Disorders of Perception can involve sensory distortions or deceptions. Sensory distortions include changes in intensity, quality, or spatial form of real stimuli. Sensory deceptions include illusions and hallucinations. Hallucinations are false perceptions without an external stimulus and can involve any sense. They are caused by intense emotions, suggestion, psychiatric disorders, sensory organ disorders, sensory deprivation, or central nervous system disorders. Auditory hallucinations in psychiatry range from elementary sounds to fully formed voices. Visual hallucinations include flashes of light or fully formed visions. Hallucinations of other senses like smell are rarer.

1. Disorders of Perception
Dr Lagnajit Dash
1st Year PG
Dept of Psychiatry
IMS & SUM Hospital

2. • Definition
• Sensory distortions
– Changes in intensity
– Changes in quality
– Changes in spatial form (dysmegalopsia)
– Distortions of the experience of time
• Sensory deceptions
– Illusions
• Definition
• Types of illusions
– Hallucinations
• Definition
• Causes
• Hallucinations of induvidual senses
• Hallucinatory syndromes
• Special kinds of hallucination
• The patients attitude to hallucinations
• Body image distortions

3. PERCEPTION
Ability to see, hear or become aware of something
through the senses. It’s a way in which something is
regarded interpreted or understood.
2 Types
– Sensory distortions : constant real perceptual object, perceived in a distorted way,
– Sensory deceptions : new perception occurs that may or may not be in response to an external
stimulus.
Sensory Distortions
– These are changes in perception that are the result of a change in the intensity and
quality of the stimulus or the spatial form of the perception.

4. • Changes in intensity
– Hyperaesthesia
• Increased intensity of sensations (hyperaesthesia) due to intense emotions or a
lowering of the physiological threshold.
• Eg : a person may see roof tiles as a brilliant flaming red
hear the noise of a door closing like a clap of thunder.
• IN : Anxiety and depressive disorders
Hangover from alcohol ↑Sensitivity of
Noise
Migraine
– Hypoaesthesia
• Hypoacusis occurs in delirium, where the threshold for all sensations is raised.
Talk slowly and loudly
• Seen - depression and attention-deficit disorder.
• Visual and gustatory sensations may also be lowered in depression, for example,
everything is black or all foods taste the same.

5. • Changes in quality
– It is mainly visual perceptions that are affected by this, brought about by toxic substances.
• Colouring of yellow, green and red have been named xanthopsia, chloropsia and erythropsia.
Eg: drugs (santonin, poisoning with mescaline or digitalis) - used in the past to treat various
disorders.
– Metallic taste associated with the use of lithium, although this is not a hallucination but a true
change in gustation.
– Derealisation - unreal and strange,
– Mania - perfect and beautiful.
• Changes in spatial form (dysmegalopsia)
– Change in the perceived shape of an object.
• Micropsia - visual disorder in which the patient sees objects as smaller than they actually are.
• The opposite = macropsia or megalopsia.
• The terms used to describe the changes of size in dreams and hallucinations (Lilliputian
hallucinations).
– Metamorphosia - objects are irregular in shape.
– Seen in -
• temporal and parietal lobe lesions (m.c)
• retinal disease, disorders of accommodation & convergence
– oedema of retina micropsia.
– Scarring of retina macropsia,

6. – Complete paralysis of accommodation - macropsia,
– Partial paralysis of accommodation - micropsia
– If accommodation is normal but convergence↓ = macropsia occurs and vice versa.
during the aura or in the course of the fit
• Distortions of the experience of time
– From the psychopathological point of view there are two varieties of time:
• physical and personal, the latter being determined by personal judgement of the passage of
time. It is the latter that is affected by psychiatric disorders.
– Influence of mood on the passage of time, so when happy ‘time flies’, and when sad passes more
slowly.
1. In severe depression = time passes very slowly and even stands still.
2. By contrast the manic patient feels that time speeds by and that the days are not long enough
to do everything.
3. Some patients with schizophrenia believe that time moves in fits and starts, and may have a
delusional elaboration that clocks are being interfered with.
4. In acute organic states, disorders of personal time are shown in temporal disorientation and
overestimation of the progress of time.
5. Some patients with temporal lobe lesions may complain that time either passes slowly or
quickly.

7. SENSORY DECEPTIONS
– Illusions - misinterpretations of stimuli arising from an external object,
– Hallucinations - Perceptions - without an adequate external stimulus.
Illusions
– stimuli from perceived object are combined with a mental image to produce a false
perception.
Muller-Lyer illusion in which two lines of equal length can be made to appear unequal
depending on the direction of the arrowheads at the end of each respectively.
– Not indicative of psychopathology - occur in the absence of psychiatric disorder,
e.g person walking along a dark road may misinterpret innocuous shadows as
threatening attackers.
– llusions occur in delirium
– Visual illusion (m.c) f/b auditory illusions Eg . when a person hears words in a
conversation that resemble their own name and they believe they are being talked
about.
Fantastic illusions - xtraordinary modifications to their environment.
e.g pt– head in mirror--pig

8. Three types of Illusions
1. Completion illusions: Inattention such as misreading words in
newspapers or missing misprints because we read the word as if it were
complete.
e.g word ‘–ook’ misread as ‘book’ when faded letter was an ‘l’.
2. Affect illusions: these arise in the context of a particular mood state.
For example,
– Bereaved person may momentarily believe they ‘see’ the deceased
person,
– Delirious - innocent gestures as threatening.
– Severe depression - delusions of guilt
3. Pareidolia: Vivid illusions without the patient making any effort.
Excessive fantasy thinking and vivid visual imagery.
e.g Vivid pictures in fire or in clouds

9. Illusions have to be distinguished from intellectual
misunderstanding.
Distinction between Illusion and a functional
hallucination
functional hallucination - both stimulus and hallucination
are perceived by the patient simultaneously.
Illusion - Stimulus from the environment changes but forms an essential
and integral part of the new perception.
Trailing phenomenon - Moving objects are seen as series of
discreet and discontinuous images.
Associated with hallucinogenic drugs.

10. Hallucinations
A false perception which is not a sensory distortion or a misinterpretation, but
which occurs at the same time as real perceptions’.
Diff from true perceptions is that they come from ‘within’.
Perceptions Mental images Pseudo-hallucinations
substantial incomplete lack the substantiality
appear in objective space exist in subjective space subjective space
clearly delineated not clearly delineated clear and vivid
constant Inconstant -
sensory elements are full and
fresh
sensory elements have to be
recreated
-
Involuntary known to be real
perceptions
dependent on the will Involuntary and seen in full
consciousness known to be
not real perceptions (insight +)

11. Hallucinations
Causes(as a result of)
1. intense emotions
2. suggestion
3. psychiatric disorder,
4. disorders of sense organs,
5. sensory deprivation
6. Disorders of the central nervous system.
1. Emotion
– Depressed patients - delusions of guilt - hear voices
reproaching them.
– These are not the continuous voices & are disjointed or
fragmentary, eg ‘rotter’, ‘kill yourself’, etc.
– Continuous persistent hallucinatory voices in severe
depression arouse the suspicion of schizophrenia

12. 2. Suggestion
– Normal subjects can be persuaded to hallucinate.(hysterical psychosis)
E.g - walk down a dimly lit corridor & stop when see a faint light over
the door at the end.
3. Disorders of a peripheral sense organ
– Auditory Hallucinations & Visual hallucinations seen – Underlying CNS
Pathlogy.
• E.g. 66yr pt -glaucoma – V.H
– Charles Bonnet syndrome (phantom visual images) complex visual
hallucinations occur absence of any psychopathology & in clear
consciousness. (Usually Elderly)
Hallucinatory images last for years

13. 4.Sensory deprivation
• If incoming stimuli are reduced to minimum, pts. begin to
hallucinate after a few hours.
• Ex :
 sensory isolation - deafness - paranoid disorders in the deaf
 sensory deprivation – Cataract surgery - protective patches -
delirium
5.Disorders of the central nervous system
• Lesions of Diencephalons & Cortex – V.H & Auditory
sometimes
• Hypnagogic and hypnopompic hallucinations are special kinds
of organic hallucination.

14. Hallucinations of individual senses
Auditory Hallucinations : (PHONEMES)
– Elementary and unformed,
exp as simple noises, bells, undifferentiated whispers or voices.
– Organic States, F20 partly organised or completely organised.
• Hallucinatory Voices are basis for the patient’s delusion of persecution
– Depression – Seen in Severe .usually less well formed than F20
IMPERATIVE HALLUCINATIONS - The voices sometimes give instructions to the
patient(May/may not Like). Spk among themselves.Running Commentary
GEDANKENLAUTWERDWEN Pt hears one’s own thoughts spoken aloud
ECHO DE LA PENSEE – Pt hears after the thoughts have occurred
‘thought echo’ or ‘thought sonorisation’.
Thought Broadcasting/Diffusion - Thoughts no longer private & are accessible to
others.

15. • How It Originates – Witchcraft , radio , TV , Telepathy , Within their
Bodies(arms)
Movement of Lips, Tongue, laryngeal muscles
• Delusional elaboration of a hallucinatory
experience
Deny hearing voices but say that people talk about them
A.H usually Abusive & patient may attack responsible people
E.g. Greek woman who had been a patient in a long-stay ward for
many years.

16. • Visual :
• Elementary in the form of flashes of light,
• Partly organised(patterns) or completely organised(visions of people,
objects or animals.)
– Acute organic states - all varieties seen
– Delirium Small animals and insects are most often hallucinated.(asso with fear
& terror)
– Delirium Tremens – Mice carryin cases (extremely suggestible -reading blank
paper.)
– Epilepsy - Scenic hallucinations. visions of Fire, Religious scenes
– Temporal-lobe epilepsy Pts have combined auditory and visual hallucinations
– Visual hallucinations are extremely rare in schizophrenia, so much so that they
should raise a doubt about the diagnosis.

17. Smell (olfactory)
– Schizophrenia
– organic states
– Depressive psychosis.(Uncommon)
It may be difficult to be sure if there is a hallucination or an illusion.
e.g. Schizophrenia – Pt smell gas and & enemies poisoning them by pumping gas
into the room.
Temporal lobe disturbance – There is an aura (odour burning paint or
rubber.)
Padre Pio phenomenon - Sometimes the smell may be pleasant, e.g. Religious people
can smell roses around certain saints.
Taste (gustatory)
– Hallucinations of taste occur in schizophrenia and acute organic states but it is
not always easy to know whether the patient actually tastes something odd
or if it is a delusional explanation of the effect of feeling strangely changed.
– Depressed patients often describe a loss of taste or state that all food tastes
the same.

18. Touch (tactile)
• Formication - Small animals crawling over the body(acute organic states.)
COCAINE BUG - In cocaine psychosis - Small animals crawling over the body along with delusions
of persecution.
Sexual hallucinations - Acute and Chronic Schizophrenia,e.g. Pt complained that she could feel the
penis of her son’s employer in her vagina.
• Tactile hallucinations are of three main types:
A. superficial hallucinations, which affect the skin,
1. thermic (e.g. a cold wind blowing across the face),
2. haptic (e.g. feeling a hand brushing against the skin),
3. hygric (e.g. feeling fluid such as water running from the head into the stomach)
4. paraestethic (pins and needles), most often - organic origin.
B. Kinaestethic hallucinations affect the muscles and joints and the patient feels that their limbs are
being twisted, pulled or moved. (In F20 , Diff from del of Passivity)
e.g. Delirium tremens - Vestibular sensations like sinking in the bed or flying through the air
C. Visceral hallucinations – ex - F20 – c/c - Twisting & tearing pain
Bizzare – flesh ripped, Organs Twisted, Pulled out
Delusional Zoopathy - Animals crawling in body (Organic Disorders)

19. Sense of Presence
Sometimes there is the feeling that someone is present, whom they cannot see, and may or
may not be able to name.
e.g.
A. St Teresa of Avil
• This experience was probably the result of lack of sleep, hunger and religious
enthusiasm.
B. Pt Complained someone on right shoulder
Caused Distress , Hid under blanket
SEEN IN
– healthy people
– organic states,
– schizophrenia
– hysteria
– patient described above also had a diagnosis of borderline personality disorder.

20. Hallucinatory syndromes (hallucinosis)
Disorder in which there are persistent hallucinations in any sensory modality in
the absence of other psychotic features.
– Alcoholic hallucinosis A.H , During periods of relative abstinence
Sensorium is clear, hallucinations persisted < 1 week and are associated with
long-standing alcohol misuse
– Organic Hallucinosis - Seen in 20−30% of patients with dementia(Alz type).
Usually AH (VH) , disorientation and memory impairment
SPECIAL KINDS OF HALLUCINATION
Functional hallucinations
An auditory stimulus causes hall. & both the stimulus is experienced as well as
the hallucination.
Hallucination requires the presence of ‘another ‘real sensation.
• For example, a patient with schizophrenia first heard the voice of God as
her clock ticked; later she heard voices coming from the running tap and
voices coming from the chirruping of the birds.

21. Reflex hallucinations
Synaesthesia
Experience of a stimulus in one sense modality producing a sensory
experience in another.
E.g. Feeling cold in spine on hearing a fingernail scratch a blackboard.
LSD Intake feeling, tasting and hearing flowers simultaneously.
Reflex hallucinations - morbid form of synaesthesia. A stimulus in one
sensory field produces a hallucination in another.
• For example, a patient felt a pain in her head (somatic
hallucination) when she heard other people sneeze (the stimulus)
and was convinced that sneezing caused the pain.
Extracampine hallucinations
Hallucination that is outside the limits of the sensory field.
– For example,
• a patient sees somebody standing behind them when they are
looking straight ahead
• hear voices talking in London when they are in Liverpool.

22. • AUTOSCOPY OR PHANTOM MIRROR-IMAGE
– Experience of seeing oneself and knowing that it is oneself.
– Can occur in healthy subjects when they are emotionally upset or
when exhausted.
– Occasionally seen in schizophrenia but are more common in acute and
sub-acute delirious states.
– Organic state assoc - epilepsy, focal lesions affecting the
parieto−occipital region & toxic infective states.
• Internal Autoscopy – Pt sees own internal Organs
• Negative Autoscopy – Pt looks in the mirror and see no image,

23. • Hypnagogic and hypnopompic hallucinations
– Seen while subject is falling asleep or waking up respectively.
– The term ‘hypnopompic’ should be reserved for those
hallucinatory experiences that persist from sleep when the eyes
are open.
– Hypnagogic hallucinations seen during drowsiness,
discontinuous, appear to force themselves on the subject and
feeling subject participates as they do in a dream.
– In a subject deprived of sleep a hypnagogic state may occur, in
which case there are hallucinatory voices, visual hallucinations,
ideas of reference and no insight into the morbid phenomena.
It resolves once the subject has a good sleep.
– The importance of hypnagogic and hypnopompic phenomena is
to recognise that they are not indicative of any
psychopathology even though they are true hallucinatory
experiences. They also occur in narcolepsy.

24. Organic Hallucinations
– Seen in eye disorders , CNS Disorders , Optic tract lesions.
– Temporal lobe Lesions - Complex scenic hallucinations.
– Charles Bonnet syndrome
– Dementias , Delirium & Substance abuse - VH
Phantom limb - most common ( >6yr age, 95% Amputation cases)
No Sensation In limbs – Due to Amp or Destr. Of Somatic Pathways
Etiology - Peripheral & Central disorders..
Third Limb – Seen in Thalamo-parietal Lesions
Phantom Limb Generation – lesion of peripheral nerve, Spinal Cord & Medulla
Phantom organs – Following surgical procedures such as mastectomy, enuleation
of the eye, removal of the larynx

25. PATIENT’S ATTITUDE TO HALLUCINATIONS
• ORGANIC HALLUCINATIONS - Patient is usually terrified by the visual hallucinations and may
try desperately to get away from them.
The combination of the persecuted attitude and the visual hallucinations
↓
resistance to all nursing care & impulsive attempts to escape from the threatening situation
• Exception is Lilliputian hallucinations, usually regarded with amusement .
• Depression - often hear disjointed voices abusing them or telling them to kill themselves.
– The instructions are not frightening since they may have thought of this for some time anyway.
• Schizophrenia:
– The onset of voices in acute schizophrenia is often very frightening and the patient at times may
attack the person he believes to be their source.
– Those with chronic schizophrenia on the other hand are often not troubled by the voices and may
treat them as old friends, but a few patients complain bitterly about them.

26. BODY IMAGE DISTORTIONS
• Hyperschemazia - Perceived magnification of body parts,
seen In various organic and psychiatric conditions.
– When part of the body is painful it may feel larger than normal.
– When there is partial paralysis of a limb, the affected segment feels heavy and large, as
in
• Brown–Sequard paralysis,
• peripheral vascular disease,
• multiple sclerosis
• thrombosis of the posterior inferior cerebellar artery.
– It may also occur in non-organic conditions such as
• hypochondriasis,
• depersonalisation
• conversions disorder,
• feelings of fatness in anorexia nervosa
• Aschemazia/Hyposchemazia - Perception of body parts as absent or diminished
– parietal lobe lesions such as in thrombosis of the right middle cerebral artery,
– following transaction of the spinal cord
– health volunteers when underwater.
Hyposchemazia must be distinguished from nihilistic delusions.

27. • Paraschemazia (Distortion of body image) Parts of the body are
distorted or twisted or separated from the rest of the body
– hallucinogenic use,
– epileptic aura
– migraine on rare occasions.
• Hemisomatognosia - unilateral lack of body image, person behaves as
if one side of the body is missing. occurs in migraine or epileptic aura.
• Anosognosia - ‘denial of illness’.
• Hemispatial neglect - Neglect of the hemispace on the contralateral
side to the lesion when performing tasks.
e.g. Gerstmann syndrome (lesion of dominant parietal lobe)
- agraphia, acalculia, finger agnosia and right/left disorientation.

28. THANK YOU