounds, no matter how complex, can be described as a combination of
sine waves. The process of breaking down a complex sound into individual
sine wave components is called Fourier analysis.
Images can be described as changes in light and dark across space. Images
can be broken down into components that capture how often changes from
light to dark occur over a particular region in space, called spatial
frequencies. They are defined as the number of these light/dark changes
across 1 degree of a person’s visual field. Thus the unit of spatial frequency
in vision are cycles per degree of visual angle.
Sensory Neuroscience and the Biology of Perception
Charles Darwin (1809-1882) proposed his revolutionary theory of continuity between
humans and animals in The Origin of Species and The Descent of Man.
Johannes Müller wrote the Handbook of Physiology in which he formulated the doctrine of
specific nerve energies, stating that the nature of a sensation depends on which sensory
fibres are stimulated, rather than how they are stimulated. We cannot be directly aware of
the world itself, but only of the activity in our nerves.
The cranial nerves leading into and out of the skull illustrate the doctrine of specific nerve
energies.
o Three of the cranial nerves, olfactory (I), optic (II), and vestibulocochlear (VIII), are
exclusively dedicated to sensory information.
The vestibulocochlear nerve serves two sensory modalities: our sense of
equilibrium and hearing.
o Three more cranial nerves, oculomotor (III), trochlear (IV), and abducens (VI), are
dedicated to muscles that move the eyes.
o The other six cranial nerves are either motor or sensory and motor together.
As processing of sensory stimuli extends beyond primary brain areas, the cortex often
becomes polysensory, meaning that information from more than one sense is being
combined in some manner.
Vitalism is the idea that there is a force in life that is distinct from physical entities.
6
,7
, Neuronal Connections
o The junction between the axon of one neuron and the dendrite of the next that
permits information transfer is called a synapse.
o The molecules that travel from the axon across the synapse to bind to receptor
molecules on the dendrite of the next neuron are called neurotransmitters.
Individual neurons are selective with respect to which neurotransmitters
excite them or inhibit them from firing.
Neural Firing: The Action Potential
o Neural firing is actually electrochemical. Voltage increases along the axon are caused
by changes in the membrane of the neuron that permit positively charged sodium
ions (Na+) to rush into the axon from the outside. Then the membrane quickly
changes again, pushing positively charged potassium ions (K +) out of the axon,
restoring the neuron to its initial resting voltage.
Neuroimaging
o Neuroimaging is a set of methods that generate images of the structure and/or
brain function of the brain. These methods allow us to examine the brain in living,
behaving humans.
o Electroencephalography (EEG) measures electrical activity through dozens of
electrodes placed on the scalp.
EEG does not allow researchers to learn what individual neurons are doing
or to pinpoint the exact area of neural activity, but it can be used to roughly
localize whole populations of neurons and to measure their activity with
excellent temporal accuracy.
o The average of many EEG recordings at the moment of a presented stimulus gives an
event-related potential (ERP), which is a measure of electrical activity from a
subpopulation of neurons in response to a particular stimulus.
o Magnetoencephalography (MEG) is a technique similar to EEG that measures
changes in magnetic activity across populations of many neurons in the brain.
It maintains much of the timing of populations of neurons while providing a
better idea of where in the brain neurons are most active. MEG takes
advantage of the fact that neurons make very small changes in their local
magnetic fields and small electrical changes.
o Computed tomography (CT) is an
imaging technology that uses X-rays to
create images of slices through
volumes of material.
It sends many X-rays through
the head and measures how
much emitted energy is lost on
the way, being absorbed by
tissue. Dense tissue absorbs
more energy. This way it gives
a 3D picture of the head.
8
Summary of the book Sensation and Perception by Wolfe et al., fifth edition.
Written by Vivianne Streefkerk, Utrecht University, 2019-2020.
Inhoudsopgave
Sensation and Perception.............................................................................................................................. 4
Chapter 1 - Introduction......................................................................................................................................4
Sensation and Perception...............................................................................................................................4
Thresholds and the Dawn of Psychophysics...................................................................................................4
Sensory Neuroscience and the Biology of Perception....................................................................................6
Development over the Life Span....................................................................................................................9
Sensation and Perception............................................................................................................................ 10
Chapter 2 – The First Steps in Vision: From Light to Neural Signals.................................................................10
A Little Light Physics......................................................................................................................................10
Eyes That Capture Light................................................................................................................................10
Dark and Light Adaptation............................................................................................................................12
Retinal Information Processing.....................................................................................................................13
Sensation and Perception............................................................................................................................ 16
Chapter 3 – Spatial Vision: From Spots to Stripes.............................................................................................16
Visual Acuity: Oh Say, Can You See?.............................................................................................................16
Retinal Ganglion Cells and Stripes................................................................................................................17
The Lateral Geniculate Nucleus....................................................................................................................17
The Striate Cortex.........................................................................................................................................18
Receptive Fields in the Striate Cortex...........................................................................................................19
Columns and Hypercolumns.........................................................................................................................20
Selective Adaptation: The Psychologist’s Electrode.....................................................................................21
Development of Vision.................................................................................................................................22
Sensation and Perception............................................................................................................................ 22
Chapter 4 – Perceiving and Recognizing Objects..............................................................................................22
From Simple Lines and Edges to Properties of Objects................................................................................22
What and Where Pathways..........................................................................................................................22
The Problems of Perceiving and Recognizing Objects..................................................................................23
Mid-level Vision............................................................................................................................................23
Object Recognition.......................................................................................................................................26
Sensation and Perception............................................................................................................................ 28
Chapter 5 – The Perception of Colour...............................................................................................................28
Basic Principles of Colour Perception...........................................................................................................28
Step 1: Colour Detection...............................................................................................................................28
Step 2: Colour Discrimination.......................................................................................................................28
, Step 3: Colour Appearance...........................................................................................................................29
Individual Differences in Colour Perception.................................................................................................30
From the Colour of Lights to a World of Colour...........................................................................................30
What is Colour Vision Good For?..................................................................................................................31
Sensation and Perception............................................................................................................................ 32
Chapter 6 – Space Perception and Binocular Vision..........................................................................................32
Monocular Cues to Three-Dimensional Space.............................................................................................32
Triangulation Cues to Three-Dimensional Space..........................................................................................33
Binocular Vision and Stereopsis....................................................................................................................33
Combining Depth Cues.................................................................................................................................34
Development of Binocular Vision and Stereopsis........................................................................................35
Sensation and Perception............................................................................................................................ 36
Chapter 7 – Attention and Scene Perception....................................................................................................36
Selection in Space.........................................................................................................................................36
Visual Search.................................................................................................................................................36
Attending in Time: RSVP and the Attentional Blink......................................................................................37
The Physiological Basis of Attention.............................................................................................................37
Disorders of Visual Attention........................................................................................................................38
Perceiving and Understanding Scenes..........................................................................................................38
Sensation and Perception............................................................................................................................ 40
Chapter 8 – Visual Motion Perception..............................................................................................................40
Motion Aftereffects......................................................................................................................................40
Computation of Visual Motion.....................................................................................................................40
Using Motion Information............................................................................................................................41
Eye Movements............................................................................................................................................41
Development of Motion Perception.............................................................................................................42
Sensation and Perception............................................................................................................................ 43
Chapter 9 – Hearing: Physiology and Psychoacoustics.....................................................................................43
What Is Sound?.............................................................................................................................................43
Basic Structure of the Mammalian Auditory System...................................................................................43
Basic Operating Characteristics of the Auditory System..............................................................................47
Hearing Loss..................................................................................................................................................48
Sensation and Perception............................................................................................................................ 49
Chapter 10 – Hearing in the Environment.........................................................................................................49
Sound Localization........................................................................................................................................49
Complex Sounds...........................................................................................................................................50
Auditory Scene Analysis................................................................................................................................50
Continuity and Restoration Effects...............................................................................................................51
Auditory Attention........................................................................................................................................51
Sensation and Perception............................................................................................................................ 52
Chapter 12 – Vestibular Sensation....................................................................................................................52
Vestibular Contributions...............................................................................................................................52
Evolutionary Development and Vestibular Sensation..................................................................................52
Modalities and Qualities of Spatial Orientation...........................................................................................52
The Vestibular Periphery..............................................................................................................................53
Spatial Orientation Perception.....................................................................................................................54
Sensory Integration.......................................................................................................................................55
Active Sensing...............................................................................................................................................55
Reflexive Vestibular Responses....................................................................................................................55
2
, Spatial Orientation Cortex............................................................................................................................56
When the Vestibular System Goes Bad........................................................................................................56
Sensation and Perception............................................................................................................................ 57
Chapter 13 – Touch...........................................................................................................................................57
Touch Physiology..........................................................................................................................................57
Sensation and Perception............................................................................................................................ 59
Chapter 15 – Taste............................................................................................................................................59
Taste versus Flavour.....................................................................................................................................59
Anatomy and Physiology of the Gustatory System......................................................................................59
The Four Basic Tastes?..................................................................................................................................60
Are There More Than Four Basic Tastes? Does It Matter?...........................................................................61
Genetic Variation in Bitter............................................................................................................................61
How Do Taste and Flavour Contribute to the Regulation of Nutrients........................................................62
The Nature of Taste Qualities.......................................................................................................................62
3
, Sensation and Perception
Chapter 1 - Introduction
Sensation and Perception
Sensation is the ability to detect a stimulus and, perhaps, to turn that detection into a
private experience.
Perception is the act of giving meaning and/or purpose to a detected sensation.
Method 1: Thresholds
o Measuring the sensitivity of our senses
Method 2: Scaling – measuring a private experience
o Are your sensory experiences the same as those of someone else?
Those experiences are called qualia: private conscious experiences of
sensation or perception (philosophy).
Method 3: Signal Detection Theory – measuring difficult decisions
o Perceptual decisions made by an expert, with real consequences.
Method 4: Sensory Neuroscience
o The ways in which sensory receptors and nerves undergird your perceptual
experience.
Method 5: Neuroimaging – an image of the mind
o Modern brain imaging techniques enable us to see traces of an experience as it
takes place in the brain.
Thresholds and the Dawn of Psychophysics
Gustav Fechner (1801-1887)
o The true founder of experimental psychology (Wilhelm Wundt started later).
o Interested in the relationship between mind and matter, which placed him in the
middle of the dualism / materialism debate.
Dualism is the idea that the mind has an existence separate from the
material world of the body.
Materialism is the idea that the only thing that exists is matter, and that all
things, including mind and consciousness, are the results of interactions
between bits of matter. The mind is what the brain does.
o He proposed to split the difference by imagining that the mind/consciousness is
present in all of nature. This is called panpsychism, the idea that the mind exists as a
property of all matter.
o After a 3-year mental breakdown (big mood) he recovered and on October 22 nd,
1850 he had a specific insight; to describe the relation between sensation (mind)
and the energy (matter) that gave rise to that sensation.
He called his methods and theory psychophysics.
Fechner was inspired by Ernst Weber (1795-1878) who was interested in touch.
o Weber tested the accuracy of our sense of touch by measuring the smallest distance
between two points that was required for a person to feel touch on two points
instead of one. Fechner called this two-point touch threshold.
o Weber tested the ability of a person to detect the difference between two weights
and found this depended greatly on the weight of the standard. He called the
difference required for detecting a change in weight the just noticeable
difference/JND/difference threshold.
4
, JNDs change in a systematic way; for virtually every measure, a constant
ratio between the change and the standard could describe the threshold of
detectable change quite well.
Fechner called these ratios Weber fractions and gave a mathematical
formula. Weber’s law states that the size of the detectable difference (ΔI) is
a constant proportion (K) of the level of the stimulus (I).
Fechner extended Weber’s law to create Fechner’s law: S=k log R , where
S is the psychological sensation and R the physical stimulus level; a principle
describing the relationship between stimulus and resulting sensation.
o An absolute threshold is the minimum amount of stimulation necessary for a person
to detect a stimulus 50% of the time.
Psychophysical Methods
o The method of constant stimuli is a psychophysical method in which many stimuli,
ranging from rarely to almost always perceivable, are presented one at a time,
multiple times. Participants respond to each presentation, saying whether they
perceive the stimulus or not.
Subtle perceptual judgments and thus threshold judgments, and other
factors, are variable. One measure is never enough.
o The method of limits is a psychophysical method in which the particular dimension
of a stimulus, or the difference between two stimuli, is varied incrementally until the
participant responds differently.
o The method of adjustment is a
method of limits in which the
participant controls the change in
stimulus. Not a commonly used
method.
Scaling Methods
o Magnitude estimation is a
psychophysical method in which
the participant assigns values
according to perceived magnitudes
of the stimuli.
The relationship between
stimulus intensity and
sensation is described by Steven’s power law: S=a I b which states that the
sensation S is related to the stimulus intensity I by an exponent n.
o A variant of the scaling method can show that different individuals can live in
different sensory worlds, even if they are exposed to the same stimuli; this method
is called cross-modality matching. Here, an observer adjusts a stimulus of one sort
to match the perceived magnitude of a stimulus of a completely different sort.
o An individual who experiences the most intense taste sensations is called a
supertaster. They also experience intense oral burn and touch sensations.
Signal Detection Theory
o The signal detection theory is a psychophysical theory that quantifies the response
of an observer to the presentation of a signal in
the presence of noise. Measures obtained from a
series of presentations are sensitivity (d’) and
criterion of the observer.
A criterion, in reference to signal
detection theory, is an internal threshold
that is set by the observer. If the internal
response is above criterion, the observer
5
, gives a positive response (I hear that), if below criterion, the observer gives a
negative response (I hear nothing).
The sensitivity, in reference to signal detection theory, is a value that
defines the ease with which an
observer can tell the difference
between the presence and absence of
a stimulus or the difference between
stimulus 1 and stimulus 2.
For a fixed value of d’, changing the
criterion changes the hits and false
alarms in predictable ways. If you plot
false alarms on the x-axis of a graph
against hits on the y-axis for different criterion values, you get a curve
known as a receiver operating characteristic (ROC) curve.
Fourier Analysis
o Joseph Fourier (1768-1830) developed analyses that help scientists to better
describe how complex sounds/motions/images can be decomposed into a set of
simpler components.
A sine wave is one of the simplest sounds (in hearing, a pure tone). The time
taken for one complete cycle of a sine wave, a wavelength, to pass a point,
is the period of the sine wave. The height of the wave is its amplitude. The
phase of the wave is its position relative to a fixed marker.
All sounds, no matter how complex, can be described as a combination of
sine waves. The process of breaking down a complex sound into individual
sine wave components is called Fourier analysis.
Images can be described as changes in light and dark across space. Images
can be broken down into components that capture how often changes from
light to dark occur over a particular region in space, called spatial
frequencies. They are defined as the number of these light/dark changes
across 1 degree of a person’s visual field. Thus the unit of spatial frequency
in vision are cycles per degree of visual angle.
Sensory Neuroscience and the Biology of Perception
Charles Darwin (1809-1882) proposed his revolutionary theory of continuity between
humans and animals in The Origin of Species and The Descent of Man.
Johannes Müller wrote the Handbook of Physiology in which he formulated the doctrine of
specific nerve energies, stating that the nature of a sensation depends on which sensory
fibres are stimulated, rather than how they are stimulated. We cannot be directly aware of
the world itself, but only of the activity in our nerves.
The cranial nerves leading into and out of the skull illustrate the doctrine of specific nerve
energies.
o Three of the cranial nerves, olfactory (I), optic (II), and vestibulocochlear (VIII), are
exclusively dedicated to sensory information.
The vestibulocochlear nerve serves two sensory modalities: our sense of
equilibrium and hearing.
o Three more cranial nerves, oculomotor (III), trochlear (IV), and abducens (VI), are
dedicated to muscles that move the eyes.
o The other six cranial nerves are either motor or sensory and motor together.
As processing of sensory stimuli extends beyond primary brain areas, the cortex often
becomes polysensory, meaning that information from more than one sense is being
combined in some manner.
Vitalism is the idea that there is a force in life that is distinct from physical entities.
6
,7
, Neuronal Connections
o The junction between the axon of one neuron and the dendrite of the next that
permits information transfer is called a synapse.
o The molecules that travel from the axon across the synapse to bind to receptor
molecules on the dendrite of the next neuron are called neurotransmitters.
Individual neurons are selective with respect to which neurotransmitters
excite them or inhibit them from firing.
Neural Firing: The Action Potential
o Neural firing is actually electrochemical. Voltage increases along the axon are caused
by changes in the membrane of the neuron that permit positively charged sodium
ions (Na+) to rush into the axon from the outside. Then the membrane quickly
changes again, pushing positively charged potassium ions (K +) out of the axon,
restoring the neuron to its initial resting voltage.
Neuroimaging
o Neuroimaging is a set of methods that generate images of the structure and/or
brain function of the brain. These methods allow us to examine the brain in living,
behaving humans.
o Electroencephalography (EEG) measures electrical activity through dozens of
electrodes placed on the scalp.
EEG does not allow researchers to learn what individual neurons are doing
or to pinpoint the exact area of neural activity, but it can be used to roughly
localize whole populations of neurons and to measure their activity with
excellent temporal accuracy.
o The average of many EEG recordings at the moment of a presented stimulus gives an
event-related potential (ERP), which is a measure of electrical activity from a
subpopulation of neurons in response to a particular stimulus.
o Magnetoencephalography (MEG) is a technique similar to EEG that measures
changes in magnetic activity across populations of many neurons in the brain.
It maintains much of the timing of populations of neurons while providing a
better idea of where in the brain neurons are most active. MEG takes
advantage of the fact that neurons make very small changes in their local
magnetic fields and small electrical changes.
o Computed tomography (CT) is an
imaging technology that uses X-rays to
create images of slices through
volumes of material.
It sends many X-rays through
the head and measures how
much emitted energy is lost on
the way, being absorbed by
tissue. Dense tissue absorbs
more energy. This way it gives
a 3D picture of the head.
8
