1. Experiencing the World
Sensation
Experiencing the World

2. Sensation
Sensation
a process by which our sensory receptors and nervous system receive and represent stimulus energy
Perception
a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

3. Sensation & Perception
Causally related with perceptions organizing sensations

4. Sensation Bottom-Up Processing Top-Down Processing
analysis that begins with the sense receptors and works up to the brain’s integration of sensory information
Top-Down Processing
information processing guided by higher-level mental processes
as when we construct perceptions drawing on our experience and expectations

5. Sensation- Basic Principles
Psychophysics - study of the relationship between physical characteristics of stimuli and our psychological experience of them
Lumens of light - brightness
Size of air wave - loudness
Pressure- weight
Chemical compounds - sweetness

6. Sensation & reality
Objective reality is very different than the way we sense and perceive it
No colors, tastes, smells, etc. in natural world
Just stimulus energy of various sorts
We process this energy and ‘psychologize’ it
We transform it into color, tastes, smells that don’t exist in natural world

7. The world is not always as we sense it...

8. Reaction Paper II: Sensation
Describe what is meant by ‘the world is not as you sense it.’ What is your reaction to this? How do you think this may change the way you view the world?
PLEASE TURN THESE IN AFTER CLASS!

9. Sensation- Thresholds
Absolute Threshold
minimum stimulation needed to detect a particular stimulus
usually defined as the stimulus needed for detection 50% of the time

10. Sensation- Thresholds
Difference Threshold
minimum difference between two stimuli that a subject can detect 50% of the time
just noticeable difference (JND)
increases with magnitude

11. Sensation- Thresholds
Signal Detection Theory
predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)
assumes that there is no single absolute threshold
detection depends partly on person’s
experience
expectations
motivation
level of fatigue

12. Sensation- Thresholds25 50 75
100
Low
Absolute
threshold
Medium
Intensity of stimulus
Percentage
of correct
detections
Subliminal
stimuli
When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”.
Threshold

13. Sensation- Thresholds
Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion
light intensity- 8%
weight- 2%
tone frequency- 0.3%
100 candles in a room need 8 more to see a difference

14. Sensation- Thresholds
Sensory adaptation- diminished sensitivity to constant stimulation

15. Spectrum of Electromagnetic Energy
Vision
Light is energy

16. Vision Transduction - conversion of one form of energy to another
Electromagnetic to electrical-chemical

17. Vision- Physical Properties of Waves
Wavelength - distance from peak to peak
Determines color (Hue)

18. Structures of the eye Cornea - outermost covering of eye
Begins process of focusing
Pupil- adjustable opening in center
Iris- a ring of muscle = colored portion
controls size of pupil opening
Lens- transparent & changes shape to focus images on retina
Accommodation

19. Vision

20. Vision Retina inner surface of eye light sensitive layers of neurons
begins visual information processing
transduction

21. Retina’s Reaction to Light
Cones (6 million)
near center of retina (fovea)
fine detail and color vision
daylight or well-lit conditions
Rods (120 million)
peripheral retina
detect black, white and gray
twilight or low light (video)

22. Retina’s Reaction to Light
Retina converges out the eye through...
Optic nerve- nerve that carries neural signals from the retina to brain
Blind Spot- optic nerve leaves the eye with no receptor cells
DEMO (close left eye look at y)
Y X

23. Eye

24. Pathways from the Eyes to the Visual Cortex

25. Visual Information Processing
Feature Detectors - neurons in the visual cortex respond to specific features
shape
angle
movement
Stimulus
Cell’s
responses

26. Visual Information Processing
Parallel Processing-simultaneous processing of several dimensions through multiple pathways
color
motion
form
depth

27. Visual Information Processing
Scene
Retinal processing:
Receptor rods and
conesbipolar cells
 ganglion cells
Feature detection:
Brain’s detector cells
respond to elementary
features-bars, edges, or
gradients of light
Abstraction:
Brain’s higher-level cells
respond to combined
information from
feature-detector cells
Recognition:
Brain matches the
constructed image with
stored images

28. Flexiblity Visual system flexible
Rapid adaptation to changing stimulus energy
Inverted vision video
Why do you think this flexibility is part of our visual system?

29. Other senses Audition Touch Taste Smell Pain
See text for this information

30. Sensation Summary Processing stimulus energies Basic principles
Reality
Thresholds
Visual processing