Sensation : is the first stage in receiving information
from outside the self.
Perception : occurs when a stimulus has undergone
processing according to its form, color, motion.
The subject is able to recognize that an object is in his
field of vision- sensation intact
He is unable to recognize what the object or its
function is - impaired perception
Constant real perceptual object in a distorted
New perception that may or may not be in response
to an external stimulus………..sensory deception.
Sensory distortions….a) Visual perception
b) Auditory perception
c) Splitting of perception
Sensory deceptions …a) Illusions
Disturbance of the mental state with/without
organic brain pathology
Involve any elementary aspects of perception like
uniqueness , size , shape, colour ,location,motion or
Perceived object is correctly
recognized and identified yet there is a deviation
from its customary appearance.
Changes in spatial form
Alteration in the customary shape of perceived object.
Retinal disease,disorders of accomodation and
convergence,temporal & parietal lobe lesions
Rare association with schizophrenia.
May occur in poisoning with atropine or hyoscine.
Macropsia : size of perception is large.
Micropsia : size of perception is small.
Hemimicropsia : apparent reduction in one hemi field
of vision – temporal lobe epilepsy
Palinopsia : recurrence or prolongation of visual
phenomenon beyond the customary limits of
appearance of the real event
eg: “cat noticed in the street one day kept appearing at
various times and situation over the next few days”
Paraprosopia :when metamorphopsia affect faces.
Changes in intensity
Visual hyperasthesia: increased intensity of colour
Acrometopsia :complete absence of colour
-unilateral/bilateral occipital lesions (lingual,
Dyschromatopsia : perversion of colour perception
-unilateral posterior lesions
Telopsia : subjects appearing far away
Pelopsia : subjects appearing nearer.
Alloaesthesia :when the perceived object is in a
Akinetopsia: unable to perceive the motion of the
object. seen in B/L posterior cortical damage.
Eg: ‘ she had difficulty in pouring tea into a cup because
the fluid appeared to be frozen’.
Changes in quality
Colouring of yellow- xanthopsia,green-chloropsia &
-poisoning with digitalis
Derealization : everything appears unreal and strange.
Eg: a factory worker sees a grass hopper and becomes
disturbed and excited at the site of this very strange
and unknown animal.
Uniqueness of perception
Palinacousis : persistance of sounds that are heard
Intensity of perception
Hyperacusis : increased sensitivity to noise.
Anxiety & depressive disorders, migraine,
hangover from alcohol.
Hypoacusis: threshold for noise is raised
Delirium, depression & attention-deficit
Unable to form the usual, assumed links between two
or more perceptions.
Described sometimes with organic states & also with
Eg: a patient watching television experienced a
feeling of competition between the visual and auditory
Physical and personal
Personal: Determined by personal judgement of passage
Influence of mood: happy-time flies, sad-slow
Affected by psychiatric disorder
Severe depression- time passes slowly
Mania- time speeds by
Illusions : Misinterpretations of stimuli arising from an
Hallucinations :Perception without an adequate
Completion illusions: depends on inattention for their
‘ _ook’ misread as ‘Book’ though the faded letter was ‘L’
Affect illusions: arise in context of particular mood
Delirious person may perceive the innocent gestures as
Pareidolia: vivid illusions without patients effort.
Subject sees vivid pictures in fire or in clouds without
any conscious effort.
A perception without an object (Esquirol 1817).
A false perception which is not a sensory distortion or
a misinterpretation ,but which occurs at the same time
as real perceptions(Jaspers ,1962).
A hallucination is an exteroceptive or interoceptive
percept that does not correspond to an actual object
A hallucination is a perception without an object or the
appearance of an individual thing in the world without
any corresponding material event (cutting 1997).
According to Slade (1976) ,3 criteria are essential (a)
percept like experience in the absence of external
stimuli, (b) percept like experience that has the full
force and impact of a real perception (c ) percept like
experience that is unwilled ,occurs spontaneously and
cannot be readily controlled by the percipient.
Disorders of sense organs
Disorders of central nervous system.
elementary & unformed- bells, whistling, machinery or
Completely organized as hallucinatory voices
May also occur in chronic alcoholic hallucinosis or
affective psychosis occasionally
Elementary- in the form of flashes of light
Partly organized- patterns
Completely organized-visions of people, objects or
Occipital lobe tumours
Metabolic disturbances-hepatic failure
Alzheimer’s disease, senile dementia
Charles Bonnet’s syndrome( phantom images)-
Individuals experience complex visual hallucinations
in association with impaired vision without any
psychopathology or disturbance of consciousness
More common in elderly
Associated with central & peripheral reduction in
Importance in differential diagnosis.
Alcohol withdrawal syndrome characterized by gross
changes in perception, mood and conscious state.
Pareidolic or affective illusions are often prodromal.
Lilliputian hallucinations-seeing tiny people or objects.
accompanied by pleasure & amusement.
Superficial : Affecting skin sensation
Thermic - heat and cold (‘my feet on fire’)
Haptic - of touch (‘a dead hand touched me’)
Hygric – a perception of fluid (‘ I can feel a water level
in my chest’)
Kinaesthetic hallucinations : The patient feels that his
limbs are being bent or twisted or his muscles
Withdrawal state from benzodiazepine or alcohol
Eg: ‘I thought my life was outside my feet and made
Olfactory hallucination: schizophrenia , epilepsy.
Hallucination of smell which may or may not be
Eg : people are pumping anaesthetic gas into the house
which the patient alone can smell.
Gustatory hallucinations: schizophrenia, depression,
temporal lobe epilepsy, psychotropic drugs- lithium or
Eg: In schizophrenia and depression the flavour of food
may disappear alltogether or become unpleasant.
Autoscopy (phantom mirror image) : subjects see an
image of themselves in external space viewed from
within their own physical body.
Negative autoscopy : for instance, the patient looks in
the mirror and sees no image at all.
Extracampine hallucination (concrete awareness):
experienced outside the limits of the sensory field,
outside the visual field or beyond the range of
Eg:‘ I keep on hearing them talking about my disease
down in the post office’ (half a mile away)
Hypnogogic hallucination: perceptions that occur
while going to sleep.
Hypnopompic hallucination: perceptions that occur on
May be visual, auditory or tactile
Occur in many people in good health
Described with narcolepsy, cataplexy and sleep
Toxic states- glue sniffing , acute fever , post
infective depressive states.
Eg - ‘a feeling of someone pushing him over the bed’
‘seeing a man coming across the bedroom’
Functional hallucination : External stimulus is
necessary to provoke hallucination but the stimulus is
experienced as well as the hallucination
Eg : ‘ A schizophrenic patient heard hallucinatory voices
only when water was running through the pipes’.
Reflex hallucination : A stimulus in one sensory
modality producing a hallucination in another.
Eg : ‘ I can feel you writing in my stomach’
SIMS’ Symptoms in the mind psychopathology, fourth
Fish’s clinical psychopathology, third edition.