1. Intro to Sensation Module 12

2. If you stare long enough, the grey will fade….

3. Sensation & Perception
How do we construct our representations of the external world?
To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation.
When we select, organize, and interpret our sensations, the process is called perception.
OBJECTIVE 1| Contrast sensation and perception, and explain the difference between bottom-up and top-down processing.

4. SENSATION: how we detect physical energy from the environment and encode it as neural energy.
Sensation involves transducers-specialized receptor cells.
Transduction – converting stimuli into neural impulses

5. Stimulation-but meaningless?
...one great, blooming, buzzing confusion.”-William James, on a baby’s first perceptual experience.

6. Perception: how we select, organize, and interpret sensations.
An active process that imposes some organization on the meaningless sensations.

7. Bottom-up Processing
Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind.
Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

8. THE CHT Top-Down Processing
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations.
THE CHT

9. Making Sense of Complexity
Our sensory and perceptual processes work together to help us sort out complex images.

10. Psychophysics
A study of the relationship between physical characteristics of stimuli and our psychological experience with them.
Physical World
Psychological World
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet

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

12. Thresholds
Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.
Proportion of “Yes” Responses
Stimulus Intensity (lumens)
OBJECTIVE 2| Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute thresholds and be influenced by them.

13. Absolute Thresholds for Various Senses
Stimulus
Receptors
Threshold
Vision
Light Energy
Rods and cones in the eyes
The flame from a single candle flickering about 30 miles away on a dark, clear night

14. Absolute Thresholds for Various Senses
Stimulus
Receptors
Threshold
Hearing
Sound Waves
Hair cells in the ears
The ticking of a watch placed about 20 feet away from a listener in a quiet room.

15. Absolute Thresholds for Various Senses
Stimulus
Receptors
Threshold
Taste
Chemical substances that contact the tongue
Taste buds on the tongue
About one teaspoon of sugar dissolved in two gallons of water

16. Absolute Thresholds for Various Senses
Stimulus
Receptors
Threshold
Smell
Chemical substances that enter the nose.
Receptor cells in the upper nostrils.
About one drop of perfume dispersed in a small house.

17. Absolute Thresholds for Various Senses
Stimulus
Receptors
Threshold
Touch
Movement of, or pressure on, the skin.
Nerve endings in the skin.
The wing of a bee falling on the cheek from about one centimeter away.

18. Subliminal Threshold
Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness.
Kurt Scholz/ Superstock

19. Difference Threshold
Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND).
Difference
Threshold No No
Yes
Observer’s Response
Tell when you (observer) detect a difference in the light.

20. Weber’s Law
Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.
Stimulus
Constant (k)
Light 8%
Weight 2%
Tone 3%

21. Examples of Weber’s Constants
Sensation
Weber’s Constant (approx)
Saltiness of Food
1/5
Pressure on Skin
1/7
Loudness of Sound
1/10
Odor
1/20
Heaviness of Weights
1/50
Brightness of Lights
1/60
Pitch of Sounds
1/333

22. Example
Weights = 1/50 or 2%
You are lifting 50 Lbs, how much more weight would you need to add to notice?
100 lbs?
200 lbs?

23. 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 experience
Expectations
Motivation
Level of fatigue
Carol Lee/ Tony Stone Images

24. Sensory Adaptation
Diminished sensitivity as a consequence of constant stimulation.
OBJECTIVE 3| Describe sensory adaptation, and explain how we benefit from being unaware of changing stimuli.
Put a band aid on your arm and after awhile
you don’t sense it.

25. An example of selective attention is:
Cocktail Part Effect: ability to listen to one voice among many.