1. Sensation & Perception

2. 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

3. What is Perception?
The interpretation of sensory signals.

4. Example? Hearing your ringtone = sensation
Recognizing the song = perception
Hearing a voice = sensation
Recognizing your mother’s voice = perception

5. 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)

6. 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.

8. 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

9. 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.

10. 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.

11. 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

12. 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

13. Measuring the Senses

14. 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.

15. Absolute Threshold Absolute Threshold Intensity No No No Yes Yes
Observer’s Response
Detected
Tell when you (the observer) detect the light.

16. Absolute Thresholds for Humans
SENSE
STIMULUS
RECEPTORS
THRESHOLD
Vision
Electromagnetic Energy
Rods & Cones in the retina
A 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 room
Smell
Chemical substances in the air
Receptor cells in the nose
About 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 water
Touch
Pressure on the skin
Nerve endings in the skin
The wing of a fly falling on a cheek from a distance of about 0.4 inches

17. 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.

18. Weber’s Law
Idea that, to perceive a difference between two stimuli, they must differ by a constant percentage; not a constant amount.

19. 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.

20. 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

21. 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

22. 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.

23. 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.

24. Sensory Deprivation
Some become disoriented, confused, restless, or grouchy.
Some enjoy limited periods of deprivation, and some perceptual and intellectual abilities actually improve.

25. 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.

26. Read this.
Now read it again.

27. Selective Attention Example: Cocktail Party Effect
Ability to listen to one voice among many.
To pay attention despite many distraction.

28. Inattentional Blindness
The inability to see an object or a person in our midst.
Is Google
Glass
dangerous?