1. 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

2. 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

3. Sensation- Basic Principles
Psychophysics
study of the relationship between physical characteristics of stimuli and our psychological experience of them
Light- brightness
Sound- volume
Pressure- weight
Taste- sweetness

4. Sensation- Thresholds
Absolute Threshold
minimum stimulation needed to detect a particular stimulus
usually defined as the stimulus needed for detection 50% of the time
Difference Threshold
minimum difference between two stimuli that a subject can detect 50% of the time
just noticeable difference (JND)
increases with magnitude

5. 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”.

6. Sensation- Thresholds
Weber’s Law- to perceive a difference between two stimuli, they must differ by a constant proportion
a constant for each sense:
light intensity- 8%, weight- 2%
tone frequency- 0.3%
Just noticable difference has a proportion to be met in order to sense difference

7. Weber’s Law
Classic and still identified today but it did not account for extreme values….175 watt and a 200 watt…
Ability to recognize difference diminishes….so in 1860s

8. Sensation- Thresholds
Fechner’s Law- “upgrade” of Weber’s law
includes increase of jnd with extreme measures/magnitude
Adding the relationship of the perceived magnitude to physical intensity of a stimuli
Same basic idea:
½ pound book in 2lb vs. 60lb backpack
1 voice in chorus of 10 versus 2 in 20

9. Sensation- Thresholds
Steven’s Power Law - upgrade to Fechner (Fechner’s law didn’t work for pain*, other stimuli)
Strength of a sensation related to the intensity of the stimuli raised to some power
So pain like electric shock you will sense a a small change at higher intensities than at the lower intensities when more may be needed to recognize difference

10. Stevens
Fechner

11. Sensation - Thresholds
Note that one of the implications of Steven’s law is that with higher levels of pain you get MORE sensitive!
Sensory adaptation- diminished sensitivity with constant stimulation

12. 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

13. Sensation- Thresholds
Signal Detection Theory
Assumes TWO things going on:
1. sensitivity to stimulus (physical)
2. response bias – also called decision criterion (psychological)
Can measure & plot these in a Receiver Operating Characteristic curve (ROC curve)

14. Vision
Transduction- conversion of one form of energy to another (for us, it’s specifically: converting physical energy to neural impulses)
Properties of light and vision
Physical Psychological
intensity brightness
wavelength hue (color)
wave purity saturation

15. Vision
Wavelength- the distance from the peak of one wave to the peak of the next
Amplitude - the height (strength) of a wave
Hue- perceived “color” of the light
Intensity- amount of energy in a wave determined by amplitude
Saturation - perceived “purity” of a color (e.g. pastels have low saturation)

16. Vision- Spectrum of Electromagnetic Energy (quantum particle/waves)

17. Vision- Physical Properties of Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Small amplitude
(dull colors, soft sounds)

18. Vision Pupil- adjustable opening in the center of the eye
Iris- a ring of muscle the forms the colored portion of the eye around the pupil and controls the size of the pupil opening
Lens- transparent structure behind pupil that changes shape to focus images on the retina

19. Vision

20. Vision Accommodation Retina change in shape of lens focus near objects
inner surface of eye
light sensitive
contains rods and cones
layers of neurons
beginning of visual information processing

21. Vision Acuity- the sharpness of vision Nearsightedness Farsightedness
nearby objects seen more clearly
lens focuses image of distant objects in front of retina
Farsightedness
faraway objects seen more clearly
lens focuses near objects behind retina

22. Retina’s Reaction to Light- Receptors
Cones
near center of retina (fovea)
fine detail and color vision
daylight or well-lit conditions
Rods
peripheral retina
detect black, white and gray
twilight or low light
Saccades - quick eye movements

23. Retina’s Reaction to Light
Bipolar cells- neurons that combine info from multiple receptors
Ganglion cells – neurons that combine info from multiple bipolar cells.
Optic nerve – bundle of axons of the ganglion cells that carry info from retina to brain.

24. Vision- Receptors Receptors in the Human Eye Cones Rods
Number
Location in
retina
Sensitivity in
dim light
Color sensitive?
Yes
Low
Center
6 million No
High*
Periphery
120 million
*Why pirates wore eyepatches? Arrrr…

25. Retina’s Reaction to Light
Optic nerve- nerve that carries neural impulses from the eye to the brain
Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there
Fovea- central point in the retina, around which the eye’s cones cluster

26. Pathways from the Eyes to the Visual Cortex

27. Vision- Stabilized Images on the Retina

28. Retina’s Reaction to Light
Receptive fields – regions in which receptors respond to light
Lateral inhibition – receptor (or neuron) making it’s neighbors less sensitive
Helps in things like edge detection

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

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

31. 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

32. Visual Information Processing
Neural pathways (multiple!)
Optic nerve through optic chiasm (crossover), becomes the optic “tract” then…
Primary visual cortex (striate cortex) then splits into…
The “what” path (thru temporal lobes)
The “where” path (up into parietal lobes)

33. Visual Information Processing – Color vision
Trichromatic (three color) Theory
The Young–Helmholtz theory
three different retinal color receptors sensitive to
red
green
Blue

34. Visual Information Processing – Color vision
But Tri-chromatic didn’t explain afterimages or color-blindness! So…
Opponent Process Theory
Black-white receptors (for brightness & saturation)
Red-green receptors (for hue)
Blue-yellow receptors (for hue)

35. Opponent Process- Afterimage Effect

36. Color-Deficient Vision
People who suffer red-green blindness have trouble perceiving the number within the design

37. Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable color vision
“ON” “OFF”
red green
green red
blue yellow
yellow blue
black white
white black

38. Visual Information Processing – Color vision
So who’s right???
Turns out they’re both right:
Tri-chromatic theory works in the retina
Opponent process works in the higher visual processing parts of the brain
Together they explain what we know about color vision quite well.

39. Audition Audition the sense of hearing Properties of sound and hearing
Physical Psychological
intensity loudness
wavelength pitch
wave purity timbre (tone)

40. Audition Timbre - tonal quality; “richness” Frequency Pitch
the number of complete wavelengths that pass a point in a given time
Pitch
a tone’s highness or lowness
depends on frequency
Timbre - tonal quality; “richness”

41. The Intensity of Some Common Sounds

43. Audition- The Ear Outer Ear Middle Ear Inner Ear Auditory Canal
Eardrum
Middle Ear
hammer
anvil
stirrup
Inner Ear
oval window
cochlea
basilar membrane
hair cells

44. Audition Place Theory Frequency Theory
the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated
Frequency Theory
the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

45. Audition So who’s right? At low frequencies: frequency theory
They’re both probably right:
At low frequencies: frequency theory
At high frequencies: place theory
At middle frequencies: both

46. How We Locate Sounds

47. How we locate sounds Two cues:
Differences between the two ears in loudness
Differences in the arrival time at the ears

48. Audition Conduction Hearing Loss Nerve Hearing Loss
hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea
Nerve Hearing Loss
hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve

49. Audition
Older people tend to hear low frequencies well but suffer hearing loss for high frequencies 1
time 10
times
100
1000 32 64
128
256
512
1024
2048
4096
8192
16384
Frequency of tone in waves per second
Low
Pitch
High
Amplitude required for
perception relative to
20-29 year-old group

50. Touch Skin Sensations pressure warmth cold pain
only skin sensation with identifiable receptors
warmth
cold
pain

51. Pain Gate-Control Theory
theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain
“gate” opened by the activity of pain signals traveling up small nerve fibers
“gate” closed by activity in larger fibers or by information coming from the brain

52. Taste Taste Sensations Sensory Interaction sweet sour salty bitter
the principle that one sense may influence another
as when the smell of food influences its taste

53. Smell nerve Olfactory bulb Receptor cells in Nasal olfactory membrane
passage
Olfactory
bulb
nerve

54. Age, Sex and Sense of Smell
Women
Men
Age Group 4 3 2
Number
of correct
answers
Women and young adults
have best sense of smell

55. Smell
Less important in humans than animals but we still can detect:
Pheromones
Smell-communicated chemicals secreted by organisms
People can often identify gender by smell of sweaty hands or articles of clothing!

56. Body Position and Movement
Kinesthesis
the system for sensing the position and movement of individual body parts
Vestibular Sense
the sense of body movement and position
including the sense of balance