Perception involves processing sensory input and organizing it to produce meaningful experiences. Sensation is the initial unprocessed stimulation of receptors, while imagery involves internal mental representations drawn from memory. Perception can be abnormal in the form of sensory distortions or deceptions. Sensory distortions alter qualities like intensity, spatial form, or time. Sensory deceptions include illusions, which combine stimuli with mental images, and hallucinations, which are false perceptions without an external stimulus. Hallucinations are further classified by modality and organization level, and can occur in schizophrenia, organic disorders, or during states like delirium tremens. Abnormal perceptions are evaluated in mental status exams based on characteristics like timing, modality, clarity, and patient

1. Perception
By
Dr. Leena Shingavi
M.B.B.S., PhD Clinical Neurosciences (first year)

2. OVERVIEW
• What is sensation, perception & imagery?
• Differences between them.
• Disorders of perception
• Perception in MSE.

3. Sensation:
• It is the first stage of perception in receiving information from outside the
self through the means of various sensory pathways viz. auditory, visual,
olfactory, tactile, gustatory, kinaesthetic and proprioceptive pathways.
• An immediate, unprocessed stimulation of receptors of sense organs.

4. Imagery:
• Imagery is the internalmental representation of the world and is actively
drawn from memory.
• It is crucial in cognitiveactivities such as mental arithmetic, map reading,
visualizing and imagining places previously visited and recollecting spoken
speech.
• „seeing in mind‟s eyes‟ and „hearing in mind‟s ears‟.

5. Perception:
• Processing of sensory input, organizing and interpreting it to produce a
meaningful experience to the outside world. (DSM)
• Thus, sensation is the bottom-up processing and perception is the top-down
processing of the sensory information provided in external world.

6. Formal characteristics of normal perception
and imagery:
Normal Perception
• Are of concrete reality
• Occur in the external objective space
• Clearly delineated
• Constant and remain unaltered
• The sensory elements are full and fresh
• Independent of our will
Imagery
• Images are figurative and have a character of
subjectivity.
• Occur in the inner subjective space
• Not clearly delineated and come before as
incomplete
• Images dissipate and have to be recreated.
• The sensory elements are relatively insufficient
• Dependent on our will

7. Abnormal Perception:
1. Sensory distortion
Distortion in any of the components or elementary aspects of the
perception, such as uniqueness, intensity, size, shape, colour,
location, motion or general quality.
2. Sensory Deception
A new perception arises which may or may not be in response to a
real stimuli.

8. Classification:
• Sensory distortion is further classified as:
1. Changes in intensity (hyper-
or hypo-aesthesia)
2. Changes in quality
3. Changes in spatial form
(dysmegalopsia)
4. Distortions of the experience
of time
• Sensory deception is further classified as:
1. Illusion
2. Hallucination
3. Pseudo hallucination

9. Changes in intensity:
• 1. Hyperaesthesia:
e.g. hyperacusis. Seen in intense emotions, anxiety and depressive
disorders, hangover from alcohol, migraine.
2. Hypoaesthesia:
e.g. hypoacusis-the threshold for hearing is raised.
Seen in delirium, attention deficit states like depression and
attention-deficit disorder.

10. Changes in quality
• Mainly in visual perception.
• 1. Visual hyperaesthesia; wherein the intensity, the actual hue and quality of colour can be
affected.
• E.g. Xanthopsia: yellow.
• erythropsia: red.
• drugs (for eg, santonin, poisoning with mescaline or digitalis)
• 2. Achromatopsia:
seen in u/l or b/l occipital lesions, usually of lingual and fusiform
gyrus.

11. Changes in spatial form
(dysmegalopsia/metamorphosia)
• a change in the perceived shape of an object.
• Micropsia
• Porropsia is the experience of the retreat of objects into the distance without
any change in size.
• Macropsia
• Causes: mostly from temporal and parietal lobe lesions, retinal diseases,
diseases of accommodation. Rarely, in schizophrenia.

12. Distortions of the experience of time
• Slowing down of time - psychotic depressive symptoms.
• In mania - time speeds
• Schizophrenia - delusional elaboration that clocks are being interfered with.
• Evidence- abnormalities of time judgement, estimating intervals to be less
than they are.
• Age disorientation - with chronic schizophrenia, noted even in the absence
of any other features of confusion.

13. Miscellaneous
• Palinopsia
• Hemimicropsia
• Paraprosopsia
• Alloesthesia
• Dyschromatopsia
• Teleopsia
• Akinetopsia
• Derealization
• Palinacusis

14. Sensory Deception Disorders
• Illusion: stimuli from a perceived object is combined with a mental image to
produce a false perception.
• Illusions in themselves are not indicative of psychopathology
• Visual illusions are the most common, though they can occur in any
modality.
• Causes: normal people, delirium, anxious and bewildered patient/persons.

15. Three types of illusions are described. They are as follows:
1.Completion illusions depend on inattention for their occurrence.
An incomplete perception that is meaningless in itself is filled in by a
process of extrapolation from previous experience and prior
expectation to produce significance.
2.Affect illusions: these arise in the context of a particular mood
state. For example, a bereaved person may momentarily believe they
„see‟ the deceased person.

16. Illusions continued
• 3.Pareidolia: vivid illusions occur without the patient making any effort.
These illusions are the result of excessive fantasy thinking and a vivid visual
imagery.
E.g. a person sees vivid pictures in fire or in clouds, without any
conscious effort on his part and sometimes even against his will.

17. • Hallucinations:
• The most significant type of false perceptions.
• Five definitions of hallucination are as follows:
• 1.A perception without an object (Esquirol, 1817).
• 2. Hallucinations proper are false perceptions that are not in any way distortions of
real perceptions but spring up on their own as something quite new and occur
simultaneously with and alongside real perception. (Jaspers, 1962).
• 3. A hallucination is an exteroceptive or interoceptive percept that does not
correspond toan actual object (Symythies, 1956).

18. Hallucinations conti…
• 4.According to Slade (1976a),three criteria are essential for an operational definition:
(a)percept-like experience in the absence of an external stimulus;
(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. This definition is derived from Jasper‟s formal
characteristics of a normal perception.
• 5.A hallucination is a perception without an object (within a realistic philosophical
framework) or the appearance of an individual thing in the world without any
corresponding material event according to Cutting (1997).

19. Hallucination continued
• Causes: intense emotions or psychiatric disorder, suggestion, disorders of
sense organs, sensory deprivation and disorders of the central nervous
system.
• Classification: according to individual senses.

20. Auditory hallucinations:
• Auditory hallucinations can be elementary, partially organized or completely organized.
• 1.Elementary: noises;
organic states.
2.Partially organized: music
3.Completly organised: hearing voices, as in schizophrenia.
• Imperative/commentary hallucinations: Voices instructing the patient.
• Also, first person, second person and third person auditory hallucinations is another way of
classifying.

21. Visual Hallucinations:
• Elementary: flashes of light.
• Partially organized: patterns
• Completely organized: visions of people, objects or animals.
• E.g. In delirium tremens- “mice carrying suitcases on their backs as they
boarded a flight to Lourdes.”
• Mostly in organic states viz. occipital lobe tumours, post-concessional states,
epilepsy, metabolic disturbances like hepatic failure.

22. Olfactory Hallucination:
• E.g. “Smell gas and that enemies have sprayed a poisonous gas in the room”.
• Schizophrenia and organic states like temporal lobe disturbances.
• Padre Pio Phenomenon: in religious people; who smell roses around certain
saints.

23. Gustatory Hallucination:
• Schizophrenia and acute organic states like epilepsy, especially with a
temporal lobe focus.
• Commonly form the aura in epileptic attacks.

24. Tactile Hallucination:
• Sims classification :
• 1.Superficial (affects skin), further divided in 4 types:
• a)thermic-cold wind blowing across face.
• b)haptic-hand brushing against skin
• c)hygric-water running from head to stomach
• d)paraesthetic- organic origin.
• 2.Kinesthetic- schizophrenia and delirium tremens, alcohol intoxication, BZD withdrawal.
• 3.Visceral-pain and deep sensations; chronic schizophrenia.
• Cocaine bugs

25. Pseudohallucinations:
• Named by Hagen
• Described extensively by Kandinsky and then Jaspers
• Kadinsky-”subjective perceptions which in vividness and characterare real
hallucinations except that they do not have objective reality”.
• Jaspers – “similar to normal perception except that it occurs in inner subjective
space”.
• Hare differentiated between true and pseudo hallucinations based on INSIGHT

26. Hallucination PH Imagery N perception
Origin In In In Out
Perceived in Objective Subjective Subjective objective
Insight absent Present Present
Sensory modality Changes Same Same
Observer
dependent
No Yes Yes
Clarity Yes Yes No
Constancy Yes Yes No
Behavioral
relevance
Yes Yes No
Under will No no yes

27. Other abnormalities of perception:
• Autoscopy/Phantom mirror image: experience of seeing oneself and
knowing that it is oneself.
• Seen in schizophrenia, temporal lobe epilepsy and parietal lesions.
• Negative Autoscopy: does not see his image in the mirror.

28. Other abnormalities of Perception continued
• Extracampine hallucination: outside the limits of the sensory fields; no
diagnostic importance.
• Hypnagogic and hypnopompic hallucinations: normal people,
narcolepsy, glue sniffing, acute fevers, postinfective depressive states and
phobic anxiety neurosis.

29. Other abnormalities of Perception continued
• Functional hallucination: normal perception of external stimulus and
hallucination in the same modality are experienced simultaneously.
e.g. hallucinatory voices heard only when water runs through t
drainage pipes in the ward.
• Reflex Hallucinations: stimulus in one sensory modality produces a
hallucination in another sensory modality.
E.g. pain only on mention of certain words.

30. Perception in MSE:
• 1. Perception – differentiate from thought
• 2. False
• 3. Timing - awake / hypnagogic/hypnopompic – differentiate from dream
• 4. Modality – visual/auditory/tactile/gustatory/somatic/olfactory
• 5. Description - Intensity, Distance, content, no of persons,
• 6. Clarity
• 7. Control
• 8. Insight
• 9. Precipitating factor
• 10. Patient‟s attitude to the hallucinations
• 11. Special types

31. Summary

32. References
• Fish‟s clinical psychopathology.
• SIMS
• Basic Definitions and MSE.

33. Thank you