Section 1 - Sensing the World Around Us
MAIN IDEA QUESTIONS
What is sensation, and how do psychologists study it?
What is the relationship between a physical stimulus and the kinds of sensory responses that result from it?
VOCABULARY
sensation - the activation of the sense organs by a source of physical energy
perception - the sorting out, interpretation, analysis, and integration of stimuli by the sense organs and brain
stimulus - energy that produces a response in a sense organ
psychophysics - the study of the relationship between the physical aspects of stimuli and our psychological experience of them
absolute threshold - the smallest intensity of a stimulus that must be present for the stimulus to be detected
difference threshold (just noticeable difference) - the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred
Weber's law - a basic law of psychophysics stating that a just noticeable difference is a constant proportion to the intensity of an initial stimulus (rather than a constant amount).
adaptation - an adjustment in sensory capacity after prolonged exposure to unchanging stimuli
Human sensory capabilities go way beyond the basic five senses (sight, sound, taste, smell, touch). For example, we are sensitive not merely to touch but to a wider set of stimuli - pain, pressure, temperature, vibration, etc. Vision has two subsystems, relating to day and night vision, and the ear is responsive to information that allows us not only to hear but also to keep our balance. Sensation is the activation of the sense organs, while perception is the sorting out of the information the sense organs receive. A stimulus is any passing source of physical energy which triggers a sense organ. Stimuli vary in their type and intensity - the study of which is called psychophysics.
ABSOLUTE THRESHOLDS: DETECTING WHAT'S OUT THERE
When a stimulus becomes strong enough for our sense organs to detect it, this is known as an absolute threshold. Interference with the absolute threshold can occur by the presence of noise (background stimulation that intereferes with the perception of other stimuli). 'Noise' is not simply auditory.
EX: A group of talkative people inside a smoke-filled room. The din of the crowd makes it hard to hear individual voices and the smoke makes it difficult to see or taste the food.
DIFFERENCE THRESHOLD: NOTICING DISTINCTIONS BETWEEN STIMULI
You go to the supermarket and choose the six best apples on display - the biggest, reddest, sweetest apples. You would compare one apple with another systematically until you were left with six apples that had no real difference - they eventually became so similar you couldn't tell the difference. This is known as the difference threshold (the smallest level of added or reduced stimulation). It is the minimum change in stimulation required to detect a difference between two stimuli (just noticeable difference).
Weber's law states that a just noticeable difference is a constant proportion of the intensity of an intitial stimulus, rather than a constant amount. EX: The just noticeable difference for weight is 1:50. It takes a 1 ounce increase in a 50-ounce weight to notice a difference. Likewise, it takes a 10-ounce increase to produce a noticeable difference in a 500-ounce weight. In both cases, the constant remains 1:5. This law explains why a person in a quiet room is more startled by a telephone ring than a person in a noisy room.
SENSORY ADAPTATION: TURNING DOWN OUR RESPONSES
You walk into a movie theater and are overwhelmed with the smell of popcorn. After a while, however, you barely notice the smell. This is sensory adaptation which occurs after a prolonged exposure to a stimuli. This happens as a result of the sensory receptors inability to fire off messages to the brain indefinitely.
Judgments of sensory stimuli are also affected by the context in which judgments are made. EX: Imagine 15 nickels inside a small envelope and 15 nickels inside a large envelope. People often respond that the smaller envelope weighs more because the visual context of the smaller envelope interferes with the sensory perception of weight.
Section 2 - Vision: Shedding Light on the Eye
MAIN IDEA QUESTIONS
What basic processes underlie the sense of vision?
How do we see colors?
VOCABULARY
retina - the part of the eye that converts the electromagnetic energy of light to electrical impulses for transmission to the brain
rods - thin, cylindrical receptor cells in the retina that are highly sensitive to light
cones - cone-shaped, light-sensitive receptor cells in the retina that are responsible for sharp focus and color perception, particularly in bright light
optic nerve - a bundle of ganglion axons that carry visual information to the brain
feature detection - the activation of neurons in the cortex by visual stimuli of specific shapes or patterns
trichromatic theory of color vision - the theory that there are three kinds of cones in the retina, each of which responds primarily to a specific range of wavelengths
opponent-process theory of color vision - the theory that receptor cells for color are linked in pairs, working in opposition to each other
Although human vision is far more complicated than the most sophisticated camera, in some ways basic visual processes are analogous to those used in photography. Like the automatic lighting system on a traditional, nondigital camera, the human eye dilates to let in more light and contacts to block out light. A camera's lens focuses the inverted image on the film in the same way the eye's lens focuses images on the retina.
ILLUMINATING THE STRUCTURE OF THE EYE
Light travels through the eye in the following steps; cornea --> pupil --> lens --> retina.
Reaching The Retina
It is within the retina that the electromagnetic energy of light is converted to electrical impulses for transmission to the brain. The retina consists of a thin layer of nerve cells at the back of the eyeball. Two kinds of light-sensitive receptor cells in the retina are rods and cones. Rods are highly sensitive to light while cones are responsible for sharp focus and color perception. Cones are primarily responsible for the sharply focused perception of color, particularly in brightly lit situations; rods are related to vision in dimly lit situations and play a key role in peripheral vision and night vision. Both rods and cones are involved in the process of dark adaptation (i.e. walking into a dark movie theater and groping your way to a seat, but a few minutes later seeing the seats quite clearly). They are also involved in the reverse process, adjusting to bright light after being in a dimly lit situation. Light adaptation occurs much faster (1 or 2 minutes) while dark adaptation can take as long as 20-30 minutes.
Sending The Message From The Eye To The Brain
Coding of the visual information takes place upon reaching the rods and cones, before being transmitted to the brain. The travel of information occurs in the following process; rods/cones --> bipolar cells --> ganglion cells --> optic nerve --> brain.
Processing The Visual Message
Images are processed in the visual cortex. Many of the neurons in the cortex are extraordinarily specialized, only being activated by visual stimuli of a particular pattern or shape - a process known as feature detection. Some cells are activated only by lines of a particular width, shape, or orientation. Other cells are activated only by moving, as opposed to stationary, stimuli. Different parts of the brain process nerve impulses in several individual systems simultaneously; one system relates to shapes, one to colors, and others to movement, location, depth.
COLOR VISION AND COLOR BLINDNESS: THE 7-MILLION-COLOR SPECTRUM
A person with normal color vision is capable of discerning no less than 7 million different colors. Approximately 7% of men and 0.4% of women are color blind. Some commonalities;
Red fire engine = yellow
Green grass = yellow
Three colors of traffic lights = yellow
In the most common forms, all red and green objects are seen as yellow. In other forms, people are unable to tell the difference between yellow and blue. In extreme cases, people perceive no color at all.
Explaining Color Vision
There are two primary theories to explain color vision.
~The first is the trichromatic theory of color vision, which suggests that there are three kinds of cones in the retina which respond to a specific range of wavelengths. One is most responsive to blue-violet colors, another to green, and the third to yellow-red. If we see a blue sky, the blue-violet cones are primarily triggered. This process works in the retina only. Does not explain later stages of neuronal processing (i.e. yellow, black, green flag).
~The second is the opponent-process theory of color vision. This theory posits that the three receptor cells are linked in pairs; blue-yellow, red-green, black-white. If an image gives off more blue than yellow, for example, the cells distinguishing blue are triggered. The color stimuli can tire, however, leaving the other cells to do the work. (i.e., flag example).
Section 3 - Hearing and the Other Senses
MAIN IDEA QUESTIONS
What role does the ear play in the senses of sound, motion, and balance?
How do smell and taste function?
What are the skin senses, and how do they relate to the experience of pain?
VOCABULARY
sound - the movement of air molecules brought about by a source of vibration
eardrum - the part of the ear that vibrates when sound waves hit it
cochlea - a coiled tube in the ear filled with fluid that vibrates in response to sound
basilar membrane - a vibrating structure that runs through the center of the cochlea, dividing it into an upper chamber and a lower chamber and containing sense receptors for sound
hair cells - tiny cells covering the basilar membrane that, when bent by vibrations entering the cochlea, transmit neural messages to the brain
place theory of hearing - the theory that different areas of the basilar membrane respond to different frequencies
frequency theory of hearing - the theory that the entire basilar membrane acts like a microphone, vibrating as a whole in response to a sound
semicircular canals - three tubelike structures of the inner ear containing fluid that sloshes through them when the head moves, signaling rotational or angular movement to the brain
skin senses - the senses of touch, pressure, temperature, and pain
gate-control theory of pain - the theory that particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain
Q: What role might the senses have in causing the sickness of astronauts?
A: The experience of the astronaut, a major problem for space travelers, is related to the basic sensory process; the sense of motion and balance. The sense allows people to navigate their bodies through the world and keep themselves upright without falling. The sense of motion and balance resides in the ear.
SENSING SOUND
The outer ear acts as the reverse megaphone. The location of the outer ear gives the brain a clue as to the origin of the sound (ears on opposite sides of your head). Sound is funneled to the eardrum, which acts as a miniature drum by vibrating when sound waves hit it. Sound then enters the inner ear, entering the cochlea. Inside the cochlea is the basilar membrane which divides the cochlea into upper and lower chambers. The basilar membrane is covered by tiny hair cells which are bent by vibrations and subsequently send a neural message.
The Physical Aspects Of Sound
Sound can be seen in some instances (i.e. the vibration of an amplifier at a music concert). Frequency is the distance between wavelengths - humans can hear between 20 cycles per second and 20,000 cycles per second. Amplitude is the height of each wavelength and is measured in decibels. Sounds above 120 decibels are painful to the human ear. Age effects the level of decibels which we are able to hear.
-Sorting Out Theories of Sound; 1) Place Theory of Hearing - different areas of the basilar membrane respond to different frequencies. The area nearest to the oval window is most sensitive to high-frequency sounds, while the cochlea's inner ear is most sensitive to low-frequency. Problem with the theory - low-frequency sounds still may trigger neurons all across the membrane.
2) Frequency Theory of Hearing - The entire membrane acts as a microphone. Impulses are sent to the brain based on the number of frequencies.
-Balance: The Ups and Downs of Life. The vestibular system is a collection of structures in the ear which responds to the pull of gravity and allows us to maintain our balance. The semicircular canals of the inner ear consist of three tubes containing fluid that sloshes through them when the head moves - signaling rotational or angular movement to the brain. Inside these tubes are otoliths - tiny motion-sensitive crystals which shift when we move. These crystals contact specialized receptor hair cells which communicate to the brain - the brain, however, is ineexperienced at interpreting messages from weightless otoliths (which is why astronauts suffer space sickness).
SMELL AND TASTE
Smell
The human sense of smell permits us to detect more than 10,000 separate smells. We have a good memory for smells, and long-forgotten events and memories - good and bad - can be brought back with a mere whiff of an odor associated with a memory. Women generally have a better sense of smell than men do. People have the ability to distinguish males from females based on smell alone. Distinguishing happy and sad emotions, as well as a woman's ability to identify her baby, can both happen asa result of our sense of smell alone.
Taste
There are four basic stimulus qualities; sweet, salty, sour, bitter. There are roughly 10,000 taste buds - which wear out and are replaced every ten days or so. The sense of taste differs greatly from one person to another as a result of genetic factors. There are two categories of people involving taste; "supertasters" (who are highly sensitive to taste), and "nontasters" who have half as many taste buds as supertasters and are highly insensitive to taste.
THE SKIN SENSES: TOUCH, PRESSURE, TEMPERATURE, AND PAIN
All of our skin senses play a critical role in our survival, making us aware of potential dangers to our bodies. Some areas of the body, such as fingertips, have more receptor cells and are more sensitive to touch. The most researched skin sense is pain, which is a response to a great variety of stimuli. When a cell is damaged, it releases a chemical known as substance P which transmits to the brain. Women are generally more sensitive to pain than men due to the production of hormones related to menstrual cycles.
Women report that the pain experience of childbirth is moderated due to the joy of the event. In contrast, even minor pain can feel extreme during times of anxiety. Pain is a perceptual response which depends greatly upon our thoughts and emotions. According to the gate-control theory of pain, particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain. When these receptors are activated due to injury or a problem with a part of the body, the "gate" to the brain is opened. However, another set of neural receptors can, when stimulated, close the "gate" to the brain.
HOW OUR SENSES INTERACT
Synesthesia is an unusual condition in which exposure to one sensation (a note of music) evokes an additional one (such as seeing the color blue). The origins of synesthesia are a mystery.
Section 4 - Perceptual Organization: Constructing Our View of the World
MAIN IDEA QUESTIONS
What principles underlie our organization of the visual world and allow us to make sense of our environment?
How are we able to perceive the world in three dimensions when our retinas are capable of sensing only two-dimensional images?
What clues do visual illusions give us about our understanding of general perceptual mechanisms?
VOCABULARY
gestalt laws of organization - a series of principles that describe how we organize bits and pieces of information into meaningful wholes
top-down processing - perception that is guided by higher level knowledge, experience, expectations, and motivations
bottom-up processing - perception that consists of the progression of recognizing and processing information from individual components of a stimuli and moving to the perception of the whole
depth perception - the ability to view the world in three dimensions and to perceive distance
perceptual constancy - the phenomenon in which physical objects are perceived as unvarying and consistent despite changes in their appearance or in the physical environment
visual illusions - physical stimuli that consistently produce errors in perception
THE GESTALT LAWS OF ORGANIZATION
Gestalt is another word for 'pattern.' This idea was developed in the early 1900s and focused on four key principles of visual stimuli; closure, proximity, similarity, and simplicity.
Closure - we usually group elements to form enclosed or complete figures rather than open ones.
Proximity - We perceive elements that are closer together as grouped together.
Similarity - Elements that are similar in in appearance we perceive as grouped together.
Simplicity - When we see a pattern, we perceive it in the most basic, straightforward manner that we can.
~Gestalt psychology no longer plays a prominent role in contemporary psychology.
TOP-DOWN AND BOTTOM-UP PROCESSING
Top-down - perception is guided by higher-level knowledge, experience, expectations, and motivations (you are able to figure out a sentence with missing letters because of prior reading experience and because written English contains redundancies).
Bottom-up - perception which recognizes and processes information from individual components of a stimuli and moving the perception to a whole (i.e. understanding the shapes of letters within words and sentences).
DEPTH PERCEPTION: TRANSLATING 2-D TO 3-D
Depth perception is the abilitiy to view the world in three dimensions (due largely to the fact that we have two eyes). The brain integrates two images into one, but recognizes the difference between the two. We sometimes receive cues which permit us to obtain a sense of depth and distance with just one eye (i.e. focusing on a tree from a moving car - the nearer objects will move backwards at a faster speed, while objects behind the tree will appear to move in the same direction as you are). Also, the quality of an image helps us to determine distance, as well as the knowledge that distant images tend to appear closer (i.e. railroad tracks).
PERCEPTUAL CONSTANCY
Perceptual constancy leads us to view objects as having an unvarying size, shape, color, and brightness, even if the image on our retina varies (i.e. we do not perceive an airplane flying overhead as changing shape). In some cases, perceptual constancy can mislead us - the moon appears to be huge when it is on the horizon and rising. It is actually the same size as when it is high in the sky. This can be explained by surrounding visual stimuli in our view of the horizon moon - stimuli which doesn't appear in our view of the risen moon.
MOTION PERCEPTION: AS THE WORLD TURNS
Several cues provide us with information about the perception of motion. First, there is a stable, unmoving background. If the image is heading towards us, the image expands in size. Sometimes we perceive motion when it doesn't occur (i.e. a stationary train that may appear as if it is moving because an adjacent train is moving). Another example is the movie theater effect where it feels as if you are falling (i.e. plane or roller coaster). This is the result of apparent movement which occurs when different areas of the retina are quickly stimulated, leading us to interpret motion.
PERCEPTUAL ILLUSIONS: THE DECEPTIONS OF PERCEPTION
Visual illusions are physical stimuli that consistently produce errors in perception. Consider the drawings on the whiteboard in class... the two lines which were the same size but appeared to be of different lengths due to the upward and downward angles at the ends. Also consider the "devil's tuning fork" - which is something we cannot imagine in three dimensions. Variations in learning and experience produce cross-cultural differences in perception. There is a basic connection between our prior knowledge, needs, motivations, and expectations about how the world is put together and the way we perceive it. Our world is very much an outcome of fundamental psychological factors.
Subliminal Perception
Subliminal perception refers to the perception about messages about which we have no awareness. E.g. People who are exposed to the image of a Coke can and the word 'thirst' do later rate themselves as thirstier, and they actually do drink more when given the opportunity (but they may not particularly care if they drink Coke).
Extrasensory Perception (ESP)
This is perception that does not involve our known senses. Although half of the general population of the United States believes it exists, most psychologists reject the existence of ESP. The poor quality of research, as well as a lack of any theoretical explanation for how it might take place, the vast majority of psychologists continue to believe that there is no reliable scientific support for ESP.