Subject: Sensation and Perception

Written and Compiled by the Beyond the Five and ProcrastiNote Team

Last Updated: February 19, 2021

Contents

1 Commentary 3

2 Sensation and Perception

2.1 Principles of Sensation

2.1.1 Processing Sensation 3

2.1.2 Thresholds 4

2.2 Principles of Perception

2.2.1 Perceptual Organization 5

2.2.2 Grouping 5

2.2.3 Perceptual Set 5

2.2.4 ESP (Extrasensory Perception) 6

2.3 Visual Anatomy

2.3.1 The Stimulus Input: Light Energy 6

2.3.2 The Eye 6

2.4 Visual Perception

2.4.1 The Eye-to-Brain Pathway 7

2.4.2 Color Processing 7

2.4.3 Feature Detection 8

2.4.4 Parallel Processing 8

2.4.5 Depth Perception 8

2.4.6 Binocular Cues 8

2.4.7 Monocular Cues 9

2.4.8 Perceptual Constancy 9

2.4.9 Perceptual Interpretation 9

2.5 Auditory Sensation and Perception

2.5.1 Hearing 10

2.5.2 Stimulus Input: Sound Waves 10

2.5.3 The Ear 10

2.5.4 Hearing Different Pitches 11

2.6 Chemical Senses

2.6.1 Taste 12

2.6.2 Smell 12

2.7 Body Senses

2.7.1 Pain 12

2.7.2 Body Position and Movement 13

2.7.3 Sensory Interaction 13

3 Images 14

4 TL;DR 15

A Credits 17

A.1 Contributions

A.2 External Sources

A.3 Image Credits

B Extra Resources 17

1 Commentary

This unit in AP Psychology contains information about how humans understand and process

their surroundings using their senses and transform those observations into perceptions that

impact our behavior and thought processes. This unit involves the ways humans experience and

process stimuli, roles culture, expectations, and experience play in perception, and systems of the

senses and how sensory disorders arise. On the AP Exam, this generally represents 6%-8% of all

questions.

2 Sensation and Perception

2.1 Principles of Sensation

2.1.1 Processing Sensation

● Prosopagnosia - face blindness; the inability to recognize people’s faces (remember that

part of the temporal lobe is responsible for facial recognition).

● 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.

● Bottom-up processing - analysis that begins with the sensory receptors and works up to

the brain’s integration of sensory information. Enables your sensory systems to detect the

lines, angles, and colors that form an object.

● Top-down processing - information processing guided by higher-level mental processes,

as when we construct perceptions drawing on our experience and expectations. It enables

us to interpret what our senses detect.

● Selective attention - the focusing of conscious awareness on a particular stimulus. A

particular type of it is called the cocktail-party effect - your ability to attend to one voice

among a sea of other voices.

- Inattentional blindness - failing to see visible objects when our attention is

directed elsewhere. Maybe you have seen this before, but there’s a video where

they tell you to focus on how many times a basketball team wearing a certain

colored jersey passes the ball. A gorilla walks through the setting, and if you

didn’t notice it, that would demonstrate this concept.

- Change blindness - failing to notice changes in the environment, a form of

inattentional blindness.

2.1.2 Thresholds

● Absolute threshold - the minimum amount of 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). On the AP exam, they

frequently ask a question about a weary wildlife ranger who hears the sounds of a twig

snapping more vividly. This is because he is more alert of his surroundings.

● Subliminal - below one’s absolute threshold for conscious awareness.

● Difference threshold - the minimum difference between two stimuli required for detection

50 percent of the time. (just noticeable difference). For instance, if you’re listening to

music at 40 decibels and increase it to 41 decibels, you may not notice the difference.

When you do notice the difference, subtract the two values.

● 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. For instance, weight - 2%,

intensity - 8%.

● Priming - the activation, often unconsciously, of certain associations, thus predisposing

one’s perception, memory, or response.

● Sensory adaptation - diminished sensitivity as a consequence of constant stimulation. For

instance, staying in a car when someone smokes, or getting acclimated to the temperature

of the water.

● Psychophysics - The study of the relationships between the physical characteristics of

stimuli, such as their intensity, and our psychological experience of them. For instance,

the texture of the buttery popcorn and its taste.

2.2 Principles of Perception

2.2.1 Perceptual Organization

● Perception - the process of organizing and interpreting sensory information, enabling

us to recognize meaningful objects and events.

● In the early 20th century, a group of German psychologists noticed that people who

were given a cluster of sensations tend to organize them into a gestalt - an organized

whole.

- In perception, the whole may exceed the sum of its parts.

● Figure-ground - the organization of the visual field into objects that stand out from

their surroundings. I.e. Necker cube picture

2.2.2 Grouping

● The perceptual tendency to organize stimuli into coherent groups.

● Proximity - we group nearby figures together.

● Continuity - We perceive smooth, continuous patterns rather than discontinuous ones.

● Closure - we fill in gaps to create a complete, whole object.

2.2.3 Perceptual Set

● Perceptual Set - A mental predisposition to perceive one thing and not another -

ABC, 12, 13,14

● Our immediate context, and the motivation and emotion we bring to a situation

affect our interpretation of it. For instance, when climbing a staircase, it seems

steeper when you are thirsty. Or hearing sad music can predispose people to

perceive a sad meaning in spoken homophonic words.

2.2.4 ESP (Extrasensory Perception)

● Extrasensory perception - the controversial claim that perception can occur apart

from sensory input - includes telepathy, clairvoyance (perceiving remote events,

such as a house on fire in another state), and precognition (perceiving future

events, such as an unexpected death in the next month)

● Parapsychology - the study of paranormal phenomena, including ESP and

psychokinesis.

● Skeptics argue that to believe in ESP, you must believe the brain is capable of

perceiving without sensory input and researchers have been unable to replicate

ESP phenomena under controlled conditions.

2.3 Visual Anatomy

2.3.1 The Stimulus Input: Light Energy

● Wavelength - the distance from one peak of light or sound wave to the peak of the

next. Short wavelength - blue, long wavelength - red.

● Hue - the dimension of color that is determined by the wavelength of light.

● Intensity - the amount of energy in a light wave or sound wave, which influences

what we perceive as brightness or loudness, determined by the wave’s amplitude.

Bright colors - great amplitude; small amplitude - dull colors

2.3.2 The Eye

● Cornea - the clear, protective outer layer, covering the pupil and iris.

● 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.

● Lens - the transparent structure behind the pupil that changes shape to help focus

images on the retina.

● Retina - Where transduction in the eye takes place. The light sensitive inner surface

of the eye, containing the photoreceptor cells that begin the processing of visual

information. Rods and cones.

● Accommodation - the process by which the eye’s lens changes shape to focus near or

far objects on the retina.

2.4 Visual Perception

2.4.1 The Eye-to-Brain Pathway

● 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. Low color and detail sensitivity. Located in the periphery of the retina.

● Cones - retinal receptors that are concentrated near the center of the retina and

function in daylight or in well-lit conditions. Detect fine detail and give rise to

color sensations. High color and detail sensitivity, and concentrated in the center

of the retina.

● 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.

● Fovea - the central focal point in the retina, around which the eye’s cones cluster.

● Transduction pathway - rods and cones → bipolar cells → ganglion cells → optic

nerve → thalamus → visual cortex → image.

2.4.2 Color Processing

● Young-Helmholtz Trichromatic Theory - theory that the retina contains three

different types of color receptors - sensitive to red, green, and blue - which, when

stimulated in combination, can produce the perception of any color.

● However, this theory does not explain why we see afterimages.

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

blue-yellow, black-white) enable color vision. Some cells are stimulated by green

and inhibited by red, and vice versa. If you were to stare at a green, black, and

yellow flag, the after image would be the colors of the American flag.

2.4.3 Feature Detection

● David Hubel and Torsten Wiesel - feature detectors - nerve cells in the brain’s visual

cortex that respond to specific features of the stimulus, such as shape, angle, or

movement. Feature detectors pass this specific information to other cortical areas, where

teams of cells called supercell clusters respond to more complex patterns.

2.4.4 Parallel Processing

● We talked about it in an earlier unit, but recall it is processing many aspects of a problem

simultaneously. To recognize something, we simultaneously process the motion, form,

depth, color, etc. of it to form a picture.

● Summary of visual processing: Scene → retinal processing → feature detection →

parallel processing → recognition

2.4.5 Depth Perception

● The ability to see objects in three dimensions although the images that strike the

retina are two-dimensional, allowing us to judge distance.

● Eleanor Gibson and Richard Walk created a visual cliff - a laboratory device for

testing depth perception in infants and young animals.

● Taught us that depth perception is innate, but some people develop it faster than

others.

2.4.6 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.

● Convergence is another binocular cue, in which the inward angle of the eyes focuses on a

near object.

2.4.7 Monocular Cues

● A depth cue that is available to each eye alone.

● Phi phenomenon - an illusion of movement created when two or more adjacent lights

blink on and off in quick succession.

● Stroboscopic movement - our brain also perceives a rapid series of slightly varying

images as continuous movement. I.e. Bugs bunny, cartoons, etc.

● Relative height - we perceive objects higher in our visual field as farther away.

● Relative motion - As we move, objects that are actually stable may appear to move.

● Relative size - if we assume two objects are similar in size, most people perceive the one

that casts the smaller retinal image as farther away.

● Linear perspective - Parallel lines appear to meet in the distance. The sharper the angle of

convergence, the greater the perceived distance.

● Interposition - If one object partially blocks our view of another, we perceive it as closer.

● Light and shadow - shading produces a sense of depth.

2.4.8 Perceptual Constancy

● Perceiving objects as unchanging even as illumination and retinal images change. This is

a top down process.

● Color constancy - perceiving familiar objects as having consistent color, even if changing

illumination alters the wavelengths reflected by the object.

● Relative luminance - the amount of light an object reflects relative to its surroundings.

● Size constancy - we perceive an object as having an unchanging size, even when our

distance from it varies.

● Shape constancy - we perceive the form of familiar objects as constant even while our

retinas receive changing images of them.

● Ames Room - illusion of size, in which our distance from the people causes one to look

bigger and another smaller.

2.4.9 Perceptual Interpretation

● German philosopher Immanuel Kant maintained that knowledge comes from our inborn

ways of organizing sensory experiences.

● John Locke argued that through our experiences, we learn how to perceive the world.

● Critical period - Wiesel and Hubel - there is an optimal period when exposure to certain

stimuli or experiences is required for proper maturation.

● Perceptual adaptation - the ability to adjust to changed sensory input, including an

artificially inverted or displaced visual field.

2.5 Auditory Sensation and Perception

2.5.1 Hearing

● Audition - the sense or act of hearing

2.5.2 Stimulus Input: Sound Waves

● Frequency - the number of complete wavelengths that pass a point in a given time; short

wavelength = high frequency → high-pitched sounds, and vice-versa.

● Pitch - a tone’s experienced highness or lowness, depending on frequency.

● Great amplitude → loud sounds; and vice-versa.

● Timbre - a tone quality; allows you to distinguish between instruments, such as choir or

musical instruments.

2.5.3 The Ear

● The process of hearing begins when sound waves strike your eardrum, causing the tight

membrane to vibrate.

● Middle ear - the chamber between the eardrum and cochlea containing three tiny bones

(hammer, anvil, and stirrup, or malleus, incus, and stapes) 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 travelling through

the cochlear fluid trigger nerve impulses. Where transduction in the ear occurs.

● Inner ear - the innermost part of the ear, containing the cochlea, semicircular canals, and

vestibular sacs.

● The incoming vibrations cause the cochlea’s membrane covered opening, the oval

window, to vibrate, jostling the fluid inside the cochlea, causing ripples in the basilar

membrane, bending the hair cells lining its surface.

● Hair cell movements trigger impulses in adjacent nerve cells, whose axons converge to

form the auditory nerve. The auditory nerve carries the neural messages to your thalamus

and to the auditory cortex. Outer ear → middle ear → cochlea → auditory nerve →

thalamus → auditory cortex.

● Sensorineural hearing loss (nerve deafness) - hearing loss caused by damage to the

cochlea’s receptor cells or to the auditory nerves

● Conduction hearing loss - a less common form of hearing loss caused by damage to the

mechanical system that conducts sound waves to the cochlea; i.e. middle ear, eardrum,

etc.

● Cochlear implant - a device for converting sounds into electrical signals and stimulating

the auditory nerve through electrodes threaded into the cochlea.

2.5.4 Hearing Different Pitches

● Place Theory - in hearing, the theory that links pitch we hear with the place where the

cochlea’s membrane is stimulated. High frequencies produce large vibrations near the

beginning of the basilar membrane, and low frequencies vibrated more of the membrane

and were not so easily localized. Therefore, it cannot determine how we hear low-pitched

sounds.

● Frequency theory (temporal theory) - the theory that the rate of nerve impulses travelling

up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch.

However, neurons cannot fire faster than 1000 times per second, in which sound waves

cannot reach that high of frequency per second.

● The theory cannot explain high-pitched sounds then. Therefore, the volley principle was

created, which explains how neurons can alternate firing in rapid succession to achieve a

frequency of above 1000 waves per second.

● Sound localization - the idea that sound waves strike one ear sooner and more intensely

than another, which allows us to understand the relative location as to where it came

from.

2.6 Chemical Senses

2.6.1 Taste

● Gustation - our sense of taste

● Sweet - energy source, salty - sodium essential for physiological processes, sour and

bitter - poisons, and umami - proteins to grow and repair tissue

2.6.2 Smell

● Olfaction - the sense of smell

● During olfaction, odorants bind to receptors, olfactory receptor cells are activated and

send electrical signals, the signals are relayed via converged axons, and the signals are

transmitted to higher regions of the brain.

● The part of the brain that processes smell is near the area that is involved with memory

storage, which may explain why a smell can trigger a memory.

2.7 Body Senses

2.7.1 Pain

● Our experience of pain reflects bottom-up sensations and top-down cognition, since pain

is a biopsychosocial event. This is due to factors, such as placebos, distractions, people

around you, etc.

● Nociceptors - sensory receptors in your skin and muscles that detect hurtful temperatures,

pressure, or chemicals.

● Women are more sensitive to pain than men are. Sorry, women.

● Gate-control theory - the theory that the spinal cord contains a “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.

● Phantom limb sensations - after a limb amputation, without normal sensory input, the

brain may misinterpret and amplify spontaneous but irrelevant central nervous system

activity.

● Tinnitus - the phantom sensation of ringing in the ears that’s accompanied by auditory

brain activity.

2.7.2 Body Position and Movement

● Kinesthesia - our movement sense - our system for sensing the position and movement of

individual body parts.

● Vestibular sense - our sense of body movement and position that enables our sense of

balance. The semicircular canals and vestibular sacs help us with balance. You may feel

dizzy because the fluid in your semicircular canals are not at rest.

2.7.3 Sensory Interaction

● The principle that one sense may influence another, as when the smell of food influences

its taste. For instance, when you are sick, your smell is impaired, which causes food to

taste more bland.

● Embodied cognition - the influence of bodily sensations, gestures, and other states on

cognitive preferences and judgments.

3 Images

Source: Helmenstine, Anna M. (2019, December 02). Structure and Function of the Human Eye. ThoughtCo.Retrieved from: https://www.thoughtco.com/how-the-human-eye-works-4155646

Source: McKinney, Julia. (n.d.). Gcse Psychology. Pinterest. Retrieved from:https://www.pinterest.com/pin/457467274630924247/

Source: (N.d.) 5.3 Hearing. BCcampus. Retrieved from:https://opentextbc.ca/introductiontopsychology/chapter/4-3-hearing/

Source: Matthews, Stephanie. (N.d.) Vision. Slideplayer. Retrieved from: https://slideplayer.com/slide/13540615/

Source: (N.d.) Sound Waves Test – 3/12. Quizlet, uploaded by gracedupree8. Retrieved from:https://quizlet.com/379299977/sound-waves-test-312-diagram/

4 TL;DR

● Sensation - the process by which our sensory receptors and nervous system receive and

represent stimulus energies from our environment.

● 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.

● Selective attention - the focusing of conscious awareness on a particular stimulus. A

particular type of it is called the cocktail-party effect - your ability to attend to one voice

among a sea of other voices.

● Absolute threshold - the minimum amount of stimulus energy needed to detect a

particular stimulus 50 % 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).

● Difference threshold - the minimum difference between two stimuli required for detection

50 percent of the time. (just noticeable difference).

● 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.

● Perception - the process of organizing and interpreting sensory information, enabling us

to recognize meaningful objects and events.

● Figure-ground - the organization of the visual field into objects that stand out from their

surroundings.

● Perceptual Set - A mental predisposition to perceive one thing and not another.

● Extrasensory perception - the controversial claim that perception can occur apart from

sensory input - includes telepathy, clairvoyance (perceiving remote events), and

precognition (perceiving future events).

● Wavelength - the distance from one peak of light or sound wave to the peak of the next.

Short wavelength - blue, long wavelength - red. (High wavelength, short frequency, and

vice versa. For sound waves, high wavelength / low frequency is low pitched sounds.

● Hue - the dimension of color that is determined by the wavelength of light.

● Intensity - the amount of energy in a light wave or sound wave, - what we perceive as

brightness or loudness, determined by the wave’s amplitude. Bright colors - great

amplitude, vice versa. For sound waves, great amplitude = loud sounds, and vice versa.

● Monocular cue- depth cue that is available to each eye alone (From Phi. to Inter.)

● Phi phenomenon - an illusion of movement created when two or more adjacent lights

blink on and off in quick succession.

● Stroboscopic movement - our brain also perceives a rapid series of slightly varying

images as continuous movement. I.e. Bugs bunny, cartoons, etc.

● Relative height - we perceive objects higher in our visual field as farther away.

● Relative motion - As we move, objects that are actually stable may appear to move.

● Relative size - if we assume two objects are similar in size, most people perceive the one

that casts the smaller retinal image as farther away.

● Linear perspective - Parallel lines appear to meet in the distance. The sharper the angle of

convergence, the greater the perceived distance.

● Interposition - If one object partially blocks our view of another, we perceive it as closer.

● 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.

● Volley principle - explains how neurons can alternate firing in rapid succession to achieve

a frequency of above 1000 waves / sec. (Place and Frequency don’t explain both)

● Conduction hearing loss - a less common form of hearing loss caused by damage to the

mechanical system that conducts sound waves to the cochlea; i.e. middle ear, eardrum.

● Kinesthesia - our movement sense - our system for sensing the position and movement of

individual body parts.

● Vestibular sense - our sense of body movement and position that enables our sense of

balance. The semicircular canals and vestibular sacs help us with balance. You may feel

dizzy because the fluid in your semicircular canals are not at rest.

A Contents

A.1 Contributions

● Drafted by D. Gormezano

● Contributions by:

- ProcrastiNote. Team

A.2 External Sources

BCcampus

Google

Pinterest

Quizlet

Slideplayer

ThoughtCo

A.3 Image Credits

● Clock: Veronica Cruz

B Extra Resources

All resources mentioned retain the same licensing as the original creators intended. The

ProcrastiNote Team has checked every one of these to make sure that our usage of the materials

remains within the legal realm. If you are the owner of these materials and you believe there is a

mistake in our citations, please contact us at official.procrastinote@gmail.com . Thanks!