Sensation & Perception I: Vision
Brian J. Piper, Ph.D.
Goals
• Sensation• Perception• Myth: Perception = Sensation
• Reality: Perception ≠ Sensation
Terminology
• Sensation: the process by which sensory receptors receives stimulus energy from our environment
• Perception: the process of organizing & interpreting sensory information
Psychophysics
• the study of the relationship between the physical characteristics of stimuli & our psychological experiences
• jnd: minimum difference a person can detect between two stimuli
• Weber’s Law: 2 stimuli must differ by a proportion (light: 8%, weight: 2%, tone: 0.3%)
1795-1878
Below jnd (Subliminal)
• A double-blind study had volunteers listen to tapes for 4 weeks (memory or self-esteem).
• Self-reported memory and self-esteem was measured before and after listening.
Label RealityMemory Memory
Memory Self-esteem
Self-esteem Self-esteem
Self-esteem Memory
Greenwald et al. (1991). Psychological Science, 2, 119-122.
Predicted Results
• This study has four groups (Label/Material)– Self-Esteem/Self-Esteem; Memory/Memory; Self-
Esteem/Memory; Memory/Self-Esteem• What impact, if any, will the labels have?• In terms of Memory, please rank them from
highest (best) to lowest.• In terms of Self-Esteem, please rank them
from highest to lowest.
Greenwald et al. (1991). Psychological Science, 2, 119-122.
InterpretationSelf-esteem and memory post-test were expressed as relative to pre-test.
What discussion section would you write?
Greenwald et al. (1991). Psychological Science, 2, 119-122.
InterpretationSelf-esteem and memory post-test were expressed as relative to pre-test.
What discussion section would you write?
Greenwald et al. (1991). Psychological Science, 2, 119-122.
Interpretation
Greenwald et al. (1991). Psychological Science, 2, 119-122.
• People that want to improve, improve.• No benefits of subliminal messages consistent
with their advertised intent.
Energy to Action Potentials
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
Wave Properties
• Amplitude: height, small = dull; large = bright• Wavelength: distance from peak to peak,
determines color:– blue < green < red
Wavelength
Different wavelengths of light resultin different colors.
400 nm 700 nmLong wavelengthsShort wavelengths
Violet Indigo Blue Green Yellow Orange Red
The Eye
Parts of the eye
1. Cornea: Transparent tissue where light enters the eye.
2. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.
3. Lens: Focuses the light rays on the retina.
4. Retina: Contains sensory receptors that process visual information and sends it to the brain.
Retina
Retina: The light-sensitive inner surface of the
eye, containing receptor rods and cones in
addition to layers of other neurons (bipolar, ganglion
cells) that process visual information.
Optic Nerve, Blind Spot & Fovea
http://www.bergen.org
Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. Fovea: Central point in the retina around which the eye’s cones cluster.
Test your Blind Spot
Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from
your eye. At some point the car on the right will disappear due to a blind spot.
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Young-Helmholtz Trichromatic “Theory”
• Physician/Physicist Thomas Young & Hermann von Helmholtz predicted that the eye would have three kinds of color receptors.
1773-1829
1821-1894
“Whoever in the pursuit of science, seeks after immediate practical utility may rest assured that he seeks in vain.”
Color Blindness
Ishihara Test
Genetic disorder in which people are blind to green or red colors. This supports the
Trichromatic specialization of cones.
Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus
connects to the visual cortex.
Feature Detection
Nerve cells in the visual cortex respond to specific features, such as edges, angles,
and movement.
Ros
s K
inna
ird/
Alls
port
/ Get
ty I
mag
es
Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel
processing. The brain divides a visual scene into subdivisions such as color, depth, form,
movement, etc.
Dorsal & Ventral Streams
Edgar Rubin
Figure/Ground
Sandro Del-Prete: “Message d’Amour desDauphins” 1987
Grouping & Reality
Although grouping principles usually help us construct reality, they may occasionally lead us
astray.
Both photos by W
alter Wick. R
eprinted from G
AM
ES
Magazine. .©
1983 PCS G
ames L
imited Partnership
Which one is continuation?
Johann Christian Poggendorff
Parallel Lines?
Ewald Hering
Parallel Lines?
Johann Karl Friedrich Zöllner
Depth Perception
Visual Cliff
Depth perception enables us to judge distances. Gibson and Walk (1960)
suggested that human infants (crawling age) have depth perception. Even newborn
animals show depth perception.
Inne
rvis
ions
Size-Distance RelationshipBoth girls in the room are of similar
height. However, we perceive them to be of different heights as they stand in the
two corners of the room.
Both photos from S. Schwartzenberg/ The Exploratorium
Ames Room
The Ames room is designed to demonstrate the size-distance illusion.
Which one is bigger?
Ponzo Illusion
Which one is bigger?
Ponzo Illusion
Which one is bigger?
Ponzo Illusionhttp://www.youtube.com/watch?v=hdZHfzjJf-g
Which one is bigger?
Ebbinghaus Illusion
Hermann Ebbinghaus1850-1909
Volunteer?
Volunteer?
• Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
Compare Darkness
Edward H. Adelson Checker Shadow Illusion
Compare Darkness
Edward H. Adelson Checker Shadow Illusion
Compare Darkness
Edward H. Adelson Checker Shadow Illusion
How many colors do you see?
Number-Color Synesthesia
V.S. Ramachandran1951-
Number-Color Synesthesia
Static Image I: Akiyoshi Kitaoka
Static Image II: Akiyoshi Kitaoka
Mars Surface: Viking I-1976
Devil?
Not Politically Correct
Eye-tracking
“Fusiform Facial Area”
Prosopagnosia• Inability to recognize faces• Sensation without Perception Video Worth -> Sensation & Perception
Selective Attention• http://
www.youtube.com/watch?v=vJG698U2Mvo• http://www.youtube.com/watch?v=Ahg6qcgoay4
Floating Cube
http://www.youtube.com/user/Rxe08?blend=8&ob=5
Street Art
http://www.youtube.com/watch?v=8r26AwT7PTMWest Vancouver (15 sec):
Summary
•Perception > Sensation
• Retina -> Optic Nerve -> Thalamus -> Visual Cortex -> Beyond• Illusions:
– Figure ground– Faces– “Motion”– Impossible