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