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Perception - PowerPoint PPT Presentation

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Perception. Supervision Prof. Dr. Ramez N. Bedwani. Outcomes giving meaning to external stimuli is affected by external factors ( symbols and signals) and internal factors (receptors, habit, set, attitude). Faulty perception occurs both in normal and diseased persons. Perception.

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Prof. Dr. Ramez N. Bedwani



  • giving meaning to external stimuli is affected by external factors ( symbols and signals) and internal factors (receptors, habit, set, attitude).

    Faulty perception occurs both in normal and diseased persons.


  • Giving meaning to sensation i.e. to know environment by the use of senses.

  • We receive signs and perceive meanings.

Signs are of two types
Signs are of two types.

  • Symbols:

    • Stimuli which stand for an object e.g.: a name of any one stands for the person named.

  • Signals:

    Stimuli received from the object e.g. smoke is a signal for fire.

  • We perceive object and relations between them

  • We perceive sounds, distance and time.

  • We perceive ideas conclusions and concepts which are our tools of thinking.

  • We perceive much about our body(body image, e.g. where is my toe etc)

  • We perceive much about our psyche and its functions like emotions and thoughts. (and occasionally our motives)

  • We perceive some bodily functions. e.g. sense of micturition.

Factors affecting perception
Factors affecting perception

  • Perception is related to a meaningful whole

Figural factors
Figural factors:

1. Similarity:

Similar stimuli tend to be grouped together.


Proximate objects tend to be grouped together.


Stimuli tend to be grouped together in order to perceive a defective whole as a closed one.


For example asymmetric triangles are liable to be perceived as symmetrical ones. (see figure)


5. Approximation:

There is a tendency to perceive the poor figure as if they were exact and good.

6. Good continuation:

In the figure we see how we tend to continue lines to make rectangles instead of perceiving lines separately.

7. Competition and cooperation of grouping tendencies.

In every stimulus pattern the elements of stimulus have some degree of proximity , similarity, continuity etc. At a time all kind of grouping tendencies are at work. (Sometimes they work in the same direction of or- .and sometimes they compete with one another lowest figure)

Personal factors
Personal factors

  • Mood (emotion)

    Our mood influences markedly our perception e.g when you are sad you perceive every thing as bad

  • Need: when we are hungry we selectively perceive(smel) odours of food.

  • Interests: every one perceives what he is interested in more than any other thing.

  • Mental set: as much as you are prepared to do something or to find something, it is likely to do it or find it and to overlook other things

  • Habit &Familiarity habit is based on past experience. You read AMATONY as ANATOMY out of habit.

  • Aesthetic factors = (the same as good form in figural factors): The pleasant figure will be perceived where aqn irregular figure will be overlooked.

Abnormal faulty perception
Abnormal (faulty perception):

  • Illusion:-

    False perception of an external stimulus. may occur by factors in the individual, in the stimulus or in both

  • Illusion due to physical causes e.g. mirrors illusion: a person looking in the mirror perceives his figure as if it exists behind the mirror on the others side.

  • Habit and familiarity e.g. as said before, AMATONY is read as ANATOMY due to habit..

  • Set and expectation (e.g. waiting and important telephone call may make us perceive the bell door as a telephone call.


  • Déjà vu phenomenon: illusion of familiarity: the person feels that he has previously experienced what he is experiencing at the present time.

  • Under normal conditions particularly during adolescence.

  • In disease, in temporal lobe epilepsy.


  • Hallucinations:

    Hallucinations: are mental impressions of sensory vividness occurring without external stimulus.

    occur normally or under experimental conditions:

  • Dreaming and hypnagogic states (hypnagogic states are states just before sleep).

  • With severe emotions

  • With stimulation of the sense organs (Wax in the ears, or pressure on the eye globe).

  • During sensory deprivation experiments.


Set reaction time
Set & Reaction time the following examples:

  • Set

  • Definition

  • Set refers to the fact that the organism is usually prepared at moment for the stimuli he is going to receive and for the response he is going to make.

Types of sets
Types of sets: the following examples:

  • Preparatory set:

    The organism is preparing himself to the act that the he will soon perform. e.g. an athlete runner is training daily for physical fitness and developing skills.

    2. The set to start:

    You know what is going to happen and you prepare yourself to start reacting to a specific stimulus (e.g. runner on the mark waiting to listen to the pistol shot to start)

    3. The set to continue: It means that the activity continues towards the goal.


1. Mental set: the following examples:

This refers to the sets when the task is predominantly mental such as studying or solving a mathematical problem

2. Situational set:

The set differs according to the situation e.g. A singer singing to himself in the bath room performs differently from when singing to his audience in a theatre

Reaction time
Reaction time the following examples:

  • Definition:-

    It is the time that elapses between receiving a stimulus and responding to it. It differs with the type of reaction which could be:


  • Simple reaction time the following examples:

    Here the individual knows the single stimulus he will receive and the single response he has to make e.g. to press a button on hearing a signal. It usually lasts for 0.14 sec for a sound or a touch and 0.18 sec for light.

    That reaction corresponds to our behavior in everyday life expecting the next green traffic lights.


  • Choice reaction time the following examples:

    The individual is required to make certain different responses to specific different stimuli e.g. raise right hand whenever a red light is shown its duration is usually 0.24 sec for sound and 0.28 for light

    This reaction corresponds to our behavior in everyday life in playing tennis


  • The associative reaction tennis the following examples:

    The individual knows nothing about the definite specificity of the coming stimulus, although he knows its nature and the rule how to respond.

    This reaction corresponds to our behavior in everyday life in answering questions in mathematical problems in spotting slides under the microscope or in MCQ examinations.

Questions: the following examples:

All correct except one

1. Extroceptor are

  • Distant receptors

  • Contact receptors

  • Visceroceptos

    2. We perceive

  • Signs

  • Symbols.

  • Attention

    3. Faulty perception

  • Camouflage

  • Illusion

  • Hallucinations

  • Proximity

Assignments students are requested to prepare slides about the following topics
Assignments the following examples:Students are requested to prepare slides about the following Topics