I CAN: Explain the Relationship

Between Perceptionand Sensation?

Copyright © Allyn and Bacon 2006

Perception brings meaning to sensation, so perception produces an interpretation of

the external world, not a perfect representation of it

Copyright © Allyn and Bacon 2006

What is the Relationship Between Perception and Sensation?

Percept : Percept : WhatWhat we perceive we perceive The meaningful product of perception –often an

image that has been associated with concepts, memories, emotions, and motive

The primary goal of perception is to get an accurate ‘fix’ on the world – to recognize friends, foes, opportunities, and dangers.

The first step in Perception is Attention

• We sense 11,000,000 bits of information per second.

• We consciously only process about 40 bits (Wilson 2002).

• The process by which we attend to these bits is called selective attention

• Selective Attention can miss things!

The Machinery ofThe Machinery ofPerceptual ProcessingPerceptual Processing

• Feature Detectors Cells in the cortex that specialize in extracting certain features of a stimulus

• Binding Problem The physical processes used by the brain to combine many aspects of sensation to a single percept

• Example: Recognizing a face• This is one of the major unsolved mysteries in psychology

Bottom-Up andTop-Down Processing

• Bottom-Up ProcessingBottom-Up Processing Analysis that stress features of the stimulus, rather than internal concepts

• Example: Noticing a flower in a field• If your attention is drawn to a flower in a field, it

may be simply that the flower is more visually outstanding than the surrounding field….you didn’t have to think about it

Bottom-Up Processing

• In bottom-up processing, the resulting percept is determined by stimulus features.

– Color, size, shape…

Bottom-Up andTop-Down Processing

• Top-Down Processing

• --Expectations --Memories --Knowledge --Cultural background --and other cognitive factors

….influence perception

Top-Down Processing

• Top-down processing is also known as conceptually driven processing.

• Top-down does not emphasize stimulus features

Olny srmat poelpe can raed tihs.  I cdnuolt blveiee taht I cluod aulaclty  uesdnatnrd

waht I was rdanieg. The phaonmneal pweor of the hmuan mnid, aoccdrnig  to a

rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in

a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm.

Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as

a wlohe.

• Even though the second letter in each word is ambiguous, top down processing allows for easy disambiguation based on the context.

Top-Down Processing• Your dog has been lost

for three days, and you cannot stop thinking about him.

• When you hear a dog bark, you assume that it is your dog.

Perception Experiment

• Group A- tables along hallway

• Group B- tables along windows

Group A

• You are going to look briefly at a picture and then answer some questions about it. The picture is a rough sketch of a poster for a costume ball. Do not dwell on the picture. Look at it only long enough to “take it all in” once. After this, you will answer YES or NO to a series of questions.

Group B

• You are going to look briefly at a picture and then answer some questions about it. The picture is a rough sketch of a poster for a trained seal act. Do not dwell on the picture. Look at it only long enough to “take it all in” once. After this, you will answer YES or NO to a series of questions.

Picture

In the picture was there . .

1. A car?2. A man?3. A woman?4. A child?5. An animal?6. A whip?7. A sword?8. A man’s hat?9. A ball?10. A fish?

Conclusion

• Top Down processing – you go beyond the sensory information to try to make meaning out of ambiguity in your world

• What you expect (your experiences and your perceptual set) drives this process

• Today we will see what expectations we all have in common.

Copyright © Allyn and Bacon 2006

Perceptual ConstancyPerceptual Constancy

Ability to recognize the same object under different conditions, such as changes in light, distance, or location

A dog is running at you – you don’t perceive it as growing

larger

• Shape Consistency:

Explains why we do not see people morphing in shape as they walk past us and we see them from a different perspective.

 • Color Consistency:

Explains why a shirt will look the same shade of blue in dim light or sunlight

Copyright © Allyn and Bacon 2006

CAN I ?: Explain the Relationship

Between Perceptionand Sensation?