UNIT 3: Sensation and Perception

Learning Targets

20-1 Describe sensation and perception, and explain the difference between bottom-up processing and top-down processing.

20-2 Discuss how selective attention directs our perceptions.

20-3 Describe the three steps that are basic to all our sensory systems.

20-4 Discuss the difference between absolute thresholds and difference thresholds.

20-5 Discuss how we are affected by subliminal stimuli.

20-6 Explain the function of sensory adaptation.

What are sensation and perception?

sensation

The process by which

our sensory receptors and nervous system receive and represent

stimulus energies from our environment.

perception

The process of

organizing and interpreting

sensory information, enabling us

to recognize meaningful objects and events.

So what does that actually mean?

sensation

Your nose, eyes or other sensory organs bring in information…. a smell… a color… a tall, blond boy with freckles…

perception

Your brain makes sense of that information… oh.. that is my granddad’s rhubarb pie, that turquoise shirt is stunning, hey… is that my brother?

Does this image represent sensation or perception?

How do you know?

For each of the senses below, provide an example of how sensing differs from perceiving.

vision

audition (hearing)

gustation (tasting)

touch, temperature and pain

How does processing of stimuli work?

bottom-up processing

Starting with the sensory input, the brain attempts to understand/make sense.

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You see a long, slim, slithering creature on the ground… you process… ah! A snake!

top-down processing

Guided by experience and higher-level processes, we see what we expect to see.

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An experienced hiker, you expect to see snakes on your hike so windy stick, lizards, etc. all seem like snakes.

In the image below, what can we detect through bottom-up processing? Top down processing?

Did you see it?

Our sensory and perceptual processes work together to help us sort out complex images, including the hidden couple in Sandro Del-Prete’s drawing,

The Flowering of Love.

1. What Would You Answer?

What occurs when experiences influence our interpretation of data?

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1. selective attention

B. transduction

C. bottom-up processing

D. top-down processing

5. signal detection theory

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What is selective attention?

• Our tendency to focus on just a particular stimulus among the many that are being received.

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• Although we are surrounded by sights and sounds, smells and tastes, we tend to pay attention to only a few at a time.

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Has this happened to you?

• You are at a crowded party with lots of your friends and everyone is talking so it is LOUD!
• You are focusing your attention on the conversation with your friend nearby.
• Then someone on the other side of the room says

YOUR name…and you HEAR it!!

• This is called the cocktail party effect – you focused your attention on one particular voice (that person who called your name) amidst the crazy loudness of all those other voices.
• The cocktail party effect is a great example of selective attention.

Do you text or talk on your cell phone while driving your car?

Selective attention and accidents

Let’s consider the research on selective attention…

fMRI scans show a 37% decrease in brain activity in areas vital to driving when a driver is listening to a conversation. (Just et al., 2008)

University of Sydney researchers found that cell phone users were four times more at risk of a car crash.

(McEvoy et al., 2005, 2007)

The National Safety Council found that 28% of traffic accidents occur when drivers are chatting on cell phones or texting. (NSC, 2010)

It is not about the cell phone.. it’s about distracting your attention!

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Using a cell phone (even a hands-free set)

carries a risk 4 times higher than normal—

equal to the risk of drunk driving

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(McEvoy et al., 2005, 2007).

What is selective inattention?

At the level of conscious awareness, we are in only one place at a time and so we miss salient objects that are available to be sensed.

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Inattentional blindness: ��failing to see visible objects when our attention or focus is directed elsewhere

Viewers of this basketball drill are asked to count the number of passes between white-shirted players.

An umbrella toting woman saunters across the screen.

Only 21% reported the presence of the woman.

(Neisser, 1979)

Change blindness:��failing to notice changes in the visual environment

While a white-haired man provides directions to a construction worker…

two researchers rudely pass between

them interrupting his vision…

the original worker switches places with another person. 67% failed to notice the change.

What are the three steps involved in �sensation and what is transduction?

Transduction:

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conversion of one form of energy, such as light waves, into another form, like neural impulses that our brain can interpret

STEP ONE

receive

STEP TWO

transform

STEP THREE

deliver

2. What Would You Answer?

As Jeff reads his psychology textbook, he is able to convert the light waves into signals that his brain can interpret due to the concept of

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1. transduction.

B. perception.

C. priming.

D. signal detection theory.

5. threshold.

What is psychophysics?

The study

of relationships between the physical characteristics of stimuli,

such as their intensity, and our psychological experience of them.

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For instance…

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…what is it about the smell, taste, and texture of buttery popcorn that produces a delicious, satisfied, happy response in you?

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What is the difference between �absolute threshold and difference threshold?

absolute threshold

The minimum stimulation

needed to detect a particular stimulus 50 percent of the time.

difference threshold

The minimum difference between two stimuli required for detection 50 percent of the time.

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This is termed the just noticeable difference or JND.

How do we test for absolute threshold in a sense like audition?

A hearing specialist exposes both of your ears to varying sound levels.

For each tone the test defines the pitch at which you can detect the tone 50% of the time.

Why are some people better at detecting signals than others?

• Have you ever been caught texting on your phone during class by a teacher in one class but can get away with it regularly in another class?
• Did you know that even when parents of a newborn are exhausted from sleep deprivation, they can still hear the slightest whimper from their baby even though the loud sounds of the trash truck or screeching car on the street outside may go completely unnoticed?
• Do you or your friends have different opinions about how much onion is too much onion on a burger?

A theory predicting how and when we detect the presence of a faint stimulus amid background stimulation

What is the signal detection theory?

the strength of the signal

(how loud the sound is, how bright the light, how heavy the touch….)

our psychological state

(our experience, our expectations, our motivation, and how alert we are)

Depends on two conditions:

So you can see the light…but how can you tell when it gets brighter?

Have you ever been in a crowd of families, like at a waterpark or amusement park, and you yell “Dad!” to get your father’s attention? How does YOUR Dad know to turn around?

How does a musician know when they are playing a little flat or sharp of their intended note?

How can you tell when just the slightest note of irritation is in your friend’s voice?

What is Weber’s Law?

To be able to tell the difference between degrees of stimulation, two stimuli must differ by a constant minimum percentage.

How will I notice the difference?

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• Two lights must differ in intensity by 8% for you to notice the change.
• Two objects must differ in weight by 2%.
• Two tones must differ in frequency by .3%.

How does Weber’s Law help explain the �just noticeable difference (jnd) ?

The difference threshold is the minimum difference between two stimuli required for detection

50 percent of the time.

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We experience the difference threshold as a just noticeable difference (or jnd).

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Weber’s law tells us that the difference must vary by a constant percentage (as shown on the last slide), not a constant amount.

How many lines are required for you to experience a just noticeable difference (jnd)?

3. What Would You Answer?

What principle states that to be perceived as different, two stimuli must differ by a minimum percentage rather than a constant amount?

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1. absolute threshold.

B. difference threshold.

C. signal detection theory.

D. priming.

5. Weber’s law

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What are subliminal stimuli and �how are we affected by them?

Subliminal stimuli are not detectable 50% of the time. They are below your absolute threshold.

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You may not notice subliminal stimuli at all if they are weak.

What is priming?

Priming is the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.

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Even if YOU don’t think YOU notice a stimuli, your brain might, and that can impact you.

What is sensory adaptation?

Sensory adaptation is diminished sensitivity to stimuli as a consequence of constant stimulation.

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Evolutionary psychologists suggest that once we notice and evaluate a new stimuli as non-threatening, we can pay less attention to it.

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This saves our attention for new incoming stimuli, or changes in the existing stimuli. This could be adaptive for survival.

Stop and talk. Has this happened to you?

Ever notice how your friend’s home has a certain….smell? And have you noticed that it “goes away” after you have been there a few minutes? Why?

Do you ever look all around for your cell phone only to realize it is in your pocket?

Has a family member fallen asleep in front of the TV and to be kind, you turn off the TV and cover them with a blanket? Do they wake up? Why?

So why does sensory adaptation occur?

• Being able to ignore unthreatening/unchanging stimuli leaves us free to focus on the stimuli that IS changing.
• Our sense receptors are alert to novelty…a new situation means we need to evaluate and assess it and check for danger.
• So it is functional…adaptive.

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• We perceive the world not exactly as it is, but as it is useful for us to perceive it.

4. What Would You Answer?

Tyshane went swimming with friends who did not want to get into the pool because the water felt cold. Tyshane jumped in and after a few minutes declared, “it was cold when I first got in, but now my body is used to it. Come on in!” Tyshane’s body became accustomed to the water due to

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1. priming.

B. the absolute threshold.

C. the difference threshold.

D. selective attention.

5. sensory adaptation.

Learning Target 20-1 Review

Describe sensation and perception, and

explain the difference between bottom-up processing and top-down processing.

• Sensation is receiving signals from our sensory receptors.
• Perception is processing and interpreting those signals.
• Bottom-up processing begins at the sensory level.
• Top-down processing is guided by higher-level perceptions and expectations.

Learning Target 20-2 Review

Discuss how selective attention

directs our perceptions.

• We selectively attend to, and process, a very limited portion of incoming information, blocking out much and often shifting the spotlight of our attention from one thing to another.
• Focused intently on one task, we often display inattentional blindness (including change blindness) to other events and changes around us.

Learning Target 20-3 Review

Describe the three steps that are basic

to all our sensory systems.

Our senses (1) receive sensory stimulation (2) transform that stimulation into neural impulses, and (3) deliver the neural information to the brain.

• Transduction is the process of converting one form of energy into another.
• Researchers in psychophysics study the relationships between stimuli’s physical characteristics and our psychological experience of them.

Learning Target 20-4 Review

Discuss the difference between

absolute thresholds and difference thresholds.

• absolute threshold: minimum stimulation necessary to be consciously aware of it 50% of the time.
• signal detection theory: perception depends on 1) signal strength and 2) experience and expectations
• difference threshold (just noticeable difference, or jnd): minimum stimulus difference we can discern 50% of the time.
• Weber’s law states that two stimuli must differ by a constant percentage to be perceived as different.

Learning Target 20-5 Review

Discuss how we are affected by

subliminal stimuli.

• Priming shows that we can be affected by stimuli so weak that we don’t consciously notice them, and we can evaluate a stimulus even when we’re not consciously aware of it.
• We can be primed by subliminal stimuli, but research indicates that such stimuli cannot persuade us or change our behavior.

Learning Target 20-6 Review

Explain the function of

sensory adaptation.

Sensory adaptation (our diminished sensitivity to constant odors, sights, sounds, and touches) focuses our attention on informative changes in our environment.