AP Psychology – Topic V: Sensation and Perception
Myers: Chapter 5 and 6
Barron’s: Chapter 3
Chapter 5 – Sensation
Sensing the World: Some Basic Principles
A. Terms
1. Sensation – the process which our sensory receptors and nervous system receive and represent stimulus energies from our environment.
2. Perception – the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.
3. Bottom-Up Processing – analysis that begins with the sense receptors and works up to the brain’s integration of sensory information.
4. Top-Down Processing – information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectation.
B. Thresholds
1. Psychophysics – the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.
2. Absolute Thresholds – the minimum stimulation needed to detect a particular stimulus 50 percent of the time.
3. Signal Detection Theory – predicts how and when we detect the presence of a faint stimulus ("signal") amid background stimulation ("noise"). Assumes that there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and level of fatigue.
i. With a more heightened responsiveness comes more false alarms.
ii. A person’s reactions vary as circumstances change.
4. Subliminal Stimulation – below one’s absolute threshold for conscious awareness.
i. We can process information without being aware of it.
ii. The near-consensus opinion of research psychologists is that subliminal persuasion has no real effect.
iii. Subliminal tapes have no effect beyond that of a placebo – an effect of one’s belief in them.
5. Different Threshold – the minimum difference that a person can detect between two stimuli. We experience the difference threshold as a just noticeable difference (Also called just noticeable difference or jnd).
i. Weber’s Law – the principle that, to perceive their difference, two stimuli must differ by a constant minimum percentage (rather than a constant amount).
a. For an average person to perceive their differences, two lights must differ in intensity by 8 percent.
b. Two objects must differ in weight by 2 percent.
c. Two tones must differ in frequency by only 0.3 percent.
C. Sensory Adaptation – diminished sensitivity as a consequence of constant stimulation.
1. Our sensory receptors are alert to novelty; bore them with repetition and they free our attention for more important things.
2. We perceive the world not exactly as it is, but as it is useful for us to perceive it.
Vision
D. Transduction – conversion of one form of energy into another. In sensation, the transforming of stimulus energies into neural impulses.
1. Your eyes receive light energy and then transduce (transorm) the energy into neural messages that the brain processes into what we consciously see.
E. The Stimulus Input: Light Energy.
1. Scientifically speaking, what strikes our eyes is not color but pulses of electromagnetic energy that our visual system experiences as color.
2. Two physical characteristics of light and sound help determine our sensory experience of them.
i. Wavelength – the distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission.
a. Hue – the dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth.
ii. Intensity – the amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the waves amplitude.
F. The Eye. (Figure 5.5, pg. 179)
1. Terms
i. Pupil – the adjustable opening in the center of the eye through which light enters.
ii. Iris – a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.
iii. Accommodation – the process by which the eye’s lens changes shape to focus images on the retina.
iv. Retina - the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the process of visual information.
v. Acuity – the sharpness of vision.
2. Focus of the Eye (Figure 5.6, pg. 180)
i. Note that images are projected upside down onto the retina. Light inverts as it passes through the lens.
3. The Retina’s Receptor Cells (Figure 5.7, pg. 180
i. Rods – retinal receptors that detec black, white, and gray; necessary for peripheral and twilight vision, when cones don’t respond.
ii. Cones – receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensations.
iii. Optic Nerve – the nerve that carries neural impulses from the eye to the brain (the visual cortex is in the occipital lobe.
iv. Blind Spot – the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there.
v. Fovea – the central focal point in the retina, around which the eye’s cones cluster.
G. Visual Information Processing
1. The retina is actually a piece of the brain that migrates to the eye during early fetal development.
2. The retina’s neural layers help to encode and analyze the sensory information.
3. Pathway from the eyes to the visual cortex (Figure 5.9, pg. 182)
4. Feature Detectors – nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.
i. This information is pooled for interpretation by higher-level brain cells.
ii. This information will determine our response, if any, to the stimulus.
iii. As the same image continues to strike the retina, the brain constructs varying perceptions of it. (i.e. Necker cube, pg. 183)
iv. Our mind can create a type of virtual reality by responding to illusory contours. (Figure 5.12, pg. 183)
a. All images that we perceive can be broken down into patterns of changing light intensity that can be described mathematically.
b. The brain may actually be processing mathematical-like codes that represent perceived images.
5. Parallel Processing – the processing of several aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving.
i. We simultaneously process color, motion, form and depth. (See picture of bird, pg. 184).
ii. Our brains do many things at once, automatically and without our awareness.
iii. Blindsight – the ability to respond to something not consciously perceived.
H. Color Vision
1. Color, like all aspects of vision, resides not in the object but in the theater of the brain. Even while dreaming, we may perceive things in color.
2. We can discriminate some 7 million different color variations.
3. About 1 person in 50 has color-deficient vision (usually males).
4. Young-Helmholtz Trichromatic (three-color) Theory – the theory that the retina contains three different color receptors-one most sensitive to red, one to green, one to blue – which when stimulated in combination can produce the perception of any color.
5. Most color-deficient people are not actually "colorblind." They simply lack functioning color sensitive cones.
i. Dichromatic color blindness – cannot see either red/green shades or blue/yellow shades.
ii. Monochromatic color blindness – see only shades of gray.
6. Opponent-Process Theory – the theory that opposing retinal processes (red-green, yellow-blue, white-black) enables color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green. If one sensor is stimulated, its pair is inhibited from firing.
i. If you stare at the color red for a while, you fatique the senors for red. Then switch your gaze to a blank white page and the opponent pair for red will fire, and you will see a green afterimage.
7. Most researchers agree with a combination of trichromatic and opponent-process theory. Both concepts are needed to explain color vision fully.
8. Color Constancy – perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.
i. We take into consideration the surrounding context.
a. Put on yellow-tinted ski goggles and the snow, after a second, looks as white as before.
b. Our experience of color comes not just from the object, but from everything around it as well. (See figure 5.18, pg. 188)
Hearing
I. The Stimulus Input: Sound Waves
1. Terms
i. Audition – the sense of hearing.
ii. Frequency – the number of complete wavelengths that pass a point in a given time (i.e. per second). Put simply, frequency is how frequent the waves come by.
iii. Pitch – a tone’s highness or lowness; depends on frequency. (This is also called amplitude).
a. The longer the waves (the lower their frequency), the lower the pitch.
b. The shorter the waves (the higher their frequency), the higher the pitch.
iv. Decibels – the measuring unit for sound energy.
a. The absolute threshold for hearing is arbitrarily defined as 0 decibels. Every 10 decibels correspond to a tenfold increase in sound.
b. Exposure to sounds above 85 decibels can produce hearing loss.
c. Decibel Chart, pg. 189.
J. The Ear
1. Terms
i. Middle Ear – the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.
ii. Inner Ear – the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.
iii. Cochlea (KOHK-lee-uh) – a coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses.
2. Figure 5.20, pg. 190
3. The brain can interpret loudness from the number of activated hair cells in the Basilar Membrane.
K. How Do We Perceive Pitch?
1. Pitch Theory – in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated.
i. Place theory best explains how we sense high pitches
2. Frequency Theory – in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.
i. Frequency theory best explains how we sense low pitches
3. A combination of place and frequency seems to handle the pitches in the intermediate range.
L. How Do We Locate Sounds?
1. Figure 5.21, pg. 192
2. Locating a sound that is equidistant from two ears is not very easy.
M. Hearing Loss and Deaf Culture.
1. Conduction Hearing Loss – hearing loss caused by damage to the mechanical system that conducts sound waves. (ear canal, eardrum, hammer/anvil/stirrup, or oval window)
2. Sensorineural Hearing Loss – hearing loss caused by damage to the hair cells in the cochlea’s receptor or to the auditory nerves; also called nerve deafness.
i. Prolonged exposure to load noise can permanently damage the hair cells, which do not regenerate.
ii. The only way to restore hearing among people with nerve deafness is a sort of bionic ear called a cochlear implant.
3. People who lose hearing, or any other channel of sensation, seem to compensate with a slight enhancement of their other sensory abilities.
The Other Senses
N. Touch
1. Our "sense of touch" is actually a mix of at least four distinct skin senses – pressure, warmth, cold, and pain.
2. Only pressure has identifiable receptors.
3. The relationship between warmth, cold, and pain and the receptors that respond to them remains a mystery.
4. Other skin sensations are variations of the basic four.
5. Pain – a property not only of the senses – of the region where we feel it – but of the brain as well.
i. The brain can sometimes misinterpret pain (i.e. phantom limb sensations).
ii. Gate-Control Theory – theory that the spinal cord contains a neurological "gate" that blocks pain signals or allows them to pass on to the brain. The "gate" is opened by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger fibers or by information coming from the brain.
iii. There is more to pain than what stimulates the sense receptors. Consider a sports injury that is not felt until after the game.
iv. The brain creates pain.
v. Pain producing brain activity may be triggered with or without sensory input.
6. Pain Control
i. If pain is both a physical and psychological phenomenon, then it should be treatable both physically and psychologically.
ii. Therapies include drugs, surgery, acupuncture, electrical stimulation, message, exercise, hypnosis, relaxation training, and thought distraction.
O. Taste (or Gustation)
1. Our sense of taste involves four basic sensations – sweet, sour, salty, and bitter. All other tastes are a mixture of these.
2. Taste is a chemical sense.
3. Taste receptors reproduce themselves every week or two.
4. As you grow older, the number of taste buds decreases, as does taste sensitivity.
5. Taste buds are located on papillae, which are the bumps you can see on your tongue.
6. Smell not only adds to our perception of taste, it also changes it.
i. Sensory Interaction – the principle that one sense may influence another, as when the smell of food influences its taste
ii. Smell + texture + taste = flavor.
P. Smell (or Olfaction) - Figure 5.24, pg. 202
1. Smell is a chemical sense.
2. Precisely how olfactory receptors work remains a mystery.
3. Olfactory receptors recognize odors individually.
4. As the alphabet’s 26 letters can combine to form many words, so odor molecules bind to different receptor arrays, producing the 10,000 odors we can detect.
5. Despite our skill at discriminating scents, we aren’t nearly so good at describing them.
6. Each individual has their own identifiable chemical signiture.
7. Odors have the power to evoke memories and feelings – the olfactory bulb connects to the brain at the amygdala and then to the hippocampus.
Q. Body Position and Movement
1. We are equipped with millions of position and motion sensors that are continually providing information to the brain.
2. Kinesthesis (kin-ehs-THEE-sehs) – the system for sensing the position and movement of individual body parts. Gives us feedback about the position and orientation of specific body parts. (i.e. you can reach down with one finger and touch your kneecap with a high degree of accuracy because your kinesthetic sense provides information about where your finger is in relationship to your kneecap.
3. Vestibular Sense – the sense of body movement and position, including the sense of balance. It tells us how our body is oriented in space.
i. This sense monitors the head’s (and thus the body’s) position and movement.
ii. The biological gyroscope for this sense of equilibrium are in the inner ear. The fluid in the inner ear canals moves with our movement. The fluid movement causes the movement of hair cells, activating neural impulses to the brain.
R. Sensory Restriction
1. The loss of a sense is one type of sensory restriction.
2. Sensory monotony is another type of sensory restriction.
i. Examples: prisoners in solitary confinement, nighttime truck drivers, animals in a barren zoo.
3. Sensory restriction does not disturb most people.
4. Periods of solitude and sensory restriction have traditionally fostered human fulfillment.
i. This has been demonstrated through at therapy called REST – restricted environmental stimulation therapy.
Chapter 6 – Perception.
Perceptual Theories – each theory describes different examples or parts of perception.
A. Signal Detection Theory – investigates the effects of the distractions and interference we experience while perceiving the world. It tries to predict what we will perceive among competing stimuli.
1. Takes into account how motivated we are to detect certain stimuli and what we expect to perceive.
i. These factors are called response criteria (or called receiver operating characteristics).
ii. Tries to explain and predict the different perceptual mistakes we make.
a. False Positive – we think we perceive a stimulus that is not there.
b. False Negative – not perceiving a stimulus that is present.
B. Top-Down Processing – we us top-down processing in perceiving by filling in gaps in what we sense.
1. Our experience creates schemata.
i. Our schemata influence how we perceive the world.
ii. Schemata can create a perceptual set.
a. A perceptual set is a predisposition to perceiving something in a certain way.
C. Bottom-Up Processing (also called feature analysis) – we use only the features of the object itself to build a complete perception.
1. Start at the bottom with the individual characteristics of the image and put all those characteristics together into our final perception.
a. This is hard to imagine because it is an automatic process.
2. Bottom-up processing takes longer but is more accurate.
a. Top-down processing is faster but more prone to error.
Principles of Visual Perception – perception decisions are based on figure-ground relationship.
D. Optical Illusions – what part of the visual image is the figure and what part is the ground or background?
1. Figure 3.5. Optical Illusion (Barron’s, pg. 56)
E. Gestalt Rules – govern how we perceive groups of objects.
1. Gestalt psychologists pointed out that we normally perceive images as groups, not isolated elements.
2. Several Factors influence how we will group objects:
i. Proximity – objects that are close together are more likely to be perceived as belonging in the same group/
ii. Similarity – objects that are similar in appearance are more likely to be perceived as belonging in the same group.
iii. Continuity – objects that form a continuous form (such as a trail or a geometric figure) are more likely to be perceived as belonging in the same group.
iv. Closure – Objects that make up a recognizable image are more likely to be perceived as belonging in the same group even if the image contains gaps that the mind needs to fill in. Similar to top-down processing.
F. Constancy – our ability to maintain constant perception of an object despite the changes we perceive due to angle of vision, variations in light, and so on.
1. Size Constancy – We keep a constant size in mind for an object and know that it does not grow or shrink in size as it moves closer or farther away.
2. Shape Constancy – Objects viewed from different angels will produce different shapes on our retinas, but we know the shape of an object remains constant.
3. Brightness Constancy – We perceive objects as being a constant color even as the light reflecting off the object changes.
G. Depth Cues
1. One of the most important and frequently investigated parts of visual perception is depth.
i. Visual Cliff Experiment – an infant old enough to crawl will not crawl across the visual cliff, implying the child has depth perception.
ii. Depth perception develops when we are about three months old.
2. Monocular Cues – depth cues that do not depend on having two eyes.
i. Linear Perspective – one of the most common cues.
a. example – railroad tracts that converge as the tracts become further away.
ii. Relative Size Cues – images that are closer are viewed as larger.
iii. Interposition Cues – objects that block the view to other objects must be closer to us.
iv. Texture Gradient – Objects closer at view are perceived with more detail and texture.
v. Shadowing – By shading, you can perceive where the light source is and thus see depth and position of objects.
3. Binocular Cues – we see the world with two eyes set a certain distance apart, and this feature of our anatomy gives us the ability to perceive.
i. Binocular Disparity (also called retinal disparity)
a. Each eye sees any object from a slightly different angle. The closer the object is, the more disparity there will be between the images coming fromeach eye.
ii. Convergence
a. As an object gets closer to your face, our eyes must move toward one another to keep focused on the object.
b. The more the eyes converge, the closer the object must be.
Effects of Culture on Perception
H. Differing cultures = differing perception.
1. Some of the perceptual rules psychologists once thought were innate are actually learned.
a. For example, cultures that do not use monocular depth cues in their art do not see depth in pictures using these cues.
2. Some optical illusions are not perceived the same way by people from different cultures.
a. For example, the famous Muller-Lyer illusion.
b. People who come from noncarpentered cultures that do not use right angles and corners often in their building and architecture are not usually fooled by this illusion.
3. Cross-cultural research demonstrates that some basic perceptual sets are learned from our culture.