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AP Psychology. 2.3 Sensation and Perception. Sensation. Process by which our sensory receptors respond to light, sound, odor, textures, and taste Our eyes, ears, nose, tongue, and skin comprise an elaborate sensory system that receives and processes information from the environment. Sensation.

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ap psychology

AP Psychology

2.3 Sensation and Perception

  • Process by which our sensory receptors respond to light, sound, odor, textures, and taste
  • Our eyes, ears, nose, tongue, and skin comprise an elaborate sensory system that receives and processes information from the environment
  • Each sense organ contains specialized cells called receptors which detect and then convert…
    • light waves - vision
    • sound waves - hearing
    • chemical molecules – taste, smell
    • pressure – touch

… into neural impulses that are transmitted to the brain.

  • adults totally deprived of sensory input for long periods of time
    • experience hallucinations
    • impaired efficiency in all areas of intellectual functioning
  • Process by which the brain actively selects, organizes and assigns meaning to incoming neural messages sent from sensory receptors
  • Example…
    • Sensory point of view – the American flag is a mass of red, white, and blue colors and horizontal and vertical lines
    • Perception – you interpret these splotches of color and array of lines as the American flag
basic principles of sensation
Basic Principles of Sensation
  • Transduction
    • Process by which sensory receptors convert the incoming physical energy of stimuli (ie. Light waves) into neural impulses the brain can understand
    • Philip Zimbardo – “process seems so immediate and direct that it fools us into assuming the sensation of redness is characteristic of a tomato or the sensation of cold is a characteristic of ice cream”
    • In reality…sensations such as “red” or “cold” occur only when neural impulses reach the brain
basic principles of sensation1
Basic Principles of Sensation
  • Absolute Threshold
    • min. amount of a stimulus that an observer can reliably detect at least 50% of the time
    • Anything less goes unnoticed


    • Vision – candle flame 30 miles (clear, dark night)
    • Hearing – watch ticking 20 feet away
    • Smell – one drop of perfume in a 3-room apartment
    • Taste – 1 tsp. of sugar in 2 gallons of water
    • Touch – a bee wing dropped on your back from a cm
basic principles of sensation2
Basic Principles of Sensation
  • Difference Threshold
    • Minimal difference needed to notice a stimulus change
    • aka – JND / “Just Noticeable Difference”
    • Example – TV volume at 50, take it down a notch until you notice the difference
basic principles of sensation3
Basic Principles of Sensation
  • Weber’s Law
    • German Psychologist – Ersnt Weber (1795-1878)
    • Observed the JND will vary dependent on its relation to the original stimulus
    • The size of the JND is proportional to the strength of the original stimulus
    • Example
      • Weight lifter bench pressing 50 lbs would notice an additional 5 pounds
      • Weight lifter bench pressing 500 lbs would not notice an additional 5 pounds
basic principles of sensation4
Basic Principles of Sensation
  • Signal Detection Theory
    • Problem with traditional thresholds
      • Assumed if signal exceeded one’s AT, it would be sensed / if below one’s AT, it would not
      • Did not account for characteristics of the perceiver
        • Example – notice change in volume because that is the focus
    • A new theory
      • No single absolute threshold
      • Detection is based on a combination of stimulus intensity, background noise, and a person’s physical condition, biases, and level of motivation
      • EX – a soldier in wartime would detect fainter stimuli than one in peacetime
basic principles of sensation5
Basic Principles of Sensation
  • Signal Detection Theory cont.
    • When using in experiments, psychologists sort the trials into one of four categories…
    • Signal is present – the person can decide that it present or absent (called hits or misses)
    • Signal is absent – the person can still decide that the signal is either present or absent (called false alarms or correct rejections)
basic principles of sensation6
Basic Principles of Sensation
  • Sensory Adaptation
    • Occurs when a constant stimulus is presented for a length of time. When this happens receptors fire less frequently and the sensation often fades or disappears.
    • Examples…
      • Jogger puts on a new pair of shoes, he or she immediately notices the different feel. However, after going for a jog, he or she does not notice the difference
      • Swimmer dives into a pool, you notice the water is chilly. However, after swimming for a while, you do not notice the water temperature
the human visual system
The Human Visual System
  • Our most important and complex sense!
  • Transduces light waves into neural messages that the brain processes into what we consciously see.
the human visual system1
The Human Visual System
  • From the Cornea to the Retina…
  • Cornea
    • Light waves from the outside world first enter through
    • Clear membrane / protects eye / helps gather and direct incoming light waves
  • Pupil
    • Small opening in middle of iris
    • Changes size to let in different amounts of light
the human visual system2
The Human Visual System
  • From the Cornea to the Retina…
  • Iris
    • Colored part of the eye
    • Ring of muscle tissue that contracts or expands to control the size of the pupil (respond to light and emotions)
    • Sympathetic (dilate) Parasympathetic (constrict)
the human visual system3
The Human Visual System
  • From the Cornea to the Retina…
  • Lens
    • Transparent structure behind the pupil that focuses and bends light as it enters the eye
    • Accommodation – change in the curvature of the lens that enables the eye to focus on objects at various distances (eye adjusts itself)
the human visual system4
The Human Visual System
  • Nearsightedness (Myopia)
  • Visual acuity problem that results when the cornea and lens focus an image in the front of the retina
  • As a result, distant objects appear blurry
  • 25% of US population
the human visual system5
The Human Visual System
  • Farsightedness (Hyperopia)
  • Visual acuity problem that results when the cornea and lens focus an image behind the retina
  • As a result, objects near the eye appear blurry
  • 25% of the US population
the human visual system6
The Human Visual System
  • Retina
  • Light-sensitive membrane at the back of the eye
  • Contains millions of sensory receptors for vision
  • Transduction of light waves into neural messages occurs
the human visual system retina
The Human Visual System - Retina



Photoreceptors in the retina

Sensitive to colors and bright light

Concentrated in the center of the retina (fovea)

Images that do not fall on the fovea tend to be perceived as blurry or indistinct

  • Photoreceptors in the retina
  • Sensitive to dim light but not to color
  • Allow you to see in poorly lit environments
  • Cats have better night vision than humans because they have a higher portion of rods to cones than humans
the human visual system7
The Human Visual System
  • Retina…
  • Bipolar Cells – specialized neurons that connect rods and cones with the ganglion cells
  • Ganglion Cells – specialized neurons that connect to the bipolar cells (bundled axons form the optic nerve)
the human visual system8
The Human Visual System
  • Blind Spot
  • Point where the optic nerve leaves the eye there are no rods or cones
  • Because there are no rods or cones, we have a tiny hole or blind spot
  • Normally we are unaware because our eyes are always moving
the human visual system9
The Human Visual System
  • Visual Cortex
  • Optic nerve carries visual information to
  • Lies in the occipital lobe at the back of the brain
the human visual system10
The Human Visual System
  • Color Vision
    • Humans can identify about 7 million different color combinations
    • Two color vision theories
      • Trichromatic or three-color theory
      • Opponent-process theory
the human visual system11
The Human Visual System
  • Trichromatic Theory (three-color)
    • Three primary colors (red, green, blue)
    • Any color can be created by combining light waves of these three colors
    • Hermann von Helmholtz (1821-1894) proposed that the eye must have color receptors that correspond to these primary colors
      • Has been proven that the retina does have cones especially sensitive to the three primary colors
the human visual system12
The Human Visual System
  • Opponent-process theory
    • The Trichromatic theory explains how color processing works in cones, but not what happens in the ganglion cells and the rest of the visual system
    • The ganglion cells process color in opposing pairs
      • Red-green / black-white / blue-yellow
    • Visual cortex also encodes color in terms of these three pairs
    • Explains afterimages
the human visual system13
The Human Visual System
  • Afterimage
  • Visual experience that occurs after the original source of stimulation is no longer present
  • Example
    • green, black, yellow flag
    • red, white, blue flag
the human visual system14
The Human Visual System
  • Color Blindness
    • Genetic disorder (recessive – X) that prevents an individual from distinguishing between certain colors
    • Have a deficiency in their cones
    • Most common form is red-green deficiency (certain pigments)
    • Rare to see no color at all (only about 500 reported cases ever!!)
    • 1 in 10 men / very few women
the human auditory system
The Human Auditory System
  • Hearing plays a role in language development and social interactions. It also alerts us to dangerous situations
  • It transduces sound waves into neural messages that the brain then processes into what we consciously hear
  • aka – audition
  • Amplitude – loudness
  • Frqeuency - pitch
the human auditory system1
The Human Auditory System
  • Outer Ear
    • Pinna
      • Flap of skin and cartilage
      • Catches sound waves and channels them to the auditory canal
    • Auditory Canal
      • Sound waves travel down and bounce into the ear drum
    • Eardrum (tympanic membrane)
      • Tightly stretched membrane located at the end of the auditory canal
      • Vibrates when hit by sound waves (match the intensity and frequency of sound waves)
the human auditory system2
The Human Auditory System
  • Middle Ear
    • Amplifies sound waves
    • Hammer, anvil, and stirrup
      • Three tiny bones
      • Joint action doubles the amplification of sound
    • Oval Window
      • Stirrup transmits the amplified vibrations to oval window
      • Small membrane separating the middle ear from inner ear
      • Relays vibrations to the cochlea
the human auditory system3
The Human Auditory System
  • Inner Ear
    • transduces sound waves into neural messages
    • Cochlea
      • Spiral-shaped, fluid filled structure that contains the basilar membrane and hair cells
      • Greek word for “snail”
    • Basilar membrane
      • Runs length of cochlea / holds hair cell receptors
    • Hair cells
      • Sensory receptors embedded in basilar membrane
      • Transduce the physical vibration of sound waves into neural impulses
the human auditory system4
The Human Auditory System
  • Brain
  • As hair cells bend, they stimulate the cells of the auditory nerve
  • The auditory nerve carries the neural impulse to the thalamus and then to the temporal lobe’s auditory cortex
distinguishing pitch highness lowness
Distinguishing Pitch (highness/lowness)
  • Frequency Theory
  • Basilar membrane vibrates the same frequency as sound waves
  • Explains how low frequency sounds are transmitted
  • Does not explain faster high frequency sounds (neurons cannot fire faster than 1000 times per second)
  • Place Theory
  • Different frequencies excite different hair cells at different locations along the basilar membrane
  • High-frequency sounds cause max vibrations near the stirrup
  • Lower-frequency sounds cause maximum vibrations at the opposite end

Frequency Theory ^^^

  • Place Theory >>>
loss of hearing most due to damage or old age
Loss of Hearing*most due to damage or old age

Conductive Deafness

Nerve (Sensorineural) Deafness

Caused by damage to the cochlea, hair cells, or auditory nerve

Exposure to noises such as headphones playing at full blast can damage cells and cause permanent hearing loss

Hearing aids cannot help nerve deafness since damage to hair cells and auditory nerve is almost always irreversible

  • Caused when the tiny bones in the middle ear are damaged and cannot transmit sound waves
  • Hearing aides can amplify sound and help overcome
the chemical sense
The Chemical Sense
  • Smell and taste
  • Respond to chemical molecules rather than forms of energy (light and sound waves)
  • Smell and taste receptors are located near each other and often interact
  • We often have difficulty separating the two sensations
the chemical senses
The Chemical Senses
  • Smell or Olfaction
    • mucous membrane at the top of each nostril contain receptor cells that absorb airborne chemical molecules
    • Olfactory receptors detect over 10,000 distinct smells (flagrant flowers to leaking gas)
    • Receptor cells communicate neural messages to the olfactory bulb
    • Unlike other sensations, impulses do not go through the thalamus
    • Nerve fibers connect at the brain near the amygdala and then to the hippocampus – limbic system (explains why smell is so closely related to vivid memories and emotions)
the chemical senses1
The Chemical Senses
  • Taste or Gustation
    • tongue covered with bumps called papillae
    • Papillae are covered with taste buds (taste buds are also found in palate and back of throat)
    • Major taste sensations
      • Sweet, sour, salty, bitter, umami (proteins in meats)
    • Least critical of senses, but plays role in survival by helping us avoid harmful substances
    • Aided by smell, plays a role in enjoyment
skin and body senses
Skin and Body Senses
  • Skins Senses
    • Largest sense organ
    • Protects our internal organs, holds body fluids, produces sensations of touch, warmth, and cold and provides essential info about pain
  • Body Senses
    • Provide essential information about your position and orientation in space
skins senses
Skins Senses
  • Touch
    • Receptors not evenly distributed on body
    • i.e.. more densely concentrated in hands, face, and lips than on leg or back
    • Plays role in human relationships – help communicate feelings of support, conformity, love
  • Pain
    • Unpleasant sensation of physical discomfort or suffering
    • Plays a key role in survival by warning about potential or actual injuries
skin senses
Skin Senses
  • Gate-control Theory of Pain
    • The brain regulates pain by sending signals down the spinal cord that either open of close sensory pathways (gates)
    • If the brain signals the gates to open, pain is experienced or intensified
    • If the brain signals the gates to close, pain is reduced
    • Psychological factors such as anxiety and fear can intensify pain while positive emotions such as laughter can help minimize pain
the vestibular sense
The Vestibular Sense
  • Provides a sense of balance and equilibrium
  • Inner ear contains receptors that are especially important for maintaining balance
  • The semicircular canals are filled with fluids and lined with hairlike receptor cells that shift in response to motion
    • They provide the brain with information about the body’s posture and head positions
  • Vestibular and auditory systems are alike in that both depend upon hair cells to transduce a stimulus into a neural message
  • Selecting where to direct our attention is the first step in perception
  • Selective Attention and feature detectors help explain why we pay attention to some stimuli in our environment and not to other
selective attention
Selective Attention
  • Cognitive process of selectively concentrating on one or more aspects of the environment while filtering out or ignoring other information
  • Example
    • Gavin is playing a new video game with his friend. He doesn’t hear his mother call for him to come to dinner. However, he does respond when his cell phone rings because he is expecting a call from his girlfriend
selective attention1
Selective Attention
  • Perceptual Adaptation - ability of the body to adapt to an environment by filtering out distractions.
    • Example - someone who lives near a train can perceptually adapt such that they can ignore the train whistle in order to sleep at night. If someone came to visit, however, they would not have perceptually adapted to the train and would most likely not be able to sleep.
  • Sensory Adaptation – decreasing responsiveness to a stimuli due to constant stimulation
    • Example – you felt your socks when you put them on, but you stopped feeling them after a while
  • Sensory Habituation – our perception of sensations is partially due to how focused we are on them
    • Example – you do not focus on your socks anymore ^^^^
selective attention2
Selective Attention
  • Cocktail Party Effect
    • being able to focus one's auditory attention on a particular stimulus while filtering out a range of other stimuli, much the same way that a partygoer can focus on a single conversation in a noisy room
    • Spotlight Effect - reading
  • Cocktail Party Phenomenon
    • situation in which one can attend to only part of a noisy environment, yet highly pertinent stimuli such as one's own name can suddenly capture attention
change blindness
Change Blindness
  • psychological phenomenon that occurs when a change in a visual stimulus goes unnoticed by the observer
  • Example…an individual fails to notice a difference between two images that are identical except for one change
feature detectors
Feature Detectors
  • Brain has specialized neurons called feature detectors that respond only to certain stimuli
  • In occipital lobe’s visual cortex
  • Respond to special features of an image (angles, lines, curves, movements)
  • Example … area behind ear perceives faces
    • Prosopagnosia – damage to this area causes inability to detect differences in faces
    • Cannot recognize own face in mirror!
gestalt principles of organization
Gestalt Principles of Organization
  • Max Wertheimer founded in early 1900s
  • We process sensations according to perceptual rules
  • These rules create whole perceptions that are meaningful, symmetrical, and as simple as conditions will allow
figure ground perception
Figure-Ground Perception
  • Most fundamental Gestalt Principle
  • Figure – main element of a scene that clearly stands out
  • Ground – less distinct background of a scene
  • Example – on this page…the letters constitute the figure, while the white page is the ground
  • There is a tendency to perceive objects of a similar size, shape or color as a unit or figure
  • Example – crowd at football game is a wide assortment of different people; you organize them into home fans, visitor fans, band members, cheerleaders
  • There is a tendency to perceive objects that are physically close to one another as a single unit
  • Example – home fans and visiting fans usually group themselves on opposing sides of the stadium; you would group visiting fans into one homogenous group
  • Tendency to fill in the gaps in an incomplete image
  • Example – scoreboards have HOME and VISITORS on them. If it said HO E and VISI ORS, you would fill in the missing letters M and T.
phi phenomomenon
Phi Phenomomenon
  • Illusion movement created by presenting still pictures in rapid succession
  • Example - TV
depth perception
Depth Perception
  • Ability to perceive 3-D space and accurately judge distance
  • It is possible to use sound and even smell to judge distance, we rely heavily on vision
visual cliff experiment
“Visual Cliff” Experiment
  • Famous experiment, Eleanor Gibson
  • Placed infants old enough to crawl on a Plexiglas-topped table
  • Side 1 – high-contrast red-and-white check cloth flush against the underside of the glass (appearance of solid surface)
  • Side 2 – placed the same material 4-feet below the glass
  • Created an illusion of “deep end” with a “visual cliff”
visual cliff experiment1
“Visual Cliff” Experiment
  • Infants almost always refused to venture beyond the shallow side of the visual cliff
  • They turned away from the “deep end” even when their mothers held a spinning toy and encouraged them to crawl forward
  • Supports the conclusion that depth perception in humans is innate that emerges during infancy
monocular one eye depth cues
Monocular (one eye) Depth Cues
  • Linear Perspective
  • Parallel lines appear to converge toward a vanishing point as they recede into the distance
monocular one eye depth cues1
Monocular (one eye) Depth Cues
  • Aerial Perspective
  • Distant objects appear hazy and blurred compared to close objects
monocular one eye depth cues2
Monocular (one eye) Depth Cues
  • Relative Size
  • Two or more objects are assumed to be similar in size, the object that appears larger is perceived as being close
monocular one eye depth cues3
Monocular (one eye) Depth Cues
  • Motion Parallax
  • as you move, you use the speed of passing objects to estimate the distance of the objects
  • Example – when you are driving on an interstate, nearby poles, fences, and roadside signs seem to zip by faster than distant hills
binocular both eyes depth cues
Binocular (both eyes) Depth Cues
  • Convergence
  • Closer the object, the more the eyes converge, or turn inward
binocular both eyes depth cues1
Binocular (both eyes) Depth Cues
  • Retinal Disparity
  • Separation of the eyes cause different images to fall on each retina
  • When two retinal images are very different, we interpret the object as being close by.
  • When two retinal images are more nearly identical, the object is perceived as being farther away
  • A person with only one eye lacks retinal disparity and would have difficulty climbing an irregular set of stairs