Basic Principles of Sensation and Perception

• Sensation and Perception

  • Sensation—the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment

  • Perception—the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

    • How we interpret our environment

  • Are one continuous process

  • Bottom-up processing—analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information

    • Starting with senses and working your way up to integrating it

  • Top-down processing—information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

    • Already have an expectation for what the sensory experience will be like

• Selective attention—the focusing of conscious awareness on a particular stimulus

  • There are so many stimuluses around us (clothes, sounds, sights, etc.) that our brains focus on just a few things, blocking out the rest

  • Cocktail party effect—at an event, over everything going on around you, you can hear a friend call your name

  • We cannot multitask—our brains can only focus on one thing at a time

  • Inattentional blindness—failing to see visible objects when our attention is directed elsewhere

    • How magicians fool us—draw our attention to one place and pull sleight of hand in another

  • Change blindness—failing to notice changes in the environment

    • Don’t recognize that a change has happened unless we expect it

    • One person ducks behind a counter and someone else pops up—most don’t notice

• 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 brains can interpret

  • Psychophysics—the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

  • How we consciously perceive the physical world around us

• Thresholds (when we notice stimuli)

  • Absolute threshold—the minimum stimulation necessary to detect a particular stimulus 50% of the time

    • How much perfume has to be in the room in order for you to smell it half the time? How much flavoring in your water? How hard does the wind have to blow?

  • 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

    • “Do you smell that?” would cause you to notice the scent that you may not have picked up on, etc.

  • Subliminal—below one’s absolute threshold for conscious awareness

    • Was a controversy about subliminal messaging in advertising, music, etc. in the 80s

  • Priming—the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response

    • Ex. flashing a disturbing clown picture on a screen (priming stimulus) (so quickly that you can’t consciously process it) then showing a picture of a face (masking stimulus) makes you think the face is creepy

  • 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 (jnd)

    • When the optometrist shows you 1 and 2 and eventually they’re so similar you can’t tell which is which

    • 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)

      • If I took one needle out of a pile of 100 needles, you would be less likely to notice than if I took one needle out of a pile of 2 needles (because I would have taken out a constant amount)

• Sensory adaptation—diminished sensitivity as a consequence of constant stimulation

  • When you wear glasses all day every day, you don’t notice them anymore

  • Our brain decides the constant stimulation isn’t important or useful, so it stops listening

  • Emotion adaptation—our awareness of other people’s emotions

    • If we think someone is angry, we will treat them differently, even if they just look that way and are actually just fine

Influences on Perception

• Perceptual set—a mental predisposition to perceive one thing and not another

  • When we see a picture of the Loch Ness monster, we are predisposed to think that’s what it is, rather than the more logical description of a log or something

  • Schemas

    • When I say chair, you imagine something that you can sit in

• Context Effects

  • We use context clues to perceive objects

• Emotion and Motivation

  • Motivation on perception

    • When you’re really thirsty and water is really far away, you don’t mind going to get it, but when you’re just laying in bed and your water is just out of reach, you don’t want to get it

  • Emotions on perception

    • You anticipate when you go to a haunted house that someone will jump out at you or you will be scared by a noise, etc.

    • Your psychological state determines how you will react

• Parapsychology—the study of paranormal phenomena, including ESP and psychokinesis

  • Extrasensory perception (ESP)—the controversial claim that perception can occur apart from sensory input; includes telepathy, clairvoyance, and precognition

    • Telepathy—communication by the mind

    • Clairvoyance and precognition—being able to predict the future

  • Psychokinesis—being able to move things with your mind

  • The supernatural

  • Highly controversial—cannot really be objectively studied

  • Not scientifically validated

Vision

• The Stimulus Input: Light Energy

  • 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

    • 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 or sound wave, which we perceive as brightness or loudness, as determined by the wave’s amplitude

    • The brighter the light or the louder the sound, the higher the amplitude of the wave

    • A dim light or quiet sound means a lower amplitude

  • Electromagnetic Energy Spectrum

    • Visible light is a small part of the entire electromagnetic spectrum

• The Structure of the Eye

  • Cornea—outer covering of the eye

  • Pupil—the adjustable opening in the center of the eye through which light enters

  • 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

    • When there is little light, the iris dilates, and when there is a lot of light, the iris restricts

  • Lens—the transparent structure behind the pupil that changes shape to help focus images on the 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

    • Rods—retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don’t respond

      • Many more rods than cones

    • Cones—retinal 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

  • Blind spot—the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there

  • Fovea—the central focal point in the retina, around which the eye’s cones cluster

  • Optic nerve—the nerve that carries neural impulses from the eye to the brain

• Visual information processing

  • Feature Detectors—nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement

  • Parallel processing—the processing of many 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

    • Motion, form, depth, and color are processed all at once

• Color Vision

  • 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

    • Red-green colorblindness could be a result of deficiency in red or green color receptors, or both

    • Monochromatic—you have errors with two colors and can only see one

    • Dichromatic—you have errors with one color and can only see two

  • Opponent-process theory—the theory that opposing retinal processes (red-green, 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

    • Three sets of colors

    • Afterimage—you wear out your receptors for yellow and green, so then you see the opposite (red and blue)

Visual Organization and Interpretation

• Visual Organization

  • Gestalt—an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes

    • Looking at the whole, not individual pieces

  • Form Perception

    • Figure-ground—the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground)

    • Grouping—the perceptual tendency to organize stimuli into coherent groups

      • Proximity—when things are close together, we are more likely to group them together

      • Continuity—we tend to see things as continuous, not segmented (one squiggly line, not a bunch of semicircles)

      • Closure—we close the gaps in an image with our minds, even if nothing is there (seeing shapes or lines where there are none)

  • 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

    • Innate ability

    • Visual-cliff—a laboratory device for testing depth perception in infants and young animals

      • Older infants/animals are less likely to cross the glass for fear of falling—they know there is a difference in depth (a cliff)

    • Binocular cues—depth cues, such as retinal disparity, that depend on the use of two eyes

      • Retinal Disparity—a binocular cue for perceiving depth. By comparing images from the retinas in the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object

      • The two eyes are at different locations, thus, they perceive different angles

    • Monocular cues—depth cues, such as interposition and linear perspective, available to either eye alone

      • Used in 2D art to create a sense of depth even where there is none

        • Horizontal-vertical illusion—two lines of the exact same length, the vertical one appears taller

        • Relative height—things that are higher appear further away

        • Relative size—the further something is from you, the smaller it appears, and the blurrier it is, and vice versa

        • Interposition—when something is blocking your view of something else, it must be closer to you than the other thing

        • Linear perspective—lines converge at a vanishing point; on a long, straight road, it looks like the road comes to a point, but it doesn’t

        • Relative motion—if you’re moving and looking out at stable objects, and you focus on one point ahead of you, the point will appear to move with you, while the other objects will appear to move in the opposite direction

        • Light and shadow—shading can make things look like they are within or on top of something else

      • All of these together create realistic depth

  • Motion Perception

    • Changing size of objects (determine whether something is coming closer or moving further away)

    • Stroboscopic movement—animated film (24 pictures every second, each slightly different, to simulate motion)

    • Phi phenomenon—an illusion of movement created when two or more adjacent lights blink on and off in quick succession

      • Christmas lights that appear to move when one light turns off as the next turns on

      • The wave at a football game

  • Perceptual constancy—perceiving objects as unchanging (having consistent shapes, size, lightness, and color) even as illumination and retinal images change

    • Color and Brightness

      • Color constancy—perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object

        • Based on surrounding context and objects

    • Shape and Size

      • Moon illusion—the moon looks bigger when it is closer to Earth, but doesn’t change size

• Visual Interpretation

  • Restored vision

    • People who were born with cataracts and then had their eyes fixed years later still have perception issues

      • Cannot recognize objects by sight, but can by feel/sound/other senses

    • There is a critical window in youth where sensory deprivation makes perception skills not develop properly

  • Perceptual adaptation—in vision, the ability to adjust to an artificially displaced or even inverted visual field

    • Upside-down world goggles—eventually your brain adjusts

Hearing

• Audition—the sense or act of hearing

• Sound waves

  • Amplitude—how high or low the wave goes

    • Determines loudness and intensity

    • The greater the amplitude, the louder the sound

  • Frequency—the number of complete wavelengths that pass a point in a given time (i.e. per second)

    • Pitch—a tone’s experienced highness or lowness; depends on frequency

    • The higher the frequency, the higher the pitch

• The ear

  • Outer ear

    • Pinna—collects the sound waves

    • Auditory canal—bring sound waves to the eardrum

    • Eardrum—tight membrane that vibrates when struck by sound waves

      • AKA Tympanic membrane

  • 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

    • Piston—Hammer (Malleus), Anvil (Incus), Stirrup (stapes)

  • Inner ear—the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs

    • Oval window—where the stirrup connects to the cochlea

    • Cochlea—a coiled, body-fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

      • Basilar membrane—organ within your cochlea which houses the cilla

      • Cilla—hairs in the cochlea that bend in response to sound, triggering a neural impulse

    • Auditory nerve—nerve which sends the auditory message to the brain via the thalamus

  • Perceiving loudness

    • Prolonged exposure to sounds above 85 decibels produces hearing loss

    • Hearing loss

      • Conduction hearing loss—hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea

        • Injury

        • Cochlear implant—electrode that electrically stimulates the nerves to perceive sound

      • Sensorineural hearing loss—hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerves; also called nerve deafness

        • Loud noise, disease/illness, genetic, certain drugs, etc.

        • You can hear someone is talking, but it sounds muffled

      • Signing

      • Tinnitus—auditory disorder which causes constant noise which is not actually there (ringing, etc.)

      • Hearing aids compress sounds

  • Perceiving pitch

    • 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

      • Why there is a threshold of the highest frequencies we can hear—our nerves can only send impulses so quickly

      • Volley principle—when frequency gets too high, the nerves take turns

  • Locating Sounds

    • Stereophonic hearing—one ear can hear one thing, and the other can hear something else (certain songs play one thing in one ear and something else in the other)

    • Localization of sounds

      • Intensity—if something sounds louder or you hear it slightly sooner on one side, it is in that direction