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In 1984, three years after retiring from boxing, Muhammad Ali was diagnosed with
Parkinson's disease. Outside of his Hall of Fame boxing career, he played an
instrumental role in the civil rights movement and was a world-recognized advocate
raising awareness for those suffering with Parkinson’s disease. Muhammad Ali
passed away from complications of the disease on June 3, 2016, at the age of 74.
R. McPhedran/ Stringer/Hulton Archive/Getty Images
Recent studies offer an exciting direction for future efforts to repair the damaged
brain. Neuroscientists have long held that new nerve cells cannot be produced in the
adult brain. New axons and dendrites may sprout, forming new synaptic connections.
While the growth of new neurons was once considered impossible, neurogenesis
researchers have since discovered that the adult human brain does spawn new nerve
cells in the hippocampus, a structure that is important in learning and memory. This
discovery, and the possibility that neuroscientists may some day find a way to
stimulate the growth and migration of nerve cells, has led some researchers to
speculate that the human brain harbors great potential for its own repair (Doidge,
2007; Fawcett, Rosser, & Dunnett, 2001).
Thinking Like a Psychologist About Behavioral
Neuroscience
The study of the split-brain patient described at the outset of this chapter gave us
a glimpse into the fascinating and developing world of behavioral neuroscience. This
research illustrates why it is valuable to observe individuals who are exceptional in
some way and tells us that each region of the brain is involved in different
psychological processes. But as we have seen elsewhere in this chapter, researchers
use other methods as well, including powerful brain scans, to discover linkages
among the brain, the mind, and behavior. And although different areas of the brain act
as “specialists,” the healthy human brain operates as an integrated system—and has
the capacity to change as a result of usage, practice, and experience.
To this day, the human brain and nervous system remain one of the great frontiers
in science. From the trillions of tiny building blocks, consisting of axons, dendrites,
synapses, and neurotransmitters, to the structures of the brainstem, limbic system,
and cerebral cortex, there is a solid biological foundation for the study of mind and
behavior. The goal, as we’ll explore in later chapters, is to understand the links
between the human body and psychological processes that range from visual
perception to moral development, social aggression, and the health benefits of
psychotherapy.
SUMMARY
Phineas Gage’s dramatic brain injury showed that the human brain and nervous
system form an integrated system of specialized parts—the concern of behavioral
neuroscience.
The Body’s Communication Networks
The body has two communication networks: the nervous system and the
endocrine system.
The Nervous System
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The human nervous system has two basic parts. The central nervous system
(CNS) includes the brain and the spinal cord. The peripheral nervous system
(PNS) consists of the nerves that radiate from the CNS to the rest of the body.
The PNS is divided further into two components. The somatic nervous system
transmits signals from the sensory organs and skin to the CNS. It also relays motor
commands from the CNS to the skeletal muscles. The autonomic nervous system
connects the CNS to the involuntary muscles, organs, and glands, thus regulating
such functions as heartbeat and temperature. The autonomic nervous system has
two parts: the sympathetic nervous system, which energizes the body for action,
and the parasympathetic nervous system, which returns the body to its normal
state.
The Endocrine System
The endocrine system is a collection of ductless glands that regulate growth,
metabolism, and other functions by secreting hormones into the bloodstream. These
secretions are controlled in the brain by the hypothalamus, which signals the
pituitary gland.
The Neuron
Neurons, or nerve cells, transmit and receive information throughout the nervous
system. Sensory neurons transmit information from the senses, skin, muscles, and
internal organs to the CNS. Motor neurons send commands from the CNS to the
muscles, glands, and organs. Interneurons serve as connectors within the CNS.
Neurons cluster into interconnected working groups called neural networks. Glial
cells help support, insulate, and nourish the neurons. A simple reflex like the knee
jerk illustrates the speed of neural signals.
Structure of the Neuron
Each neuron has a rounded body, called the soma, and two types of branched
fibers: dendrites, which receive impulses, and an axon, which sends impulses
through its terminals. Many axons are covered with myelin sheath, a fatty insulating
layer that speeds impulses.
The Neuron in Action
A neuron transmits messages by means of an electrical process. When dendrites
receive signals of sufficient strength, the cell’s membrane breaks down. Positively
charged sodium ions rush in, altering the charge inside in such a way that a burst of
electrical energy known as an action potential surges through the axon as soon as a
certain necessary level of stimulation, or threshold, is reached.
How Neurons Communicate
To transmit a signal across the synapse, the tiny gap between two neurons, the
sending neuron releases chemical neurotransmitters from vesicles in its axon
terminals. These chemicals bind to receptors on the dendrites of a receiving neuron.
There are many neurotransmitters in the body, and each fits only certain receptors.
Neurotransmitters
Acetylcholine (ACh) is a neurotransmitter that links motor neurons and muscles.
ACh has an excitatory effect on muscles. Dopamine, in contrast, inhibits muscles
and helps control voluntary movements. Alzheimer’s disease, Parkinson’s disease,
and schizophrenia have all been linked to problems with these chemical messengers.
Other neurotransmitters called endorphins serve as the body’s own pain relievers.
The Brain
The basic anatomy of the brain has long been known, but behavioral
neuroscientists face the more difficult task of understanding how it functions.
Tools of Behavioral Neuroscience
Although phrenology was misguided in linking mental characteristics to bumps
on the skull, it correctly supposed that functions are localized in particular parts of the
brain.
Today, neuroscientists use four methods to study brain functions: (a) clinical case
studies of people with brain damage; (b) invasion of the brain through surgery, drugs,
or electrical stimulation; (c) electrical recordings of activity using the
electroencephalograph (EEC); and (4) brain-imaging techniques, such as
computerized tomography (CT) scan, positron emission tomography (PET)
scan, and magnetic resonance imaging (MRI).
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Regions of the Brain
The brain consists of three main parts: the brainstem, the limbic system, and the
cerebral cortex. Each of these comprises several important structures.
The brainstem is the inner core. It contains the medulla, which controls vital
involuntary functions such as breathing; the pons, involved in sleep and arousal; and
the reticular formation, a netlike group of cells that filter sensory information and
help control sleep, arousal, and attention. Nearby are the cerebellum and basal
ganglia, which play an important role in balance and coordination.
Above the brainstem is the limbic system, which helps govern motivation,
emotion, and memory. It includes the thalamus, a relay station for sensory
information; the amygdala, linked to fear, anger, and aggression; the hippocampus,
which performs a key function in memory formation; and the hypothalamus, which
helps regulate the autonomic nervous system, emotions, and basic drives.
The outermost 80 percent of the brain, the wrinkled cerebral cortex, controls
higher order mental processes. Anatomically, it consists of two hemispheres and four
lobes. It can also be divided into areas based on function: (a) Sensory areas
specialize in receiving sensory information. For example, the somatosensory cortex
receives information from the touch receptors in the skin. (b) The motor cortex
controls the voluntary muscles. (c) The association cortex areas communicate with
the sensory and motor areas and house higher mental processes. Within the
association cortex, two areas specialize in language. Broca’s area directs the
production and comprehension of speech, and Wernicke’s area is involved in
language comprehension.
The Split Brain
Researchers have investigated Fechner’s idea that each side of the brain has its
own mind (Fechner, 1860). The studies rely on the fact that the left hemisphere
communicates with the right side of the body, and the right hemisphere with the left
side. The hemispheres are connected by, and share information through, the corpus
callosum. Experiments with split-brain patients, in whom the corpus callosum has
been severed, show that each hemisphere has a somewhat different version of
experience.
Other research has tried to determine which functions have a tendency toward
cerebral lateralization, or control by a single side of the brain. The key language
centers are in the left hemisphere. The right hemisphere plays a crucial role in
nonverbal functions. But the most important distinction may be the style of
processing. The left hemisphere seems to rely on analytical processing, whereas the
right hemisphere is more holistic.
Research supports the notion that the two hemispheres, when their links are cut,
produce separate streams of consciousness. But in the healthy brain, they exchange
information so quickly that our mental experience is a seamless whole.
Prospects for the Future
Recent advances in the study of the brain have addressed two questions: Does
the adult brain have a capacity to change and adapt as a result of experience, and is
it possible to repair a damaged brain?
The Brain’s Capacity for Growth and Reorganization
Research shows that the brain has plasticity, a capacity to change. Specifically,
certain experiences can spark the branching of new dendrites and the growth of new
synaptic connections. This enables the brain to compensate for damage. But it also
causes people with amputated limbs to experience phantom pain.
Repairing the Damaged Brain: New Frontiers
Advances in understanding the brain have shown that neurogenesis continues
past infancy and have led to attempts at brain repair. With the neural graft
procedure, researchers have transplanted brain tissue from one animal to another in
an effort to reduce deficits in brain function. Among human beings, the greatest hope
may involve the transplantation of fetal tissue, a highly controversial procedure.
Contrary to what has been believed, recent studies show that new nerve cells can be
produced in the mature brain.
Critical Thinking
Thinking Critically About Behavioral Neuroscience
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1. What is the difference between the “mind” and the “brain”?
2. Advances in brain-imaging technology allow us to observe the human brain at
work. What kinds of questions do you think we might be able to answer with
these sophisticated techniques?
3. Research investigating neural plasticity suggests that life experiences can
alter the neural circuitry of the brain. What are the advantages and
disadvantages of this phenomenon? What are some of the real-world
implications of this research (e.g., for child rearing or the treatment of stroke
victims)?
4. What is your opinion of the concussion protocols in sports? For example,
should a sports league be forced to make changes if concussions are a known
risk of the sport? Do athletes need to be better educated on the risks involved?
In your answer, explain how science and, specifically, psychology can help
inform how to protect athletes going forward.
Career Connection: Research
Research Assistant
Research assistants aid in the collection and analysis of data at universities, think
tanks, market research firms, consulting and polling companies, and other
organizations. Pursuing a career as a research assistant is a great way to put a
bachelor’s degree in psychology to good use. Assistants who work in labs are heavily
involved in research and experimental psychology. Those who work in government
agencies and private-sector businesses that study human behavior put their
understanding of psychology to work alongside many of the more general research
and critical-thinking skills that are essential for a psychology major. Research
assistants may review and summarize existing data, write or edit documents, conduct
experiments, log data, organize materials and information, and generally assist the
lead researchers for whom they work.
Key skills for this role that psychology students learn to develop:
Scientific reasoning to interpret psychological phenomena
Critical thinking and analysis
Effective communication across a variety of contexts
Key Terms
acetylcholine (ACh) (p. 55)
action potential (p. 54)
amygdala (p. 64)
association cortex (p. 67)
autonomic nervous system (p. 49)
axon (p. 53)
basal ganglia (p. 63)
brainstem (p. 63)
Broca’s area (p. 68)
central nervous system (CNS) (p. 49)
cerebellum (p. 63)
cerebral cortex (p. 65)
cerebral lateralization (p. 72)
computerized tomography (CT) scan (p. 60)
concussion (p. 77)
corpus callosum (p. 69)
dendrites (p. 53)
dopamine (p. 56)
electroencephalograph (EEG) (p. 59)
endocrine system (p. 50)
endorphin (p. 57)
glial cells (p. 52)
hippocampus (p. 65)
hormones (p. 50)
hypothalamus (p. 65)
interneurons (p. 52)
limbic system (p. 64)
magnetic resonance imaging (MRI) (p. 60)
medulla (p. 63)
motor (motion-producing) neurons (p. 52)
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motor cortex (p. 66)
myelin sheath (p. 53)
neural graft (p. 79)
neural networks (p. 52)
neurogenesis (p. 77)
neurons (p. 52)
neurotransmitters (p. 54)
parasympathetic nervous system (p. 49)
peripheral nervous system (PNS) (p. 49)
phrenology (p. 58)
pituitary gland (p. 50)
plasticity (p. 75)
pons (p. 63)
positron emission tomography (PET) scan (p. 60)
receptors (p. 55)
reflex (p. 52)
reticular formation (p. 63)
sensory neurons (p. 52)
soma (p. 53)
somatic nervous system (p. 49)
somatosensory cortex (p. 66)
split brain (p. 69)
sympathetic nervous system (p. 49)
synapse (p. 54)
thalamus (p. 64)
threshold (p. 54)
Wernicke’s area (p. 68)
Descriptions of Images and Figures
Back to Figure
The nervous system is divided into 2 main systems as follows.
1. The Central Nervous System. This includes the brain and the spinal cord.
2. The Peripheral Nervous System. The peripheral nervous system breaks
down into the Somatic and Autonomic systems. The autonomic system divides
further into the Sympathetic and Parasympathetic systems.
The diagram features a human outline with the nervous system illustrated as a
network throughout the body. The central nervous system is highlighted in pink. The
peripheral nervous system is highlighted in yellow.
The brain is highlighted in pink. The spinal cord is also highlighted in pink and
stretches down the length of the back.
The nerves of the peripheral nervous system create an interconnected network
throughout the body.
Back to Figure
The steps in the withdrawal reflex are:
1. A hand touches a hot object (an iron box);
2. The pain receptor in the skin directs the information through the dendrite of
the afferent neuron to the cell body of the afferent neuron to the axon of the
afferent neuron.
3. Within the spinal cord, the information passes from the axon of the efferent
neuron to the cell body of the interneuron, and to the cell body of the efferent
neuron.
4. The information then passes through the axon of the efferent neuron that
exits the spinal cord, and is relayed to the muscle of the affected hand.
5. The muscle contracts and the stimulated body part is withdrawn.
The steps in the knee jerk reflex are:
1. A knee is hit by a reflex hammer.
2. The golgi tendon organ, which is a nerve ending within the tendon that
passes over the knee directs the information to a sensory neuron, to the cell
body, to the spinal cord, and to a motor neuron.
3. The information from the motor neuron is then relayed to the muscle of the
leg which facilitates muscle contraction.
4. The muscle contracts and a knee jerk reaction ensues.
Back to Figure
The steps in the communication of the action potential are:
1. The action potential passes through the axon to a presynaptic terminal.
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2. The presynaptic terminal is a bulb shaped organ containing Ca2+ions.
3. In the terminal, there are numerous sacs called “vesicles”, which are filled
with neurotransmitters.
4. At the level of the synaptic cleft, some vesicles of the axon that are fused with
the membrane release the neurotransmitters into the synapse.
5. The neurotransmitters bind on to the numerous post synaptic channel
receptors that are present on the surface of the cell body of the receiving neuron.
6. The action potential enters the cell body, and passes downwards.
7. The electrical charge at the synaptic level is negative outside the cells, and
positive inside the cells.
8. Below the synapse, the charges get interchanged.
Back to Figure
The various waves of the EEG are described as follows:
1. Awake; Fast, random, low voltage: A series of very short, closely packed
waves at 50μV per second.
2. Drowsy, relaxed; Alpha waves: A series of very short, densely packed waves,
denser than the waves while awake.
3. Stage 1 sleep; Theta waves: A series of short, closely packed waves, slightly
far apart than the waves while awake, with occasional dense waves.
4. Stage 2 sleep; Sleep spindles, K complexes: A series of slightly longer
loosely packed waves, longer than the theta waves.
1. Sleep spindle: Occurrences of densely packed waves that resemble a
spindle in between the loosely packed series.
2. K complex: A long, wide wave amidst other short waves.
5. Stage 3/Stage 4 sleep; Slow-wave sleep: A series of long, slow, loosely
packed waves.
6. REM sleep; Fast, random: A series of very short, closely packed waves,
slightly slower than the waves of Stage 1 sleep.
Back to Figure
The different parts of the brain labelled in the clockwise direction are:
1. Cerebral cortex,
2. Thalamus,
3. Parietal lobe,
4. Pineal gland,
5. Superior and inferior colliculus,
6. Occipital lobe,
7. Midbrain,
8. Cerebellum,
9. Spinal cord,
10. Medulla,
11. Pons,
12. Pituitary gland,
13. Hypothalamus,
14. Nucleus accumbens,
15. Lateral ventricle,
16. Corpus callosum,
17. Frontal lobe,
18. Cingulate gyrus.
Back to Figure
The different parts of the brain labelled are:
1. The lateral fissure: which separates the frontal and temporal lobes.
2. The central sulcus: which separates the frontal and parietal lobes.
3. The frontal lobe: which lies to the front of the skull.
4. The parietal lobe, which lies to the back of the skull.
5. The temporal lobe: which lies to the sides of the skull.
6. The occipital lobe, which lies to the base of the skull.
The different areas of the brain labelled are:
1. The motor cortex in the frontal lobe just in front of the central sulcus.
2. The prefrontal cortex and Broca’s area in the frontal lobe just above the
lateral fissure.
3. The somatosensory cortex in the parietal lobe just behind the central sulcus.
4. The auditory cortex and Wernicke’s area in the temporal lobe just below the
lateral fissure.
5. The visual cortex in the occipital lobe.
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Back to Figure
The different parts of the brain labelled are:
1. The lateral fissure: which separates the frontal and temporal lobes.
2. The central sulcus: which separates the frontal and parietal lobes.
3. The primary motor cortex in the frontal lobe just in front of the central sulcus.
4. The primary somatosensory cortex in the parietal lobe just behind the central
sulcus.
5. The secondary somatosensory cortex in the parietal lobe just behind the
primary somatosensory cortex and just above the lateral fissure.
The cerebral hemispheres are represented to be split, with the cortex curving
downwards towards the center.
The primary motor cortex is zoomed into a motor homunculus, which is described
in the clockwise direction as follows:
1. The toes, ankle, knee, hip, trunk and shoulder are represented at the upper
end of the cerebral hemisphere.
2. The elbow, wrist, hand, little, ring, middle, and index fingers are represented
at the upper end to middle of the cerebral hemisphere.
3. The thumb, neck, brow, eyelid and eyeball, face, lips, jaw, tongue, and
actions such as swallowing, mastication, salivation, and vocalization are
represented at the middle to lower end of the cerebral hemisphere.
The primary sensory cortex is zoomed into a motor homunculus, which is
described in the anticlockwise direction as follows:
1. The toes, foot, leg, hip, trunk, neck, shoulder, arm, elbow, forearm, wrist,
hand, little, ring, middle, index fingers, and the thumb are represented at the
upper end to the middle of the cerebral hemisphere.
2. The eye, nose, face, upper and lower lip, teeth, gums, jaw, tongue, pharynx,
and the intra-abdominal organs are represented at the middle to lower end of the
cerebral hemisphere.
3. The genitalia are represented in an area of the cerebral hemisphere beyond
the toes.
Back to Figure
The process is described as follows:
1. There are two sources of information, A and B, which are positioned over the
left and right eye respectively.
2. Information enters both eyes from both sources and passes through the
respective optic nerve of each eye.
3. The optic nerve meets at a point called optic chiasm, wherein the information
from source A is directed towards the right side, and the information from source
B is directed towards the left side.
4. The redirected information goes to the respective lateral geniculate nucleus
of each side.
5. From the nucleus, the information from source A is relayed to the right visual
cortex, and information from source B is relayed to the left visual cortex.
Back to Figure
The experiment is described as follows:
1. A woman sits at the table with a partition blocking the contents of the other
side. The objects placed on the other side are a pair of scissors, a spoon, a
pencil, an apple, and a cup.
2. In the first image, the spoon is placed on her left side from across the barrier.
3. In the second image, a callout near the woman says “I saw nothing.”
4. In the third image, the woman is shown to put out her left hand across the
barrier and pick the spoon.
Back to Figure
The experiment is described as follows:
1. In part A, a woman faces a composite image of a face that comprises of two
halves: the left half is a sketch of a child’s face and the right half is a sketch of an
adult woman’s face. There is a dot in between the two faces which the woman is
shown to be looking at.
2. In part B, the woman faces four sketches: a young man and an elderly man at
the top row, the full face of the child and the adult woman whose half face was
shown earlier, at the left and right sides of the bottom row respectively. A callout
near the woman says “I see a child.”
3. In part C, the same four sketches are displayed, and the woman points out to
the face of the adult woman whose right half of the face was shown earlier.
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Back to Figure
A photo shows a football player getting pushed to the ground upon contact with
another player.
The next two illustrations show the process of injury at the level of the brain:
1. The player’s head is shown to have not hit the ground yet, and the direction
of impact to the head is downwards.
2. The player’s head is shown to have hit the ground, and the brain is shown to
have moved a little in the upward direction away from the region of impact.
3. The impact on the brain is shown to be on the frontal and temporal lobes.
The three illustrations show the process of the injury at the level of the neuron:
1. An axon of a normal neuron is shown, with the myelin sheath intact.
2. The myelin sheath is shown to bend and twist across the axon.
3. The axon is shown to be swollen, with pieces of myelin sheath disintegrated.
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3 SENSATION AND PERCEPTION
Lucas Vallecillos / Alamy Stock Photo
Learning Objectives
Distinguish between a stimulus and a sensation; recognize the
interplay between the two that inspired some of the first psychologists to
measure them.
Imagine what life would be like for one day without sensation.
Summarize the steps we take to perceive our world as adults.
WHAT'S YOUR PREDICTION: DOES CULTURE
INFLUENCE PERCEPTION?
The Situation
You have always assumed that when it comes to vision, hearing, and other
biological senses, people are basically the same. But you also suspect that the way
each of us perceives the world is influenced by our life experiences and cultural
backgrounds. So, which is it? Thinking about the problem, you realize that one
possible way to tease apart biological and cultural influences is to select an important
aspect of perception, create a task to measure it, and then compare people from
different parts of the world.
In reading up on the visual system, you learn that images projected on the eye's
retina are flat and two-dimensional. So, you wonder, how do people judge depth and
distance? How do people know that one object in the visual field is closer than
another? Is depth perception innate among humans, or are certain types of life
experience necessary? To examine these questions, you create the drawings
demonstrated in Figure 3.1 and ask the following question: Which animal is closer to
the hunter: the antelope or the elephant? The task seems easy. To you, the elephant
looks farther away because its image is so small and because it stands either on a
hill that is partly blocked (top) or at the top of a road with converging lines that form
an upside-down V (bottom).
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Description
Figure 3.1 Which Animal Is Closer to the Hunter?
Monica Wierzbicki/Body Scientific Intl.
Make a Prediction
Determined to test people from very different backgrounds and cultural
experiences, you show the drawings to English speakers. Then you travel to southern
Africa and present the same pictures to both illiterate and educated Bantus living in a
rural area. What will you find? Will everyone, as you do, see the pictures in threedimensional terms and see the antelope as closer than the elephant? Which
participant groups will see the antelope as closer than the elephant: educated
Westerners, educated Bantus, or illiterate Bantus?
The Results
This study, conducted by W. Hudson (1960), was one of the first to examine
perception from a cross-cultural perspective. Using drawings like those shown,
Hudson found that compared to Western adults, illiterate Bantu participants saw the
pictures as flat and the elephant as closer to the hunter. And what about the schooleducated Bantus? It is interesting that in this group, most participants saw the
antelope as closer. Apparently, seeing three-dimensional depth in two-dimensional
displays is a skill that people develop—probably from exposure to books,
photographs, artwork, and other flat visual representations of reality.
What Does It All Mean?
Among researchers who study vision and other senses, certain aspects of
perception—such as our ability to perceive depth and distance—seem biologically
“hardwired” and universal. From the two eyes to the neural pathways that carry visual
signals to the brain, most humans are similarly equipped. Yet other researchers, such
as those who study people from different cultures, have come to realize that in some
ways our perceptions are influenced by our experiences. For example, people living
in urban environments that contain many edges and right angles are more
susceptible than those living in open spaces to certain line-based optical illusions
(Deregowski, 1989). So, are the processes of perception biologically based or
learned? As we will see in this chapter, both views are correct.
Thud. Giggle. Thud. Giggle. Thud. Splat. Giggle.
Have you ever watched a baby in a highchair? The joys of dinnertime with a 10month-old are numerous. You may have even wondered, “When will this baby tire of
throwing stuff on the ground?” One can quickly get caught up in the “go fetch” game,
especially if the baby rewards you with a fantastic giggle. But have you pondered
what the baby might be thinking and experiencing with every toss of the object? Might
the falling object be magical? Take a moment to drop something unbreakable from
about 4 feet above the ground. What happens on the object’s way down? Does the
object appear to get smaller? When it stops on the ground below, what happens? Is
there a noise and a wobbly movement? Now, do it again. Test for consistency. You
will probably find that the movement changes. Sometimes it might wobble to the left,
sometimes to the right, and sometimes, it might hit flat and not wobble at all. When
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