Sensation and Perception

Sensation and Perception Chapter 4

Sensory Processes • We are so used to processing information from the senses that we take this ability for granted. • Our brains has set up all kinds of methods for handling complex information. • For example, when people read…we must rely on shapes to be able to read as fast as we do. The eye skips and jumps from one part of the sentence to another. • The normal process for reading is to focus on the beginning letters of a sentence and determine what basic shapes the rest of the words in the sentence have.

Sensory Processes • Before we can retrieve information from our senses, though, we must first pay attention to it. The incoming information must be strong enough to make us notice it. • A very dim light will not be seen in the daylight and very soft noises will not be heard, especially around other sounds. The level of sensory stimulation necessary for that stimulation to register is called the absolute threshold. • Once we are aware of some kind of sensory information – a sound, we do not necessarily continue to pay attention to it. If we ignore it or put it in the background, this is called adaptation. This is the gradual loss of attention to unneeded or unwanted sensory information.

Sensory Processes • If we didn’t have adaptation, we would pay attention to everything that went on in our environment, which would be extremely confusing. • Sensation – the process of receiving information from the environment. • Perception – the process of organizing sensory information to make it meaningful. These two processes are intermixed.

Sensation • Vision – dominates the human senses. We always tend to believe what we see first. If you eat a green-colored steak (food coloring) it will taste different to you because of what you see. • Even though your sense of smell says it is okay, that will make no difference because the taste will be funny.

Light • Light is based on the same principle as snapping a whip. With a whip snap, the energy starts at the wrist and is sent in the shape of a wave down to the end of the whip. These waves can very in their length. • Light starts out as white light. Color is seen only after the waves of light hit objects and bounce back at us in different speeds or frequencies. There really is no such thing as “color”. We give certain light waves different names. “Color” is seen because different receptors for different wave lengths are visible. • Frequencies like (ultraviolet light waves) are too rapid for our eyes to be able to see the light, but other creatures can see them. Others are too slow to be seen (infrared light waves) are used by snakes at night to see.

Vision • The key to color, then, is white light hitting various objects in the environment and bouncing off different wavelengths, which in turn hit receptors in our eyes. • The speed of movement in light waves varies depending on the texture and solidity of what they hit.

The Cornea and Iris • The cornea is a clear outer covering, behind which is fluid. The eye is shiny because of this fluid. • The iris is a colored circular muscle that opens and closes into larger or smaller circles in order to control the amount of light getting into the eye.

The Lens • The lens is very much like a camera lens. It helps you focus the objects you see onto the back of the eye, where there are receptors. If the lens is not shaped correctly, the image coming in will either overshoot or fall short of the receptors at the back of the eye, and this causes images to blur. • Eyeglasses are designed to change the angle at which the light hits the lens, causing the lens automatically to adjust to whatever object we want to see.

The Pupil • The pupil is just an opening that changes size as the iris muscles move to cover and uncover the lens. Lights entering inside the pupil will change color. This is what makes “red eye” in films. • Psychological factors can control the iris muscles and thus the size of the pupil. Pupils get smaller when people are disgusted. They get larger with someone or something they really like. • Pupils can also open up large when the person is afraid. This makes it possible for the person to explore a threat in their environment.

Retina • When the light coming inside the eye hits the back of the eyeball, it hits the retina. Millions upon millions of receptors are embedded within the retina. • There is a place where the nerve cells leave the eye in what’s called the optic nerve. Retinal receptors are to the right and left of this point, but there are none where the nerve bundle leaves. This is called the blind spot. We can’t see anything when light waves hit that point.

Rods and Cones • The retina is made up of two different kinds of receptors. The first type of receptor is the rod and is shaped like one. • The second type of receptor is the cone because it has that shape too. • Rods are very sensitive to violet-purple range of wavelengths, but we only see black and white with them. • There are about 100 million rods in the retina, and they are used for night vision because they respond well to low levels of light. • Rods are heavily packed into the sides of the retina. If you are trying to see something in the dark, look out the sides of your eyes as the rods will help you pick up the shape.

Color Vision • All the colors we see are: red, blue, green, or a mixture of these three. • Throughout the center part of the retina are millions of cones connected together. Some receive red, some green, and some blue wavelengths. • Light will bounce back from each part of the object and the brain will mix these wavelengths, making objects appear a significant color.

Color Defects • Color blindness – is the inability to see the difference between certain colors. • The most common form of this problem is found in those who can see color only in the yellow-blue range and cannot see red or green color. • About 8% of males have this inherited defect. Only 0.5% of females do. For these people, the red and green cone system does not work as others do. • The receptors do respond to light wave energy, but they don’t see it as colored. • Truly color blind people are very rare. They respond to light waves only with rods. Bright light can be very painful to them. Animals see in color. It is a myth that they see in black and white. A bull does not respond to red, but responds to movement.

Afterimages • The cone network of the eyes tries to stay in balance. If you stare at a colored object for awhile, the chemicals in the cones for the colors you are seeing will be partially used up as changes in the chemicals creating electrical impulses. No message has been sent to the brain for them because you haven’t seen the colors. The cone system is not in balance. If you stare at a piece of white paper, you will see other colors appear. These are known as afterimages. This is from unused cones firing.

Hearing • Hearing, like vision, depends on energy. In hearing, or audition the energy form is sound waves. Sound waves have a much slower range of speed than light waves but move in toughly the same fashion. • Animals use sound more than humans do. The dolphin will use clicks. The echoes that come back tell it the size and shape of what the sound waves have hit. • Bats find extremely small objects by bouncing sound waves off of them.

The Characteristic of Sound • Sounds vary in pitch – how high or low a sound is. • Timbre – refers to the complexity of a tone. The sounds made by different instruments. • Intensity – how loud or soft they are. • Decibels – is the measurement of intensity. • When sounds reach the decibel level of 130, they can become painful. Continuous loud noises can kill receptor cells in the ear.

The Structure of the Ear • The cupped design of the outer ear catches the sound waves and funnels them in toward the eardrum. • The eardrum is a piece of skin stretched tightly (like a drum) over the entrance to the rest of the ear. When the sound waves hit the drum, it vibrates. This bone is attached to another bone that acts as a lever causing it, in turn, to vibrate. • A third bone is attached to a snail-shaped unit called the cochlea. The cochlea is filled with fluid and lined with special cells.

The Structure of the Ear • The key to hearing is the existence of hair cells. The cells have hair-like extensions called cilia that are lined up in the cochlea and “tuned” to receive different frequencies, just as strings are tuned on a musical instrument. • The cilia will respond to movement of only a trillionth of an inch, about the space between two atoms. As this movement occurs, it causes a flow of electrical particles in the nerve cell connected to each hair. • How strong the sound is when it arrives at one ear is contrasted by the brain with the strength and arrival time at the other ear. The difference between them helps us locate where sound is coming from.

Cutaneous Senses (Touch) • Our skin contains three types of cutaneous or touch receptors. Each sends a message to the brain where it is recorded. • One records pressure. • The second repsonds only to changes in temperature. • A third kind remains active continuously to record an injury or poison. • The last receptors cause the painful feelings we all dread, because they can fire for hours and hours after a burn or major cut.

Smell • The sense of smell or olfaction depends on the ability to detect chemicals. The human comes in a poor second to the animals. A shark can sense odor molecules in the water to determine if you are worth eating. • Smell is the most animal-like of the human senses. Odors are very hard to define using words, but when an odor is associated with an emotional event, we never will forget it. If we smell that odor again, it will recreate a very strong emotional memory.

Mechanisms of Smell • Inside the nasal cavity, embedded in a layer of mucus, are microscopic hairs, or cilia. They are similar to cilia in the ear. These cilia in the nasal cavity collect molecules of odor. When they attach themselves to the hair, an electrical signal is sent to the olfactory bulbs, which generate a “code” that is sent to the brain for interpretation. • Smell is the most important sense when we eat.

Smell • Animals use smell to communicate sexual interest. An animal’s body sends out chemicals called pheromones. • Human pheromones are difficult to study. Human sexual interest is also a mixture of clothing, perfumes, fads about body shape, and so forth.

Taste • Taste receptors operate by chemical communication. The major receivers are the little red spots on the tongue. These are called “taste buds” because they resemble flowers. • The mucus and saliva in the mouth cleanse the buds, but it takes awhile to do so. • There are 4 types of receptors: salt, sweet, sour, and bitter.

Salt Needs • Salt is necessary for survival. It operates nerve cells, helps keep body chemistry in balance, and is used for muscle contraction. A very low salt diet can make you sick and dizzy. Excess salt is removed from the body quickly through fluid intake. There is a biological need in the body for salt. • The newborn does not like salt, but from a few months onward…they want salt. Children tend to dislike spicy, sour, and bitter food. • The desire for salt reappears older in life. If their stomachs don’t rebel, they are able to eat it. Taste receptors are not as sharp as they once were. Pregnant women seek extra salt for their fetus.

Sugar Needs • Most animals need sugar. Human newborns can tell when something has sugar in it, and they will actively seek it. Sugar is vital for energy to run the body. Too little sugar makes the body tremble, and feel faint, and causes mental confusion.

Sourness and Bitterness Detectors • We have more than one type of bitterness detector on the tongue. These detectors are critical. Almost all poisons are bitter. We need to know if something is has poison instantly. • Sourness detection is a protective part of the body. Food that has gone bad has a sour taste to it. We can tend to smell this before we put food in our mouths.

Perception • Usually, the world seems to be organized and stable. Through a combination of inborn abilities and experience, we gradually are able to handle billions of bits of information correctly. • We make the world make sense. This is perception. Perception is the process of assembling sensory information so that we can understand what the incoming energy means. Perception is a matter of interpretation and expectation.

Perceptual Constancies • The word constancy means holding steady. This is what we must do to make order and control and sense out of our environment. • Size constancy – the ability to retain in memory the size of an object no matter where it is located. This skill is so important that it appears in an infant only a couple of weeks old.

Perceptual Constancies • Color constancy – we have three different color receptors (red, blue, and green). That blend varying energy waves together to give an object color. • Color constancy – the ability to perceive an object as the same color regardless of the environment.

Brightness Constancy • Brightness constancy - the ability to keep an object’s brightness constant as the object is moved to various environments. • Shape Constancy – once we know an object’s shape, we perceive it as always taking that form. We will attempt to keep the object the same shape even if the view of the object changes the shape within the retina. • Space Constancy – the ability to keep objects in the environment steady by perceiving either ourselves or outside objects as moving. There are two types of objects: self-motion and object motion. If we allow two items to move at the same time, we have dizziness.

Depth Perception • This is the ability to see objects “out there” in space. It is built into a baby from a very early age. • Visual cliff – this experiment uses a large table when retaining walls of wood on three sides. The fourth side is left open. Babies from 6-14 months old were placed on a table enticed by their mothers to leave the table and “fall” over the fake cliff. Most babies would not go beyond the plexiglass. This showed that human beings have depth perception from the very beginning.

Retinal Disparity • There are many cues for depth perception. Some of them require both eyes to work. They are called “binocular” cues to distance is retinal disparity. • We also use the actual angles of our eyeballs to gauge the distance of an object. The eyes turn inward toward the nose to focus on a near object and are straighter for far ones. The angle at which the eyeballs converge to focus on something is yet another clue to its distance from us.

Texture Gradient • Not all cues are binocular. Some of them only use one eye. The amount of detail we can distinguish is referred to as the visual texture of objects, called the texture gradient. • “Texture” refers to how smooth or rough something appears to be, how clear the details are. • “Gradient” means the different levels of texture we can see at different distances. • Another monocular clue to distance is the relative size of similar objects we are looking at. The smaller the object, the farther away it appears to be. • Animals of many kinds develop early depth perception including: kittens, chicks, lambs, baby goats, and rats.

Perceptual Organization • When given incomplete perceptual information, we tend to organize it so that it makes sense. We interpret information the way we think it should be, not the way they actually are. • We organized this information and constructed something more complete from it. In the language of perception, this is called common region or gestalt, meaning an organized whole, shape, or form. • Similarity – a perceptual cue that involves grouping like things together. • Proximity – a perceptual cue that involves grouping together things that are near one another. • Closure – the process of filling in the missing details of what is viewed.

Illusions • Illusions occur when we perceive something inaccurately. They are misperceptions (in a way). They show how we construct the world. • Many people think of illusions as “mistakes” that we make. That is not really the case. Over the years, we learn to change what we perceive so that the world makes more sense. • Muller-Lyer illusion – is an illusion in which one line in a picture has two equal-length lines which seem longer. • Reversible figure – illusion in which the same object is seen as two alternating figures – first one, then the other.

Sensation and Perception