Cognitive Psychology and Cognitive Neuroscience by Wicki - HTML preview
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are many evolutionary theories to explain this. As proposed by Gaulin and McBurney (see references
below), we attend to three major theories: Group selection, an intuitive approach to describe social
behaviour. Kin selection, a more advanced theory considering laws of genetics to cause social
behaviour. Reciprocal alturism is a sophisticated approach to treat the individual in social barter-deals.
These theories all have in common that the goal of the described agents is to pass on their genetic
material into the next generations. And this common goal creates the social interaction we can observe.
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Vero Wynne-Edwards (1906-1997) proclaimed this theory first in the 1960's. On an evolutionary
perspective a group is a number of individuals who affect the fitness of each other. Notice that
biological relatedness and periods of time are not taken into account with this definition. Group
selection now means that if any of the individuals of a group is doing benefit to its group, the group is
more likely to survive and pass its predisposition to the next generation. This again improves the
chance of the individual to spread its genetic material. So in this theory an alturist is more likely to
spread his alleles than a non-alturistic organism. The distinction to the „classical“ theory of evolution is
that not only the fittest individuals are likely to survive, but also the fittest groups, so to speak the ones
with the most cooperation.
Let's consider an example: Take some bacteria in the human mouth. These bacteria are very slow
moving. The first group of bacteria, which perform cell division as fast as possible, soon waste all their
nutriments and have no resources left. Instead, they have to face their bordering bacteria colonies. So
the first group is facing death very fast.
The second group of bacteria, which perform a more moderate cell division, leave more resources
to their bordering colonies. Whereas first group offspring always have to compete for the resources
with its neighbours, the second groups offspring have savings of resources and so survives more likely
a longer time period. The altruism of the second group makes it fitter as a whole. In the case of bacteria
swimming in a growing medium, in which the bacteria can move freely, the fast group always
overwhelms the second group. This indicates the problem of the group selection theory: it needs certain
circumstances to describe things properly. Additionally, every theory about groups should include the
phenomenon of migration. So in this simple form, the theory is not capable in handling selfish
behaviour of some agents in altruistic groups: Alturistic groups which include selfish members would
turn into pure selfish ones over time, because alturistic agents would work for selfish agents, thereby
increasing the cheaters' fitness while decreasing their own. So generally, group selection is a poor
explanation for altruism and sociality.
A more sophisticated approach to explain cooperative behaviour is kin selection. Kin selection
theory is embedded in the natural selection theory and the inclusive fitness theory (the later one arose
from kin selection), which we do not inspect further here. William D. Hamilton and John M. Smith
puplished the kin selection theory in 1964. The improvment compared to group selection is, that not the
individuals are seen as actor, but the genes are identified as the actual „players“. The theory declares:
An agent acts cooperatively, if the adressee is genetically related to him, because he wants the genetic
material to spread which he has in common with the beneficiary. The more genetic material two agents
have in common, the more they will cooperate. To help its own kin, an agent improves the chance its
own genetic material to spread, at least the part he has in common with its kin.
As a rule of thumb we propose: "The relative benefit to the adressee of an altruistic action, has to
be higher than the costs to the giver."
Hamiltons rule also considers the relatedness between giver and adressee of a favor, which he
expressed in his famous formula:
Evolutionary Perspective on Social Cognitions
r * B > C
r is the relatedness (value between zero and one) - it shows how akin the actor and the
B is the benefit to the beneficiary;
C are the costs to the giver
If the left value is greater than the costs of the right side, the behaviour increases the fitness of the
giver and should therefore be done.
In general reciprocal alturism is to do benefit to any organism in expectation of a reciprocation, so
to speak a benefit pay-back. This behaviour establishes a system by which social interaction can be
viewed as barter-deals. These barter-deals are concrete described by the prisoner's dilemma, which
Albert W. Tucker formalized as follows:
Two suspects, A and B, are arrested by the police. The police have insufficient evidence for a conviction, and,
having separated both prisoners, visit each of them to offer the same deal: if one testifies for the prosecution
against the other and the other remains silent, the betrayer goes free and the silent accomplice receives the full
10-year sentence. If both stay silent, the police can sentence both prisoners to only six months in jail for a
minor charge. If each betrays the other, each will receive a two-year sentence. Each prisoner must make the
choice of whether to betray the other or to remain silent. However, neither prisoner knows for sure what
choice the other prisoner will make. So the question this dilemma poses is: What will happen? How will the
Enhanced prisoner's dilemma looks like this:
Agents A and B making a barter-deal.
If A cheats on B, whereas B cooperates with A, B gets no points, A gets more than average
If A cooperates with B and vise versa, both get average points.
If both cheat on each other, none of them gets points.
Iterated prisoner's dilemma reminds strongly on social interactions and many strategies for it were
designed. A famous iterated prioner's dilemma strategie is tit for tat, which can be viewed as specification of reciprocal alturism. Among the „simple“ stategies, it is the most effective one. Tit for
tat means if an organisms cooperation is reciprocated, it keeps the cooperation running, otherwise it
stops cooperating with the organism, who did not cooperate. Because it is often hard to determine who
is cooperating and who only pretends to be reliable, but actually acts selfish, organisms developed
mechanisms to detect cheaters and selfish agents in altruistic groups in order to withhold favors from
them. The development of cognitive abilities to detect cheaters is important for altruistic groups to
survive - as we have seen, migration of selfish agents into altruistic groups infects it which in the end
leads in dying out of the altruistic allele. Therefore, to keep altruism efficient and still benefit from its
advantages, complex organism have developed various social cognitive abilities.
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Possible selection pressures favoring human sociality
From an evolutionary perspective, sociality is another adaptation of some species to their
environment - just like eyes, pelt, legs and the like. We know that adaptations are constantly tested
against their environment, and that those traits (genes) who increase the fitness of the bearer are more
likely to get passed on to the next generation. So what are the benefits and costs of living-within-a-
group in general? One of the first principal costs is of course increased competition in almost any area
of life. Animals that live solitary don't have to fight for rare resources such as foods or possible mates
with companions. In addition, groups tend to attract more predators, as you can imagine. However,
these two issues also have a positive side: A group tends to be more successful in finding food and is
more powerful in defense against mentioned predators: More eyes/ears simply see/hear more than
fewer do. This leads us to the first conclusion (which in principal can be generalized for all
adaptations): Selection favors social habits if the benefits of living in a group outweights the costs.
Knowing that, what were the conditions of our ancestors in the Environment of Evolutionary
Adaptedness (EEA)? Of course nobody can exactly say how they lived, but by considering life of
contemporary great apes and hunter-gatherer societies, we can make a reasonable guess on which we
can draw some conclusions: Presumably, early humans inhabited more open, less forested country than
the majority of primates, which certainly increased their exposure to predators. Also, open habitats
typically contain herds of grazing animals. Thus, if our ancestors' diet depended on meat, cooperative
hunters maybe were more successful than solitary ones. Other food than meat also may support living
in a group: If resources are generally rich, but scattered over the landscape, the costs of sharing the
found food with others is low - while the benefits of getting help in finding them in the first place are
very high. Another possible pressure was revealed by observing social great apes like gorillas: Neither
their food comes in patches (they eat leaf material and do never hunt), nor have they natural enemies
after reaching adulthood. It seems that the standard reasons for sociality have not much force on them -
but one aspect of their behaviour gives a hint anyway: Killing among members of their own species.
Especially female apes are at risk of having their infants killed by males that did not father those
infants, so female gorillas cluster around strong, powerful males that are capable of protecting their
children. Life of chimpanzees also includes fatal violence, concentrated onto struggles between
communities: Males invade other groups to kill infants of unfamiliar females or even other males, if the
numerical advantage is sufficient. These kinds of risk clearly favor sociality over living in solitude.
So we get a small overview of the probable pressures on our ancestors that lead to sociality:
• inhibiting open country,
• gathering rich but scattered patches of food,
• hostilities/infanticide among neighbours.
Having talked about various processes and theories about evolution, the further discussion in this
chapter will require detailed elaboration on the term 'social cognition'. While 'cognition' for itself is
already a rather complex term, 'social cognition' is even more specific. In order to make it accessible
and to understand the general idea behind it, several main aspects and the respective vocabulary to talk
about it need to be introduced. The suggestions of Tomasello et al 2004 will serve as a basis for this.
Evolutionary Perspective on Social Cognitions
First of all it has to be said that, when talking about 'social cognition', we talk about human
cognitive skills, for, as we will see, humans are the only species abilities in the respective sense
evolved. Trying to find the reasons for this fact will go hand in hand with inquiring into the nature of
social cognition as a species unique human faculty.
Drawing a rough sketch of the topic, what we are interested in is the ability to participate with
others in collaborative actions with not only common but also shared goals. The term introduced to
describe this aspect is called shared intentionality. This presupposes the ability to read the intentions
of other agents, as well as a broad background of cultural learning during the development of a human
being. Especially the latter is a strictly human phenomenon, since it arises from a unique motivation to
share psychological states, which in turn needs unique forms of cognitive representation for doing so.
Hence it is proposed that the creation of linguistic symbols is closely related, as well as the rise of
social norms and the establishment of social institutions.
The human faculty of social cognition
Around a child's first birthday the capability emerges to understand the intentions of other people.
Humans are by far the most skillful species at reading the minds of specimen, i.e. successfully guessing
or reasoning about what other fellow humans perceive, intend, believe, know, desire, etc. - which is
crucial in order to decide what someone else is doing in the first place. While the action might be quite
the same, it is the respective intention according to which the action has to be judged. For example,
seeing somebody breaking a window has to be judged differently if somebody has just lost his keys, if
he tries to break in somewhere or if someone simply exerts wanton destruction. While reading the
intentions of another agent is not a strictly human capability, humans also collaborate and interact
culturally, that means we have complex collaborative activities, shared symbolic artifacts and social
institutions that allow for communication and structure, which lead to powerful abstract levels and
organizational concepts like societies, states, etc., and give the possibility to convey knowledge on
these levels from one generation to another, hereby creating a vast complexity and variety over
It is proposed that reading intentions and cultural learning give rise to species unique processes of
cultural cognition and evolution.
In order to explain the level of complexity found in human cultural and collaborative activities, we
need the term of shared intentionality. Apparently it is a strictly human faculty to participate in
collaborative actions that involve shared goals and socially coordinated action plans, which is also
called joint intentions. This requires an understanding of the goals and perceptions of other involved
agents, as well as sharing and communicating these, which again seems to be a strictly human
behavior. This then may have brought forth elaborate cognitive representations for dialogs, like the
human faculty for language, mathematics and the creation of social practices and institutions. For
further discussion, the questions of how humans come to understand intentional action and how they
participate in actions born of shared intentionality will have to be dealt with.
Understanding intentional action
For our purposes, we will consider intentional action as an organism's intelligent behavioral
interaction with its environment and the factors that play a role in that.
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According to cybernetic theory this presupposes an organizational structure consisting of three
1. a goal,
2. perceiving the environment,
3. acting towards the goal by changing the environment.
This is a circular organization that causes action, which in turn causes a change in perception,
which again determines the action. In this way, the system is self-regulating. This model is used by
Tomasello et al to describe human intentional action.
Let's look at an example: A closed box which a person wants open. The latter obviously is the goal
state, however, apparently it is necessary to distinguish between an external goal, which is the actual
state of an open box in the environment, and an internal goal, which is something like a mental
representation of the goal state, that the person needs to operate towards that goal.
Furthermore, a sharp distinction is drawn between a goal and an intention. Whereas a goal
describes merely the state desired by the person, an intention includes this goal and the means to
achieve it, that is a sort of action plan the person decided for to achieve the goal. In the given example,
this might be cutting the box open with a sharp knife or scissors. As mentioned earlier, since an
intention includes the goal, the same action can have different intentional interpretations. As we saw
with breaking a car window for example, it can either be a means to get to the keys, or merely an
expression of wanton destruction.
The results of the action are a change in the state of the environment, which, according to a
person's internal goal, can be a failed attempt, a success, where the state of the environment matches
the internal goal, or an accident, which is in a way a failed attempt with unpredicted consequences in
the environmental state. Since we are talking about a human person, the results of an action are usually
accompanied by an emotional reaction, like happiness, sadness, anger or surprise.
On the part of perception, the term 'selective attention' is introduced to point out that the
monitoring of the environment done by the organism is focused on the goals at hand, which means that
only those facts that are relevant for opening the box in the example before are taken into active
consideration. The color of the box, for example, plays an unimportant role in the action plan chosen to
open the box.
Depending of the complexity of the goal, the means may include the creation of subgoals, or even
a whole subplan. Also, the organism probably wants the box open for a reason, which would be in the
context a higher level goal. Concerning the intention involving this potential higher level goal, the act
of opening the box may itself be just a subgoal. Choosing appropriate subgoals is referred to as
'decision making' by Tomasello et al.
Finally, the action itself might be the actual goal, consider for example the act of jogging, of
dancing or of singing, where the respective action is not meant to bring about some immediate goal but
represents by itself already the desired state.
These are all considerations that have to be taken into account in order to understand the
intentional action of other organisms, which, as was pointed earlier, is a crucial point for social
cognition. Referring to children's understanding of intentional action, the latter can be divided into
Evolutionary Perspective on Social Cognitions
three groups representing more and more complex level of grasp.
The first one to be mentioned is the perception of animate action. This means that after a couple of
months, babies can differentiate between motion that was caused by some external influence to some
passive object, and actions that an object or organism has performed by itself, as animate being. At this
stage, however, the child has not yet any understanding of potential goals the observed actor might
The next stage of comprehension includes the understanding that the organism acts with
persistence towards achieving a goal, including trial and error, and is developed by children after about
9 months. This also means that the child knows that the person it observes has a certain perception. At
this stage, a certain amount of predicting the behavior of the actor is possible. After one year of age, a
child understands that an actor pursuing a goal may have a variety of action plans to achieve the goal,
and is choosing between them. Furthermore a certain sense for the selective attention of the actor will
have developed, and the child realizes that action and attention are directed towards a goal. This allows
a broad variety of predictions of behavior of organisms in a certain environment.
By 14 months of age, children fully comprehend intentional action, including the basics of rational
decision making. According to Tomasello et al, this leads to powerful forms of cultural learning, which
is especially important since a child not only learns to predict behavior in an environment, but it also
learns, foremost by imitation, how things are conventionally done in their culture.
According to Tomasello et al, shared intentionality might emerge whenever socially interacting
agents in an environment understand each other as acting intentionally. What this means is that the
agents work together towards a shared goal in collaborative interaction. Furthermore, they do that in
coordinated action roles and mutual knowledge about them. The nature of the activity or its complexity
is not important, as long as the action is carried out in the described fashion. It is important to mention
that the notion of 'shared goals' means that the internal goals of each agent include the intentions of the
others. If you take a group of apes on a hunt, for example, the apes appear to be acting in a
collaborative fashion, however, it is reasonable to assume that neither do they have coordinated action
roles, nor do they have a shared goal, but rather act as seen fit towards the same individual goal state.
Summing up, the important characteristics of the behavior in question are that the agents are mutually
responsive, have the goal of achieving something together, and coordinate their actions with distributed
roles and action plans.
Tomasello et al argue that in complex social groups the repeated sharing of intentions in a
particular interactive context leads to the creation of habitual social practices and beliefs, that may form
normative or structural aspects of a society, like government, money, marriage, etc., which of course
form the notion of society itself. Society might hence be seen as a product and an indicator of social
The social interaction that builds the ground for activities involving shared intentionality is
proposed to be divided into three groups:
The first one is called 'dyadic engagement'. What is meant here is the simple sharing of emotions
and behavior, by means of a direct mutual responsiveness, for example by expressing emotions. The
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motivation to share emotions, repeatedly, is already a key factor for social cognition and a main
difference between humans and other species, as for example primates.
The next level is called 'triadic engagement', where two agents act together towards a shared goal,
while monitoring the perception and goal-direction of the other agent. Sharing a goal is one step further
than simply a direct responsiveness as in dyadic engagement.
The last supposed level is called 'collaborative engagement', which comprises, as introduced
earlier, joint intentions and attention. At this point the agents share a goal, act in different, even
complementary roles with a complex action plan and mutual knowledge about selective attention and
intentions of one another. The latter aspect allows the agents to assist each other and reverse or take
These different levels of social engagement require the understanding of the different aspects of
intentional action, as introduced above, and presuppose the uniquely human motivation to share
psychological states with each other.
According to Tomasello et al, human infants develop very early in ontogeny the strong motivation
to share emotions, goals and perception and participate in collaborative pretense activities in fictional
The special motivation to share psychological states of course needs means to do so. These means
have to be certain complex cognitive representations, especially for the joint intentions that require at
least two sets of action plans, since in the spirit of shared goals those of the other one have to be
represented as well for true shared intentionality. Since these representations have as content mostly
social engagement, Tomasello et al make use of the term 'dialogic cognitive representations' at this
point. Closely related with this is the communication and use of linguistic symbols. Dialogic cognitive
representations allow in some sense a form of 'collective intentionality', which is important to construct
social norms, conceptualize beliefs and, most importantly, share them. This gives rise to something like
social rationality: by internalizing collective norms children learn to regulate their own behavior.
In this sense, social cognition is what enables us to create culture and lays the foundation for
society. With this knowledge we can now return to the discussion of how and why this particular kind
of human behavior may have evolved during evolution and in what way it is useful.
• M. S. Gazzaniga, R. B. Ivry, G. R. Mangun; Conitive Neuroscience, Norton & Company,
• M. Tomasello; Understanding and sharing intentions: The origins of cultural cognition,
Cambridge University Press, 2004
• Steven J. C. Gaulin, Donald H. McBurney; Psychology: An evolutionary approach,
Prentice-Hall New Jersey, 2001
Behavioral and Neuroscience Methods
4 BEHAVIORAL AND NEUROSCIENCE METHODS
and act. There are many different methods which help us to analyze the
brain and as well to give us an overview of the relationship between
(Electroencephalography) which records the brain’s electrical activity
and the fMRI (functional magnetic resonance imaging) method which Lobes of the brain
method, are not as well-known but still very influential in today's neuroscientific research.
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Methods can be summmed up in the following categories: There are techniques for assessing brain
anatomy and others for assessing physiological functions. Furthermore there are techniques for
modulating brain activity, analyzing behaviour or for modeling brain- behaviour relationships. In some
cases, as in the lesion method, patients with brain damage are examined to determine which brain
structures were damaged and to what extent this influences the patient's behaviour.
Studies on humans with brain damages
The brain is a complicated structure, composed of many structures. It seems obvious that any task
a person performs needs the successful work of the brain's components. A long-standing method of the
neurophysiologist has been to study how behaviour is altered by selectively removing one or more of these parts. If a neural structure contributes to a task, then rendering structure dysfunctional should
impair the performance of that task. A lesion is an area of the brain that is damaged in both structure
and function. If this damage of the brain region leads to an inability of performig a particular mental
function, then this function and brain region must be correlated with each other. This means that the
function depended on the brain region, and is called lesion method. Lesions can occur accidentally in
the course of life events, or can be caused deliberately, in a laboratory. The lesion method relates the
area of a lesion, to loss in behaviour. Put simply: If structure X is damaged, and changes in behavior Y
occur, we can infer that structure X caused, or at least had to do with, behaviour Y.
Broca found a lesion in the left frontal lobe. Based on several examples of this, he concluded that the
ability to speak is at least partially controlled by this area, now referred to as Broca's area.
Because of the nature of non-laboratory settings, lesions such as these cannot be considered
experimentally valid. So experimental lesioning occurs mainly with animals. Various animals are used
for chemically inducing lesions in their brains, thereafter they are compared to various control groups
in order to determine specifically where, and to what degree, a structure controls a behaviour.
Areas where it is used
where lesions are created in a particular brain region, and then the effects on the behaviour of this
lesion are observed. Humans obviously cannot be subjected to brain lesions to investigate their nervous
sytem’s function. Human neuropsychology requires patients with naturally occurring lesions, generally accidentally under particular circumstances. Because of this fact the researchers have no control over
the location or extent of the lesion, and because of this research on humans is only rarely possible.
According to the goal of the researcher, he can choose between two approaches concerning the
lesion method. One of the approach serves for investigation of neural systems, whereby the other
approach accentuates cognitive processes. The approach of neural systems deals with the task to find
out what functions are correlated with a specific brain region. Due to the fact that it is possible that a
specific function is not only supported by one brain region, but can also be supported by other brain
Behavioral and Neuroscience Methods
regions, it is important to do experiments with groups of patients who had damage in a brain region and
because of this a loss of a specific function, but also to do experiments with groups of patients, who
had damage in an other brain region. This allows the researchers to find out if a function is correlated
with one specific brain region or also with other brain regions. This research enables inestimable
information about the relationship between brain areas and cognitive functions, which in turn is useful
for other medically related professionals, like neurosurgeons, clinical neuropsychologists etc.
The approach which distinguishes the cognitive processes fiddles with behavioral signs, where
primarily the region of the brain damage plays little role. It is important that the group of patienst have
the same behavioral deficit, so the researchers have the possibility to examine each patients damaged
brain region. If the researchers determine that there is similarity in the location of the damages brain
region, they can allege hypotheses, that a specific brain region supports a cognitive function. Research
in this field allows to affect the location of the brain damage more closely, when patients show the
same behavioral signs. This facilitates to say more about the particular neural structure of the damaged
brain area and which loss of function results.
Problems which can occur
Even though the lesion method is an important
method and so to say the cornerstone of cognitive
neuroscience, because it enables to make
hypotheses about the relationship between brain
and behaviour, it has limitations. These limitations
depend on the variableness of the properties of the
brain damage, as well as on the variability of the
attributes of the patients. For example the location
and extent of the damage could be variable in the
different cases of patients. And also the different
characteristics of the patients make it difficult to
give definitive conclusions about the correlation
between a specific brain region and a particular
Comparative Brain Size
Experimental lesions done with animals, resemble in the accomplishment. Generally the animals
for the experiments are raised in the same environment, have the same lesion at the same age, so their
characteristics are near the same. Because of this resemblance in general the same behavioral deficits
are observable after the lesion. Contrary to the lesions with animals, individuals with brain damages are
absolutely different. They are not raised in the same environment, have different ages at time of the
lesion and other differences. This fact makes it difficult to give definite statements about the correlation
between specefic brain regions and cognitive fuctions. These difficulties can also result in improper
conclusions. Moreover the lesions created in animals are more specific, because the researcher creates
the lesion in a certain manner, and because of this has more control over the lesion, whereby lesions by
humans are much less specific. The lesions vary in location, extent and origin, this complicates to make
definite inferences about neural strucures and their influence on cognitive functions. Another limitation
of the lesion mehtod reflects in the fact, that it is hardly possible to determine which function is
supported by the damaged brain region. It is only possible to watch how the rest of the brain works without the damaged brain region. First of all, only the brain regions which are crucial for a specific
function can be determined, but not the rest of the brain regions which may be as well important for
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that function. Furthermore it is not definitively find out, if a brain region is really crucial for a specific
function, or if this brain region connects only other brain regions, which are important for the
performance of this specific function. All in all one can say that the lesion method has two major
limitations, which occur, because of the complex structure of the brain, and because it is never possible
to determine definitively if the damaged brain region is the real reason for the loss of a cognitive
function. These perceived limitations of the lesion method provided a strong incentive for the parallel
development of functional imaging, which offered a new means of studying the dynamic neural
correlates of cognitive processes in normal humans. Two key techniques were developed: positron-
emission tomography (PET) and functional magnetic resonance imaging (fMRI).
single case studies
Perhaps the most famous single case study involving lesions occurred in the 19th century. A young
man named Phineas Gage was working on railroad construction in 1848. One day, a 3ft, 7in (1.0922m)
tamping iron (a long metal pole), 1.25in (0.381m) in diameter, was propelled through Gage's skull,
through the left frontal lobe of his brain and out the other side of his head. Miraculously, Gage
survived, but he was not the same. Phineas had previously been the foreman of the construction crew.
He was well regarded as stable, well mannered, good handeling money. After his left frontal lobe was
destroyed, his personality changed. He began to cuss inappropriately, gamble, drink. In other words, he
exhibited personality changes dealing with self control.
Because his left frontal lobe was damaged in the accident, it can be inferred that that is the area of
the brain that deals with personality traits and self control. Unfortunately, because this is a case study,
and not a controlled experiment, any inferences can't be truly accepted, but this idea of connecting
brain damage to behavioral changes is the core idea behind lesion experiments.
Techniques for Assessing Brain Anatomy
Are the art of creating images of the inside of an organism without (necessarily) killing it. There's
a lot of complexity on the inside of something that you can't guess from the outside, to explore or
create images of the inside of an organism e.g. brain without killing it or cutting it in slices CAT as
well as MRI are imaging technique which use changes in electrically charged molecules when they are
placed in a magnetic field to assess differences in cerebral activity in different regions of the brain.
Both technologies are more precise than ordinary X-ray and help us “map” the brain regions associated
with different behaviours, often by studying people with specific brain injuries. MRI images are clearer
than CAT scans and don't use radiation; they show brain atrophy and increased cerebrospinal fluid
CAT scanning was invented in 1972 by the British engineer Godfey N. Hounsfield (later Sir
Godfrey) and the South African (later American) physicist Alan Cromack.
CAT (computed axial tomography) is a painless test that uses multiple x-ray images, taken from
different angles, to create three-dimensional images of body structures. Increasingly, CAT scans use
digital x-rays to produce their images on a computer screen. The tomograms ``cuts`` for the CAT scan
are usually made 5 or 10 mm apart. The CAT machine rotates 180 degrees around the patient's body;
Behavioral and Neuroscience Methods