Sensation & Perception

What is Sensation?

• Passively receiving information through sensory inputs.

• Cells that detect physical energy are located in sense organs– Eyes– Ears– Nose– Tongue– Skin– Internal body tissue

What is Perception?

• The interpretation of sensory signals.

Example?

• Hearing your ringtone = sensation

• Recognizing the song = perception

• Hearing a voice = sensation

• Recognizing your mother’s voice = perception

How Many Senses Do We Have?

• More than five, though scientists disagree on how many.– Vision (eyes)– Hearing (ears)– Taste (tongue)– Touch (skin)– Smell (nose)

How Many Senses Do We Have?

• BUT WAIT! THERE’S MORE!– Skin can also sense heat, cold, pain, itching,

tingling– Ear also contains receptors for balance– Skeletal muscles contain receptors for a sense of

bodily movement.

Why are Senses Important?

• Help us survive• Even pain is a crucial part of our evolutionary

heritage– Alerts us to illness and injury

• But they also…– Entertain us– Amuse us– Soothe us– Inspire us

Sensation

• Sensation begins with sense receptors– Cells located in sense

organs• Receptors detect

appropriate stimulus—light, pressure, or chemical molecules—and convert the energy into electrical impulses that travel along nerves to brain.

Think of it like this…

• Sense receptors are like military scouts who scan terrain for activity.– Scouts can’t make decisions on their own.– Must transmit what they see to field officers (neurons).– Field officers report to generals at the command center

(brain).• Brain cells responsible for analyzing reports

(stimulus), combining information brought in by different scouts (senses), and deciding what it all means.

Think of it like this…

• “Field officers”—sense receptors—all use the same form of communication, a neural impulse, or pulse of electrical energy.

Sensory Receptors Neurons Brain

Doctrine of Specific Nerve Energies

• Different

What if we could sense everything?

• Life would be a headache.

• We can only take in a window of what is out there.– Known as the study of

psychophysics– Studies how the strength

or intensity of a stimulus affects the strength of sensation

Measuring the Senses

Absolute Threshold

• The smallest amount of energy that a person can detect reliably (50% of the time)

• Not really absolute: people detect borderline signals on some occasions and not others.

http://www.youtube.com/watch?v=wVhiezByMSUhttp://www.youtube.com/watch?v=4G60hM1W_mk

Absolute Threshold

No

Intensity

AbsoluteThreshold

Detected

YesYesNo No

Observer’s Response

Tell when you (the observer) detect the light.

Absolute Thresholds for HumansSENSE STIMULUS RECEPTORS THRESHOLDVision Electromagnetic

EnergyRods & Cones in the

retinaA candle flame viewed from a

distance of about 30 miles on a dark night

Hearing Sound Waves Hair cells of the inner ear

The ticking of a watch from about 20 feet

away in a quiet roomSmell Chemical substances

in the airReceptor cells in the

noseAbout one drop of perfume diffused

throughout a small house

Taste Chemical substances in saliva

Taste buds on the tongue

About 1 teaspoon of sugar dissolved in 2

gallons of waterTouch Pressure on the skin Nerve endings in the

skinThe wing of a fly falling on a cheek from a distance of about 0.4 inches

Difference Thresholds

• The smallest difference in stimulation that a person can detect reliably (50% of the time)

• The just noticeable difference

• Ex: Comparison of the weight of two blocks, brightness of two lights, or saltiness of two liquids.

http://www.youtube.com/watch?v=hyEoVN97J1c

Weber’s Law

• Idea that, to perceive a difference between two stimuli, they must differ by a constant percentage; not a constant amount.

Weber’s Law• When comparing 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.

Signal-Detection Theory

• Predicts how and when we detect the presence of a faint stimulus (signal).

• SDT assumes there is no single absolute threshold

• Detection depends on…– Person’s experience– Expectations– Motivation– Level of fatigue

Signal-Detection Theory

• Measurements for any given individual may be affected by the person’s general tendency, when uncertain, to respond, “Yes, I noticed a signal (or difference)” or “No, I didn’t notice anything.”

• Some people are habitual yea-sayers, others nay-sayers

Sensory Adaptation

• Diminished sensitivity as a consequence of constant stimulation.

• Ex: Put a band aid on and after a while, you don’t sense it.

Sensory Adaptation

• Hold your hand over one eye and stare at the dot in the middle of the circle.

• Gradual change from light to dark does not provide enough contrast for visual receptors firing at a steady rate.

Sensory Deprivation

• Some become disoriented, confused, restless, or grouchy.

• Some enjoy limited periods of deprivation, and some perceptual and intellectual abilities actually improve.

http://www.youtube.com/watch?v=dtZNjzeShYw

Selective Attention

• Focusing conscious awareness on a particular stimulus to the exclusion of others.

• The ability to focus on one stimulus at a time.

• Allows a person to function in a world filled with many stimuli.

• People with ADD have trouble doing this.

Read this.

Now read it again.

Selective Attention

• Example: Cocktail Party Effect– Ability to listen to one voice among many.– To pay attention despite many distraction.

Inattentional Blindness

• The inability to see an object or a person in our midst.

• Is Google Glass dangerous?

https://www.youtube.com/watch?v=Yu3zlWVCcjY