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HOW do we Sense Things?SENSE RECEPTORS are cells located

in the sense organs (eyes, ears, etc.) that convert _______________ energy to ______________ energy

SENSE RECEPTORS▼

SENSORY NEURONS▼

BRAIN CELLS

I’m not the only one who has electrical currents running through my body!

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Your brain interprets info. in 2 different ways

1) _____________________ your sense organs (eyes, ears, nose, etc.) send impulses along designated nerve pathways to specific parts of the brain.

► Tells the various senses apart!

EXAMPLE: Eye info. goes to the visual cortex

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2) _____________________ rely on the fact that sensory neurons fire, or are inhibited from firing, only when presented with specific stimuli.

► Tells the difference between

sensations WITHIN a

particular sense!

EXAMPLE: Color vs. Shape

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What do you think might happen if your sensory neurons sent information to

the wrong part of the brain?

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WEIRD, but TRUE!• _______________: A rare condition in

which stimulation of one sense also evokes a sensation in anotherIn other words, a person might see sounds or smell

colors

EXAMPLE 1: A person may say that the aroma of cinnamon feels like velvet

EXAMPLE 2: One might say that the sound of a clarinet tastes like cherries.

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Sensing the World:Some Basic Principles

Threshold Absolute Threshold

Difference Threshold

Subliminal Stimulation

Signal Detection Theory

Sensory Adaptation

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THRESHOLDS

1) ________________________:

The smallest quantity of physical energy

that can be reliably detected by an observer

RELIABLE = Detection _____ of the time

EXAMPLE:What’s the smallest line you will

read correctly 50% of the time?

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9

No

Detection

Intensity

AbsoluteThreshold

Detected

YesYesNo No

Observer’s Response

Tell when you (the observer) detect the light.

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Thresholds

Absolute Threshold: Minimum stimulation needed to detect one particular stimulus 50% of the time.

Pro

port

ion

of

“Yes”

Resp

on

ses

0.0

0

0

.50

1.0

0

0 5 10 15 20 25 Stimulus Intensity (lumens)

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NORMAL SENSORY ABILITIESVISION: A candle flame on a clear, dark night

from _____ miles away.

HEARING: A ticking watch in perfectly quiet room

from _____ feet away

TASTE: A teaspoon of sugar diluted in _____gallons of water

SMELL: A drop of perfume diffused through a ____-room apartment

TOUCH: Feel the wing of a bee falling in yourcheek from a height of ______

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THRESHOLDS

2) _________________________:

The smallest difference in stimulation that can be reliably detected when comparing two things

A.K.A. Just Noticeable Difference

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Difference Threshold

Difference Threshold: Minimum difference between two stimuli required for

detection 50% of the time, also called just noticeable difference (JND).

DifferenceThreshold

Tell when you (observer) detect a difference in the light.

No

Observer’s Response

No Yes

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Weber’s Law

Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as

different.

StimulusConstant

%

Light 8%

Weight 2%

Tone .3%

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DIFFERENCE THRESHOLD

• When comparing 2 objects, A and B, the difference threshold will depend on the intensity or size of A.

– The larger or more intense A is, the greater the change must be before you can detect a difference.

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DIFFERENCE THRESHOLD EXAMPLE

• In comparing 2 pebbles, you might be able to detect a difference of only a fraction of an ounce

• In comparing 2 massive boulders, such a subtle difference would most likely not be noticed.

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How did Scientists figure this out?......Psychophysics

A study of the relationship between physical characteristics of stimuli and

our psychological experience with them.

Physical WorldPsychological

World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet

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Signal Detection Theory (SDT): highlights the limitations of measuring absolute and

difference thresholds

Signal Detection Theory (SDT): Predicts how and when we detect the presence of a faint

stimulus (signal) amid background noise (other stimulation). SDT assumes that there is no

single absolute threshold and detection depends on: Person’s

experienceExpectationsMotivationLevel of fatigue

Carol L

ee/ Tony Stone Im

ages

___________________: some ___________________: some people are habitual yea-sayers people are habitual yea-sayers and others are habitual and others are habitual naysayers which can greatly naysayers which can greatly affect and disrupt data affect and disrupt data collection techniques.collection techniques.

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SDT Matrix

Decision

Yes No

Signal

Present Hit Miss or False Negative

AbsentFalse

Alarm or False Positive

Correct Rejection

The observer decides whether she hears the tone or not, based on the signal being present or not. This translates into four

outcomes.

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Subliminal Threshold

Subliminal Threshold: When stimuli are below

one’s absolute threshold for conscious

awareness.

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SUBLIMINAL ORIGINS• 1950s

• Movie theater owner claimed to sell more refreshments when he flashed the words “EAT MORE POPCORN” or “DRINK COKE” for a split second on the screen.

• Turned out to be a hoax

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SUBLIMINAL MESSAGES

• Subliminal messages have appeared in all kinds of places:

– Magazines– Movies– Political Campaigns– Weight Loss Strategies– Self-Improvement Books– Memory Enhancers and Study Aids

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SELF-HELP SUBLIMINAL TAPES

• Many promise to help you stop smoking, lose weight, relieve stress, or stop taking drugs

• Study = Placebo tapes vs. “Real Tapes”

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The Effect of Subliminal Stimuli • “Absolute” threshold is merely the point at which

we detect a stimulus half the time. Therefore it is possible to sense subliminal (below threshold) stimuli.

• Laboratory research reveals that subliminal stimuli has a subtle, fleeting effect that may prime (or heighten) a feeling that already exists.

• Research in subliminal priming confirms that much of our information processing occurs automatically without detection by our conscious mind and supports evidence in the powers of intuition.

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Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

Put a band aid on your arm and after awhileyou don’t sense it.

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Now you see, now you don’t