1. Sensation and Perception
True or False???
On a clear, dark night most of us can see a candle flame 30 miles away.
Advertisers are able to shape our buying habits through subliminal messages.
Constant eye movements prevent our vision from being seriously disrupted.

2. Introducing,….Sensation!
“Seeing is believing.”
For each of the following visuals, simply write down what you see. (Do not share with your neighbor.)

6. Analyzing what we see….
Each visual provides sensory information that gives rise to two totally different perceptual interpretations.
Now, lets try it again…
Write down what you see first in the next visual image.

8. Sensation and visual images
Why is it that no matter how many times we look at the image, we tend to see the image we saw the first time we observed it?
First impression = schema
Have to consciously seek the other figure
After practice, we can see both images, but not simultaneously

9. So, what is Sensation & Perception?
How we detect physical energy from the environment and encode it as neural signals (what we sense and send to the brain)
Perception
How we select, interpret and organize this information (what the brain does with it)
5.2 Top Picture—to show the difference between sensation and perception. Looks like a meaningless blotch, students will try to figure it out—stimulation/sensation is being received but not perceived. The subject is a dog, and only part of a dog. Students will probably try to see the whole dog; you cannot tell figure from ground
5.2 Bottom picture—Fraser Spiral—it looks like a spiral but is actually a set of concentric circles

10. In other words…
Sensation provides the raw information that perception constructs into our experiences

11. Sensation : The Forest Has Eyes
sensation and perception work together to 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…

12. Sensation Bottom-Up Processing Top-Down Processing
Sensory 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
we construct perceptions drawing on our experience and expectations
Top Down is the involvement of the brain in making meaning out of stimuli. For example there are people who can see everything clearly (sensation) but cannot recognize even their own faces (perception).
Placing meaning to sensations and stimuli is the act of perception

13. Top Down Processing
Aoccdrnig to rscheearch at Cmabridge Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can still raed it wouthit a porbelm. This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the word as a wlohe.

14. Top Down Processing
How were you able to immediately make sense of these scrambled words?
Our experience and expectations enable us to immediately perceive the scrambled letters as meaningful words and sentences.
IOW: Higher level processes guide our perceptions.

15. Distinguishing Between Sensation and Perception
See Handout
“Blotch”: (5.2)
Fraser Spiral (5.2)
Place one finger on any line composing the spiral.
Place a finger from your other hand beside it and begin tracing the circle while holding your first finger in place.
What happens?

16. Failures of Perception
Prosopagnosia: complete sensation but incomplete perception (“face blindness”)
Can sense visual information, but can’t recognize it (can’t relate stored knowledge to sensory input)
Damage to temporal lobe area (recognition)

17. Sensation- Basic Principles
Psychophysics
study of how physical energy relates to our psychological experience (What we can and can’t detect.)
Light- brightness
Sound- volume
Pressure- weight
Taste- sweetness

18. Gustav Fechner Pioneer in Psychophysics
(U. of Leipzig)
Theory: consciousness and matter coexist
Mind / body: two aspects of fundamental unity
Stared at sun! Afterimage of blue and yellow
Mathematical relationship b/n force of stimuli and intensity of sensation

19. Sensation- Thresholds
Absolute Threshold
minimum stimulation needed to detect a particular stimulus 50% of the time
Difference Threshold
minimum difference between two stimuli required for detection 50% of the time
just noticeable difference (JND)
Three methods to test
Method of Limits: begin with a minimal stimulus and increase until it is perceived by subject
Method of right and wrong cases: subject sees identical stimuli repeatedly and says yes if perceives them or it they are different, and no if not perceived or the two are not different—informs how likely it is that any given stimulus level or difference between stimuli will be perceived by subject.
Method of adjustment—adjust a comparison stimulus until it appears to be identical to the standard stimulus, errors occur and are noted then averaged to give a measure of jnd
Try the timer in the kitchen—put it in a quiet room, move away and then move back—the point at which the ticking is perceived is the absolute threshold, at that point they may be able to hear sometimes and others time not, needing to move a few feet one way or the other—lapses of attention, fatigue other factors influence

20. Absolute threshold “An absolute threshold is anything but absolute…”
Why is this? What factors typically affect the absolute threshold?
Repetition
Fatigue
Competing stimuli
Expectation

21. 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

22. Sensation- Thresholds25 50 75
100
Low
Absolute
threshold
Medium
Intensity of stimulus
Percentage
of correct
detections
Subliminal
stimuli
Subliminal
When stimuli are below one’s absolute threshold for conscious awareness
Lay audiences accept the idea of subliminal persuasion but it has not been substantiated in research

24. 1957 James Vicary 1/3000 second Repetition Sales increase Popcorn= 57%
Coke = 18%
6 week study
Falsified results
Gateway to subliminal marketing, then images,“sexploitation”

25. “Priming Effect” Feel what we do not know and cannot describe
subliminal images: Imperceptibly brief stimulus

26. What’s the reasoning…?
The average American will see over 6 million ads in a lifetime…
Appeal to the subconscious will make consumer feel more positively about a product

27. Sensation- Thresholds
Weber’s Law- to perceive as different, two stimuli must differ by a constant minimum percentage (Difference thresholds grow with magnitude of stimulus)
light intensity- 8%
weight- 2%
tone frequency- 0.3%
Try the following experiment: two envelopes, one with two quarters in it, the subject will be able to tell the difference, but then put the envelopes in a pair of shoes and try to tell the difference
Weber's Principle: difference thresholds grow with the magnitude of the stimulus
If you make $5 p/h a 25 cent hour raise will be noticeable but at $10 p/h you may need 50 cents.
If you are in sales, three piece suit and sweater, sell the suit first because after the suit the man will be more likely to buy
In car sales, after the sale customer won’t really notice $500 stereo
ADAPTation—habituation
After drinking tea with lemon, a grapefruit will not taste as sour
…but after a roll, it will taste especially sour
After holding salty water in mouth, it will taste less salty, and drinking fresh water afterwards, it will taste sweet

28. Weber’s Law
As a salesman, how might one use Weber’s law to increase chances of selling the following to one customer?
Built in ipod accessory: $100
New Truck: $25,000
Navigation system: $200
Sliding rear window: $125

29. Envelopes, Quarters and boxes…. (Meyers, p. 7)
Can you detect a difference in weight between the two envelopes?
Can you detect a difference in weight between the two envelopes now?
How can we explain this development?

30. Vision: Sensory Adaptation
Sensory adaptation- diminished sensitivity as a consequence of constant stimulation
Eyes: constant quiver to ensure enough continual stimulation to eye’s receptors
Otherwise full visual image is lost

31. Vision- Stabilized Images on the Retina
5.3—to demonstrate that the eye is always moving
5.3 a—looking at the center will lead to the perception of movement, stare for 30 seconds and then stare at a white surface (wall or paper) , most will see after image of rotary motion
5.3b---stare at black dot in the middle for about 60 seconds and then look at the white dot, even if try to look hard, still will see an image of the grid pattern jiggling on top of the figure due to involuntary eye movements
5.3c—stare at the fuzzy contoured disc on the right, after about 30 seconds the disc will disappear, but this is almost impossible to do with the sharp contoured disc because the fizzy image jiggling on the retina causes only slight changes in the amount of light stimulating the receptors and if eyes are kept still this small change is not enough to maintain perception and disc fades from view. On the sharp one, the slight jiggling of the eyes causes sharp contour to fall first on some receptors and then on others so the amount of light stimulating the receptors is constantly changed and disc remains visible

32. Vision How do we transform particles of light into meaningful images?
Transduction
conversion of one form of energy to another
in sensation, how our sensory systems transform stimulus energies into neural impulses

33. Vision
Two physical characteristics of light help determine how we visually sense them…
1. Wavelength
the distance from the peak of one wave to the peak of the next (determines hue)
Hue: color we see determined by wavelength of light
2. Intensity
amount of energy in a light wave determined by amplitude
brightness
loudness

34. Vision- Physical Properties of Waves (from an atom to a mile…)
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)

35. The spectrum of electromagnetic energy: (light that we transduce into color)

36. Vision

37. Match the following Cornea D Pupil A Iris
Adjustable opening in the center of the eye
Ring of muscle, color portion of the eye around pupil- controls size of pupil opening
Transparent- behind pupil, changes shape to focus images on retina
Protects eye, bends light to provide focus
Eyes light sensitive inner surface- rods, cones, neurons that process visual info.
Cornea D
Pupil A
Iris B
Lens C
Retina E

38. Vision
Accommodation- the eye’s lens changes shape to help focus near or far objects on the retina
Retina- the light-sensitive inner surface of the eye, containing receptor rods, cones and layers of neurons that begin the processing of visual information

39. Retina’s Reaction to Light- Receptors
Rods
peripheral retina
detect black, white and gray
twilight or low light
Cones
near center of retina
fine detail and color vision
daylight or well-lit conditions

40. Rods and Cones

41. Making sense of our vision…
So why is our peripheral vision more blurred than our focused vision? (in front of us)
Cones = center of retina
Rods = periphery of retina
How do you walk effectively on a trail on a very dark night? Why?
Why can a cat see better than us at night?

42. 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

43. From the eye to the brain…
Optic Nerve
Rope-like axons from ganglion cells- carries information from the eye to the brain (1,000,000 messages at once!)

44. Close your left eye- move forward to a spot in which the car disappears. What is this called? How do we explain it?
The blind spot occurs is the location in the retina where the visual cortex exits to the brain, there are no receptors there
What our brain does, typically, is fill in that missing piece based on what it estimates to be there
Blindsight—we can see things we don’t perceive

45. Retina’s Reaction to Light
Blind Spot- point at which the optic nerve leaves the eye- creates “blind spot” because no receptor cells located there
Fovea- central point in the retina, around which the eye’s cones cluster (contains only cones- direct connection to visual cortex through bipolar cells = fine detail)

46. Vision Acuity- the sharpness of vision
Nearsightedness- nearby objects are seen more clearly than distant objects because distant objects in front of retina
Farsightedness- faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

47. Vision
Normal Nearsighted Farsighted Vision Vision Vision

48. Retinal ganglion cells---go back to 5.3 and then to 5.4
5.4a is the cover of a catalog and students complained of seeing gray spots
The grid pattern is called the Hermann grid after the German physiologist who first discovered it
The elusive gray spots can be explained in terms of the receptive fields of the retinal ganglion cells
Some of the cells are an on center surrounded by an off (like a donut). Light has opposite, antagonistic effects

49. Pathways from the Eyes to the Visual Cortex

50. Visual Information Processing
Retina: Brain tissue / analyzes, encodes info & routes to Thalamus
Process becomes more complex as continues

51. Visual Information Processing
Feature Detectors
(Hubel and Wiesel, 1979)
nerve cells in the visual cortex that respond to specific features (send to specific parts of cortex)
shape
angle
movement
Stimulus
Cell’s
responses
Feature detectors respond to specific features of a scene, edges, lines, angles, movements, and from these the brain assembles the perceived image
Illusory Figures
5.6a—just three dots produce a triangle
5.6—the last three on the page highlight the complexity of illusory figures, curved vase, x-mas tree, 3-d pyramid

52. How does this explain Prosopagnosia?

53. The Key to Perception
Perception = combining sensory input with assumptions, expectations

54. How the Brain Perceives Stare at the Necker Cube. What happens?

55. How can we explain our changing perception of the Necker Cube?
Same image continues to meet your retina, your brain constructs varying perceptions every couple of seconds.

56. Illusory Contours Stare at the center of the image

57. Parallel Processing
simultaneous processing of several aspects of visual stimulus (color, depth, movement, form- different parts of cortex integrate all info at once to form perception)

58. Parallel Processing Facial recognition = 30% of cortex
Neural networks: synchronized integration
¼ of second- neurons, parts of brain collaborate at once(40 impulses per second) = conscious recognition!

59. Parallel Processing

60. Isaac Newton, 1704 Color Vision
“Light rays are not colored. Color, like all aspects of vision, resides not in the object but in the theater of our brains.”
Isaac Newton, 1704

61. Visual Information Processing
Trichromatic (three color) Theory
Young and Helmholtz
three different retinal color receptors
red
green
Blue
Combination of these cones = other colors

62. Color-Deficient Vision
Dichromatic
Monochromatic
Dichromatic
5.7 is an initial test for color blindness, students with scores above 16 have an 81 percent chance of failing a standard screening for color vision
8 percent of males, .05 percent of females show color weaknesses
Color defects are genetically transmitted, recent research has conclusively mapped this transmission
Monochromats—have no or only one type of functioning cone type and respond to light like a black and white film—colors are records only as gradations of intensity, likely to find daylight uncomfortable if no functioning cones, those with one cone okay but still can’t discriminate colors—very small number of people have this
Dichromats—one malfunctioning cone system, depending on type, various colors will not be perceived, inability to perceive blue is the rarest, in 1950 England, found 17 people

63. Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable color vision (in retina& thalamus, some neurons turned on/off by certain colors)
“ON” “OFF”
red green
green red
blue yellow
yellow blue
black white
white black
5.9—shows that colors can be subjective, no wavelengths of light
Look in the center of this and many people will see wavy patterns of pastel , because the eye is constantly moving and these movements displace the image of the diagonal lines over the retinal receptors and create a pattern of receptor activity that typically occurs from viewing colored stimuli

64. Visual Information Processing
Color Constancy
Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object (perception of color comes from object and those things around it)