# Cognitive Psychology and Cognitive Neuroscience/Imagery


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of issues concerning their copyright.**

## Introduction & History

Mental imagery was already discussed by the early Greek philosophers.
Socrates sketched a relation between perception and imagery by assuming
that visual sensory experience creates images in the human\'s mind,
which are representations of the real world. Later on, Aristoteles
stated that \"thought is impossible without an image\". At the beginning
of the 18th century, Bishop Berkeley proposed another role of mental
images - similar to the ideas of Sokrates - in his theory of idealism.
He assumed that our whole perception of the external world consists only
of mental images.

At the end of the 19th century, Wilhelm Wundt - the generally
acknowledged founder of experimental psychology and cognitive
psychology - called imagery, sensations and feelings the basic elements
of consciousness. Furthermore, he had the idea that the study of imagery
supports the study of cognition because thinking is often accompanied by
images. This remark was taken up by some psychologists and gave rise to
the *imageless-thought debate*, which discussed the same question
Aristoteles already had asked: Is thought possible without imagery?

In the early 20th century, when Behaviourism became the main stream of
psychology, Watson argued that there is no visible evidence of images in
human brains and therefore, the study of imagery is worthless. This
general attitude towards the value of research on imagery did not change
until the birth of cognitive psychology in the 1950s and -60s.

Later on, imagery has often been believed to play a very large, even
pivotal, role in both memory (Yates, 1966; Paivio, 1986) and motivation
(McMahon, 1973). It is also commonly believed to be centrally involved
in visuo-spatial reasoning and inventive or creative thought.

## Concept

Imagination is the ability to form images, perceptions, and concepts. In
fact, images, perceptions and concepts are not perceived through sight,
hearing or other senses. Imagine the work of the mind and help create
fantasy. Imagination helps to provide meaning and provide an
understanding of knowledge; imagination is the basic ability of people
to create meaning for the world; imagination also plays a key role in
the learning process. The basic training method for cultivating
imagination is to listen to stories; when listening to stories, the
accuracy of wording is the basic factor of "generating the world".
Imagine any power we face. We combine what we touch, see and hear into a
\"picture\" by imagination. It is widely believed that as an intrinsic
ability, as a factor in perceiving the public world from the senses, in
the process of inventing a partial or complete personal domain in the
mind, the term is used in the professional use of psychology, meaning
the mind. In the recovery process, \[source request\] restores the
sensory object previously presented to the perception. Because the use
of this term contradicts the use of everyday language, some
psychologists tend to describe this process as an \"image process\" or
\"image\", or as a \"regeneration\" imaginary process, using
\"generating or constructive\" The imaginary process \"images of
imagination\" are seen with the \"eye of the soul.\" Imagination can
also be expressed through fairy tales or imaginary situations. The most
famous invention or entertainment product is created by one\'s
imagination. One hypothesis about the evolutionary process of human
imagination is that imagination allows conscious species to solve
problems by using psychological simulations. Children are often
considered to be imaginative groups. Because their way of thinking has
not yet formed, there are fewer ideological restrictions and rules than
adults. Therefore, it is often imaginative. Children often use stories
or pretend games to practice their imagination. When children have
fantasies, they play a role on two levels: on the first level, they use
role-play to achieve what they create with imagination; at the second
level, they pretend to believe that the situation is to play games.

In terms of behavior, what they create seems to be a real reality, and
this already exists in the myth of the story. Artists often need a lot
of imagination because they are engaged in creative work, and
imagination can help them break existing rules and bring aesthetics into
a new model. Imagine the universal use of this term, which means the
process of forming an image that has not been experienced before in the
mind, or the process of forming an image that is at least partially
experienced or formed by different combinations. Some typical examples
are as follows: fairy tale Fiction The illusion of forms inspired by
fantasy novels and science fiction spurs readers to pretend that these
stories are real, and by resorting to fantasy objects such as books or
fantasy, these objects are not in the fantasy world. Imagination in this
sense (not limited to the precise knowledge gained from actual needs) is
somewhat exempt from objective limitations. Imagine being in the
position of another person. This ability is very important for social
relationships and social understanding. Einstein said: \"Imagination\...
is more important than knowledge. Knowledge is limited. Imagination
encompasses the world.\" \[8\] However, in all fields, even imagination
is limited: therefore, one Human imagination does violate the basic law,
or the inevitable principle of violating the actual possibility, or the
possibility of rationality in a certain situation, is considered a
mental disorder. The same limitations place imagination in the realm of
scientific assumptions. The advancement of scientific research is
largely due to some temporary explanations; these explanations are based
on imagination. However, these assumptions must be made up of previously
identified facts and must be coordinated with the principles of a
particular science. Imagination is an experimental part of thinking that
creates functional-based theories and ideas. Separate objects from real
perceptions and use complex \"features\" to envision creating new ideas
or changing ideas. This part of the thinking is crucial to improving and
improving the way new and old tasks are completed. These experimental
ideas can be implemented steadily in the field of simulation; then, if
the concept is very likely and its function is real, then the concept
can be implemented in reality. Imagination is the key to the new
development of the soul. It shares with others and progresses together.
Imagination can be divided into: Automatic imagination (from dreams and
daydreams) Don\'t automatically imagine (renewable imagination, creative
imagination, future dreams)

## The Imagery Debate

Imagine yourself back on vacation again. You are now walking along the
beach, while projecting images of white benzene-molecules onto the
horizon. At once you are realizing that there are two real little white
dots under your projection. Curiously you are walking towards them,
until your visual field is filled by two seriously looking, but fiercely
debating scientists. As they take notice of your presence, they invite
you to take a seat and listen to the still unsolved imagery debate.

Today's imagery debate is mainly influenced by two opposing theories: On
the one hand Zenon Pylyshyn's (left) propositional theory and on the
other hand Stephen Kosslyn's (right) spatial representation theory of
imagery processing.

### Theory of propositional representation

The theory of Propositional Representation was founded by Dr. Zenon
Pylyshyn who invented it in 1973. He described it as an epiphenomenon
which accompanies the process of imagery, but is not part of it. Mental
images do not show us how the mind works exactly. They only show us that
something is happening. Just like the display of a compact disc player.
There are flashing lights that display that something happens. We are
also able to conclude what happens, but the display does not show us how
the processes inside the compact disc player work. Even if the display
would be broken, the compact disc player would still continue to play
music.

#### Representation

The basic idea of the propositional representation is that relationships
between objects are represented by symbols and not by spatial mental
images of the scene. For example, a bottle under a table would be
represented by a formula made of symbols like **UNDER(BOTTLE,TABLE)**.
The term *proposition* is lend from the domains of Logic and Linguistics
and means the smallest possible entity of information. Each proposition
can either be true or false.

If there is a sentence like \"Debby donated a big amount of money to
Greenpeace, an organisation which protects the environment\", it can be
recapitulated by the propositions \"Debby donated money to Greenpeace\",
\"The amount of money was big\" and \"Greenpeace protects the
environment\". The truth value of the whole sentence depends on the
truth values of its constituents. Hence, if one of the propositions is
false, so is the whole sentence.

#### Propositional networks

This last model does not imply that a person remembers the sentence or
its single propositions in its exact literal wording. It is rather
assumed that the information is stored in the memory in a propositional
network.

!Figure 1: Example of a propositional
network

In Figure 1, each circle represents a single proposition. Regarding the
fact that some components are connected to more than one proposition,
they construct a network of propositions. Propositional networks can
also have a hierarchy, if a single component of a proposition is not a
single object, but a proposition itself. An example of a hierarchical
propositional network describing the sentence \"John believes that Anna
will pass her exam\" is illustrated in Figure 2.

!Figure 2: Propositional network with
hierarchy

#### Complex objects and schemes

Even complex objects can be generated and described by propositional
representation. A complex object like a ship would consist of a
structure of nodes which represent the ships properties and the
relationship of these properties.

Almost all humans have concepts of commonly known objects like ships or
houses in their mind. These concepts are abstractions of complex
propositional networks and are called schemes. For example our concept
of a house includes propositions like:

`Houses have rooms.`\
`Houses can be made from wood.`\
`Houses have walls.`\
`Houses have windows.`\
`...`

Listing all of these propositions does not show the structure of
relationships between these propositions. Instead, a concept of
something can be arranged in a schema consisting of a list of attributes
and values, which describe the properties of the object. Attributes
describe possible forms of categorisation, while values rep- resent the
actual value for each attribute. The schema-representation of a house
looks like this:

*`House`*\
`Category: building`\
`Material: stone, wood `\
`Contains: rooms`\
`Function: shelter for humans`\
`Shape: rectangular`\
`...`

The hierarchical structure of schemes is organised in categories. For
example, \"house\" belongs to the category \"building\" (which has of
course its own schema) and contains all attributes and values of the
parent schema plus its own specific values and attributes. This way of
organising objects in our environment into hierarchical models enables
us to recognise objects we have never seen before in our life, because
they can possibly be related to categories we already know.

#### Experimental support

In an experiment performed by Wisemann und Neissner in 1974, people are
shown a picture which, on first sight, seems to consist of random black
and white shapes. After some time the subjects realise that there is a
dalmatian dog in it. The results of this show that people who recognise
the dog remember the picture better than people who do not recognise
him. An possible explanation is that the picture is stored in the memory
not as a picture, but as a proposition.

In an experiment by Weisberg in 1969, subjects had to memorise sentences
like \"Children who are slow eat bread that is cold\". Then the subjects
were asked to associate the first word from the sentence that comes in
their mind to a word given by the experiment conductor. Almost all
subjects associated the word \"children\" to the given word \"slow\",
although the word \"bread\" has a position that is more close to the
given word \"slow\" than the word \"children\". An explanation for this
is that the sentence is stored in the memory using the three
propositions \"Children are slow\", \"Children eat bread\" and \"Bread
is cold\". The subjects associated the word \"children\" with the given
word \"slow\", because both belong to one proposition, while \"bread\"
and \"slow\" belong to different ones. The same evidence was proven in
another experiment by Ratcliff and McKoon in 1978.

### Theory of spatial representation

Stephen Kosslyn\'s theory opposing Pylyshyn\'s propositional approach
implies that images are not only represented by propositions. He tried
to find evidence for a spatial representation system that constructs
mental, analogous, three-dimensional models.

The primary role of this system is to organize spatial information in a
general form that can be accessed by either perceptual or linguistic
mechanisms. It also provides coordinate frameworks to describe object
locations, thus creating a model of a perceived or described
environment. The advantage of a coordinate representation is that it is
directly analogous to the structure of real space and captures all
possible relations between objects encoded in the coordinate space.
These frameworks also reflect differences in the salience of objects and
locations consistent with the properties of the environment, as well as
the ways in which people interact with it. Thus, the representations
created are models of physical and functional aspects of the
environment.

#### Encoding

What, then, can be said about the primary components of cognitive
spatial representation? Certainly, the distinction between the external
world and our internal view of it is essential, and it is helpful to
explore the relationship between the two further from a process-oriented
perspective.

The classical approach assumes a complex internal representation in the
mind that is constructed through a series of specific perceived stimuli,
and that these stimuli generate specific internal responses. Research
dealing specifically with geographic-scale space has worked from the
perspective that the macro-scale physical environment is extremely
complex and essentially beyond the control of the individual. This
research, such as that of Lynch and of Golledge (1987) and his
colleagues, has shown that there is a complex of behavioural responses
generated from corresponding complex external stimuli, which are
themselves interrelated. Moreover, the results of this research offers a
view of our geographic knowledge as a highly interrelated
external/internal system. Using landmarks encountered within the
external landscape as navigational cues is the clearest example of this
interrelationship.

The rationale is as follows: We gain information about our external
environment from different kinds of perceptual experience; by navigating
through and interacting directly with geographic space as well as by
reading maps, through language, photographs and other communication
media. Within all of these different types of experience, we encounter
elements within the external world that act as symbols. These symbols,
whether a landmark within the real landscape, a word or phrase, a line
on a map or a building in a photograph, trigger our internal knowledge
representation and generate appropriate responses. In other words,
elements that we encounter within our environment act as external
knowledge stores.

!Figure 3: Internal representation
map{width="350"}

Each external symbol has meaning that is acquired through the sum of the
individual perceiver\'s previous experience. That meaning is imparted by
both the specific cultural context of that individual and by the
specific meaning intended by the generator of that symbol. Of course,
there are many elements within the natural environment not \"generated\"
by anyone, but that nevertheless are imparted with very powerful meaning
by cultures (e.g., the sun, moon and stars). Man-made elements within
the environment, including elements such as buildings, are often
specifically designed to act as symbols as at least part of their
function. The sheer size of downtown office buildings, the pillars of a
bank facade and church spires pointing skyward are designed to evoke an
impression of power, stability or holiness, respectively.

These external symbols are themselves interrelated, and specific
groupings of symbols may constitute self-contained external models of
geographic space. Maps and landscape photographs are certainly clear
examples of this. Elements of differing form (e.g., maps and text) can
also be interrelated. These various external models of geographic space
correspond to external memory. From the perspective just described, the
total sum of any individual\'s knowledge is contained in a multiplicity
of internal and external representations that function as a single,
interactive whole. The representation as a whole can therefore be
characterised as a synergistic, self-organising and highly dynamic
network.

#### Experimental support

##### Interaction

Early experiments on imagery were already done in 1910 by Perky. He
tried to find out, if there is any interaction between imagery and
perception by a simple mechanism. Some subjects are told to project an
image of common objects like a ship onto a wall. Without their knowledge
there is a back projection, which subtly shines through the wall. Then
they have to describe this picture, or are questioned about for example
the orientation or the colour of the ship. In Perkys experiment, none of
the 20 subjects recognised that the description of the picture did not
arise from their mind, but were completely influenced by the picture
shown to them.

##### Image Scanning

Another seminal research in this field were Kosslyn\'s image-scanning
experiments in the 1970s. Referring to the example of the mental
representation of a ship, he experienced another linearity within the
move of the mental focus from one part of the ship to another. The
reaction time of the subjects increased with distance between the two
parts, which indicates, that we actually create a mental picture of
scenes while trying to solve small cognitive tasks. Interestingly, this
visual ability can be observed also with congenitally blind, as Marmor
and Zaback (1976) found out. Presuming, that the underlying processes
are the same of sighted subjects, it could be concluded that there is a
deeper encoded system that has access to more than the visual input.

##### Mental Rotation Task

Other advocates of the spatial representation theory, Shepard and
Metzler, developed the mental rotation task in 1971. Two objects are
presented to a participant in different angles and his job is to decide
whether the objects are identical or not. The results show that the
reaction times increases linearly with the rotation angle of the
objects. The participants mentally rotate the objects in order to match
the objects to one another. This process is called \"mental
chronometry\".

Together with Paivio\'s memory research, this experiment was crucial for
the importance of imagery within cognitive psychology, because it showed
the similarity of imagery to the processes of perception. For a mental
rotation of 40° the subjects needed two seconds in average, whereas for
a 140° rotation the reaction time increased to four seconds. Therefore,
it can be concluded that people in general have a mental object rotation
rate of 50° per second.

##### Spatial Frameworks

Although most research on mental models has focussed on text
comprehension, researchers generally believe that mental models are
perceptually based. Indeed, people have been found to use spatial
frameworks like those created for texts to retrieve spatial information
about observed scenes (Bryant, 1991). Thus, people create the same sorts
of spatial memory representations no matter if they read about an
environment or see it themselves.

##### Size and the visual field

If an object is observed from different distances, it is harder to
perceive details if the object is far away because the objects fill only
a small part of the visual field. Kosslyn made an experiment in 1973 in
which he wanted to find out if this is also true for mental images, to
show the similarity of the spatial representation and the perception of
real environment. He told participants to imagine objects which are far
away and objects which are near. After asking the participants about
details, he supposed that details can be observed better if the object
is near and fills the visual field. He also told the participants to
imagine animals with different sizes near by another. For example an
elephant and a rabbit. The elephant filled much more of the visual field
than the rabbit and it turned out that the participants were able to
answer questions about the elephant more rapidly than about the rabbit.
After that the participants had to imagine the small animal besides an
even smaller animal, like a fly. This time, the rabbit filled the bigger
part of the visual field and again, questions about the bigger animal
were answered faster. The result of Kosslyn\'s experiments is that
people can observe more details of an object if it fills a bigger part
of their mental visual field. This provides evidence that mental images
are represented spatial.

### Discussion

Since the 1970s, many experiments enriched the knowledge about imagery
and memory to a great extend in the course of the two opposing point of
views of the imagery debate. The seesaw of assumed support was marked of
lots of smart ideas. The following section is an example of the
potential of such controversities.

In 1978, Kossylyn expanded his image screening experiment from objects
to real distances represented on maps. In the picture you see our island
with all the places you encountered in this chapter. Try to imagine, how
far away from each other they are. This is exactly the experiment
performed by Kossylyn. Again, he predicted successfully a linear
dependency between reaction time and spatial distance to support his
model.

!Figure 5: Support for Kosslyn\'s theory of spatial
representation{width="400"}

In the same year, Pylyshyn answered with what is called the
\"tacit-knowledge explanation\", because he supposed that the
participants include knowledge about the world without noticing it. The
map is decomposed into nodes with edges in between. The increase of
time, he thought, was caused by the different quantity of nodes visited
until the goal node is reached.

!Figure 6: Support for Pylyhsyn\'s theory of propositional
representation{width="400"}

Only four years later, Finke and Pinker published a counter model.
Picture (1) shows a surface with four dots, which were presented to the
subjects. After two seconds, it was replaced by picture (2), with an
arrow on it. The subjects had to decide, if the arrow pointed at a
former dot. The result was, that they reacted slower, if the arrow was
farer away from a dot. Finke and Pinker concluded, that within two
seconds, the distances can only be stored within a spatial
representation of the surface.

!Figure 7: Counter model by Finke and
Pinker{width="400"}

To sum it up, it is commonly believed, that imagery and perception share
certain features but also differs in some points. For example,
perception is a bottom-up process that originates with an image on the
retina, whereas imagery is a top-down mechanism which originates when
activity is generated in higher visual centres without an actual
stimulus. Another distinction can be made by saying that perception
occurs automatically and remains relatively stable, whereas imagery
needs effort and is fragile. But as psychological discussions failed to
point out one right theory, now the debate is translocated to
neuroscience, which methods had promising improvements throughout the
last three decades.

## Neuropsychological approach

### Investigating the brain - a way to resolve the imagery debate?

Visual imagery was investigated by psychological studies relying solely
on behavioural experiments until the late 1980s. By that time, research
on the brain by electrophysiological measurements such as the
event-related potential (ERP) and brain-imaging techniques (fMRI, PET)
became possible. It was therefore hoped that neurological evidence how
the brain responds to visual imagery would help to resolve the imagery
debate.

We will see that many results from neuroscience support the theory that
imagery and perception are closely connected and share the same
physiological mechanisms. Nevertheless the contradictory phenomena of
double dissociations between imagery and perception shows that the
overlap is not perfect. A theory that tries to take into account all the
neuropsychological results and gives an explanation for the
dissociations will therefore be presented in the end of this section.

### Support for shared physiological mechanisms of imagery and perception

Brain imaging experiments in the 1990s confirmed the results which
previous electrophysiological measurements had already made. Therein
brain activity of participants was measured, using either PET or fMRI,
both when they were creating visual images and when they were not
creating images. These experiments showed that imagery creates activity
in the striate cortex which is, being the primary visual receiving area,
also active during visual perception. Figure 8 (not included yet due to
copyright issues) shows how activity in the striate cortex increased
both when a person perceived an object ("stimulus on") and when the
person created a visual image of it ("imagined stimulus"). Although the
striate cortex has not become activated by imagery in all brain-imaging
studies, most results indicate that it is activated when participants
are asked to create detailed images.

Another approach to understand imagery has been made by studies of
people with brain damage in order to determine if both imagery and
perception are affected in the same way. Often, patients with perceptual
problems also have problems in creating images like in the case of
people having both lost the ability to see colour and to create colours
through imagery. Another example is that of a patient with unilateral
neglect, which is due to damage to the parietal lobes and causes that
the patient ignores objects in one half of his visual field. By asking
the patient to imagine himself standing at a place that is familiar to
him and to describe the things he is seeing, it was found out that he
did not only neglect the left side of his perceptions but also the left
side of his mental images, as he could only name objects that were on
the right hand side of his mental image.

The idea that mental imagery and perception share physiological
mechanisms is thus supported by both brain imaging experiments with
normal participants and effects of brain damage like in patients with
unilateral neglect. However, also contradictory results have been
observed, indicating that the underlying mechanisms of perception and
imagery cannot be identical.

### Double dissociation between imagery and perception

A double dissociation exists when a single dissociation (one function is
present another is absent) can be demonstrated in one person and the
complementary type of single dissociation can be demonstrated in another
person. Regarding imagery and perception a double dissociation has been
observed as there are both patients with normal perception but impaired
imagery and patients with impaired perception but normal imagery.
Accordingly, one patient with damage to his occipital and parietal lobes
was able to recognise objects and draw accurate pictures of objects
placed before him, but was unable to draw pictures from memory, which
requires imagery. Contrary, another patient suffering from visual
agnosia was unable to identify pictures of objects even though he could
recognise parts of them. For example, he did not recognise a picture of
an asparagus but labelled it as "rose twig with thorns". On the other
hand, he was able to draw very detailed pictures from memory which is a
task depending on imagery.

As double dissociation usually suggests that two functions rely on
different brain regions or physiological mechanisms, the described
examples imply that imagery and perception do not share exactly the same
physiological mechanisms. This of course conflicts with the evidence
from brain imaging measurements and other cases of patients with brain
damage mentioned above that showed a close connection between imagery
and perception.

### Interpretation of the neuropsychological results

A possible explanation for the paradox that on the one hand there is
great evidence for parallels between perception and imagery but on the
other hand the observed double dissociation conflicts with these results
goes as follows. Mechanisms of imagery and perception overlap only
partially so that the mechanisms responsible for imagery are mainly
located in higher visual centres and the mechanisms underlying
perception are located at both lower and higher centres (Figure 9, not
included yet due to copyright issues). Accordingly, perception is
thought to constitute a bottom-up-process that starts with an image in
the retina and involves processing in the retina, the Lateral Geniculate
Nucleus, the striate cortex and higher cortical areas. In contrast,
imagery is said to start as a top-down process, as its activity is
generated in higher visual centres without any actual stimulus, that is
without an image on the retina. This theory provides explanations for
both the patient with impaired perception but normal imagery and the
patient with normal perception but impaired imagery. In the first case,
the patient's perceptual problems could be explained by damage to early
processing in the cortex and his ability to still create images by the
intactness of higher areas of the brain. Similarly, in the latter case,
the patient\'s impaired imagery could be caused by damage to
higher-level areas whereas the lower centres could still be intact. Even
though this explanation fits several cases it does not fit all cases.
Consequently, further research has to accomplish the task of developing
an explanation that is able to explain the relation between perception
and imagery sufficiently.

## Imagery and memory

Besides the imagery debate, which is concerned with the question how we
imagine for example objects, persons, situations and involve our senses
in these mental pictures, questions concerning the memory are still
untreated. In this part of the chapter about imagery we are dealing with
the questions how images are encoded in the brain, and how they are
recalled out of our memory. In search of answering these questions three
major theories evolved. All of them explain the encoding and recalling
processes different, and as usual validating experiments were realised
for all these theories.

In search of answering these questions, three major streams evolved. All
of them try to explain the encoding and recalling processes differently
and, as usual, validating experiments were realised in all streams.

### The common-code theory

This view of memory and recall theories that images and words access
semantic information in a single conceptual system that is neither
word-like nor spatial-like. The model of common-code hypothesis that for
example images and words both require analogous processing before
accessing semantic information. So the semantic information of all
sensational input is encoded in the same way. The consequence is that
when you remember for example a situation where you were watching an
apple falling down a tree, the visual information about the falling of
the apple and the information about the sound, which appeared when the
apple hit the ground, both are constructed on -- the -- fly in the
specific brain regions (e.g. visual images in the visual cortex) out of
one code stored in the brain. Another difference of this model is that
it claims images require less time than words for accessing the common
conceptual system. Therefore images need less time to be discriminated,
because they share a smaller set of possible alternatives than words.
Apart from that words have to be picked out of a much larger set of
ambiguous possibilities in the mental dictionary. The heaviest point of
criticism on this model is that it does not declare where this common
code is stored at the end.

### The abstract-propositional theory

This theory rejects any notion of the distinction between verbal and
non - verbal modes of representation, but instead describes
representations of experience or knowledge in terms of an abstract set
of relations and states, in other words *propositions*. This theory
postulates that the recall of images is better if the one who is
recalling the image has some connection to the meaning of the image
which is recalled. For example if you are looking at an abstract picture
on which a bunch of lines is drawn, which you cannot combine in a
meaningful way with each other, the recall process of this picture will
be very hard (if not impossible). As reason for this it is assumed, that
there is no connection to propositions, which can describe some part of
the picture, and no connection to a propositional network, which
reconstructs parts of the picture. The other case is, that you look at a
picture with some lines in it, which you can combine in a meaningful way
with each other. The recall process should be successful, because in
this case you can scan for a proposition which has at least one
attribute with the meaning of the image you recognised. Then this
proposition returns the information which is necessary to recall it.

### The dual-code theory

Unlike the common-code and abstract-propositional approaches, this model
postulates that words and images are represented in functionally
distinct verbal and non - verbal memory systems. To establish this
model, Roland and Fridberg (1985) had run an experiment, in which the
subjects had either to imagine a mnemonic or how they walk the way to
their home through their neighbourhoods. While the subjects did one of
this tasks, their brain was scanned with the positron emission
tomography (PET). Figure 10 is a picture combining the brains of the
subjects, which achieved the first and the second task.

!Figure 10: Green dots represent regions which showed a higher activity
during the walking home task; yellow dots represent regions which showed
a higher activity during the mnemonic
task.

As we can see on the picture, for the processing of verbal and spatial
information different brain areas are involved. The brain areas, which
were active during the walking home task, are the same areas which are
active during the visual perception and the information processing. And
among those areas which showed activity while the mnemonic task was
carried out, the Broca-centre is included, where normally language
processing is located. This can be considered as an evidence for both
representation types to be somehow connected with the modalities, as
Paivio's theory about dual-coding suggests Anderson (1996). Can you
imagine other examples, which argue for the dual-code theory? For
example, you walk along the beach in the evening, there are some beach
bars ahead. You order a drink, and next to you, you see a person, which
seems to be familiar to you. While you drink your drink, you try to
remember the name of this person, but you fail stranded, even if you can
remember where you have seen the person the last time, and perhaps what
you have talked about in that situation. Now imagine another situation.
You walk through the city, and you pass some coffee bars, out of one of
them you hear a song. You are sure that you know that song, but you
cannot remember the name of the interpreter, nor the name of the song
either where you have heard it. Both examples can be interpreted as
indicators for the assumption that in these situations you can recall
the information which you perceived in the past, but you fail in
remembering the propositions you connected to them.

!Figure 11: An abstract picture vs. a smiling Knut with a baseball
cap

In this area of research, there are of course other unanswered
questions, for example why we cannot imagine smell, how the recall
processes are performed or where the storage of images is located. The
imagery debate is still going on, and ultimate evidence showing which of
the models explains the connection between imagery and memory are
missing. For now the dual-code theory seems to be the most promising
model.

## References

Anderson, John R. (1996). Kognitive Psychlogie: eine Einfuehrung.
Heidelberg: Spektrum Akademischer Verlag.

Bryant, D. J., B. Tversky, et al. (1992). "Internal and External Spatial
Frameworks for Representing Described Scenes." Journal of Memory and
Language 31: 74-98.

Coucelis, H., Golledge, R., and Tobler, W. (1987). Exploring the anchor-
point hypothesis of spatial cognition. Journal of Environmental Psychol-
ogy, 7, 99-122.

E.Bruce Goldstein, Cognitive Psychology, Connecting Mind, Research, and
Everyday Experience (2005) - .

Marmor, G.S. and Zaback, L.A. (1976). Mental Rotation in the blind: Does
mental rotation depend on visual imagery?. Journal of Experimental
Psychology: Human Perception and Performance, 2, 515-521.

Roland, P. E. & Fridberg, L. (1985). Localization of critical areas
activated by thinking. Journal of Neurophysiology, 53, 1219 -- 1243.

Paivio, A. (1986). Mental representation: A dual-coding approach. New
York: Oxford University Press.

## Links & Further Reading

Cognitive Psychology
Osnabrueck

Dr. Rolf A. Zwaan\'s Homepage with many
Papers

**Articles**

Cherney, Leora (2001): Right Hemisphere Brain
Damage

Grodzinsky, Yosef (2000): The neurology of syntax: Language use without
Broca's
area.

Mueller, H. M., King, J. W. & Kutas, M. (1997). Event-related
potentials elicited by spoken relative
clauses;
Cognitive Brain Research 4:193-203.

Mueller, H.M. & Kutas, M. (1996). What's in a name?
Electrophysiological differences between spoken nouns, proper names and
one's own
name;
NeuroReport 8:221-225.

Revised in July 2007 by: Alexander Blum (Spatial Representation,
Discussion of the Imagery Debate, Images), Daniel Elport (Propositional
Representation), Alexander Lelais (Imagery and Memory), Sarah Mueller
(Neuropsychological approach), Michael Rausch (Introduction, Publishing)

Authors of the first version (2006): Wendy Wilutzky, Till Becker,
Patrick Ehrenbrink (Propositional Representation), Mayumi Koguchi, Da
Shengh Zhang (Spatial Representation, Intro, Debate).

