Visual Illusions

A misinterpretation of visual stimulus in which our perception consistently differs from objective reality, even with the knowledge of the misinterpretation.

Two lines of equal length in which have opposite shaped ends.

The feather tail is incorrectly perceived as being longer than the arrow head.

Biological Factors - genetically inherited the biological tendency to misinterpret simple 2D geometric patterns.

Cognitive Factors - perceptual error due to using inappropriate mental strategies when perceiving visual cues.

Based on Gestalt Principles of convergeance and divergeance: the lines at the sides seem to lead the eye inward or outward, creating a false impression of length.


-The lines with arrows pointing inwards may simply look longer because the arrows itself extend past the line.

We make a perceptual compromise: and understand that while the length of the two lines is the same, the length of each whole figure differs.

We use closure automatically to mentally fill in the gaps of the horizontal line lengths, thus the feather tail is perceived as longer.

Occurs when two or more visual cues conflict whlie we are interpreting visual information

we compromise by taking the middle ground making an interpretation not solely based on one visual cue or the other.

Monocular depth cues available
Binocular depth cues are not

no retinal disparity, convergence
Size and shape conflict.

Demonstrates that shape constancyis maintained and overrides size constancy which is not maintained.

Our inability to maintain size constancy when our use of depth cues are restricted or misleading size constancy fails because the retinal information (people shrinking) cannot be corrected due to the lack of accurate depth info.

use of past experiences - our past experiences of rectangle rooms leads us to believe that people in the room are both the same distance from us.

ADT - When two retinal images are the same size, but one image appears to be at a greater distance. The one appearing further away will be interpreted as larger.

Based on our experiences with buildings.

Feather tail - perceived as being 'inward' corner of the room and this apparently more distant line is perceived as being larger.
Arrowhead - "outward" corner of a building.

- Is acutally trapezoid in shape -

- When viewed with monocular vision through the small peep-hole, it appears as a normally rectangle room with the two back corners appearing the same distance away from the viewer

- Physically equal sized objects in the two back corners appear at different sizes

Trapezoid in shape.

One back corner is taller and further away than the other back corner, the floor slopes downwards and the ceiling slopes upwards towards the taller corner.

The peep-hole is located in the middle of the front wall so that the image of the room looks like a familiar rectangle room.

A person shrinking or growing in size despite Bernard's familiarity with the illusion.