AP Psychology Study Sheet
Sensation & Perception
Basic Principles of Sensation
● Sensation is the process by which our sensory receptors and nervous system receive and
represent stimulus energies from our environment.
● Perception is the process of organizing and interpreting sensory information, enabling us to
recognize meaningful objects and events.
● They blend into a continuous process.
Bottom-level processing, sensory analysis that starts at the entry level, begins with the
sensory receptors and works up to the brain's integration of sensory information.
Top-down processing, our experience and expectations, is information processing
guided by higher-level mental processes.
● Selective attention focuses one's conscious awareness on a particular stimuli.
● Selective inattention follows this:
Inattentional blindness is the failure to see visible objects when attention is redirected.
Change blindness is the failure to notice changes in the environment.
Change deafness can also occur.
Choice blindness, in which one forgets the choice they made, can occur.
● Psychophysics is the study of the relationship between the physical characteristics of stimuli,
such as their intensity, and our psychological experience of them.
● Gustav Fechner studied awareness of faint stimuli, calling them absolute thresholds, the
minimum stimulation necessary to detect a particular stimulus 50 percent of the time.
● Detecting a weak stimulus depends not only on the signal's strength, but on one's physical
state (i.e. their experience, expectation, motivation, and alertness).
Signal detection theory predicts when one will detect weak signals.
It is measured as the ratio of “hits” to “false alarms.”
It assumes there is no single absolute threshold and that detection depends partly on
one's experience.
● Subliminal stimulation occurs below one's absolute threshold for conscious awareness.
At or slightly below the absolute threshold, a stimulus is detected some of the time.
A person can be primed, in which certain associations are activated, predisposing one's
perception, memory, or response.
Much information processing occurs automatically, outside of the conscious mind.
However, these subliminal messages are subtle and fleeting.
● The difference threshold, or the just noticeable difference is the minimum difference
between two stimuli required for detection 50 percent of the time.
The detectable difference increases with the size of the stimulus.
Weber's Law states that for the difference to be perceptible, two stimuli must differ by a
constant proportion, not a constant amount.
● Sensory adaptation is diminished sensitive as a consequence of constant stimulation.
● It results in nerve cells firing less frequently.
● Although sensory adaptation reduces sensitivity, it offers the benefit of focusing on
informative changes in environment without being distracted by uninformative background
stimulation.
Vision
● Our eyes receive light energy and transform it into neural messages that our brain then
processes.
● Transduction is the conversion of one form of energy into another. The brain transduces
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light energy into color.
● Light's wavelength, the distance from one wave's peak to the next, determines its hue, or the
color experienced.
● Intensity, the amount of energy in light waves, is determined by the wave's amplitude, and it
influences brightness.
Light enters the eye through the cornea, which protects the eye and bends light to provide focus.
● The light then passes through the pupil, a small adjustable opening surround by the iris, a
colored muscle that adjusts light intake.
The iris dilates or constricts in response to light intensity and inner emotions.
● Behind the pupil is a lens that focuses incoming light rays into an imagine on the retina, a
multi-layered tissue on the eyeball's inner surface.
The lens focuses the rays by changing its curvature in accommodation.
● Millions of receptor cells convert particles of light energy into neural impulses.
Beyond the retina's outer layer of cells lies its receptors cells, the rods and cones.
● Rods are retinal receptors that detect black, white and gray.
They are necessary for peripheral and twilight vision, when cones don't respond.
They are sensitive to dim light.
They share bipolar cells with other rods, sending combined messages.
● Cones are retinal receptor cells that are concentrated near the center of the retina.
They function in daylight or in well-lit conditions.
They detect fine detail and give rise to color sensations.
Cones cluster around the fovea, the retina's area of central focus.
The visual cortex devotes a large area to input from the fovea.
● At the receptors, light energy triggers chemical changes that sparks neural signals,
activating neighboring bipolar cells.
● The bipolar cells in turn activate the neighboring ganglion cells.
● Axons from this network of ganglion cells converge to form the optic nerve that carries
information to the brain.
Where the optic nerve leaves the eye, there are no receptor cells, creating a blind spot.
The retina's neural layers, in addition to passing electrical impulses, also help encode and
analyze sensory information.
● Any retinal area relays information to a corresponding location in the visual cortex.
● Feature detectors are nerve cells in the brain that respond to specific features of a stimulus.
In the visual cortex, they pass information to other cortical areas where teams of cells,
supercell clusters, respond to more complex patterns.
● Our brain engages in parallel processing, in which it processes many aspects of a problem
simultaneously.
It is the brain's natural mode of information processing, contrasting with step-by-step or
serial processing.
Perceptions are constructed by integrating the separate but parallel works of different
feature detectors.
Color exists strictly in the brain.
● The Young-Helmholtz trichromatic theory worked on the inference that the eye must have
three corresponding types of color receptors to the three primary colors of light.
The retina has three types of color receptors.
● Hering's opponent-process theory states that opposing retinal processes (red-green, yellowblue, and white-black) enable color vision.
Cells are stimulated by one color, and inhibited by the other.
● Color processing occurs in two stages.
The retina's red, green, and blue cones respond in varying degrees to different color
stimuli.
Their signals are then processed by the nervous system's opponent-process cells.
Hearing
● Audition is highly adaptive.
● Also, we are attuned to variations in sounds.
● The strength, or amplitude of sound waves, determines their loudness.
Sounds are measured in decibels.
The absolute threshold is defined as zero decibels (arbitrarily).
● Waves vary in length and frequency, determining their pitch (long waves have low
frequency and low pitch; short waves have high frequency and high pitch).
● The outer ear channels the sound waves through the auditory canal to the eardrum, a tight
membrane that vibrates with the waves.
● The middle ear then transmits the eardrum's vibrations through a piston made of three small
bones (the hammer, anvil, and stirrup) to the cochlea, a snail-shaped tube in the inner ear.
● Incoming vibrations cause the cochlea's membrane, the oval window, to vibrate, moving the
fluid that fills the tube.
The motion causes ripples in the basilar membrane, bending the hair cells lining its
surface.
Hair cell movement triggers impulses in adjacent nerve cells, whose axons converge to
form the auditory nerve, sending neural messages to the auditory cortex.
Ringing of the ears suggests hair cells have been damaged and potentially harmed.
● The brain interprets loudness from the number of activated hair cells.
● If a hair cell loses sensitivity to soft sounds, it may still respond to loud sounds.
● Really loud sounds may seem loud to both people with and without hearing loss.
● Those with hearing problems prefer sound compressed, meaning harder-to-hear sounds are
amplified more than loud sounds.
● Perceiving pitch:
● Helmholtz's place theory suggests that we hear different pitches because different sound
waves trigger activity at different places along the cochlea's basilar membrane.
The brain determined a sound's pitch by recognizing the specific place on the membrane
that is generating the neural signals.
High frequencies produce large vibrations near the beginning of the membrane, and low
frequencies near the end.
However, this theory did not explain well how we hear low-pitched sounds, since
signals for low-pitched sounds are not neatly localized on the basilar membrane.
● The frequency theory suggests that the brain reads pitch by monitoring the frequency of
neural impulses traveling up the auditory nerve.
The basilar membrane vibrates with an incoming sound wave, triggering neural
impulses at the same rate as the sound wave.
Frequency theory explains how we can hear low-pitched sounds.
The volley principle states that neural cells can alternate firing; by doing so, they can
achieve a combined frequency in order to fire faster than 1000 waves per second.
● Place theory explains how we sense high pitches and frequency theory explains how we
sense low pitches.
Some combination of both handles pitches in the intermediate rage.
● Our supersensitive auditory system can detect minute differences to sound due to the lag
between both ears.
● A sound will be easily pointed out from either side because of this.
However, one is more likely to make mistakes when a sound comes from directly behind,
above, or below.
● This explains why one cocks their head when trying to hear a sound.
Problems with the mechanical system that conducts sound waves to the cochlea causes
conduction hearing loss.
● Damage to the cochlea's hair cell receptors or their associated nerves can cause more
common sensorineural hearing loss, or nerve deafness.
The only way to restore hearing in the case of nerve deafness is a cochlear implant, an
electronic device that translates sounds into electrical signals that convey information
about sound to the brain.
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Touch
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Touch is essential to our development.
● It is a mix of distinct senses, with different types of specialized nerve endings within the
skin.
Some spots are sensitive to pressure, others to warmth, others to cold, and others to pain.
Only pressure has identifiable receptors.
● Other skin sensations are variations of the basic four.
Stroking adjacent pressure spots creates a tickle.
Gentle stroking of a pain spot causes an itching sensation.
Touching adjacent cold and pressure spots triggers a sense of wetness.
Stimulating nearby cold and worm spots produced the sensation of hot.
● There is a top-down influence on touch sensation.
It is a product of bottom-up sensations and top-down expectations.
Sensors in the joints, tendons, bones, ears, and skin enable kinesthesis, the sense of position on
movement of one's body parts.
● A companion vestibular sense monitors one's head's (and thus body's) position and
movement.
The biological gyroscopes for this sense of equilibrium are in the inner ear.
The semicircular canals and the vestibular sacs, which connect the canals with the
cochlea, contain fluid that moves when one's head rotates or tilts.
This movement stimulates hairlike receptors, sending messages to the cerebellum, and
enabling one to sense body position and maintain sense of balance.
Feelings of pain combines both bottom-up sensations and tow-down processes.
● There are different nociceptors, sensory receptors that detect hurtful temperatures, pressure,
or chemicals.
● Psychologist Ronald Melzack and biologist Patrick Wall conceived the gate-control theory,
the theory that the spinal cord contains a neurological “gate” that blocks pain signals or
allows them to pass into the brain.
The “gate “ is opened by the activity of pains signals traveling up small nerve fibers.
It is closed by activity in larger fibers or by information coming from the brain.
The release of endorphins, natural painkillers, diminishes the experience of pain.
● The brain can also create pain, as it does in experiences of phantom limb sensations, when
the brain misinterprets the spontaneous central nervous system activity that occurs in the
absence of normal sensory input.
People with nerve damage have experienced taste phantoms.
Others have experienced phantom smells.
● Memories of pain differ from the pain actually experienced.
People overlook a pain's duration.
People record the pain's peak moment as worse.
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They register how much pain they felt at the end.
Perception of pain also varies with social situation and cultural traditions.
We tend to perceive more pain when others also seem to be experiencing pain.
Thus, pain is a biopsychosocial phenomenon.
An inert placebo can help relieve pain by dampening the brain's attention and responses to
painful experiences, mimicking analgesic drugs.
Distracting people with pleasant images or drawing their attention away from painful
stimulates is an effective way to increase pain tolerance.
Taste
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The five sensations of taste are sweet, sour, salty, bitters, and umami (a savory meat taste best
experienced in monosodium glutamate).
● Taste is a chemical sense.
50 to 100 taste receptor cells in each taste bud pore project antenna-like hairs that sense
food molecules.
● Taste receptors reproduce ever week or so.
As one grows older, the number of taste buds decreases.
Taste sensitivity also decreases with age.
Smoking and alcohol accelerates these declines.
● One's expectation influences the brain's response to taste.
Taste interacts with other senses.
● To savor a taste, one breathes the aroma through their nose.
● Sensory interaction is the principle that one sense may influence another.
Smell, texture, and taste work together to form flavor.
If we see one syllable being said, and hear another, we may perceive a third known as
the McGurk effect.
The senses become joined in the phenomenon of synaesthesia, where one sort of
sensation produces another.
Smell
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The experiences of smell, or olfaction, are intimate.
● Smell is a chemical sense.
● Something is smelled when molecules of a substance carried in the air reach a tiny cluster of
5 million or more receptor cells at the top of each nasal cavity.
These olfactory receptor cells respond selectively.
They alert the brain through their axon fibers.
● Olfactory neurons bypass the thalamus.
Odor molecules come in many shapes and sizes, requiring different receptors to detect them.
● A variety of receptor proteins recognize particular odor molecules.
● These receptor proteins are embedded on the surface of nasal cavity neurons.
They recognize a molecule through a lock-and-key complex.
● Some odors trigger a combination of receptors, in patterns that are interpreted by the
olfactory cortex.
The ability to identify scent peaks in early adulthood.
● It gradually declines thereafter.
● Women's ability to smell surpasses that of men.
The attractiveness of smells depends on learned associations.
● We have a capacity to recognize long-forgotten odors and their associated memories.
● Our brain's circuitry explains this power to evoke feelings and memories.
A hotline runs between the olfactory cortex and the limbic centers of emotion/memory.
Smell is primitive.
Perceptual Organization
● A group of German psychologists noticed that when given a cluster of sensations, people tend
to organize them into a gestalt, or form/whole.
● A gestalt is an organized whole.
● The Gestalt psychologists said that the whole may exceed the sum of its parts.
● Form perception:
● The figure-ground relationship continually reverses.
We organize a stimulus into a figure seen against a ground.
● To bring order and form to basic sensations, our minds follow certain rules for grouping
stimuli together.
Proximity → we group nearby figures together.
Similarity → we group similar figures together.
Continuity → we perceive smooth, continuous patters rather than discontinuous ones.
Connectedness → we perceive things that are connected as a single unit.
Closure → we fill in gaps to create a complete, whole object.
● Depth perception:
● Depth perception is the ability to see objects in three dimensions.
The images that strike the retina are in two dimensions, however.
It allows us to judge distance.
● Binocular cues, depth cues that depend on the use of two eyes, are important in judging the
distance of nearby objects.
Retinal disparity is a binocular cue for perceiving depth → by comparing the images
from the retinas in the two eyes, the brain computes distance; the greater the disparity
between two images, the closer the object.
● Monocular cues are depth cues that are available to either eye alone.
Horizontal-vertical illusion → vertical dimensions seem longer than identical horizontal
dimensions.
Relative height → we perceive objects higher in our field of vision as farther away.
Relative size → if two objects are assumed to be similar in size, the one that casts a
small retinal image is perceived to be further away.
Interposition → if one object partially blocks the view of another, it is perceived as
closer.
Linear perspective → parallel lines appear to converge with distance.
Light and shadow → nearby objects reflect more light to eyes; thus the dimmer one
seems further away; shading produces a sense of depth consistent with our assumption
that light comes from above.
Relative motion → as we move, objects that are actually stable may appear to move.
● Motion perception:
● The brain computes motion based on the assumption that shrinking objects are retreating
and enlarging objects are approaching.
● One runs to keep a ball at a constant angle of gaze.
● The brain will perceive continuous movement in a rapid series of slightly varying images.
This phenomenon is called stroboscopic movement.
● The illusion of movement in which two stationary lights blink on and off in quick
succession is the phi phenomenon, creating the perception of a single light moving back and
forth.
● Perceptual constancy:
● Perceptual constancy is the perceiving of objects as unchanging even as illumination and
retinal images change.
Shape constancy allows one to perceive the form of familiar objects.
Size constancy allows one to perceive objects as having constant size, even when
distance from the object varies.
Distance gives cues to size, and vice-versa.
● Lightness constancy, also known as brightness constancy allows one to perceive an object
as having a constant lightness even when illumination varies.
Perceived lightness depends on relative luminance, the amount of light an object reflects
relative to its surroundings.
● Color constancy allows one to perceive familiar objects as having a consistent color, even if
changing illumination alters reflected wavelengths.
Perceptual Interpretation
● Kant maintained that knowledge comes from inborn ways of organizing sensory experiences.
● John Locke argued that through our experiences we learn to perceive the world.
● Patients could tells the difference between figure and ground and could sense colors after
surgery (when they did not have vision), suggesting we are inborn with these aspects of
perception.
However, they often could not recognize by sight objects that were familiar by touch.
● Experience guides and sustains the brain's development as it forms pathways that affect our
perceptions.
● There is a suggested critical period for normal sensory and perceptual development.
● Perceptual adaptation is the ability to adjust to an artificially displaced or inverted visual
field (in vision).
● Our experiences, assumptions, and expectations give us a perceptual set, a mental
predisposition to perceive certain things (top-down influences).
● Through experience, we forms concepts or schemas that organize and interpret unfamiliar
information.
● A given stimulus may trigger radically different perceptions because of the immediate
context.
● Stereotypes about gender can also color perception.
● Perceptions are influenced not only by expectations and context, but by emotions.
Motives also matter.
Emotions define social perceptions as well.
Perception is fed by cognition, sensation, and emotion, requiring multiple levels of
analysis.
● Extrasensory perception (ESP) is the controversial claim that perception can occur apart from
sensory input.
● Parapsychology is the study of paranormal phenomena, including ESP and psychokinesis.
● Claims of paranormal phenomena, “psi,” include astrological predictions, psychic healing,
communication with the death, and out-of-body experiences.
● There are three main types of claimed ESP:
Telepathy → mind-to-min communication.
Clairvoyance → the perceiving of remote events.
Precognition → the perceiving of future events.
● Psychokinesis is “mind over matter,” the supposed ability to move objects with one's mind.
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