1. SENSATION & PERCEPTION
CHAPTER 4
SENSATION & PERCEPTION

2. SENSATION & PERCEPTION
Sensation: The process of receiving stimulus energies from the external environment and transforming those energies into neural impulses.
How energy from the world is transformed into neural impulses that our brain can understand.
Activation of the senses
Perception: The process of organizing and interpreting sensory information so that it has meaning.
How our brain selects, organizes, and interprets sensory input.
Understanding sensations

3. BOTTOM-UP PROCESSING
Sensory receptors register information about the external environment and send it up to the brain for interpretation.
A progression from the individual elements to the whole.
Incoming sensory messages
Sensation > Perception
More accurate, slower
Example:
Feature analysis
Looking up from a city street

4. TOP-DOWN PROCESSING
Launched by cognitive processing at the brain’s higher levels, that allows the organism to sense what is happening and to apply the framework to the information from the world.
A progression from the whole to the individual elements.
Brain’s effort to make sense of incoming messages
Perception > Sensation
Faster, error prone
Example:
Gestalt principles
Perceptual set
Looking down from a skyscraper

6. PSYCHOPHYSICS
The study of how physical stimuli are translated into psychological experiences.
Physical World
(Sensation)
Psychological World
(Perception)
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweetness

7. TRANSDUCTION
The transformation of stimulus energy into neural impulses that the brain can interpret.
SENSATION TRANSDUCTION PERCEPTION

8. SENSORY RECEPTORS
Specialized cells that detect stimulus information and transmit it to sensory (afferent) nerves and the brain.
Main classes of receptors based on the type of energy that is detected:
Photoreceptors: detection of light; perceived as sight (eyes)
Mechanoreceptors: detection of pressure and vibration; perceived as touch and hearing (skin, ears)
Chemoreceptors: detection of chemical stimuli; perceived as smell and taste (nose, tongue)
Thermoreceptors: detection of temperature; perceived as warm and cold (skin)

9. SYNESTHESIA
An experience in which one sense (sensation) induces an experience (perception) in another sense.
Examples:
“see” music
“taste” colors

10. THRESHOLDS Absolute Threshold Difference Threshold
The minimum amount of stimulus energy that a person can detect 50% of the time.
Examples:
Vision: candle flame at 30 miles on a dark, clear night
Hearing: ticking clock at 20 feet under quiet conditions
Touch: wing of a fly falling on your neck from 1 centimeter
Taste: 1 teaspoon of sugar in 2 gallons of water
Smell: 1 drop of perfume diffused throughout 3 rooms
The smallest degree of difference that must exist between 2 stimuli before the difference is detected.
Also called just noticeable difference (JND)
Examples:
You change the temperature from 74 degrees to 73 degrees, and all of a sudden someone in the house is cold.
You change the volume of the car by one level and someone complains that it is too loud.

11. JUST NOTICEABLE DIFFERNCE
Weber’s law
Fechner’s Law
Ernst Weber
The size of a JND must be a constant percentage of the size of the initial stimulus to perceive the difference.
Constant minimum percentage
Example:
Light-8%
Weight-2%
Tone-.3%
Gustav Fechner
The magnitude of a sensory experience is proportional to the number of JNDs that the stimulus is above absolute threshold.
Scaling
Example:
You walk into a dark room
1st lamp- difference is HUGE
2nd lamp- twice the light, but not twice as bright
3rd lamp- barely notice difference

12. SUBLIMINAL PERCEPTION
The detection of information below the level of conscious awareness.
Occurs below absolute threshold
May influence behavior (slightly effective)

13. SIGNAL DETECTION THEORY
Theory of perception that focuses on decision making about stimuli in the presence of uncertainty.
Ability to discriminate between noises
Noise: Irrelevant and competing/distracting stimuli for our senses.
Detection depends on:
Fatigue
Expectation (high vs. low)
Motivation/Urgency
Experience

14. SIGNAL DETECTION THEORY
(False negative)
(False positive)

15. ATTENTION The process of focusing awareness.
Selective attention: The process of focusing on a specific aspect of the environment while ignoring others.
Cocktail party effect: The ability to concentrate on one voice among many in a crowded room.
Example of selective attention
Stroop effect: Automatically reading the color’s name instead of the ink color.
Failure of selective attention
Certain stimuli attract attention:
Novel, large, vivid, moving, emotional
Perceptual Blindness:
Emotional-induced blindness
Inattentional blindness
Change blindness
SO DON’T TEXT AND DRIVE!!!

16. PERCEPTUAL SET
A predisposition or readiness to perceive something in a particular way.
The brain learns to perceive through experience
Expectations influence perceptions
Top-down influence

17. SENSORY ADAPTATION
A change in the responsiveness of the sensory system based on the average level of surrounding stimulation.
A gradual decline in sensitivity to prolonged stimulation.
Examples:
Light Adaptation
Dark Adaptation
Watch on your wrist
Odor in a room