Sensation vs Perception Bottom up vs Top down

• Sensation vs. Perception • Bottom up vs. Top down processing • Absolute Threshold

Unit 4: Sensation

With a Partner • Write down on a whiteboard: – What is the difference between sensation and perception?

Sensations: • • • What’s moving? What colors are you seeing? What sounds do you hear? Can you feel the texture of your clothing? Can you feel the pressure of the chair you’re sitting on? • Do you have any lingering tastes in your mouth? • What do you smell?

Essential Question: • What is the difference between sensation and perception? • What are different facets of our sensation abilities?

1. On a clear, dark night most of us can see a candle flame 30 miles away. 2. Advertisers are able to shape our buying habits through subliminal messages. 3. Constant eye movements prevent our vision from being seriously disrupted. 4. The retina of the eye is actually brain tissue that migrates to the eye during early fetal development 5. If we stare at a green square for a while and then look at a white sheet of paper, we see red.

6 People who live in noisy environments are more likely to suffer from high blood pressure, anxiety, and feelings of helplessness. 7. Blind musicians are more likely than sighted ones to develop perfect pitch. 8. Touching adjacent cold and pressure spots triggers a sense of wetness. 9. People who are born without the ability to feel pain usually die by early adulthood. 10. Without their smells, a cold cup of coffee may be hard to distinguish from a glass of red wine.

Sensation • The process by which our sensory systems (eyes, ears, etc) and nervous system receive stimuli from our environment

Perception • The process of organizing and interpreting sensory information

Bottom-Up Processing • Information processing that focuses on the raw material entering through the eyes, ears, and other organs of sensation

Top-Down Processing • Information processing that focuses on expectations and experiences in interpreting incoming sensory information

• “Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can still raed it wouthit a porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the word as a wlohe. • Our experience and expectations enable us to immediately perceive the scrambled letters as meaningful words and sentences.

So what does it take for us to detect something with our senses?

What is a threshold? • An edge or a boundary

Absolute Threshold • https: //www. youtube. com/watch? v=q. Nf 9 nz vnd 1 k

Absolute Threshold • The minimum stimulation needed to detect a particular stimulus • How far away do you think we have to be to hear your alarm clock? • How hard does someone have to touch you in order for you to feel them? • How strong does it have to be in order for you to smell someone’s “passed gas”?

The Absolute Threshold • http: //www. garyfisk. com/anim/threshold. sw f

Do other things affect how good we are at sensing something? • Like what? What could get in the way of us “sensing” something?

Signal Detection Theory (SDT) • A theory predicting how and when we detect the presence of a faint stimulus amid background noise Carol Lee/ Tony Stone Images • Depends partly on a person’s: • Experience • Expectations • Motivation • Level of fatigue

How do we know if two “sensations” are different? • When do you know that one coffee has more sugar than another? • When do you know if someone turned the music up? • When do you know if someone lowered the lights?

Difference Threshold • “Just noticeable difference” • The minimum difference that a person can detect between two stimuli • Example

Weber’s Law • There’s a formula to tell when two stimuli will be sensed as different. • Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Stimulus Constant (k) Light 8% Weight 2% Tone 3%

Do we get “used” to sensations? • Do they get old? • Do we get less sensitive to them?

Sensory Adaptation • Class Example • Ice Baths

Sensory Adaptation • Diminished sensitivity as a result of constant stimulation • What does that mean? • Do you have any examples? ? – Background noise – Food that smell very powerful – Altoids- very strong at first, but then less powerful – Darkness gets less dark

Now you see, now you don’t • Sensory Adaptation: after constant exposure to a stimulus, our nerve cells fire less frequently. • Then why doesn’t everything we see disappear? • Our eyes are always moving just enough