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Sensation and Perception. Sensation. The process by which our sensory and nervous systems receive stimuli/info from the environment A person’s awareness of the world through their senses. Perception. The process of selecting, organizing and interpreting sensory information

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Sensation and Perception

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  • The process by which our sensory and nervous systems receive stimuli/info from the environment
  • A person’s awareness of the world through their senses.
  • The process of selecting, organizing and interpreting sensory information
  • How you make sense of your sensory information.
perception uses top down processing
Perception usesTop-Down Processing
  • Information processing that focuses on expectations and experiences in interpreting incoming sensory information
terms to remember
Terms to Remember


  • Transforming signals into neural impulses.
  • Information goes from the senses to the thalamus , then to the various areas in the brain.

Coctail-Party Effect (phenomenon)

  • Ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations.
  • Form of selective attention.

Sensory Adaption:

Decreased responsiveness to stimuli due to constant stimulation.

vision basics
Vision Basics
  • Stimulus (input) is light energy
  • Is the dominant sense in human beings.
  • The process involves several steps:

Step 1:

  • Gathering Light-

light is reflected off of objects and gathered by the eye

step 2 within the eye
Step 2: Within the eye:
  • Cornea- transparent protective coating over the front part of the eye
  • Pupil small opening in the iris through which light enters
  • Iris-colored part of the eye
  • Lens- transparent part inside the pupil- focuses light onto the retina
  • Retinalining of the eye containing receptor cells sensitive to light.
step 3 transduction
Step 3: Transduction
  • Receptor cells- respond to a specific energy
  • Rods- receptor cells in the retina- night vision, brightness (black/white) PERIPHERAL vision
  • Cones- receptor cells in retina- color vision
  • Fovea- area of the retina that is the center of the visual field- Also the most clear vision.
  • Optic nerve- bundle of axons and ganglion cells- carry neural messages from the eye to the brain
  • Blind spot- no receptors- where the optic nerve leaves the eye
  • Optic Chasm- place at base of the brain where some fibers from the optic nerve cross to the other side of the brain.
step 4 in the brain
Step 4: In the Brain
  • Visual cortex located in the occipital lobe
  • VC receives impulses from cells of the retina that activate feature detectors
  • Dr. Huble and Dr. Weisel: groups of neurons in the VC respond to different types of visual images
  • VC has feature detectors for vertical lines, curves, and motion
  • Our visual perception is a combination
trichromatic theory
Trichromatic Theory

Three types of cones:

  • Red
  • Blue
  • Green
  • These three types of cones can make millions of combinations of colors.
  • Does not explain afterimages or color blindness well.
opponent process theory
Opponent-process Theory
  • Either/or response of the three color receptors
  • Sensory receptors organized in pairs (red/green, yellow/blue, black/white)
  • If red is stimulated, green won’t fire.
  • Explains the color after images and color blindness
combination of theories
Combination of Theories
  • A combination of both explains color vision completely
  • Colorblindness- partial or total inability to perceive hues
  • Trichromats- have normal color vision
  • Monochromats- totally colorblind
  • Dichromats- blind to red/green or blue/yellow
audition basics
Audition Basics
  • Stimulus/input is sound waves
  • Ears contain structures for hearing and balance
  • Amplitude- height of a sound wave that determines loudness- measured in decibles
  • Number of complete waves per unit of time
  • Dogs can hear sounds at higher frequencies than humans can
  • Hertz (Hz)- cycles per second= measue of the frequency of waves
more hearing basics
More hearing basics
  • Pitch- auditory experience corresponding primarily to frequency of sound vibrations resulting in higher or lower tones.
  • Decibel- the magnitude of a wave- determines loudness.
parts of the ear
Parts of the Ear
  • Ear canal- aka auditory canal
  • Eardrum- aka tympanic membrane
  • Hammer, anvil and stirrup- small bones in the inner ear relay eardrum to the inner ear
  • Cochlea- contains fluid that vibrates causing the basilar membrane to vibrate
  • Basilar membrane- inside the cochlea- contains sense receptors for sound
  • Organ of Corti- Contains receptor cells
  • Auditory nerve- bundle of neurons that carries signals from the ears to the brain.
transduction in the ear
Transduction in the ear
  • Sound waves hit the eardrum then anvil then hammer then stirrup then oval window.
  • Everything is just vibrating.
  • Then the cochlea vibrates.
  • The cochlea is lined with mucus called basilar membrane.
  • In basilar membrane there are hair cells.
  • When hair cells vibrate they turn vibrations into neural impulses which are called organ of Corti.
  • Sent then to thalamus up auditory nerve.
pitch theories
Pitch Theories
  • Place Theory- Different hairs vibrate in the cochlea when they different pitches.
  • So some hairs vibrate when they hear high and other vibrate when they hear low pitches.
  • Frequency Theory- All the hairs vibrate but at different speeds. More focused on the lower tones.
deafness hearing loss
Deafness/Hearing Loss
  • Conductive- sound vibrations from tympanic membrane are blocked (wax, fluid build-up, infection, abnormal bones growth) REPLACE THE BONES OR HEAING AIDS
  • Sensorineural – damage to auditory nerve (head injury, birth defects, LOUD NOISES, high BP) COCHLEAR IMPLANTS- CAN’T REPLACE THE HAIRS!!!
  • Prebycusis- changes in the inner ear- common in old age
  • Tinnitus- constant ringing or roaring sound. Cause may not be found.
  • When skin is indented, pierced, or experiences a change in temperature the sense of touch is activated.
  • Pain: Gate control theory
  • Spinal cord has a neural “gate” to block or allow pain signals to the brain
  • Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain.: CIPA
taste is a chemical sense
Taste is a Chemical Sense
  • Taste buds papillae-bumps on your tongue
  • We sense four tastes: sweet, salty sour, and bitter
  • All others are a combination of the basic 4
  • Umami recently discovered comes from glutamate (like MSG)
  • Different parts of the tongue detect all types
smell is a chemical sense
Smell is a Chemical Sense
  • Olfaction = Smell
  • the nose and brain work together to “smell”
  • Chemical molecules enter the nose, dissolve in mucous within a membrane called the olfactory epithelium that contains receptor cells sensitive to odors. Located about 7 cm up the nose in the nostrils
  • Pheromone– chemical the communicates info to others through smell
smell and memory
Smell and Memory
  • Why do some smells trigger memories???
  • Where are memories primarily stored?
sensory interaction
sensory interaction
  • When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor.
other senses
Other “Senses”
  • tells us about how the body is oriented in space
  • Responsible for balance (head and body’s position)
  • Semicircular canals- located in the inner ear sensitive to body rotation
  • Vestibular Sacs- inner ear responsible for sensing gravitation, forward, backward and vertical movements
  • System for sensing position and movement of individual body parts
  • Senses of force and movement of muscles
  • Stretch receptors- sense muscle strength and contractions
absolute threshold
Absolute Threshold
  • The minimum stimulation necessary for a person to detect a particular stimulus 50% of the time. (see table for examples) AKA Detection
difference threshold
Difference Threshold
  • AKA: Just Noticeable Difference (JND)
  • The smallest amount of change that a person can detect between two stimuli 50% of the time.

Absolute Threshold vs. Difference Threshold

  • If you put your hand on a burner and turned it on, the first time you felt something would be Absolute Threshold and the second you noticed it getting hotter would be Difference Threshold.
weber s law
Weber’s Law
  • Weber’s Law – detection of a stimulus depends on the original stimulus itself.
  • Example: If a 300 lb. person loses 20 lbs and a 120 lb. Person loses 20 lbs, which one would you notice lost the weight first?
  • (120 lbs because 20 lbs is a larger % of their body weight)
  • AKA- Difference Threshold

Signal Detection Theory

  • Investigates effects of distractions and interference on perceptions. Detection depends on:
    • Stimulus variables (how weak or strong the stimulus is)
    • Environmental variables (what’s going on around you)
    • Organismic variables (Your own experience, expectations, motivation and alertness)
selective attention
Selective Attention
  • Focusing conscious awareness on a particular stimulus to the exclusion of others
  • The ability to focus on one stimulus at a time
  • Allows a person to function in a world filled with many stimuli
  • People with ADD have trouble doing this.


selective attention1
Selective Attention

Perceptions about objects change from moment to moment. We can perceive different forms of the Necker cube; however, we can only pay attention to one aspect of the object at a time.

Necker Cube

perceptual organization gestalt rules
Perceptual Organization Gestalt Rules
  • When vision competes with our other senses, vision usually wins – a phenomena called visual capture.
  • How do we form meaningful perceptions from sensory information?
  • We organize it. Gestalt psychologists showed that a figure formed a “whole” different than its surroundings.
more gestalt rules review from unit 1
More Gestalt Rules (REVIEW FROM UNIT 1)
  • Form Perception- figure ground
  • Proximity- close objects are perceived as being in the same group
  • Similarity- objects that look similar are perceived to be in the same group
  • Continuity- continuous forms are perceived as the same group.
  • Closure- Closing in gaps on familiar objects
    • Similar to top down processing
depth perception
Depth Perception

Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception.


Visual Cliff

perceptual adaptation
Perceptual Adaptation

Visual ability to adjust to an artificially displaced visual field, e.g., prism glasses.

Courtesy of Hubert Dolezal

binocular depth cues both eyes required
Binocular Depth Cues (both eyes required)
  • Retinal Disparity
    • Distance cue based on the difference between the images
    • Eyes don’t perceive the exact same image (peripheral vision)
    • Overlap in the center- the brain connects them into one image
  • Stereoscopic Vision
    • Combining two retinal images to give a 3-dimensional perception.

Convergence: Neuromuscular cues. When two eyes move inward (towards the nose) to see near objects and outward (away from the nose) to see faraway objects.


Monocular Depth Cues –Visual cues requiring use of one eye


Linear Perspective

Relative Size

monocular cues
Monocular Cues

Texture Gradient: Indistinct (fine) texture signals an increasing distance- Course objects appear to be closer.

Shadowing- areas in shadows appear farther away

Relative Clarity (Ariel Perspective) the further away the less clear object appear to be

Motion Perception: Objects traveling towards us grow in size and those moving away shrink in size. The same is true when the observer moves to or from an object.

relative motion
Relative Motion

In this example, the passenger is moving past a stable world. If she fixes her gaze on the bridge, objects behind it will appear to move forward. The farther away the object is, the more slowly it will appear to move. Objects in front of the fixation point appear to move backward.

apparent motion
Apparent Motion

Phi Phenomenon: When lights flash at a certain speed they tend to present illusions of motion. Neon signs use this principle to create motion perception.

Two lights flashing one after the other.

One light jumping from one point to another: Illusion of motion.

perceptual constancy
Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal images change. Perceptual constancies include constancies of shape and size.

Don’t forget :

Color Constancy

Lightness Constancy

Shape Constancy

size distance relationship
Size-Distance Relationship

The distant monster (below, left) and the top red bar (below, right) appear bigger because of distance cues.

Alan Choisnet/ The Image Bank

From Shepard, 1990

size distance relationship1
Size-Distance Relationship

Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the two corners of the room.

Both photos from S. Schwartzenberg/ The Exploratorium

ames room
Ames Room

The Ames room is designed to demonstrate the size-distance illusion.

perceptual interpretation
Perceptual Interpretation
  • Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences.
  • John Locke (1632-1704) argued that we learn to perceive the world through our experiences.

How important is experience in shaping our

perceptual interpretation?

sensory deprivation
Sensory Deprivation

Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars.

Blakemore & Cooper (1970)

perceptual set
Perceptual Set
  • Our experiences, learned assumptions and beliefs shape our experiences
    • Streetcar scene of a black man talking to a white woman. He is holding a knife.
    • The subjects tell the story (like telephone) to another person.
    • The typical story told by the last person included the black man holding the knife- central theme in many trials.
three perceptual distortions
Three perceptual distortions
  • Leveling- the perceiver DROPS certain details because they don’t fit his/her cognitive categories or assumptions.
  • Sharpening- details of the story that are consistent with the values and interests of the perceiver are emphasized
  • Assimilation- padding and organizing are used to make the central theme fit expectations
  • All what we perceive not only comes from the environment but also from our minds. Schemas or concepts develop through experience

Assimilation vs Accommodation

perception human factors
Perception & Human Factors

Human Factor Psychologists design machines that assist our natural perceptions.

Photodisc/ Punchstock

Courtesy of General Electric

The knobs for the stove burners on the right are easier to understand than those on the left.

can there be perception without input
Can there be perception without input?
  • Most would say no.
  • Scientists tend to agree
  • What about ESP (Extrasensory Perception)?