Abnormal Perception PDF

Perception and its Abnormalities
Objectives:
1. Define perception
2. Describe the stages of perception and the factors which affect perception
3. Give examples of how the principles of perceptions are applied in
construction of psychological tests
4. Define the words which describe common abnormalities of perception
5. Discuss how perception is represented in brain and how it influences
formation of symptoms, that is, abnormalities of perception
6. Differentiate the terms Hallucinations from related terms.
Please watch the six video clips in the following order:
1. Perception and its Stages

2. Factors affecting Perception
3. Abnormal Perception
4. Agnosias
5. Hallucinations
6. Synesthesia
IVLE Folder Name: M2/MD2140 Phase II - AY2009/2010

Multimedia Psychological Medicine
Perception and its Stages
Definition: Is the process of making sensation meaningful
Stages: It consists of 3 stages
1. Selection: It is not possible for the brain to process all the sensations
that we receive. The brain decides which stimuli should be processed
2. Organization of stimuli:
a. Figure and ground: The mind must decide which part of the
sensation ids the background and which is the figure. For
example which is the words heard (Figure) and which is the
background or white-noise (ground)
b. Gestalt principles: These are the principles which explain that
the overall meaning is more than the sum of the meaning all
each components. (Whole is greater than sum of its parts)
i. Closure: Brain uses past experience and the templates
stored in the temporal lobe to see the image as complete
even when they are not complete
ii. Similarity: Brain makes meaning out of stimuli
received by grouping based on the similarity of the
stimuli. For example similar shapes, color etc.
iii. Grouping: Our mind tries to make meaning out of the
stimuli which are clustered together e.g. Braille
alphabets that blind people use to read from the
elevated clusters of dots.
3. Interpretation: This is the process of applying meaning to the

sensations after they have been selected and organized. This may
involve using past experience or knowledge to give meaning. For
example
Conclusion: We really create the image of reality inside our brain. This
depends on the way we select, organize and interpret stimuli.
Factors affecting Perception
We see what we want to see

There is no such thing as Objective data
We see the things not as they are but as we are
(Application: Based on this principle the tests of personality have been based.
These tests are called Projective tests of personality)
1. Attention:
a. Voluntary and voluntary control of attention: Complex mechanisms in the
brain decide to focus on some sensations rather than the others. This
means that we sometimes fail to see what is actually very obvious (called
inattentional blindness). This also explains how the same data is
interpreted by different people in a different way. This also applies to
medical scientific literature.
2. Integration of information: for example both ears, eyes do not transmit exactly
the same information. The brain can receive contradictory information and the
brain uses this difference to interpret the reality in terms of the size of the object,
distance of the object
3. Integration from different sensations. Similarly data from different sourses

must also be reconciled through the process of perception.
4. Biases:
a. Halo effect: Tendency to see positive qualities because it is attractive to
our senses e.g. Sweet is good
b. Confirmation bias: We try to gather information what supports our
decision. This is related to the principle of cognitive dissonance which
states that two contradictory ideas cannot coexist without anxiety. This
forces the person to make a choice between the two ideas.
5. Emotions:
a. If we are afraid we tend to perceive threatening stimuli more easily
b. If we have a hate for fatness we may perceive slight increases in out
weight
6. Context: Sensations acquire a different meaning by the change of context. Touch

can be interpreted as affection or attempt at molestation
7. Cognition: What we think may interfere with what we see e.g. Meaning of the
words may interfere with the color (Application: Based on this principle a test is
formulated called Color Stroop Test
Abnormal Perception
1. Agnosias :This is inability to recognize sensations even when the specific

sensation is not affected and there is no significant memory loss.
a. Visual agnosias
i. Akinetopsia: Inability to perceive motion. Motion is not inherent to
objects but the time difference between the two sensations. This
principle is used in cinemas.
ii. Associative agnosia:
iii. Form Agnosia: Failure to recognize the form of an object
iv. Object agnosia:
v. Prosapagnosia: Inability to recognize faces. Lesion in fisiform
gyrus.
vi. Word blindness
b. Amusia Failure to recognize music
Agnosias give good insight about how the various brain parts are organized and how
the various aspects of sensation are recognized by highly specialized brain areas.
For example depending on which specific part of the brain is involved, person may
loose the ability to recognize pitch, timber, rhythm or other specific qualities of
sounds.
2. Hallucinations
a. True hallucinations: They mave following characteristics
i. They are seen to be experienced through the sensory organs
ii. They are felt to be real like normal perceptions
iii. They are not produced voluntarily and cannot be stopped
voluntarily
iv. They occur without the stumulus
They may affect any of the sensory organs. They may or may not be enjoyable
to the individual, vary in their clarity but many people respond to these
experiences. Some people by talking to them, become violent or withdraw etc
as they patients take them as real voices.
When hallucinations do not fulfill one of these criteria they are called pseudo-
hallucinations.
Hallucinations commonly occur in psychotic disorders like schizophrenia or
neurological disorders like delirium or epilepsy.
They may give rise to delusions or make the person respond to such
experiences.
Hallucinations are elicited generally by asking question such as: When you
are awake, do you hear, see or smell things even when others around you
cant
More anterior the lesion in temporal lobe, the more formed are the
hallucinations. For example one may she flashes of light or sparks if the lesion
is in the primary visual area, it may be geometric patterns as the lesion is
anterior. Clear faces may be hallucinated when lesion is in fusiform gyrus.
b. Scenic hallucinations: These are hallucinations which are like a a cinema,
the perceiver is not involved with the image comapared with usual
hallucinations. These are seen often in Charles Bonet Syndrome.
c. Micropsia, Macropsia: This may occur as a part of paertial complex
seizures.
3. Illusions: Illusions are misinterpretations of sensation. Contrary to

hallucinations, there is sensation present in illusions.
4. Palinopsia: Persistence of an image after the disappearance of sensation.
5. Deja Wu: Feeling that you have been in this situation before. Although normal
people can experience this sometimes, this experience is quite common in
disorders like Migraine, Temporal Lobe Epilepsy etc Temporal lobe is probably
involved as the memories are stored in here and can be activated by stimulation of
this area
6. Synesthesia: Condition in which sensation in one modality evokes sensation in
other. So some we may hear taste, taste color. Insuch case fMRIs show that brain
areas for both seses is activated. This may be due to developmental or acquired
disorder when the activation in one sensory area can not reamin contained in that
area but spreads to the other sense. This often occurs after ingestion of
hallucinogenic drugs like LSD. This experience is involuntary and lasts life long.
Some normal individuals have this experience.
Other experiences which should be differentiated from hallucinations

7. Flashbacks: These experiences are like perceptual disturbances like hallucinations
but in fact they are disturbance of memory.
8. Imagination: These mimic perception but are in voluntary control of the
individual and not seen to arise out side sensory space. These characteristics are
not shared by Hallucinations hence these are very useful in differentiating these
from hallucinations.
9. Dream: These occur during sleep. This is the main feature to distinguish from
hallucination. There is increased electrical activity in corresponding brain area.
10. Intuition: Unlike hallucinations these are not a perceived through senses but ideas,
seen to originate within the mind and
Prepared by Dr Khare
Department of psychological medicine, NUHS
26.02.2010

Abnormal Perception PDF

Uploaded by

Copyright:

Available Formats

Abnormal Perception PDF

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Abnormal Perception PDF

Uploaded by

Copyright:

Available Formats

Perception and its Abnormalities

Please watch the six video clips in the following order:

1. Perception and its Stages

IVLE Folder Name: M2/MD2140 Phase II - AY2009/2010

Definition: Is the process of making sensation meaningful

Stages: It consists of 3 stages

3. Interpretation: This is the process of applying meaning to the

We see what we want to see

3. Integration from different sensations. Similarly data from different sourses

6. Context: Sensations acquire a different meaning by the change of context. Touch

1. Agnosias :This is inability to recognize sensations even when the specific

3. Illusions: Illusions are misinterpretations of sensation. Contrary to

Other experiences which should be differentiated from hallucinations

You might also like