Sensation and Perception

Sensation & Perception

How do we construct our representations of the external world?

To represent the world, we must detect physical energy (stimulus) from the environment and

convert it into neural signals, a process called sensation.

When we select, organize, and interpret our sensations, the process is called perception.

Perceptual Interpretation

Perceptual Interpretation Perceptual Adaptation

Perceptual Set

Perception and Human Factors

From Sensation to RecognitionT

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Information Processing in the Visual Cortex

• Early 1960s: Hubel and Wiesel– Microelectrode recording of axons in

primary visual cortex of animals– Discovered feature detectors: neurons that

respond selectively to lines, edges, etc.– Groundbreaking research: Nobel Prize in

1981• Later research: cells specific to faces in the

temporal lobes of monkeys and humans

Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes,

faces, chairs and houses.

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Visual Information Processing

Processing of several aspects of the stimulus simultaneously is called parallel processing. The

brain divides a visual scene into subdivisions such as color, depth, form and movement etc.

Opponent Colors

Color Constancy

Color of an object remains the same under different illuminations. However, when context changes color of an object may look different.

R. B

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Figure 4.17 Bottom-up versus top-down processing

Perception in Brain

Our perceptions are a combination of sensory (bottom-up) and cognitive (top-

down) processes.

Bottom-up Processing

Analysis of the stimulus begins with the sense receptors and works up to the level of the brain

and mind.

Letter “A” is sensed as a black blotch decomposed into features by the brain and perceived as an “A” by our

mind .

Figure 4.23 Context effects

Principles of Perception

• Gestalt principles of form perception:– figure-ground, proximity, closure, similarity,

simplicity, and continuity• Recent research:

– Perceptual hypotheses• Context

Figure 4.18 The principle of figure and ground

Figure 4.21 A famous reversible figure

Figure 4.19 Gestalt principles of perceptual organization

Our sensory and perceptual processes work together to help us sort out complex images.

Making Sense of Complexity

“The Forest Has Eyes,” Bev Doolittle

Figure 4.20 Perceptual hypotheses

Figure 4.22 The Necker cube

The Power of Misleading Cues:Visual Illusions

• Optical Illusions - discrepancy between visual appearance and physical reality

• Famous optical illusions: Muller-Lyer Illusion, Ponzo Illusion, Poggendorf Illusion, Upside-Down T Illusion, Zollner Illusion, the Ames Room, and Impossible Figures

• Cultural differences: Perceptual hypotheses at work

• Imagine that you are outside on a clear night in which there are no clouds, and there is a bright full Moon. Pretend that on a table in front of you are objects that range in size from a BB to a beach ball as follows:

1. BB

2. Pea

3. Dime

4. Penny

5. Nickel

6. Quarter

7. Golf ball

8. Baseball9. Softball10. Small salad plate11. Large dinner plate12. Frisbee13. Basketball14. Beach ball

Please pretend that you are going to pick one of these things that WHEN HELD AT ARM’S LENGTH JUST COVERS UP THE MOON. Imagine that you are picking one that when you hold it in your hand will JUST BARELY COVER UP THE MOON so that you can no longer see it.

http://www.youtube.com/watch?v=5ic7QGjGEX8

Window Mac O X

http://illusionism.org/media/ames-room.png

Figure 4.28 The Muller-Lyer illusion

http://upload.wikimedia.org/wikipedia/commons/8/8a/Mueller_lyer.svg

Figure 4.30 Four geometric illusions

Figure 4.32 Three classic impossible figures

Change Blindness

• http://www.youtube.com/watch?v=mAnKvo-fPs0&feature=related

Selective Attention

• Neisser’s SA Test– http://www.youtube.com/watch?v=JX2BJC

12uXQ&feature=related

– http://www.youtube.com/watch?v=Ahg6qcgoay4&feature=related

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy,

• it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

But does it matter?

• 1) A vheclie epxledod at a plocie cehckipont near the UN haduqertares in Bagahdd on Mnoday kilinlg the bmober and an Irqai polcie offceir

• 2) Big ccunoil tax ineesacrs tihs yaer hvae seezueqd the inmcoes of mnay pneosenirs

• 3) A dootcr has aimttded the magltheuansr of a tageene ceacnr pintaet who deid aetfr a hatospil durg blendur

the rset can be a toatl mses and you can sitll raed it wouthit

porbelm…• Short words are easy • Function words (the, be, and, you etc.) stay the same - mostly

because they are short words• Of the 15 words in this sentence, there are 8 that are still in the

correct order. • Transpositions of adjacent letters (e.g. porbelm for problem) are

easier to read than more distant transpositions (e.g. pborlem). • None of the words that have reordered letters create another word

(wouthit vs witohut). • Transpositions were used that preseve the sound of the original

word (e.g. toatl vs ttaol for total). • The text is reasonably predictable.

Tihs is bcuseae the huamn mnid deos not raed ervey lteter by

istlef, but the wrod as a wlohe... • people do not ordinarily read each letter in a

word individually • information in the shape of an entire word plays

an important role in reading. For instance, "CaSe MiXiNg" substantially slows down reading

Trehe wlil be a qiuz on potiercepn at the end of cslas

toady

Perceptual Set

A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures.

From

Shepard, 1990.

Children's schemas represent reality as well as their abilities to represent what they see.

Schemas

Schemas are concepts that organize and interpret unfamiliar information.

Courtesy of A

nna Elizabeth V

oskuil

Eye & Mouth

Eyes and mouth play a dominant role in face recognition.

Courtesy of C

hristopher Tyler

Perception & Human Factors

Human factors psychologists design machines that assist our natural perceptions.

The knobs for the stove burners on the right is easier to understand than one on the left.

Photodisc/ P

unchstock

Courtesy of G

eneral Electric

Claims of ESP

1. Telepathy: Mind-to mind communication. One person sending thoughts and the other receiving it.

2. Clairvoyance: Perception of remote events. Like sensing a friend’s house on fire.

3. Precognition: Perceiving future events. Such as a political leader’s death.

Premonitions or Pretensions?

Can psychics see the future? Can psychics aid police in identifying locations of dead bodies? What about psychic predictions of the famous

Nostradamus?

The answers to these questions are NO! Nostradamus’ predictions are “retrofitted” to

events that took place afterwards.

Anagrams

• LULB• CALEM• NUKKS• SEUMO• BAZER

Anagrams

• NORC• NOONI• MATOOT• PREPPE• TEBE

Fig. 4.14, p. 109

Fig. 4.15, p. 109

Perception Revisited

Is perception innate or acquired?