Muller Lyer illusion


Introduction– The Psychological concept of illision an interaction of logical and imperial consideration.It is a distraction of the sense which can reveal how the human brain normally organized an inter sensory stimulation.

Types of illision: There are three types of illision.

(1) Optical illusion

(2) Auditory illusion

(3) Tactile illusion

Optical illusion:It is the kind of illision in which the images perceived through the sight which can be misleading or causing error in perception and optical illusion is based on the process which create a visual world in one mind using previous memory stored in it.

Auditory illusion:Auditory illusions are false perceptions of a real sound or outside stimulus. These false perceptions are the equivalent of an optical illusion: the listener hears either sounds which are not present in the stimulus, or sounds that should not be possible given the circumstance on how they were created.

Tactical illusion: Tactile illusions are found when the perception of a quality of an object through the sense of touch does not seem to be in agreement with the physical stimulus. They can arise in numerous circumstances and can provide insights into the mechanisms subserving haptic sensations.

Name of the experiment: Muller Lyer Illusion.

Purpose: To measure the extent of Muller Lyre Illusion with the help of Method of Average Error.

Material used: Muller Lyer Apparatus, Writing material.

Subject’s details: Age, gender, Educational Qualification.


Preliminary set up: The apparatus is checked before starting the experiment. Observation tables were prepared to note the responses of the subject.

Procedure: The subject was called and seated comfortably. A rapport was established during which her/his details were sought. She/he was given the following instructions:

“I will show you an apparatus which has an arrow headed line and a feather headed line. The length of the arrow headed line is fixed whereas the length of the feather headed line can be increased or decreased. Your task is to equate the length of feather headed line with that of arrow headed line. You will be required to move the hand in which you are holding that part of the apparatus which has feather headed line. Remember that you will adjust the length in one go only i.e. do not make any back and forth movement.”

For each trial the sequence of eight conditions as shown below in the observation table is followed. Ten such trials are taken. Since each condition is repeated twice,there are twenty trials in each condition, i.e. right outward, left outward, right inward, and left inward. In two conditions subject moves variable stimulus outward and inward from right side i.e. (RO & RI) and in other two conditions the variable stimulus is moved outward and inward from left side (LO & LI).Complete counterbalancing of the space and movement is achieved by following the sequence RO, LI, LO, RI, LI, RO,RI, LO.


1. The subject equated the two lines in one go.

2. The readings were noted carefully. 

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