1. Unit 5: Senation & Perception Day 1: Sensory Thresholds & The Eye
ON YOUR DESK:
RJ 5.1 & 5.2
DAILY COMMENTARY (in a spiral notebook!):
Glance for 1 second at spot in the room and then immediately look away.
Write down everything you recall seeing.
Essential Question
How do we use our senses to perceive the world around us?
Objectives (write this down!):
I can: distinguish between top down and bottom up processing
I can generate examples that demonstrate signal detection theory

2. Unit 5: Senation & Perception Day 1: Sensory Thresholds
For Tonight:
RJ 5.3
Myers
Griggs 87-90
DUE FRIDAY:
Tatum Take Home
Today: DC
Unit Overview
Review Unit Project
Notes
Activity

3. Unit Project
Sensation Children’s Book

4. 8 ZQ F
4 0 9
W 7

5. 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.

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

7. Making Sense of Complexity
Our sensory and perceptual processes work together to help us sort out complex images.
“The Forest Has Eyes,” Bev Doolittle

8. Senses are nature’s gift that suit an organism’s needs.
Sensing the World
Senses are nature’s gift that suit an organism’s needs.
A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

9. Exploring the Senses
What stimuli cross our threshold for conscious awareness?
Could we be influenced by stimuli too weak (subliminal) to be perceived?
Why are we unaware of unchanging stimuli, like a band-aid on our skin?

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

14. 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.

15. Examples of Just Noticeable Difference
An iPod is advertised in Greensboro for $50; in Durham it is $125 – do you drive to Greensboro?
A $950 laptop is advertised in Greensboro; it is $1025 in Durham. Do you make the drive?

16. 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%

17. 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

18. SDT Matrix
The observer decides whether she hears the tone or not, based on the signal being present or not. This translates into four outcomes.
Decision
Yes No
Signal
Present
Hit
Miss
Absent
False
Alarm
Correct Rejection

19. Stevens’s Power Law
To perceive a stimulus (such as light) as twice as bright, it must increase in intensity by 8 to 9 times
Doubling the amount of light or volume will not result in our perceiving that it has in fact doubled

20. 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.

21. Assignment Your Choice:
Draw diagrams or cartoons that demonstrate the distinction between top down and bottom up processing.
Create a story scenario that demonstrates signal detection theory by showing how different factors affect an individual’s perceptive abilities

22. Reminders

23. Now you see, now you don’t