Basic Concepts of Sensation and Perception
Processing Sensation and Perception
LOQ: What are sensation and perception? What do we mean by bottom-up processing and top-down processing?
Under normal circumstances, sensation and perception blend into one continuous process.
Bottom-up processing begins at your sensory receptors and works up to higher levels of processing.
Top-down processing creates perceptions from this sensory input by drawing on your experience and expectations.
Sensation: the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
Sensory Receptors: sensory nerve endings that respond to stimuli.
Perception: the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.
Bottom-Up Processing: analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information.
Top-Down Processing: information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.
LOQ: What three steps are basic to all our sensory systems?
All of our sense
receive sensory stimulation, often using specialized receptor cells. transform that stimulation into neural impulses. deliver the neural information to our brain.
They also convert one form of energy into another
Transduction: conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brain can interpret.
Psychophysics: the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them.
LOQ: How do absolute thresholds and difference thresholds differ?
Some kinds of stimuli we are really sensitive
Signal detection theory predicts when we will detect weak signals
depends not only on its strength but also on our experience, expectations, motivation, and alertness.
Signal detection theorists seek to understand why people respond differently to the same stimuli
Stimuli you cannot consciously detect 50 percent of the time are subliminal
Absolute Threshold: the minimum stimulus energy needed to detect a particular stimulus 50 percent of the time
Signal Detection Theory: a theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person’s experience, expectations, motivation, and alertness
Subliminal: below one’s absolute threshold for conscious awareness.
Priming: the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response
We need absolute thresholds low enough to allow us to detect important sights, sounds, textures, tastes, and smell
Developed by Ernest Weber in the late 1800s
For an average person to perceive a difference, two stimuli must differ by a constant minimum percentage
Difference Threshold: the minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (or jnd).
Weber’s Law: the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)
LOQ: What is the function of sensory adaptation?
When constantly exposed to an unchanging stimulus, we become less aware of it because our
nerve cells fire less frequently
Sensory adaptation reduces our sensitivity
Sensory Adaptation: diminished sensitivity as a consequence of constant stimulation.
Point to Remember: Our sensory receptors are alert to novelty; bore them with repetition and they free our attention for more important things
LOQ: How do our expectations, contexts, motivation, and emotions influence our perceptions?
Through experience, we come to expect certain results
expectations may give us a perceptual set
To believe is also to hear.
Our expectations can also influence our taste perceptions
Our concepts, or schemas, that we form and organize and interpret unfamiliar information develop our perceptual set
Perceptual Set: a mental predisposition to perceive one thing and not another
Context, Motivation, and Emotion
Examples of the power of context:
When holding a gun, people become more likely to perceive another person as also gun-toting—a phenomenon that has led to the shooting of some unarmed people who were actually holding their phone or wallet
Imagine hearing a noise interrupted by the words “eel is on the wagon.” Likely, you would actually perceive the first word as wheel. Given “eel is on the orange,” you would more likely hear peel. In each case, the context creates an expectation that, top-down, influences our perception of a previously heard phrase
Cultural context helps inform our perceptions, so it’s not surprising that people from different cultures view things differently
Motives give us energy as we work toward a goal
Desirable objects, such as a water bottle viewed by a thirsty person, seem closer than they really are. This perceptual bias energizes our going for it.
A to-be-climbed hill can seem steeper when we are carrying a heavy backpack, and a walking destination further away when we are feeling tired. Going on a diet can lighten our biological “backpack” . When heavy people lose weight, hills and stairs no longer seem so steep.
A softball appears bigger when you’re hitting well, as researchers observed after asking players to choose a circle the size of the ball they had just hit well or poorly. There’s also a reciprocal phenomenon: Seeing a target as bigger—as happens when athletes focus directly on a target—improves performance
Emotions can cause our perceptions to change
Hearing sad music can predispose people to perceive a sad meaning in spoken homophonic words—mourning rather than morning, die rather than dye, pain rather than pane
A hill seems less steep to people who feel others understand them
When angry, people more often perceive neutral objects as guns. When made to feel mildly upset by subliminal exposure to a scowling face, people perceive a neutral face as less attractive and likeable
Emotions and motives color our social perceptions
perceive solitary confinement, sleep deprivation, and cold temperatures as “torture” when experiencing a small dose of such themselves
Much of what we perceive comes not just from what’s “out there,” but also from what’s behind our eyes and between our ears.
Vision: Sensory and Perceptual Processing
Light Energy and Eye Structures
LOQ: What are the characteristics of the energy that we see as visible light? What structures in the eye help focus that energy?
The Stimulus Input: Light Energy
When you look at a bright red tulip, the stimuli striking your eyes are not particles of the color red
What we see as visible light is but a thin slice of the wide spectrum of electromagnetic energy
Light travels in waves
The shape of those waves influences what we see.
Wavelength determines hue
A light wave’s amplitude, or height, determines its intensity
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 gamma rays to the long pulses of radio transmission.
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.
Intensity: the amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave’s amplitude (height).
Light enters the eye through the cornea
bends light to help provide focus
light then passes through the pupil
the iris, a colored muscle that dilates or constricts in response to light intensity
After passing through your pupil, light hits the transparent lens in your eye
lens then focuses the light rays into an image on your retina,
Retina: the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
Accommodation: the process by which the eye’s lens changes shape to focus near or far objects on the retina.
Information Processing in the Eye and Brain
LOQ: How do the rods and cones process information, and what is the path information travels from the eye to the brain?
The Eye-to-Brain Pathway
How light enters the brain
First, you would thread your way through the retina’s sparse outer layer of cell
Then, reaching the back of your eye, you would encounter the retina’s nearly 130 million buried receptor cells, the rods and cones
There, you would see the light energy trigger chemical changes.
could then watch the bipolar cells activate neighboring ganglion cells
axons twine together like the strands of a rope to form the optic nerve
After stopping at the thalamus, the information would fly on to the last destination, the visual cortex
Optic nerve is an information highway from the eye to the brain
can send nearly 1 million messages at once through its nearly 1 million ganglion fibers
With it being this fast, this causes blind-spots
Rods: retinal receptors that detect black, white, and gray, and are sensitive to movement; necessary for peripheral and twilight vision, when cones don’t respond.
Cones: retinal receptors that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. Cones detect fine detail and give rise to color sensations.
Optic Nerve: the nerve that carries neural impulses from the eye to the brain.
Blind Spot: the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there
LOQ: How do we perceive color in the world around us?
About 1 person in 50 is “colorblind.”
Ewald Hering trichromatic theory leaves some parts of the color vision mystery unsolved.
Young-Helmholtz Trichromatic (three-color) Theory: the theory that the retina contains three different types of 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.
Opponent-Process Theory: the theory that opposing retinal processes (redgreen, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.
LOQ: Where are feature detectors located, and what do they do?
David Hubel and Torsten Wiesel showed that our visual processing deconstructs visual images and then reassembles them
One temporal lobe area by your right ear enables you to perceive faces
a specialized neural network recognizes them from varied viewpoint
If stimulated in this fusiform face area, you might spontaneously see faces
If this face recognition region were damaged, you might recognize other forms and objects, but not familiar face
Feature Detectors: nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.
LOQ: How does the brain use parallel processing to construct visual perceptions?
To analyze a visual scene, the brain divides it into subdimensions
motion, form, depth, color
works on each aspect simultaneously
Recognizing a face has many parts
Parallel Processing: processing many aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions, including vision.
LOQ: How did the Gestalt psychologists understand perceptual organization, and how do figure-ground and grouping principles contribute to our perceptions?
A group of German psychologists noticed that people who are given a cluster of sensations tend to organize them into a gestalt
Our conscious perception is, at every moment, a seamless scene
demonstrated many principles we use to organize our sensations into perceptions
Claimed: Our brain does more than register information about the world
Perception is not just opening a shutter and letting a picture print itself on the brain.
Gestalt: an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.
Figure and Ground
Figure-ground the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground).
We must organize the figure into a meaningful form
color, movement, and light-dark contrast is processed immediately along with other basic scene features
order and form to other stimuli by following certain rules for grouping
shows how the perceived whole differs from the sum of its parts
Grouping: the perceptual tendency to organize stimuli into coherent groups.
LOQ: How do we use binocular and monocular cues to see in three dimensions, and how do we perceive motion?
Gibson and Richard Walk designed a series of experiments in their Cornell University laboratory using a visual cliff
Depth perception is also partly innate
Depth Perception: the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.
Visual Cliff: a laboratory device for testing depth perception in infants and
People ****who see with two eyes perceive depth thanks partly to binocular cues.
Binocular Cue: a depth cue, such as retinal disparity, that depends on the use of two eyes
Retinal Disparity: a binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.
We depend on monocular cues to see objects 10-100 meters away
Monocular Cue: a depth cue, such as interposition or linear perspective, available to either eye alone.
You could perceive the world as having color, form, and depth but that you could not see motion
Normally your brain computes motion based
partly on its assumption that shrinking objects are retreating (not getting smaller) and enlarging objects are approaching
We are are imperfect at motion perception
sometimes tricked into believing what it is not seeing
Perceives a rapid series of slightly varying images as continuous movement
phenomenon called the stroboscopic movement
We construct that motion in our head
Lighted signs exploit the phi phenomenon
Phi Phenomenon: an illusion of movement created when two or more adjacent lights blink on and off in quick succession.
LOQ: How do perceptual constancies help us construct meaningful perceptions?
Recognizing objects without being deceived by changes in their color, brightness, shape, or size
Perceptual Constancy: perceiving objects as unchanging (having consistent color, brightness, shape, and size) even as illumination and retinal images change.
Color and Bright Constancy
Our experience of color depends on an object’s context
Brightness constancy (also called lightness constancy) similarly depends on context
Shape and Size Consistencies
we perceive the form of familiar objects, such as the door in FIGURE 6.33, as constant even while our retinas receive changing images of them
Philosophers have debated whether our perceptual abilities should be credited to our nature or our nurture
Experience and Visual Perception
LOQ: What does research on restored vision, sensory restriction, and perceptual adaptation reveal about the effects of experience on perception?
Restored Vision and Sensory Restrictions
William Molyneux wondered whether “a man born blind, and now adult, taught by his touch to distinguish between a cube and a sphere” could, if made to see, visually distinguish the two.
Researchers have restricted the vision of infant kittens in clinical cases
Our perceptual adaptation to changed visual input makes the world seem normal again.
Perceptual Adaptation: the ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field.
The Nonvisual Senses
Our other senses such as hearing, or audition, help us to adapt and survive
Audition: the sense or act of hearing.
The Stimulus Input: Sound Waves
LOQ: What are the characteristics of air pressure waves that we hear as sound?
Sound waves vary in shape like light waves
height, or amplitude, of sound waves determines their perceived loudness
length, or frequency, determines the pitch (the high or low tone)
We measure sounds in decibels
zero decibels representing the absolute threshold for hearing
Every 10 decibels correspond to a tenfold increase in sound intensity
normal conversation (60 decibels) is 10,000 times more intense than a 20-decibel whisper
prolonged, exposure to sounds above 85 decibels can produce hearing loss
Frequency: the number of complete wavelengths that pass a point in a given time (for example, per second).
Pitch: a tone’s experienced highness or lowness; depends on frequency.
LOQ: How does the ear transform sound energy into neural messages?
Vibrating air trigger nerve impulses that your brain can decode as sounds
begins when sound waves strike your eardrum causing this tight membrane to vibrate
middle ear, a piston made of three tiny bones (the hammer, anvil, and stirrup) picks up the vibrations and transmits them to the cochlea
Incoming vibrations then cause the cochlea’s membrane-covered opening (the oval window) to vibrate
This motion causes ripples in the basilar membrane, bending the hair cells lining its surface, rather like wheat stalks bending in the wind
hair cell movements in turn trigger impulses in adjacent nerve cells
Damage to the cochlea’s hair cell receptors or the auditory nerve can cause sensorineural hearing loss (or nerve deafness)
With auditory nerve damage, people may hear sound but have trouble discerning what someone is saying
Occasionally, disease damages hair cell receptors
cannot be reversed
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.
Cochlea: a coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.
Inner Ear: the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.
Sensorineural Hearing Loss: hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerves; the most common form of hearing loss, also called nerve deafness.
Conduction Hearing Loss: a less common form of hearing loss, caused by damage to the mechanical system that conducts sound waves to the cochlear
Cochlear Implant: a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlear
Perceiving Loudness, Pitch, and Location
LOQ: How do we detect loudness, discriminate pitch, and locate sounds?
Responding to Loud and Soft Sounds
Your 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.
Explains why really loud sounds may seem loud to people with or without normal hearing
Hearing Different Pitches
There are currently a combination of two theories on how we discriminate pitch
Place theory presumes that we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane. Thus, the brain determines a sound’s pitch by recognizing the specific place (on the membrane) that is generating the neural signal. Place theory can explain how we hear high-pitched sounds but not low pitched sounds.
Frequency theory (also called temporal theory) suggests an alternative: The brain reads pitch by monitoring the frequency of neural impulses traveling up the auditory nerve. The whole basilar membrane vibrates with the incoming sound wave, triggering neural impulses to the brain at the same rate as the sound wave. If the sound wave has a frequency of 100 waves per second, then 100 pulses per second travel up the auditory nerve. But frequency theory also has a problem: An individual neuron cannot fire faster than 1000 times per second. How, then, can we sense sounds with frequencies above 1000 waves per second (roughly the upper third of a piano keyboard)? Enter the volley principle: Like soldiers who alternate firing so that some can shoot while others reload, neural cells can alternate firing. By firing in rapid succession, they can achieve a combined frequency above 1000 waves per second.
Place Theory: in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated.
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. (Also called temporal theory.)
Because of the placement of our two ears, we enjoy stereophonic (“three-dimensional”) hearing
The Other Senses
Humans would be seriously handicapped without our senses of touch, taste, smell, and body position and movement
LOQ: How do we sense touch?
Touch aids our development
Our “sense of touch” is actually a mix of these four basic and distinct skin senses
LOQ: What biological, psychological, and social-cultural influences affect our experience of pain? How do placebos, distraction, and hypnosis help control pain?
Pain is your body’s way of telling you something has gone wrong
also serves psychological purposes
provides a contrast that amplifies our experiences of pleasure
It enhances our self-awareness
Pain reflects both bottom-up sensations and top-down cognition
Pain is a biopsychosocial event
Viewing pain from the biological, psychological, and social-cultural perspectives can help us better understand it, and also help us cope with it and treat it
Pain is a physical event produced by your senses
pain differs from some of your other sensations
No one type of stimulus triggers pain the way light triggers vision
sensory receptors called nociceptors
detect hurtful temperatures, pressure, or chemicals
mostly in your skin, but also in your muscles and organs
Your experience of pain depends in part on the genes you inherited and on your physical characteristics
Psychologist Ronald Melzack and biologist Patrick Wall proposed the gate-conttrol theory
Brain can also create pain
Gate-Control Theory: the 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.
Our perception of pain is the attention we focus on it
Pain is a product of our attention, our expectations, and also our culture
Pain control therapies may include drugs, surgery, acupuncture, electrical stimulation, massage, exercise, hypnosis, relaxation training, meditation, and thought distraction
Even placebos can help
Drawing attention away from the painful stimulation is an effective way to activate brain pathways that inhibit pain and increase pain tolerance
Research suggests, maximize pain relief by combining a placebo with distraction (Buhle et al., 2012) and amplifying their effects with hypnosis
Psychologists have proposed two explanations for how hypnosis works:
Social influence theory contends that hypnosis is a by-product of normal social and mental processes. In this view, hypnotized people, like actors caught up in a role, begin to feel and behave in ways appropriate for “good hypnotic subjects.” They may allow the hypnotist to direct their attention and fantasies away from pain.
Dissociation theory proposes that hypnosis is a special dual-processing state of dissociation—a split between different levels of consciousness. Dissociation theory seeks to explain why, when no one is watching, previously hypnotized people may carry out posthypnotic suggestions (which are made during hypnosis but carried out after the person is no longer hypnotized). It also offers an explanation for why people hypnotized for pain relief may show brain activity in areas that receive sensory information, but not in areas that normally process pain-related information
Selective attention may also play a role in hypnotic pain relief
Dissociation: a split in consciousness, which allows some thoughts and behaviors to occur simultaneously with others.
Posthypnotic Suggestion: a suggestion, made during a hypnosis session, to be carried out after the subject is no longer hypnotized; used by some clinicians to help control undesired symptoms and behaviors.
Hypnosis: a social interaction in which one person (the hypnotist) suggests to another (the subject) that certain perceptions, feelings, thoughts, or behaviors ANSWER: will spontaneously occur.
LOQ: In what ways are our senses of taste and smell similar, and how do they differ?
Our sense of taste involves several basic sensations
The Survival Functions of Basic Tastes
Experience of smell is called olfaction
Olfactory neurons bypass the brain’s sensory control center, the thalamus
Our ancestors smelled molecules called pheromones, secreted by other members of their species
A smell’s appeal depends on cultural experiences
we also have trouble recalling odors by name
Our sense of smell is less acute than our senses of seeing and hearing
Gender and age influence our ability to identify scents
Women and young adults have the best sense of smell
Smokers and people with Alzheimer’s disease, Parkinson’s disease, or alcohol use disorder typically have a diminished sense of smell
sense of smell tends to peak in early adulthood and gradually declines after that
Body Position and Movement
LOQ: How do we sense our body’s position and movement?
Without kinesthesia, we wouldn’t be able to take a step forward
Vision interacts with kinesthesia
Vestibular sense monitors your head’s and body’s position and movement
Kinesthesia: the system for sensing the position and movement of individual body parts.
Vestibular Sense: the sense of body movement and position, including the sense of balance.
LOQ: How does sensory interaction influence our perceptions, and what is embodied cognition?
All our senses interact with one another and our brain blends their inputs to interpret the world
Our perceptions have two main parts
The brain circuits processing our physical sensations sometimes interact with brain circuits responsible for cognition
This is embodied cognition. Ex:
Physical warmth may promote social warmth. After holding a warm drink rather than a cold one, people were more likely to rate someone more warmly, feel closer to them, and behave more generously
Social exclusion can literally feel cold. After being given the cold shoulder by others, people judged the room to be colder than did those who had been treated warmly
Judgments of others may also mimic body sensations. Sitting at a wobbly desk and chair makes others’ relationships, or even one’s own romantic relationship, seem less stable
Our brain blends inputs from multiple channels
Sensory Interaction: the principle that one sense may influence another, as when the smell of food influences its taste
Embodied Cognition: the influence of bodily sensations, gestures, and other states on cognitive preferences and judgments.
ESP—Perception Without Sensation?
LOQ: What are the claims of ESP, and what have most research psychologists concluded after putting these claims to the test?
Extrasensory Perception (ESP)
The most testable and, for this discussion, most relevant ESP claims are
telepathy: mind-to-mind communication.
clairvoyance: perceiving remote events, such as a house on fire in another state.
precognition: perceiving future events, such as an unexpected death in the next month.
Most research psychologists and scientists have been skeptical that paranormal phenomena exist
Extrasensory Perception (ESP): the controversial claim that perception can occur apart from sensory input; includes telepathy, clairvoyance, and precognition. Do you think you might have ESP?
Parapsychology: the study of paranormal phenomena, including ESP and psychokinesis.
Premonitions or Pretensions?
“Leading psychics” reveal meager accuracy
During the 1990s, the tabloid psychics were all wrong in predicting surprising events
psychic visions offered to police departments have been no more accurate than guesses made by others
one estimate says that the chance alone would predict that more than a thousand times per day, someone on Earth will think of another person and then, within the next five minutes, learn of that person’s death
Putting ESP to Experimental Test
Both believers and skeptics agree that what parapsychology needs is a reproducible phenomenon and a theory to explain it.
Daryl Bem has made his research materials available to anyone who wishes to replicate his studies