Sensation

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What if we could sense everything?

Life would hurt.

So we can only take in a window of what is out there.

This is the study of psychophysics: relationship between physical stimuli and our psychological experiences to them.

Energy v. Chemical senses

Energy Senses Chemical Senses

Transduction

• Transforming signals into neural impulses.

• Information goes from the senses to the thalamus , then to the various areas in the brain. Remember Ethan in Sky High. He

changes his body to slime. Solid form to liquid form. Change from one form of energy to another. Click the picture to watch power placement.

Top-Down Processing

• We perceive by filling the gaps in what we sense.

• I _ant ch_co_ate ic_ cr_am.

• Based on our experiences and schemas.

• If you see many old men in glasses, you are more apt to process a picture of an old man (even when you may be in error).

Bottom-Up Processing

• Also called feature analysis.

• We use the features on the object itself to build a perception.

• Takes longer that top-down but is more accurate.

Kids.exe

Click to see an example of bottom –up processing.

Absolute Threshold

• The smallest amount of stimulus energy necessary for sensation to take place 50% of the time

Candle flame seen at 30 miles on a clear dark night.

Tick of a watch under quiet conditions at 20 feet

1 drop of perfume diffused in a 3 room apartment

1 teaspoon of sugar in 2 gallons of water

H:\AP Psych 2011\AP Psych 2010\Unit 4 Sensation and perception\videos\Psychology_-_Sensation__Perception-1.avi.wmv

(Just Notable Difference) Difference Threshold

The smallest amount of change needed to detect in a stimulus before we detect a change.

Weber’s Law

• Computes the Just Noticeable Difference.

• The change needed is proportional to the original intensity of the stimulus.

• The more intense the stimulus the more change is needed to notice the difference.

• 8% for vision.

Signal Detection theory

• Absolute thresholds are not really absolute.

• Things like motivation or physical state can effect what we sense.

• Signal detection experiment :– If stimulus is present and the person

thinks its present it is a hit– If a stimulus is present and the

person thinks it is absent it is a miss.– If a stimulus is absent and the person

thinks it is present, it is a false alarm– If a stimulus is absent and the person

thinks it is absent, it is a correct reject.

My wife could sleep through a war, but if one of our sons even whimpers, she is up!!!

Subliminal Messages

• Stimuli below our absolute threshold.

• Backmasking• 25th frame• Do Subliminal

Messages work?• Probably a placebo

effect

Do you hear "Now he uses marijuana.“?

Do you hear “Ah, see me. I'm not too young”?

Do you hear Pass the gun now. It kills the love, the love is cold”?

Do you hear"Play backwards. Hear words sung.“?

Cocktail-party phenomenon

• The cocktail party effect describes the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.

• Form of selective attention.

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An example of selective attention is:

Cocktail Part Effect: ability to listen to one voice among many.

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Inattentional Blindness

Inattentional blindness refers to inability to see a an object or a person amidst an engrossing scene. Simmons & Chabris

(1999) showed that half of the observers failed to see the gorilla-suited assistant in a

ball passing game.

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H:\AP Psych 2011\AP Psych 2010\Unit 4 Sensation and perception\videos\Experimental Psychology - Change Blindness.avi

H:\AP Psych 2011\AP Psych 2010\Unit 4 Sensation and perception\videos\Derren_Brown_-_Person_Swap.wmv

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Change Blindness

Change blindness is a form of inattentional blindness, where two-thirds of direction

giving individuals failed to notice a change in the individual who was asking for

directions.

© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.H:\AP Psych 2011\AP Psych 2010\Unit 4 Sensation and perception\videos\Experimental Psychology - Change Blindness.avi

H:\AP Psych 2011\AP Psych 2010\Unit 4 Sensation and perception\videos\Derren_Brown_-_Person_Swap.wmv

Sensory Adaptation

• Decreased responsiveness to stimuli due to constant stimulation.

Do you feel your underwear all day?