Vision Psychology: Chapter 4, Section 2

Light Light is electromagnetic energy That means light is on the same spectrum as X-rays, UV rays, microwaves and radio waves Light travels in waves The length of the waves determines the color of the light, as well as the radio station or whether it is a microwave cooking your chicken or a UV ray giving you a sunburn

Note how long the wavelengths are. They are inversely proportional to their frequency. Red has a longer wavelength than blue.

A Rainbow is Split White Light (you can memorize the colors by the name Roy G. Biv)

The Eye Light enters the eye and is projected onto a surface in the back of the eye The amount of light that enters is determined by the size of the pupil, an opening, or a hole, within the eye The pupil is the black circle in the center of the eye The size of the pupil adjusts automatically to the amount of light entering the eye Our emotions can also affect the size of the pupil, as we can become wide-eyed with fear, as pupils open widely when we are afraid

The Eye The pupil is a black-looking opening that allows light to enter the eye It appears dark because of the absorbing pigments in the retina The iris is a colored circular muscle which is pigmented to give us our eye’s color This circular muscle controls the size of the pupil so that more or less light, depending on conditions, is allowed to enter the eye. The sclera is the white of the eye

The Eye An Experiment: Turn out the lights to this room Look into a friend’s eyes in this somewhat dark room and observe the pupils Next, we’ll turn the lights on Look into your friend’s eyes What change did you observe in the pupils? Why do you think that happened?

The Eye Once the light has entered the eye, it hits the lens The lens focuses the light by thickening or thinning itself

Muscles in the eye push or pull on the lens to focus the image pupil iris lens

The Eye The focused light is then projected to the back of the eye on the retina The retina is like the projector screen The retina is a sensitive surface composed of neurons These neurons are sensitive to light and are called photoreceptors When the light hits the photoreceptors, the optic nerve carries that information to the occipital lobe in the back of the brain

Note how the image is upside down when it gets to the back of the eye

The Eye We have a blind spot in our eye It is located where at the optic nerve connection in the back of the eye There are no photoreceptors at that connection point, hence, the blind spot

Cover your left eye, look at the hat. Did you make the rabbit disappear? (Some of you will say yes, and some no)

The Eye We have two different types of photoreceptors in our retinas: rods and cones Rods are only sensitive to the how bright the light is. They only see in black and white Cones provide color vision, but need more light than rods to properly work That is why if you are outside at night, maybe only under moonlight, the world will be in black and white.

How your rods see the worldHow your cones see the world

The Eye Dark and Light Adaptation refers to how fast our eyes adjust to either dark or light It can take minutes for your eyes to fully adapt to the dark Adapting to bright light can feel painful for a brief moment, but the adapting happens much faster than it did for dark

The Eye The sharpness of vision is called visual acuity When you think of needing glasses to see clearly, you are thinking of visual acuity Often a doctor will ask you to read a Snellen Eye Chart If you can read the 8 th row from 20 feet away, you have normal vision (20/20) If you can’t read the top letter, you could be legally blind with 20/200 vision

The Eye When people get older, their lens is less flexible, and can no longer thicken so easily to see close objects That is why older people are often far sighted. I am both near sighted, which I’ve been since I was 17 years old, and far sighted, which I have been for the past few years So bifocals or multi-focals are best for me

Note that the lens to correct nearsightedness is concave, while the lens to correct farsightedness is convex

Farsightedness Some have called farsightedness “short arm syndrome,” when it seems that your arms are now too short to place your reading material far enough away so your eyes can see it

Color Vision The cones in our retina allow us to see a small percentage of the electromagnetic spectrum We see the varying wavelengths as different colors

Color Vision Experiment: A subject (helpful volunteer) sits and stares at an object The experimenter (me) places another object in the subject’s peripheral vision As soon as the object is in the subject’s peripheral vision, the subject will try to identify what the object is and what its color is What can you conclude?

Color Blindness Most people can see all the colors of the visible spectrum If there are colors that a person cannot see, then he or she may be color blind With color blindness, there is some malfunction of the cones Total color blindness can happen, but is pretty rare Partial color blindness is comparatively common 8% of males and 0.5% of females have some color blindness (so it’s 16 times more common in males than in females)

58 18 E 17 Partial color blindness is when someone is blind to some colors but not others Red-Green color blindness is the most common Take this test and tell me what you see

Assessment Complete #1-4 on page 85