Topic: representation. Very often, imagery experiences are

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Topic: Methods of Mental Imagery




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Mental imagery can
be explained as a visual representation in the absence of environmental input.
Mental images cannot be recreated upon everyone’s will. Sir Francis Galton
discovered this in 1883 when he asked 100 people, including prominent
scientists, to form an image of their breakfast table from that morning. Some
had detailed images, others reported none.


Mental Imagery is
said to be a quasi-perceptual experience; it resembles perceptual
experience, but occurs in the absence of the appropriate external stimuli. They
are varieties which are sometimes referred to as visualizing and seeing in the
mind’s eye. It is also generally understood to bear intentionality (i.e.,
images of something or other), and thereby to function as a form of
mental representation. Very often, imagery experiences are understood by their
subjects as echoes, copies, or reconstructions of actual perceptual experiences
from their past; at other times they may seem to anticipate possible, often
desired or feared, future experiences. Thus, 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 visual-spatial reasoning and inventive or creative
thought. Indeed, according to a long dominant philosophical tradition, it plays
a crucial role in all thought processes, and provides the semantic grounding
for language.




Mental imagery is a
familiar aspect of our everyday experiences. Everybody has a mental imagery
during dreams, some are capable of deep levels of hypnosis which can occur in
visual hallucinations, but this is quite unusual. Some researches state that
the same area of the brain which is used for normal perception is also
triggered by mental imagery. During early study of mental imagery by Roger
Shepard of Stanford University and various colleagues. He used
computer-generated block shapes like shown below. Three of the shapes are the
same as each other, only rotated. The fourth is different; it is a mirror image
of the others.


Can you find the
one that is a mirror image? To determine this, most subjects must mentally
rotate the figures, much as they would rotate a three-dimensional block
model, to see if each matches the others.






























The conclusion for
the following experiment with mental rotation was that it was found that the
time required for mental rotations depended upon the amount of rotation. This
was a very important finding, because it implied that mental images could be
manipulated as if real.


Despite the
familiarity of the experience, the precise meaning of the expression ‘mental
imagery’ is remarkably hard to pin down, and differing understandings of it
have often added considerably to the confusion of the already complex and
fractious debates, amongst philosophers, psychologists, and cognitive
scientists, concerning imagery’s nature, its psychological functions (if any),
and even its very existence. In the philosophical and scientific literature
(and a fortiori in everyday discourse), the expression ‘mental imagery’
(or ‘mental images’) may be used in any or all at least three different senses,
which are only occasionally explicitly distinguished, and all too often


{1} quasi-perceptual conscious experience per se;


{2} hypothetical picture-like representations in the mind and/or brain
that give rise to {1};


{3} Hypothetical inner representations of any sort (picture-like or
otherwise) that directly give rise to {1}.


it is not because they are picture-like, what is it that makes these mental
representations mental images? Presumably the idea is that a mental
representation deserves to be called an


if it is of such a type that its presence to mind (i.e., its playing a role in
some currently occurring cognitive process) can give rise to a quasi-perceptual
experience of whatever is represented. But this relies upon already having
a grasp of the experiential conception of imagery, which
therefore must, be more fundamental than the representational conception.
Many scientists and philosophers, coming from a diverse range of
disciplinary and theoretical perspectives, do not accept that imagery
experiences are caused by the presence to mind of representational tokens. It
should be admitted, however, that focusing too narrowly on the experiential
conception of imagery has its own potential dangers. It may obscure the
very real possibility, foregrounded by the representational conception,
that importantly similar underlying representations or mechanisms may sometimes
be operative both when we consciously experience imagery and sometimes when we
do not.


practice, both the experiential and the representational conceptions of imagery
are frequently encountered in the literature of the subject. Unfortunately, it
is often hard to tell which is intended in any case. Even where they are not
actually conflated, confusion can arise when one conception is favored over the
other without this ever being made sufficiently clear or explicit. Although it
would be pedantic and potentially confusing to insist on explicitly drawing the
distinction everywhere, where it seems important or helpful to do so this entry
will refer to imagery experiences (or quasi-perceptual experiences)
on the one hand, and imagery representations (or imagery
processes) on the other.



Imagery in Cognitive


revival of interest in imagery was an important component of the so called cognitive
revolution in psychology during the 1960s and early 1970s, a period when
the Behaviorist intellectual hegemony over the field was broken and the
concept of mental representation was established as central and vital to
psychological theorizing (Baars, 1986; Gardner, 1987; Leahey, 1992).


the emergence of computational models of mental processes probably played the
leading role in the rise of cognitive psychology and cognitive science, the new
interest in imagery was independently motivated, and contributed significantly
to the growing feeling, amongst psychologists, that both the ontology and
methodology of Behaviorism were excessively restrictive, and that inner mental
processes and representations could, after all, be useful, or even crucial,
scientific concepts. Quite apart from the broader talk of revolution in
psychology in this era (Hebb, 1960), there seems to have been a real sense, at
the time, that the revival of interest in imagery was, in itself, an insurgent
movement liberating psychologists from entrenched but outworn Behaviorist
dogmas. The imagery revival was depicted in dramatic terms as “the return of
the ostracized” (Holt, 1964; cf. Haber, 1970), as “a dimension of mind
rediscovered” (Kessell, 1972), and as marking “a paradigm shift in psychology”


The focus of this essay is on Methods in studying mental imagery and empirical
methods that justify the theories put forward.

a)  Visual Mental Imagery and Visual Perception


During visual
mental imagery, perceptual information is retrieved from long-term memory,
resulting in the subjective impression of ”seeing with the mind’s eye”. The
phenomenological similarity between visual imagery and visual perception has
been noted at least since the time of the Greek philosophers. At least since
the 1960s, after the cognitive revolution that followed the behaviorist years,
‘analog’ theories assume that visual mental imagery and visual perception share
numerous common representations and processes. This hypothesis led to many
behavioral predictions. For example, visual imagery selectively interferes with
visual perception more than auditory perception, i.e. more time is required to
scan greater distances across visualized objects, and eye movements during
imagery are similar to those made during perception. This view leads us to
predict substantial overlap in neural activation during visual mental imagery
and visual perception.


The study was designed specifically


To compare directly the pattern of brain activation during visual
mental imagery and visual perception across most of the brain, and quantify the
degree of overlap.

To compare stimuli and tasks that differed on the surface but were


to share numerous underlying processes.


perceptual task required participants to decide whether names were appropriate
for objects presented in canonical or non-canonical views, and the imagery task
required participants to visualize upper case letters in grids and decide
whether an X would have fallen on each letter, if it were actually present.
Positron emission tomography (PET) was used to monitor regional cerebral blood
flow as participants performed these tasks. The aim of the study was to
establish a lower bound on the amount of overlap between brain regions engaged
during visual mental imagery and perception. The main finding was that
approximately two thirds of the activated regions were engaged by both tasks,
suggesting a substantial degree of overlap in the underlying processing. This
study has two major limitations. The first is that the amount of overlap
was calculated on the proportion of regions that were activated in common over
a threshold, ignoring the extent of activation. This can be misleading. The
second limitation is that the imagery and perception tasks differed in many
ways, which is likely to lead us to underestimate the amount of overlap that
would be found in imagery and perception tasks that are more similar.


The present
study to compare the upper bound of the similarity in processing between
visual imagery and visual perception. To do so, we devised a task that could be
used in both imagery and perception conditions so that differences in the
pattern of brain activation observed in these two conditions could not be attributed
to task differences. The visual mental imagery task consisted of forming a
mental image of a previously studied line drawing and then evaluating a probed
property (e.g., judging whether the task was identical to the visual imagery
task, with the only difference being that a faint picture was presented on a
computer monitor throughout each trial and participants evaluated the visible
picture (Fig. 1). In addition, we used functional magnetic resonance imaging
(fMRI), which allows us to quantify the amount of overlap by comparing the
number of voxels activated in common during imagery and perception. This study
allowed us to assess precisely the pattern of similarities and differences in
brain activation between the two activities. Although the crucial comparisons
are between


the two conditions,
we nevertheless needed a baseline against which to assess the degree of





















The above figure
explains the schematic of the structure of a trial in the imagery and
perception conditions. In the imagery condition, participants kept their eyes
closed throughout the scan. Each trial began with the name of a previously
studied object, presented auditory via headphones. In the imagery condition,
participants had to generate a visual mental image of the object. In the
perception condition, participants saw a faint picture of the named object.
Both cases, participants had to wait for the auditory probe (4.5 s later;
”W”, meaning ”wider than tall” in this schematic) specifying the judgment
to be performed. Upon hearing the probe, participants performed the judgment as
quickly and accurately as they could, and response times (RT) and accuracy were


Both visual mental
imagery and visual perception are the product of the interplay of multiple
cortical and subcortical regions (e.g., Refs. 4,8).
Thus, we expected both conditions to engage large sets of brain areas.
Moreover, based on the study by Kosslyn et al. 6,
we expected to find a substantial amount of overlap between the conditions.
Because we used two versions of the same task in the perception and imagery
conditions, thus equating many of the task requirements in these two
conditions, we expected the overlap to be especially high in brain regions more
heavily involved in cognitive control, such as prefrontal cortex (e.g., Ref. 9) and parietal cortex (e.g., Refs. 1,2,6). Furthermore, consistent with the
results of previous studies, we also expected imagery and perception to draw on
many of the same portions of occipital and temporal cortex, including striate
cortex 2,3,5,6,7,10.



Materials and Methods


this experiment they chose twenty normal, right-handed volunteers (8 males, 12
females, mean age = 21 years) as participants to participate in the study. All
participants had normal or corrected-to-normal vision, were right-handed, and
had no history of neurological disease. All participants gave written informed
consent for the study according to the protocols approved by Harvard University
and Massachusetts General Hospital Institutional Review Boards. Five of


twenty participants were not included in the analyses because a large portion
of their data was not usable, either because of uncorrectable motion artifacts
(two participants) or because of equipment problems (three participants). The
demographics of these five participants were comparable to those of the entire
group. Thus, the analyses reported here were on data from the remaining 15
participants. The stimuli for the experiment were that they prepared 96
line drawings of common objects, using a white foreground against a black
background. The visual contrast of the drawings was 15% to reduce brain
activation that would be elicited by the stimuli in visual cortex during the
perception condition. An example of a stimulus is shown in Fig. 1. Additional
stimuli were prepared for the practice trials (four for each block). We divided
the objects into two sets, and presented one in imagery blocks, the other in
perception blocks, counterbalanced across participants. These sets, in turn,
were divided into three subsets, each used with a pair of judgments. The
possible judgments were: ”taller than wide,” ”wider than tall,” ”contains
circular parts,” ”contains rectangular parts,” ”more on top,” and ”more on
bottom.” Each judgment was associated with an auditory probe cue (e.g., ”W”
for ”wider than tall”).


The stimuli
were projected via a magnetically shielded LCD video projector onto a translucent screen placed behind the head of
the participants. Participants could see the stimuli via a front-surface mirror
mounted on the head coil. Prior to the MRI session (3–7 days in advance), the
participants a booklet with hard copies, white foreground on black background,
of all the stimuli, one per page; they were asked to study the stimuli in
preparation for the MRI experiment. The types of questions that would be asked
during the MRI session were not described to them, so as to minimize the
possibility that object characteristics might be encoded verbally during study. Each MRI session consisted of six functional scans,
alternating imagery and perception
conditions. The imagery and perception conditions were administered in separate
scans to avoid potential artifacts due to the cognitive demands associated with
task switching 31–33. Before the scans, the participants listened to the
names of all the objects to be presented in the experiment, which was intended
to help them understand the words during the noisy echoplanar imaging (EPI)
session. Before each functional scan, we gave each participant detailed
instructions, which included teaching them how to make the appropriate
judgments for that block and the meanings of the probe cue abbreviations. We
then presented four practice trials. In the imagery scans, we turned off all
room lights and asked participants to keep their eyes closed, to eliminate any
residual light that might have been present in the room (e.g., from equipment
LEDs). Each trial began with the name of a picture, presented auditorily, at
which point participants were to generate the corresponding visual mental
image. An auditory probe was presented 4.5 s later and participants performed
the corresponding judgment on the visualized object. Two judgments were used in
each scan, randomly intermixed (out of six possible judgments), to reduce the
chance that participants performed the judgment before the auditory probe.
Participants responded by pressing one of two keys with the dominant hand. We
asked the participants not to press either key if they could not understand the
name at the beginning of a trial, so that these trials could be later
identified and discarded. Participants were instructed to avoid eye movements
and to be ready for the next trial while keeping their eyes closed during the
interval between trials. In the perception scans, we asked participants to
perform the same task, but based on a visible picture instead of a


image. The structure of each trial was the same as in the imagery condition,
with the following differences: The participants kept their eyes open, and a
low-contrast line drawing of the named object was presented on the screen from
the onset of the auditory name until the response was made. Immediately after
each trial, the participants were to fixate on a small asterisk presented on
the screen and to be ready for the next trial. In both conditions, participants
were instructed to try avoid ”day dreaming” during the interval between
trials and to focus on being ready to process the next trial. They were asked
to make the appropriate judgment as quickly and accurately as possible. Each
scan consisted of 16 trials, for a total of 48 trials per condition. The
inter-trial interval was 21 s. On average, the interval between the end of one
trial and the beginning of the next was about 15s.


In conclusion,
the present results further document that visual imagery and visual perception
draw on most of the same neural machinery. However, the overlap is neither
uniform nor complete; visual imagery and visual perception appear to engage
frontal and parietal regions in more similar ways than occipital and temporal
regions. This finding may indicate that cognitive control processes function
similarly in both imagery and perception, but—perhaps counter-intuitively— at least
some sensory processes may be engaged differently by visual imagery and





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2  A. Ishai, L.G. Ungerleider, J.V. Haxby, Distributed neural systems for
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A. Ishai, J.V.
Haxby, L.G. Ungerleider, Visual imagery of famous faces: effects of memory and
attention revealed by FMRI, Neuro- Image 17 (2002) 1729– 1741.

4  S.M. Kosslyn, Image and Brain, MIT Press, Cambridge, MA, 1994.


5  S.M. Kosslyn, W.L. Thompson, When is early visual cortex activated
during visual mental imagery? Psychol. Bull. 129 (2003) 723– 746.


S.M. Kosslyn, W.L.
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7  S.M. Kosslyn, A. Pascual-Leone, O. Felician, S. Camposano, J.P.
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8  S.M. Kosslyn, G. Ganis, W.L. Thompson, Neural foundations of imagery,
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9  E.K. Miller, J.D. Cohen, An integrative theory of prefrontal cortex
function, Annu. Rev. Neurosci. 24 (2001) 167– 202.


10  K.M. O’Craven, N. Kanwisher, Mental imagery of faces and places
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11Porter K, Foster J. The mental athlete. Iowa: W.M.C. Brown
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