PSYCHMs. Shirley

Unit 2 SENSATION & PERCEPTION

Vision

We only use light energy to see.

What makes up a light wave?

WavelengthThe distance from the peak of one light wave to the peak of the next.

The wavelength distance determines the hue (color) of the light we perceive.

Intensity (Brightness)

The amount of energy in a light wave is...

determined by the height of the wave

The higher the wave...

the more intense the LIGHT is.

YouTube: See for yourself... Dark Side of the Rainbow (Begins on the MGM Lion’s 3rd Roar

APOPHENIA: The experience of seeing meaningful patterns or connections in random or meaningless data.Some have argued that the DSotR phenomenon is just the mind "playing tricks on itself" -an example of apophenia. With apophenia, the observer focuses on events in the movie that are accompanied by a change in tempo, or sudden shift in the intensity of the music, while ignoring events in the movie and changes in tempo on the album that do not correspond to anything.Pink Floyd drummer Nick Mason, in a 1997 MTV interview, said "It's absolute nonsense. It has nothing to do with The Wizard of Oz. It was all based on The Sound of Music."

SaturationIf the human eye was not responsive to differences in the purity of light waves we would not be able to perceive differences in saturation.

TransductionConversion of one form of energy to another.

How is this important when studying sensation?

Stimulus energies to neural impulses. In the system transduction occurs when environmental energy is transformed into electrical or neural energy.

Receptor cells produce an electrical change in response to a physical stimulus.

For example:

★ Light energy to vision.

★ Chemical energy to smell and taste.

★ Sound waves to sound.

Structure of the Eye

Pupil - adjustable opening in the center of the eye Iris - a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil openingLens - transparent structure behind pupil that changes shape to focus images on the retina

Structure of the Eye

Cornea - Transparent outer covering of the eye.Retina - Contains visual sensory receptors.Fovea - Point of central focus. Contains most of the eye’s cones.Optic Nerve - Pathway to the brain’s visual cortex.Blind Spot - Where optic nerve leaves eye - no receptors here.

Nearsighted FARsightedAKA: Hyperopia. Faraway objects are seen more clearly than near objects b/c eye is shortened & image would focus after it hit the retina.

AKA: Myopia. Nearby objects are seen more clearly than distant objects b/c eye is elongated & image focus before it hits the retina.

Need for Bifocals. This issue can become more pronounced after the age of 40, when the lenses of the eyes become progressively less flexible and have trouble accommodating to focus on objects at different distances.

Blind Spot occurs is the location in the retina where the visual cortex exits to the brain, there are no receptors thereYou don't notice this blind spot in

every-day life, because your two eyes work together to cover it up. Our brain, typically, fills in that missing piece based on what it estimates to be there

Blindsight—we can see things we don’t perceive

Blind Spot & Blindsight

To find the blindspot, draw a filled-in, 1/4"-sized square and a circle three or four inches apart on a piece of white paper.

Blind spot experiment

Hold the paper at arm's length and close your left eye. Focus on the square with your right eye, and slowly move the paper toward you. When the circle reaches your blind spot, it will disappear! Try again to find the blind spot for your other eye. Close your right eye and focus on the circle with your left eye. Move the paper until the square disappears.

What happened when the circle disappeared? Did you see nothing where the circle had been? No, when the circle disappeared, you saw a plain white background that matched the rest of the sheet of paper.

This is because your brain "filled in" for the blind spot - your eye didn't send any information about that part of the paper, so the brain just made the "hole" match the rest. Try the experiment again on a piece of colored paper. When the circle disappears, the brain will fill in whatever color matches the rest of the paper.

FoveaCentral point in the retina,

around which the eye’s cones cluster... because of this there is little color vision in the farthest periphery of our vision. “Rod Free Area”

The RetinaThe light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of other neurons (bipolar, ganglion cells) that process visual information.

Rods★ peripheral retina ★ detect black, white &

gray★ twilight or low light

Cones★ near center of retina ★ fine detail & color vision★ daylight or well-lit

conditions

Photoreceptor Cells

The retina contains two types of photoreceptors:

rods and conesThe rods are more

numerous, some 120 million, and are more sensitive than the cones.

However, they are not sensitive to color.

The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the "fovea centralis”, a 0.3 mm diameter rod-free area with very thin, densely packed cones.

Rods★ peripheral retina ★ detect black, white &

gray★ twilight or low light

Cones★ near center of retina ★ fine detail & color

vision★ daylight or well-lit

conditions

Photoreceptor Cells CONES RODS

NUMBER 6 MILLION 120 MIL.

LOCATION CENTER(FOVEA)

PERIPHERY

COLOR SENSITIVE?

YES NO

SENSITIVITY IN DIM LIGHT?

LOW HIGH

ABILITY TO DETECT DETAIL?

HIGH LOW

NUMBER OF BIPOLAR CELLS?

EACH HAS OWN

SHARES ONE WITH OTHER RODS

BIPOLAR CELLS:These are cells that rods and cones send messages through

Bipolar ★ Receive messages from

photoreceptor cells & transmit them to the...

Ganglion ★ which form the optic nerve (axons)

& sends messages on into the brain to the visual cortex (occipital lobe).

Bipolar & ganglion cells

Remember...

Cones each have their own bipolar cells.

Multiple rods share one bipolar cell.

Feature Detection

Cells in the visual cortex of the brain that respond selectively to specific features of complex stimuli. Edges, Angle, Length, & Movement

How is it possible that Frank Caliendo can possibly imitate so many different people so convincingly?

Parallel ProcessingThe processing of several aspects of a problem simultaneously.

COLOR MOTION FORM DEPTH

How do we see in color?

What colorS ARE the Eagles wearing?

The Eagle Uniform is anything but red.The uniform rejects the long wavelengths of light that to us are red.So red is reflected off and we see it.Also, light has no real color.It is our mind that perceives the color.

Perception of Color

2 color theories

Young-Helmholtz Trichromatic (3 color) Theory

According to the Young-Helmholtz theory of color vision, there are 3 receptors in the retina that are responsible for the perception of color. 1 receptor is sensitive to the color green, another to the color blue, and a third to the color red. These three colors can then be combined to form any visible color in the spectrum.

3 different types of receptor cells in our eyes. Together they can pick any combination of our 7 million color variations.

Most colorblind people simply lack cone receptor cells for one or more of these primary colors.

Principle of Additive Color MixingAt “Showtime” you may notice that whenever the red & green spotlights overlapped, they seemed to change to a yellow spotlight.

Opponent-Process TheoryWe cannot see certain colors together in combination. These are antagonist/opponent colors.

white-black green-red yellow-blue

★ Trichromatic theory makes clear some of the processes involved in how we see color, it does not explain all aspects of color vision.

★ Opponent-process theory of color vision was developed by Ewald Hering who noted that there are some color combinations that we never see, such as reddish-green or yellowish-blue.

★ Opponent-process theory suggests that color perception is controlled by the activity of two opponent systems; a blue-yellow mechanism and a red-green mechanism.

Opponent-Process TheoryOpposing retinal processes

enable color vision

“ON”“OFF”

red green

green red blue

yellow yellow

blue black

whitewhite

black

Which theory is accepted?Trichromatic or opponent process?

Most researchers agree with a combination of trichromatic and opponent-process theory.

Individual cones appear to correspond best to the trichromatic theory, while the opponent processes may occur at other layers of the retina.

The important thing to remember is that both concepts are needed to explain color vision fully.

People who suffer red-green blindness have trouble perceiving the number within the design.

Color defects are genetically transmitted, recent research has conclusively mapped this transmission.

Monochromats — have no or only one type of functioning cone type and respond to light like a black and white film—colors are records only as gradations of intensity, likely to find daylight uncomfortable if no functioning cones, those with one cone okay but still can’t discriminate colors—very small number of people have this.

Dichromats — one malfunctioning cone system, depending on type, various colors will not be perceived, inability to perceive blue is the rarest, in 1950 England, found 17 people.

Color Blind & Vision-Color Issues

Opposite opponent colors are never perceived together.There is no greenish-red or yellowish-blue.

You can create your own demonstration of these opponent systems by observing the effect of afterimages.

Look at the center of the the “X” on the next screen for approximately 30 seconds.

Then immediately look at the next white slide & blink to see the afterimage.

After Image ExperimentAfter Image ExperimentAfter Image Experiment

Stare at the middle of the “X” for 30 seconds.

After Image Experiment

BLINK ABOUT 10 TIMES OR SO - THEN LOOK DIRECTLY INTO THE WHITE SCREEN...DO YOU SEE THE AFTER IMAGE?

"An afterimage can retain the colors of the original stimulus (positive afterimage,) or the colors might be reverse in the afterimage, like a photographic negative (negative afterimage). The conditions favoring the production of afterimages are either brief exposures to intense or very bright stimuli, in otherwise dark conditions (a quick glance at the setting sun), or prolonged exposures to colored stimuli in well-lighted conditions (fixating steadily on a colored object for 60 sec and then averting the eyes to a gray or white background). With brief stimuli the first afterimage is usually positive (same colors as the visual stimulus), and when only a single stimulus is presented, the positive afterimage is difficult to distinguish from the initial image or sensation."(Gustav Levine & Stanley Parkinson, Experimental

Methods in Psychology, 1994)

"After staring at the red and blue shamrock, you saw a green and yellow afterimage. Opponent-process theory proposes that as you stared at the red and blue shamrock, you were using the red and blue portions of the opponent-process cells. After a period of 60 to 90 seconds of continuous staring, you expended these cells' capacity to fire action potentials. In a sense, you temporarily "wore out" the red and blue portions of these cells. Then you looked at a blank sheet of white paper. Under normal conditions, the while light would excite all of the opponent-process cells. Recall that white light contains all colors of light. But, given the exhausted state of your opponent-process cells, only parts of them were capable of firing action potentials. In this example, the green and yellow parts of the cells were ready to fire. The light reflected off of the white paper could excite only the yellow and green parts of the cells, so you saw a green and yellow shamrock."(Ellen Pastorino & Susann Doyle-Portillo, What Is Psychology? Essentials,

2010)

In a negative afterimage, the colors you see are inverted from the original image. For example, if you stare for a long time at a red image, you will see a

green afterimage. The appearance of negative afterimages can be explained by the opponent process theory of color vision.You can see an example of how the opponent-process works by staring

at the red shamrock on the next slide for about 1 minute before shifting your gaze immediately to a white sheet of paper or a blank screen.

Stare at the center dot for 1 minute. Then when you see the next blank slide, you should have an “afterimage” -- and some good luck!

Did it work?

In this fun optical illusion, you can see how your visual system and brain are actually able to briefly create a color image from a negative photo.How to Perform the IllusionStare at the dots located at the center of the woman's face below for about 30 seconds to a

minute. Then turn your eyes immediately to the center x of the white image on the right.Blink quickly several times. What do you see? If you've followed the directions correctly, you

should see an image of a woman in full-color. If you are having trouble seeing the effect, try staring at the negative image a bit longer or adjusting how far you are sitting from your computer monitor.

ExplanationsHow does this fascinating visual illusion work?What you are experiencing is known as a negative

afterimage. This happens when the photoreceptors, primarily the cone cells, in your eyes become overstimulated and fatigued causing them to lose sensitivity. In normal everyday life, you don't notice this because tiny movements of your eyes keep the cone cells located at the back of your eyes from becoming overstimulated.

If, however, you look at a large image, the tiny movements in your eyes aren't enough to reduce overstimulation. As a result, you experience what is known as a negative afterimage. As you shift your eyes to the white side of the image, the overstimulated cells continue to send out only a weak signal, so the affected colors remain muted. However, the surrounding photoreceptors are still fresh and so they send out strong signals that are the same as if we were looking at the opposite colors. The brain then interprets these signals as the opposite colors, essentially creating a full-color image from a negative photo.

According to the opponent process theory of color vision, our perception of color is controlled by two opposing systems: a magenta-green system and a blue-yellow system.

For example, the color red serves as an antagonistic to the color green so that when you stare too long at a magenta image you will then see a green afterimage. The magenta color fatigues the magenta photoreceptors so that they produce a weaker signal. Since magenta's opposing color is green, we then interpret the afterimage as green.