1. Sensation

2. Sensation
The process by which our sensory receptors and nervous system receive stimulus from the environment.

3. Perception
The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

4. 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.”

5. 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

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

7. Failures of perception: cataracts, brain damage
Prosopagnosia- complete sensation but incomplete perception. Can sense visual information but cant recognize it—(cannot process top-down) ex: faces

8. Sensation
Our sensory and perceptual processes work together to help us sort out complex processes
The Forest Has Eyes is the title of this work---in studying it we look at the expressions on the faces, there is something foreboding about this picture, and after we have read the title we notice other things…

10. 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.

11. What if we could sense everything?
Life would hurt.
So we can only take in a window of what is out there.
This is the study of psychophysics.

12. 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

13. 22nd October 1850
A relative increase in mental intensity, [Fechner] realized, might be measured in terms of the relative increase in physical energy required to bring it about
(Wozniak, 1999).
Gustav Fechner
( )

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

15. 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.

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

17. 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.

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

19. 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%
LAB

20. 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

21. 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

22. 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.

23. The concept of sensory adaptation applies to all of our senses.

24. We do not perceive the world how it really is, but as it is useful for us to perceive it.

25. See page 197 in text for example on difference threshold- 23rd psalm
Riddle page 195- bus driver
Backmasking: