Introduction to Visual Agnosias
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Welcome to the Vision and Aging Lab’s tutorial on visual agnosias. There are several
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agnosias!
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Manpreet Rai or Dr. Donald Kline
What are Visual Agnosias?
Copyright 2004 by Manpreet Rai and Donald Kline, all rights reserved
What are Visual Agnosias???
General Definition of Agnosia:
Agnosia = “a” not + “gnosis” to know.
Thus visual agnosia would therefore be the inability to know (recognize) something by
looking at it (visually).
History of Agnosias
Although very rare, Agnosia has been around for quite some time. As early as 430 BC
Thucydides said agnosia develops because of the plague.
Hippocrates also mentioned symptoms of agnosias in his writings in “On Sacred Disease”
Research in visual agnosias began in the field of experimental psychology when Monk
observed dogs with brain lesions in 1877. Monk called agnosia “seelenblindsheit”
Freud coined the term visual agnosia in 1891 as he used the term to make distinction
between perception and recognition.
Freud’s term is still used today, mostly as an impairment of visual form of visual object
agnosias. In general it the inability to recognize or identify familiar objects or faces
without having any primary visual field problems. The recognition problem is due to
neurological problems in certain brain areas depending no the type of agnosia. It seems
that most, if not all agnosias are acquired rather than congenital disorders in that most are
caused by brain lesions due to trauma, ischaemia, tumor or carbon monoxide poisoning
all of which effect higher order visual centers.
Types of Agnosias
Types of Agnosias
Although there is no DSM-IV-TR official categorization of agnosias, the most common
way of categorizations is to divide the agnosias into two main categories: the
appreceptive agnosias, and associative agnosias.
The Appreceptive Agnosias
Appreceptive agnosias also known as visual space agnosias) is a condition in
which a person has a failure of object recognition caused by impartment in the occiptotemporal vision areas with all elementary visual functions such as acuity, colour vision,
and brightness discrimination still intact. Appreceptive agnosics have trouble
recognizing, matching, or copying or discriminating between stimuli, since they cannot
make out visual shapes.
When patients do identify objects, they do so because they have made inferences about
what the object might be using colour, size, texture, and reflective cues to piece together
the whole object. They do not however use any shape information.
Picture of coin and key
chain. The patient would
describe the coin as a
key chain because of the
contours of the trim of
the coin.
Appreceptive agnosias usually occur after recovery
from cortical blindness caused by toxins (such as
carbon monoxide poisoning).
There are several subtypes of appreceptive
agnosias. Please click on the subtype below obtain
further information:
Dorsal Simultanagnosia
Visual hemi-neglect
Ventral Simultanagnosia
Associative Agnosia
Associative agnosia is also known as visual object agnosia. This agnosia is a
characterized by a variety of symptoms, but the main impairment is that of recognizing
visually presented objects despite having intact visual perception of that object. There are
three specific criteria to have a diagnosis of associative agnosia as presented by
Farah1990). The three criteria are:
1) Difficulty recognizing a variety of visually presented objects (i.e. by naming or
grouping objects together according to their semantic categories).
2) Normal recognition of a variety of objects be other senses such as touch, smell
taste or when given a verbal description of it.
3) Intact elementary visual perception, enough to redraw an object an suggestively
recognize it
Thus from these criteria a patient may be able to replicate a drawing but still not
recognize is. Thus associative agnosia is in many cases called recognition without
meaning.
Insert sample of what
associative agnosias might
draw, (with respect to object
(i.e. perfect drawing, but can’t
name what he/she just drew)
Associative agnosia usually occurs due to brain damage ranging from the right
posterior regions to the unilateral left posterior regions, and sometimes even both!
There are several types of associative agnosias as well. Please click on the tabs below
for further information.
Prosopagnosia
Colour Agnosia
Treatments of Visual Agnosia
Topographical agnosia
Dorsal Simultanagnosia
Simultanagnosia means an inability to recognize two things simultaneously.
Patients with Dorsal Simultagnosia can identify some parts of an object and use that to
make inferences of the whole object. Simultanagnosia was coined by Wolpert, and Luria
made it more specific referring to it as a visual deficit in which only one object can be
seen at a time, so an attentional problem is also a factor in this agnosia, since unattended
objects are at seen at all. Doral Simultanagnosia patients cannot localize stimuli even
when it is seen. It is due to damage in the bilateral parieto-occipital region of the brain.
Dorsal simultanagnosia patients may be impaired in their reading and counting since
theses activities involve seeing more than one thing at a time. Therefore, it may inhibit
them from working in jobs that require such activities. Dorsal simultanagnosia patients
also bump into objects that are close together, thus may act blind. Motion may further
impair their ability to perceive objects. Thus a whole object may be perceived but not in
the presence of another object, both are not perceived.
Insert photo pf overlapping objects (i.e. hockey
stick, hammer, flask, spoon etc). A patient with
dorsal simultanagnosia will only say they see one of
the items, and disregard the rest, even saying the
other items do not even exist.
Return to Appreceptive Agnosias page
Ventral Simultanagnosia
Like dorsal simultanagnosia, patients with this disorder can not identify more than
on object, or objects with complex entities at a time. However, the brain region involved
is the left inferior temporo-occipital regions. Ventral simultanagosics can see more than
one object at a time (as seen in their ability to count scattered dots, and walk around
without bumping into obstacles such as a couch and a table that are both in the same
vicinity. However ventral simultanagnosic patients are mostly impaired in their ability to
read, and describe complex pictures (Farah, 1990). These patients may be able to describe
one aspect of a picture without having a clear understanding of the picture as a whole.
Insert Picture of mountain scene, as a stimulus that patient
cannot recognize the picture as a scene from the pyramids,
since she fails to see the camel.
Return to Apperceptive Agnosias page.
Visual Hemi-Neglect
Visual hemi neglect is the inability to perceive thing on a person’s left side in
spatial orientation due to right parietal lobe damage. Tests such as block drawings, or
drawings or designs or incomplete pictures is a sign that a patient can clearly make out
the right side, but completely ignore the left side.
Insert picture of a drawing that a hemineglect patient may complete
(neglecting the left side)
Return to Apperceptive Agnosias page
Colour Agnosias
In colour agnosias visual perception of colour vision, and brightness discrimination is
still intact. Nevertheless, there is a severe impairment in the ability to name and
distinguish between colours. Colour agnosics usually have lesions in their left
occitpotemporal regions of the brain. A test to check colour agnosia may be a
combination of giving names to colours, or showing a patient an incorrectly coloured
object. If the patient identifies it as incorrect they may have colour agnosia. Thus a blue
banana may seem perfectly normal to a colour agnosics. It is important to note however
that these patients are not colour blind, slice they perform well on colour tests such as
arranging hues, and passing the Ishihara plate test. A small number of colour agnosics
may suffer from achromatopsia as well.
Insert picture of blue banana, orange apple, and some
other discolored object. Agnosics patients will identify
these objects as normal.
Return to Associative Agnosia Page
Topographical Agnosia
Topographical agnosia patients are unable to use visual cues to direct to go in a particular
direction. This happens because they are unable to recognize the objects around them,
which makes this agnosia fall under the associative category of agnosias. Topographical
agnosia patients therefore may not be able to navigate efficiently around their own
bedroom. It is important to not however that these patients have excellent topographical
memory so can describe the layout of their house, or even their workplace. Topographic
agnosia is due to right posterior cingulate lesions in the brain.
Return to Associative Agnosias Page
Prosopagnosia
Prosopagnosia is probably the most well known associative agnosias being the
inability to recognize faces, despite having adequate vision and intelligence. Bodmer first
coined the term prosopagnosia in 1947, although cases were first reports as early as 1844.
In 1962 Hecan formally defined prosopagnosia as “a failure to recognize people known
to the patient on the basis of visual perception of their faces” (Lanids, 1991). This
definition is still sued today, but has expanded somewhat in that it no longer limited just
to faces. Prosopagnosia can also be used as a way of classifying impairments in
recognizing specific types of animals (such as a bird watcher being unable to recognize
specific species of birds). Sometimes a patient with prosopagnosia can recognize an
expression on a face, but still cannot recognize the face as a whole. Other times a person
may be able to recognize a face by recognizing the person’s voice, or identifying
contours of a loved ones face. Other features such as a mole that the patient remembers
may be the cue they use to recognize a person’s face. For prosopagnosia patients there is
always a lesion in the right inferior-medial temporo-occipital area, however cases with
bilateral lesions have been reported as well. Seven out of 14 patients with unilateral
posterior artery stroke in the acute stage had prosopagnosia as well.
A great example of a prosopagnosia is with Mr. P in Sacks’ study the man who mistook
his wife for a hat. He could only recognize his wife by her voice, and could only
recognize pictures of his family and friends through specific no-facial features, (such as
military clothes that his army brother may be wearing, or a persons chipped tooth so that
of his good friend bob for instance).
Return to Associative Agnosias page
Treatment of Visual Agnosias
As one can see from the previous pages, the different visual agnosias can be very
debilitating for a person, as it may hinder their day to day functioning, and even be
traumatic for the people around the patient with agnosia, such as family and friends.
However, since brain lesions cause all of the agnosias, there is no treatment since it is not
impossible to ‘unlesion’ areas of the brain. Patients however do go on living with a
decent lifestyle as there are several ways in which to cope with agnosias. To being with
agnosia patients can still use cues to identify and recognize objects. Thus other senses
come to be very important for agnosia patients. Take Mr. P for example, he can still carry
on with his love of teaching of music, since he still has all his hearing senses in tact, thus
the agnosia may hinder his ability to recognize faces, and objects, but he can still teach
music. Furthermore, since agnosia patients have lost the ability to do something that they
could once do very quickly, such as identify a key chain as a key chain and not anything
else, making them slow down and spend some more time examining an object may help
them better identify it rather than their quick glance over and reply. This slowing down
when visualizing objects may take some time, but it can be seen as a rehabilitation
process, in which some recognition may be slowly learned again. Again all the other
taste, smell, touch, and hearing are important in this task as well.
Furthermore, a patient with agnosia may benefit greatly from consistency, such as having
his/her shirt and pants in the same place every morning, and having furniture in similar
places all the time. Since agnosia patients have intact memory, they can fund their way
around without fully recognizing an object but still get around in their job.
For patients who have lost their ability to write, such is the case with appreceptive
agnosics, a strategy called visual tracing may slowly help gain back some writing skills.
Here patients practice tracing letters with their fingers then make eye movements to track
their finger. Soon they practice writing with the finger traces, thereby learning how to
write just by using eye movements that mimic the finger traces.
Although there are ways of coping with having agnosias, a person must still go through a
major lifestyle change. For instance they most likely are depended on someone sled to
help them with getting around and about and even simple things like eating cereal with a
spoon rather than a knife. Also some patients are not as lucky as Mr. P, and may have to
leave their jobs if they cannot recognize their workplace, and the things around it. Mist
difficult however may be the prosopagnosia where family member and friends seem like
strangers. This is difficult for both the patient as well as the family members as well,
since having a loved one not recognize you can be very heartbreaking. The best way to
cope with this is just have patience with the agnosics. The patient can sue facials cues
such as birthmarks, and moles to recognize their loved one, or they can use the sound of
the loved ones voice as well to recognize them.
So there are no treatments for agnosia, the best way to deal with it is to adjust your
lifestyle to compensate for the lack of visual competence.
More information on Visual Agnosias