Helen Keller

Anne Sullivan

What is it like to live without 1 or 2 of your basic senses?

Video Clip – Cochlear Implant

What Is Sensation?

There are 6 - 8 Sensory Systems

The Basic Five were:

None of these are paranormal. (Ex- ESP)

Balance, Kinesthetic (sense of weight, strain, and position of joints & muscles in

space) and Pain. (blocking pain video clip)

Vision, Hearing, Taste, Smell, and Touch

Added to the Basic 5 are:

Sensory Thresholds

Sensation & Perception:

The Basics

Sensation – information which we receive from the the environment

The Basics

Perception – the process through which we interpret sensory stimulation.

Perception Reflects

• Learning

• Expectations

• Attitudes

Psychophysics

The study of the relationship between the perceived magnitude (strength) of a stimulus versus the

physical magnitude of the stimulus. (measurable)

• Threshold - The minimal values of sensory stimulation needed to trigger a reaction

• Absolute Threshold – stimulus value which is detectable 50% of the time.

• Difference Threshold – The smallest change in stimulation you can detect.

VISION

LIGHT

Electromagnetic energy described in Electromagnetic energy described in wavelengthswavelengths

Main colors of the spectrum:Main colors of the spectrum:RROOYYGGBBIIVV

PUPIL Dark center in middle of irisDark center in middle of iris

Pupil determines how much light determines how much light is let into the eye. is let into the eye.

Changes sizes to accommodate to accommodate

amount of light available.amount of light available.

LENS

Transparent structure inside eye structure inside eye

Focuses light rays onto retina light rays onto retina. .

Adjusts to the distance of objects Adjusts to the distance of objects by by

changing its thickness (squint)changing its thickness (squint)

                                            

                    

Eye Cataract

RETINA Neurons (Nerve layer) lining back of eye. .

Retina senses light and Retina senses light and creates impulses sent through optic nerve to the brain. to the brain.

Contains Contains (photoreceptors) that that process visual stimuliprocess visual stimuli

Photoreceptors = = rods, cones

Macula

OTHER

Macula -- Macula -- a small area in the retina a small area in the retina that contains special light-sensitive that contains special light-sensitive cells. The macula allows us to see cells. The macula allows us to see fine details fine details clearly..

VitreousVitreous -- the clear, jelly-like -- the clear, jelly-like substance that fills the middle of the substance that fills the middle of the eye. eye.

BLIND SPOT

Part of retina containing no photoreceptors. Part of retina containing no photoreceptors. This is where Optic Nerve leaves the eyeThis is where Optic Nerve leaves the eye

A Baby’s Brain and Vision

RODS & CONES Rods – respond to varying degrees of light &– respond to varying degrees of light &

dark; night vision; dark; night vision; black & whiteblack & white More More Rods than Cones Cones

@95% - > 120-125 million@95% - > 120-125 million

Cones – – mainly color vision Function in low light, Function in low light,

white, black, gray. white, black, gray. Detects movement.Detects movement. @5% (@ 5 - 10 million@5% (@ 5 - 10 million

RODS & CONES (2)

Cones Cones - thick + taperedCones - thick + tapered Bright light, Movement, Whites, Bright light, Movement, Whites,

BlacksBlacksFovea -- Center of eye w/only -- Center of eye w/only

cones (@100,000) cones (@100,000) See in colors.. Visual Acuity or sharpness of sight.or sharpness of sight.

http://escience.anu.edu.au/lecture/cg/Color/theFovea.en.html

RODS & CONES (3)

3 Types of Cones Respond to Various

wavelengths of color spectrumEyes most sensitive to

Green/Yellow under equal intensity of light.

3 Theories of Color Vision

Trichromatic Theory Red,Green & Blue Cones Correspond to short, medium, &

long waves of light *Explains Color Blindness

Opponent Process Theory Cones Work in Pairs Red - Green & Blue - Yellow

Integrated Theory Trichromatic and Opponent

Theories work together at different work together at different

stagesstages

COLOR BLINDNESS

Partial or total inability to distinguish color Why? absence of, or malfunction

in, the cones 3 types of Cones

Each sensitive to portion of light spectrum--red, blue, and green

Color perception results from the simultaneous stimulation of 3 cone types (trichromat)

COLOR BLINDNESS

“Trichromats” = People who see all colors (Greek term meaning “three colors”)

“Dichromats” = Small number of people see only two colors and the third registers as a shade of gray.

Monochromats = See the world in only black and white. Occurs in about 1 in every 100,000 men.

COLOR BLINDNESS

Colorblind men were recruited during WWI as bombardiers b/c they would not be fooled by camouflage on the ground.

Color blindness - 1 May be a hereditary condition or caused

by disease of optic nerve or retina.

Acquired color vision problems affects only the eye with the disease and may become progressively worse over time.

Patients with a color vision defect caused by disease usually have trouble discriminating blues and yellows.

Patients with a color vision defect caused by disease usually have trouble discriminating blues and yellows.

COLOR BLINDNESS -2

Inherited color blindness is most common, affects both eyes, and does not worsen over time.

Found in about 8% of males and 0.5% of females.

These color problems are linked to the X chromosome and are almost always passed from a mother to her son..

                            

                            

                            

                                                                           

COLOR VISION Color Circle/Wheel = shows how

complementary colors appear opposite one another on a color wheel

COLOR VISION

Afterimage = visual sensation that occurs after the original stimulus has been removed

-Stare at the eye of the red parrot while you count slowly to 20, then look immediately at one spot in the empty bird cage. The faint, ghostly image of the blue green bird will appear in the cage.

-Try the same thing with the green cardinal. A faint magenta bird will appear in the cage.

Animal Vision

What Do Animals See?

Most diurnal (daytime) animals see in color, while most nocturnal (night) animals don’t — but even here there are exceptions.

When considering whether animals see in color, one approach is to look to the structure of the eyes to see if cones are present. Many nocturnal animals that scientists have studied lack cones, relying instead on greater numbers of rods for extended night vision and keener detection of movement. As an exception to the nocturnal rule, owls do have cones, leading scientists to believe these animals see in color. Most species of primates, birds, cats and dogs also see in color to some degree.

• Humans three sets of cones for detecting color in different wavelengths each cone detects a wide spectrum that overlaps to create other hues.

• Animals like cats and dogs have two sets of cones, making them color-blind to specific colors. They do, however, have many more rods than humans, giving them greater night vision and a keener ability to detect motion.

Dogs can’t distinguish between green and orange which will both look grayish .

Green and Orange appear as differing shades of gray to a dog.

Feline (cats) see in color, but they have trouble distinguishing reds. . .. Reds appear

as differing shades of gray to a cat. It is believed both dogs and cats see mainly in

grays, yellows, and blues

OTHER ANIMALS

ADAPTATION

Dark adaptation = rods & cones become Dark adaptation = rods & cones become more sensitive to light more sensitive to light (entering a dark room) (entering a dark room)

Light adaptation = r & c become lessLight adaptation = r & c become less sensitive (leaving dark sensitive (leaving dark room into light) room into light)

VISUAL ACUITY Sharpness of vision Determines the ability to see visual detailsDetermines the ability to see visual details (Eye exam – (Eye exam – SnellenSnellen chart) near/far sighted chart) near/far sighted

20/20 vision is a measurement of visual acuity.

• Explanation - 20/20 means a person can see small detail from 20 feet away -- the same as a person with normal eyesight would see from 20 feet.

FOVEA

• It is possible to have vision superior

to 20/20:

Maximum acuity of the human eye

without visual aids around 20/15 to

20/10.