PPT for Absent Students

Vision

Day 4 Bell Ringer

Identify the sequence of events for a picture to be taken.

Goals for Today

• Explain how the human eye is similar to a camera

• Explain the human blind spot• Describe visual sensation and perception

– Absolute thresholds– Signal Detection Theory– Light description and categorization

Label the Eye

• On the blank EYE diagram in your guided notes: – Read the definitions for the EYE and using the

definitions as context CLUES, LABEL the diagram as best you can.

• Below the diagram– Identify the sequence of events in order for a

vision to be perceived?

How do the eyes work anyway?

• Camera vs Human Eye

Vision

Process of Seeing

• Light enters our eye through the CORNEA• Light passes through the PUPIL• The LENS focuses the light onto the RETINA• Light energy is converted into neural energy–

light TRANSDUCTION

Oh no! I’m blind!!!

• Cover your left eye and look at the star shape with your right eye.

• Move the paper closer to your face.• At some point, you will notice that the circular

dot on the right will disappear.

• Looking at your eye diagram, explain why the DOT disappeared.

Retina

Retina: sensory tissue that lines that back of

the eye. It contains millions of

photoreceptors (rods and cones) that

convert light rays into electrical impulses that are sent to the brain through the

optic NERVE.

Rods

Cones

Retina’s Reaction to Light- Receptors

Rods Help with peripheral vision detect black, white and gray Good at twilight or low light

Cones near center of retina fine detail and color vision Better in daylight or well-lit conditions

PhotoreceptorsRed

ConesGreenCones

Longwave

Mediumwave

Shortwave

When more than one type of cone is

stimulated we perceive other colors such as

yellow or purple.

BlueCones

Do you know?

• What is the afterimage color of blood?

• Why are hospital gowns the color they are?

Visual Information Processing

Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the

visual cortex.

The light we see

• Light is electromagnetic energy that travels in wave (same as sound)

– Cosmic rays wavelengths are a fraction of an inch long, sound waves can be miles long, and visible light waves are in-between.

Light Characteristics

1. Wavelength/frequency (hue/color)

2. Intensity/amplitude (brightness)

Wavelength (Hue)

Hue (color) is the dimension of

color determined by the wavelength

of the light.

Wavelength is the distance from the peak of one wave to the peak of the

next.

The spectrum of electromagnetic energy

Wavelength (Hue)

Different wavelengths of light resultin different colors.

400 nm 700 nm

Long wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

Cop lights

• Why do cops have their lights designed the way they are?

• Is there a better choice of colors or display?

Intensity (Brightness)

Intensity Amount of energy in a

wave determined by

the amplitude. It is related to perceived

brightness.

Intensity (Brightness)

Blue color with varying levels of intensity.As intensity increases or decreases, blue color

looks more “washed out” or “darkened.”

DON’T SAY IT! Write it down!Is there a number? If you see one, what number is it?

Define color-deficient vision

• If you’re color blind you most likely have a problem with what type of photoreceptor?

• Dichromatic vision- 2 cones working and 1 cone does not work properly.– Red-green color deficiency is due to lack of red or

green cones. – Seeing the world in blues, yellows and gray.– Could you drive?... Should you drive?

What is an Absolute Threshold?

Another view of thresholds: Signal Detection Theory

• Can you hear the announcements in the morning?

Assumes there is no absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness.

• This is similar to what?

Signal Detection

• Predicts when we will detect weak signals• Hearing-test tone• People’s ability to catch a faint signal diminishes

after 30 minutes– TSA screening

• When looking into a crowd and trying to identify someone, do you misidentify more people with or without knowing the shirt color?

Signal Detection Theory (SDT)

Predicts how and when we detect the presence of a faint stimulus (signal) amid background noise (other stimulation). SDT assumes that

there is no single absolute threshold and detection depends on:

Person’s experienceExpectationsMotivationLevel of fatigue

Carol Lee/ Tony S

tone Images

SDT Matrix

Decision

Yes No

Signal

Present Hit Miss

AbsentFalseAlarm

Correct Rejection

The observer decides whether she hears the tone or not, based on the signal being present or not.

This translates into four outcomes.

??????

• How do night time road construction teams set you up for better signal detection of workers in the area??

Questions• What is an astigmatism?• What is the biological problem for blind people?

– Multiple reasons mostly stemming from problems with the optic nerve.• What does Lasik eye surgery do?

– What do you think they correct?• Why do our eyes dilate more or less on drugs?

– Certain drugs affect the neurotransmitters in our eyes that tell us to dilate our pupils.

• What do 3D glasses do?– They let you see 2 movies for the price of one!

• What about drunk goggles?– What do you think???