1. Sensation &Perception

2. Sensation
the immediate response in the brain caused by the stimulation of a sensory receptor
Schacter’s definition: sensation = simple awareness due to the stimulation of a sense organ
Perception
the process of organizing sensory information into meaningful patterns

3. Historical Background
Psychophisicists
sought answers to sensory questions
what is the weakest light that can be seen?
what are the limits of the sense organs?
how much change must occur in a stimulus before a sense organ will respond?
attempted to quantitate relationship between actual physical properties of a stimulus and perceived properties of a stimulus

4. Important Figures: Johannes Muller Ernst Heinrich Weber
Gustav Theodore Fechner
Johannes Muller
(1801 – 1858)
Ernst HeinrichWeber
(1795 – 1878)
Gustav Fechner
( )

5. Johannes Muller
systematically remove organs and tested their response to various chemicals and stimuli
Noted that all nerves carry the same basic message; electrical activity
Derived the Law of Specific Nerve Energies
All nerve fibers carry the same type of message
Sensory information is specified by the particular nerve fibers that are active

6. Natural Law of Psychology
Ernst Weber
JND
smallest magnitude of change in a stimulus that can be detected by a human
Natural Law of Psychology
"the amount of change needed to produce a JND is a constant proportion of the original stimulus"
Weber's Fractions
e.g. loudness fraction is 1/10

7. If a radio is playing at volume "5", how loud must it get before you can tell that the volume has increased?

8. Gustav Fechner "What is the range over which we can detect a JND?
led to determination of absolute threshold
minimum amount of a stimulus that can be detected

9. Subliminal Perception and Perceptual Defense

10. Subliminal Perception
perception of a stimulus that is below the threshold for conscious recognition
became part of "pop" psychology
"utilized" by marketing and advertising
made famous with the presentation of the film PICNIC in 1957

11. Is subliminal perception a real phenomenon?
It can be "reproduced" to a limited degree in a laboratory under extremely precise conditions
appears to have absolutely no effect on behavior
particularly useless in attempting to influence choice and motivation

12. Perceptual Defense
resistance to perceiving threatening or disturbing stimuli
became a part of "pop" psychology - also studied by legitimate scientists
extensive investigations have dismissed the existence of perceptual defense

13. Sensation and Perception

14. General Principles of Sensory Coding
Stimulus
Reception
Transduction
Coding

15. Stimulus Reception Sensory Receptor
any external, physical energy detectable by a sensory receptor
Reception
the absorption of physical energy by a sensory receptor
Sensory Receptor
a specialized neuron that detects a particular category of physical energy

16. Transduction
conversion of the physical energy to an electrochemical pattern in the neurons
Coding
the one to one correspondence between the stimulus and the receptor activity

17. The Visual System

18. Stimulus the visible spectrum
the human visual system responds only to electromagnetic radiation of wavelengths between of nm

20. Anatomy of the Visual System
eyes are suspended in two bony pockets called the orbits
held in place and moved by three pairs of muscles

22. The Parts Cornea Sclera translucent membrane that bends light inward
focuses light
Sclera
white opaque component
provides protection and serves as an attachment for the external muscles

23. Iris Crystalline Lens pigmented aperture of the eye
opens and closes to adjust the amount of light entering the eye
Crystalline Lens
located just behind the iris
ciliary muscles adjust the shape of the lens so as to bend light and focus it on the fovea
process called accommodation

24. Retina Vitreous Humor thin layer lining the inside of the eye
receives light rays
Vitreous Humor
viscous jelly-like fluid that fills the inner compartment of the eye
maintains shape and ocular pressure

25. Common Visual Defects Myopia (nearsightedness)
eyeball is too long - image falls short of fovea
requires concave lens to adjust
Hyperopia (farsightedness)
eyeball is too short - image falls beyond fovea
requires convex lens to adjust
Astigmatic Eye or Astigmatism
misshapen cornea - part of image is in focus
requires asymetrical lens to correct focus

27. Presbyopia or Old Vision
farsightedness due to agin
lens becomes less flexible with age
treated with magnification
requires bifocal lens of hyperopia or myopia also present

28. Trace a photon of light
through the eye.

30. The Retina

33. fovea centralis or just fovea
depressed spot in the macula which contains only cones
rods are "shoved" aside
point of highest visual acuity
Why can't you see a dim star if you look directly at it?

35. Optic Disk Locate your blind spot "blind spot"
ganglion cell axons exit the sclera to form the optic nerve
no rods or cones (blind)
Locate your blind spot

36. The Photoreceptors
Two general types
Rods
Cones

38. Rods Cones named for long slender shape absent in fovea
numbers increase toward the periphery of the retina
respond well to dim light
bleached by bright light
poor detail
Cones
named for pointed shape
high density in the fovea
mixed in periphery with rods
respond poorly in dim light
respond best in bright light
detail vision is good

39. Transduction photopigments consist of two parts opsin (protein)
retinal (a lipid)

40. several different forms of the opsin protein e.g. Rhodopsin
pigment found in rods
normally exists in the all-cis state

41. when exposed to light the photogiment splits into its two component opsin and retinal
results in a change in the membrane which allows a signal to be sent to the brain

42. The Visual Information Pathway
retinal ganglion cell axons form the optic nerve
synapse in the Lateral Geniculate Nucleus (LGN) of the thalamus
neurons from the thalamus send axons to primary visual cortex via the optic radiations
some fibers synapse in the superior colliculus

45. Where does information go after reaching occipital cortex?

46. Coding How do we see color? Three Theories
The Trichromatic (Young Helmholtz) Theory
The Opponent Process Theory
The Retinex Theory

47. The Trichromatic Theory
Color is coded or perceived as the result of variations in the "firing" rate of three types of cones
short wavelength
medium wavelength
long wavelength

49. evidence for the trichromatic theory comes from
Electrode recordings in primates
color vision abnormalities in humans
genetic defects in color vision are the result of anomalies in one or more of the three types of cones

50. Protanopia and Deuteranopia
confuse red and green
see the world in shades of yellow and blue
red and green both look greenish to yellowish

51. Normal
Protanope
Deuteranope

52. Tritanopia third color defect extremely rare
equally represented in male and female populations
cannot see short wavelengths
lack blue receptor completely
Tritanope Normal Deuteranope

54. The Opponent-Process Thoery
Color is perceived in terms of paired opposites
red vs green
blue vs yellow
goes beyond trichromatic theory - can explain the negative color afterimage phenomenon

55. negative after image
the image seen after a portion of the retina is exposed to an intense visual stimulus
consists of colors which are complementary to those of the physical stimulus
complementary colors are those that make white or gray when mixed together

56. firing rate of ganglion cells appears to be most important mechanism producing negative afterimage
after being excited or inhibited for a long time, ganglion cells undergo a rebound effect
fire faster or slower than normal

57. Retinex Theory Retina and Cortex = Retinex
developed to explain the phenomenon of color constancy
despite the fact that the wavelength of stimulus is changing, we perceive the colors as constant

58. Artificial light gray filter outdoors daylight

59. How do we impose meaning on what we see?
One way is through the process of perceptual constancy
The knowledge that the physical characteristics of objects remain constant even though the image reaching the retina has changed.

60. Size and Shape constancy
perceived size and shape of physical objects remains constant even though retinal image is different or changing
requires experience - learned
e.g. experience of Dr. Colin Turnbull’s and Pygmy tribe

61. Brightness constancy
refers to the fact that the apparent brightness of an object remains constant under changing light conditions
but our experience can "fool" us into seeing lighting differences where there are none

64. clues we use to create meaningful patterns
Perceptual Grouping
clues we use to create meaningful patterns

65. Proximity
Similarity
Continuity

66. Closure
Common region

67. common fate or movement
Contiguity (occurring close in time)
- basis for drawing causal conclusions
can lead to erroneous causal conclusions
e.g. thunder and lightening

68. (both innate and learned cues)
Depth Perception
(both innate and learned cues)
Innate
Accommodation (monocular clue)
the lens of the eye adjusts its shape to focus on objects
receptors in ciliary muscles provide information about the distance of an object
works within about 4 feet of the eyes
Convergence (binocular)
eyes turn inward to focus on near objects
ciliary muscles send info to brain
Retinal Disparity (binocular)
approx. 6 cm distance between eyes (retinas)
slightly different images on retina
fusing images creates 3D vision

69. Learned Pictorial Cues
Linear Perspective
convergent parallel lines
Relative Size
requires knowledge of size constancy
Height in the Picture Frame
drawing an item closer to the horizon line makes it appear more distant
Light and Shadow
in the "real" world thre are visual differences between light and shadow
creating light and shadow in 2D space gives a 3D perception

70. Overlap or Interposition Texture Gradient
a distant object which partially blocks another object is perceived as closer
Texture Gradient
distant textures look smoother than near textures
Aerial Perspective
adding haziness or blurriness to objects make them appear more distant
Motion Parallax
imagine riding down a highway in a car - near objects appear to pass in front of more distant objects

71. The Auditory System

72. Sound Waves
Rhythmic movement of air molecules
A series of
compressions (peaks)
rarefractions (valleys)
Characteristics of sound waves
Pitch (high vs low tone)
Corresponds to frequency or waves per second
Loundness
Corresponds to the amplitude of the wave

73. Transduction Pinna Outer ear
Funnels sound waves through external canal to tympanic membrane
Tympanic Membrane
Sound waves press against it moving it in and out
Auditory Ossciles (middle ear)
Movement of tympanic membrane sets up vibrations in malleus
Malleus taps against incus
Incus attached to stapes
Stapes contacts oval window at the opening to the scala tympani
Oval Window
Begins to move in and out setting up movement of the perilymphatic fluid in the cochlea

74. Cochlea
Snail shaped organ of hearing
Contains three fluid filled chambers
Scala vestibuli
Scala media
Scala tympani
Organ of Corti
Located in the scala media
Consists of
Basilar membrane
Tectorial membrane
Hair cells
Movement of endolymphatic fluid causes displacement of basilar membrane
Hair cells embedded in basilar membrane have stereocilia that stick up through the tectorial membrane
Displacement of basilar membrane results in shearing forces of the stereocilia which causes Na+ channels to open

76. Axons of the hair cells form the auditory division of the 8th
Axons of the hair cells form the auditory division of the 8th. cranial nerve
Information is sent to
Cochlear nuclei in the brain stem
Inferiror colliculus
Thalamus
Primary Auditory Cortex in the temporal lobe

77. Anatomical or Place Coding
Coding Pitch
Anatomical or Place Coding
Different areas of the basilar membrane are stimulated by different sound frequencies
True for medium to high pitch (300 – 20,00 Hz)

78. Temporal or Frequency theory
For sound of < 200 Hz or less there is no corresponding place on the basilar membrane
Sounds < 200 Hz produce a synchronous firing pattern in the basilar membrane
Volley Theory
A modification of temporal or frequency theory
Nerve fibers work as a “squad”
Group may not respond to every wave but to every 3rd. or 4th. Etc. as a group (a volley)