Survey of Modern Psychology

Optical Illusions

Illusions generally happen when:• The stimulus is unclear• Information is missing

When we do not have sufficient information about a stimulus, we fill it in

ourselves

• Gestalt theory• Learning based inference

Gestalt Theory

The brain perceives patterns in stimulationFor example, we see a triangle as a single figure

rather than as three lines

Closure

We fill in the blank space to form a closed figure

Figure and Ground

• The figure is the part that grabs our attention

• The ground is anything surrounding the figure

• The figure can be seen as either a vase or as two faces

Huang, L., Pashler, H. (2009). Reversing the Attention in Figure-Ground

Perception. Psychological Science, 20, 1199-1201.

A

When a person focuses

their attention

on the red lines, the red lines

appear to be in front of a green backgroun

d

B

Explanation

•We look for the simplest possible explanation of stimuli, and interpret them as 3-D•In image B, when paying attention to the red lines we saw a picture of a face

•Normally, this would mean that we’re looking at a whole face with columns in front of it

•In image C, the strips were shuffled so the red or green did not form a continuous image anymore. It was therefore interpreted in the same was as figure A

X O X O X

X O X O X

X O X O X

X O X O X

X O X O X

Perceptual Grouping

• We group together stimuli that appear to belong together

• The X’s are similar to other X’s, and we therefore group them together as columns

X O X O XX O X O XX O X O XX O X O XX O X O X

Meaningfulness – “Prägnanz”

• We look for the simplest interpretation possible, with the least amount of effort

• We know what we expect to see, and that makes proofreading difficult

Meaningfulness – “Prägnanz”

Note: humans are good at this, computers are not.

This is why spammers use symbols rather than letters to get through filters

Learning Based Inference

• We use what we know/have learned to interpret new stimuli

• Our knowledge gives us a context for recognizing and interpreting new stimuli

Context and Expectation

FOX; OWL; SNAKE; TURKEY; SWAN; D?CK

BOB; RAY; DAVE; BILL; TOM; D?CK

Context and Expectation

FOX; OWL; SNAKE; TURKEY; SWAN; D?CKBOB; RAY; DAVE; BILL; TOM; D?CK

• In the first list, “U” made sense• In the second list, “I” made sense

Context and Expectation

.rat eht saw tac ehT

Turn this around in your mind and read it

.rat eht saw tac ehT

People usually interpret the sentence logically as saying “The cat saw the rat.”

In reality, when reversed the letters said, “The cat was the tar”

From Psychology Core Concepts Fifth Edition Zimbardo, Johnson and Weber

What difference(s) do you see in these two pictures?

We have difficulty seeing details of faces that violate our expectations of a face

What do you see?

Priming

The images or labels shown surrounding an ambiguous image will tend to lead to a particular interpretation.

In this case, you may have been more likely to initially see the image as a young woman

(Priming is subconsciously cuing a particular response)

The Ponzo Illusion

We look at see the tracks as cues for distance. Because A appears to be further away, we perceive it as being larger than B

Hybrid Images

Hybrid Images

Dimensions

“Spinning Dancer” illusionhttp://z.about.com/d/psychology/1/0/Z/5/Spinning_Dancer.gif

• We tend to view objects as three dimensional even if they are really not

• The image is not actually “spinning” but we interpret it as 3-D spinning

• It is processed as both counter clockwise and clockwise, but one interpretation wins at any given timeTHIS IS NOT ACTUALLY LINKED TO BEING “LEFT

BRAINED” OR RIGHT BRAINED”

Necker Cube

Cues for Depth Perception

• If two objects that one would assume are the same size show different sized images on the retina, the observer judges them as being different distances away.

• The relative size of the objects is used to judge depth and distance.

Cues for Depth Perception

• Lighter colored objects seem closer to us, and darker objects seem further away

Cues for Depth Perception

• Closer objects obstruct our vision of more distant objects behind them.

• Partially hidden objects are therefore further away than the object that hides it.

Ames

Stare at this image

Negative Afterimage

• Caused by a change in the rate of firing in retinal ganglion cells

• After the cells are inhibited or excited for an extended time, they show a rebound effect (fire faster or slower than normal)

http://www.moillusions.com/2009/05/hidden-skoda-fabia-optical-illusion.html

M C Escher

M C Escher

Julian Beever

Julian Beever

Julian Beever

Julian Beever