AP Psychology/Sensation and Perception

Introduces how humans perceive and process the world around them via their senses and convert those observations into perceptions that influence how we think and behave.[1]

Objectives and SkillsEdit

Topics may include:[2]

  • Basic principles of how humans experience and process stimuli
  • The role of experience and culture in perception
  • The mechanisms of the 5 senses and sensory disorders

Study NotesEdit

  • Sensation - How we detect physical energy from the environment and encode it as neural signals.
  • Perception - Process of organizing and interpreting sensory info.
  • Transduction - Conversion of one form of energy to another form. There are 3 steps every time you convert sensory energy to get the info to your brain.
  1. Receive (sensory stimulation)
  2. Transform (stimulation --> neural impulses)
  3. Deliever (neural info to your brain)
  • Psychophysics - Study of the relationship between physical characteristics of stimuli and our psychological experience with them. Oldest field in psychology.
  • Absolute Threshold (Gustav Fechner) - Minimum stimulation needed to detect a particular stimulus 50% of the time. Example: Vision - A single candle flame from 30 miles on a dark, clear night; Hearing - Hear a watch's tick in a quiet environment at 20 feet.
  • Signal Detection Theory - Theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulus (noise).
  1. Present - Yes: Hit
  2. Present - No: Miss
  3. Absent - Yes: False Alarm
  4. Absent - No: Correct Rejection
  • Subliminal Threshold - When stimuli are below one's absolute threshold for conscious awareness (not enough to be consciously aware of something).
  • Sensory Adaptation - Diminished sensitivity as a consequence of constant stimulation (put a band-aid on your arm for a while then you won't realize it is there).
    • Habituation - Tendency of the brain to stop attending to constant, unchanging info.
    • Microsaccades - Constant movement of the eyes (tiny vibrations) that you don't understand.
  • Phototransduction - Light energy [converts] --> neural impulses the brain can understand.
  • Short wavelength - High frequency (blue, high-pitched) = Smurf
  • Long wavelength - Low frequency (red, low pitched) = Clifford
  • Visible Light - Roy G. Biv
  • Intensity - Great amplitude (bright, loud)/Small amplitude (dull, soft)
  • Difference Threshold - Minimum difference between 2 stimuli required for detention 50% of the time (just noticeable difference [JND]).
  • Weber's Law - Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Created by Ernst Weber [300 pound person vs. 100 pound person losing 10 pounds].

Bottom-Up ProcessingEdit

Analysis that begins with sensory receptors and works up to the brain's integration of sensory info.

  • Anagram - Starting with individual pieces (letters) and works up to make bigger pieces (words). (GEGS --> EGGS).
  • When you see a mosquito, you see a mosquito and then interprets the sensor receptor's info. You then saw it away.
  • SMALL --> BIG

Perception directs cognition and/or behaviour

Top-down ProcessingEdit

Information processing is guided by higher-level mental processes, which is influenced by our own experience and expectations. You see the whole image and see the individual pieces.

Perception constructed by cognition

  • Bathroom in the dark: You don't need to turn the lights on in the middle of the night because you're guided by your expectations in the bathroom.


  • Cornea - Where light enters
  • Pupil - Small adjustable opening
  • Irus - Colour of the eye; surrounds the pupil and is the muscle that expands and contracts to change the size of the pupil for light.
  • Lens - Changes shape to help focus on images on the retina.
  • Process of Acommadation - Reflex that changes the lens' shape to focus near or far objects on the retina.
  • Retina [contains the visual receptor cells] - Inner surface of the eye that contains sensory receptors, called rods and cones, that process visual info and sends it to the brain. Transduction takes place. If the retina falls/dislocated, then you can't see anything.
  • Blind Spot - Optic nerve leaves the eye - no receptors here.
  • Optic Nerves - Long axons that carry neural impulses from the eye to the brain.
  1. Light is gathered from photoreceptors in our eyes
  2. Light --> Neural messages
  3. Sent to the occipital lobe in the brain for translation
  4. Transduction takes place in retina
  5. Cones and Rods interpret up to 5 million colors


Point of central focus on the retina [you're seeing stuff upside down if you have good lens. If you're near-sighted, the image is upside down and closer to the lens. The far-sighted is the opposite of this.

  • Optic Chiasm - X-shaped structure formed by the crossing of the optic nerves in the brain.
  • Feature Detectors - Nerve cells in the visual cortex that responds to specific features, such as edges, angles and movement. A fMRI helps us locate feature detectors. Made by David Hubel and Torsten Wiesel [Shapes, Angles, Movements].
  • Parallel Processing - Processing of several aspects of the stimulus simultaneously.
  • Cones - Retinal receptors cells concentrated near the center of the retina. Detects fine detail and color. Low sensitivity to dim light (dark).
  • Rods - Retinal receptor cells that detect black, white and gray; necessary for peripheral and twilight vision. High sensitivity to dim light.
  • 120 mil
  • Peripheral
  • High sensitivity to dim light
  • Low color/detail sensitivity
  • 6 mil
  • Center
  • Low sensitivity to dim light.
  • High color/detail sensitivity.

Vision IssuesEdit

  • Cataracts - Clouding of the lens of the eye (affects color vision).
  • Retinopathy - Damage to the small blood vessels begins to leak and causes floaters.
  • Gluacoma - Fluid pressure builds up inside the eye, damaging the optic nerve; causes blurred vision/loss of peripheral vision.
  • Macular Degeneration - Inability to see objects clearly/distorted.
  • Young-Helmholtz Trichomatic Theory - Retina is sensitive to red, blue and green colors. Color blindness causes people to be blind to green/red colors.
  • Opponent Process Theory - Theory that opposing retinal processes enable color vision. [Red --> Green], [Yellow --> Blue] and [White --> Black].
  • Color Constancy "is the tendency of objects to appear the same colour even under changing illumination. A yellow banana appears yellow whether you see it in the tungsten light of the kitchen or in sunlight outdoors." https://www.cell.com/current-biology/pdf/S0960-9822(07)01839-8.pdf


  • Place Theory "is a theory of hearing which states that our perception of sound depends on where each component frequency produces vibrations along the basil membrane. Therefore, the pitch of a pure tone would be determined by where the membrane vibrates." https://psychology.wikia.org/wiki/Place_theory
  • Frequency Theory "is how we hear sounds states that there are pulses that travel up the auditory nerve, carrying the information about sound to the brain for processing, and that the rate of this pulse matched the frequency of whatever tone you are hearing exactly." https://www.alleydog.com/glossary/definition.php?term=Frequency+Theory
  • Volley Principle states that groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analyzed [en.wikipedia].
  • Cochlear Implants - Small device in the ear that electronically stimulates the cochlear nerve (nerve for hearing).
  • Outer Ear - Collect sounds and pass them along the ear.
    • Pinna
    • Ear Canal
  • Middle Ear - Makes sound louder, so that they travel through the liquid of ear.
    • Eardrum (tympanic membrane)
    • 3 bones: Hammer (malleus), Anvil (incus) and stirrup (stapes). These bones are called the auditory ossicles.
  • Inner Ear - Turn physical vibrations into electrical impulses that the brain will understand as sounds (cochlea).
    • Cochlea - Coiled, liquid-filled tube in the inner ear that transforms sound vibrations to auditory signals.
    • Vestibulary System - Help maintain your equilibrium [semicircular canals, vesticular sacs].


Sound consists of two parts: the physical stimulus and the sensation we experience from it. The answer to, "If a tree falls in a forest and no one is around to hear it, does it make a sound?" is that:

  • Yes: It produces a physical stimulus.
  • No: No one is around to receive the physical sensation from it.

Acoustical transduction - Conversion of sound waves into neural impulses in the hair cells of the inner ear.

Hearing LossEdit

  • Conduction Hearing Loss - Causes damage to the mechanical system that conducts sound waves to the cochlea.
  • Sensorineural Hearing Loss - Hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerve (nerve deafness) [damage to cochlea].

When one sense is lacking, the other sense makes up for it.


The sense of touch is a mix of 5 distinct skin senses.

  1. Pressure
  2. Warmth
  3. Cold
  4. Pain
  • Gate-Control Theory - Spinal cord that contains neurological "gates" that either block/allow pain in order for it to be sensed. Skin can either feel cold or pain - not at the same time.
  • Phantom Pain - Pain coming from a body part that is no longer there.


  • Pain tells the body that something has gone wrong, usually pain resulting from damage to the skin and other tissues.
  • The sensitive ends of pain neurons are stimulated in the skin or other tissues, sending neural messages to your brain.


  • Sweet
  • Sour
  • Salty
  • Bitter
  • Umami (Savory)

If you suppress your smell, the taste is poor (sensory interaction). Most damage-resistant sense.

McGurk Effect
  • What we see overrides what we hear (mouth movement)


Odors enter the nasal cavity to stimulate 5 mil receptors to sense smell. Smell goes to the olfactory bulb.

  • Kinesthesis - Sense of our body parts' position and movement.
  • Vestibular Sense - Monitors the head (and body's) position.
  • Synthesia - A condition in which stimulation of one sense also evoked another.


  • Selective Attention - Perceptions about objects change from moment to moment.
  • Cocktail Party Effect - Tune irrelevant stuff until something relevant pops up.
  • Inattention Blindness - Refers to the inability to see an object/person in our midst.
  • Change Blindness - Refers to the inability to see a change.
  • Depth Perception - Enables us to judge distance [visual cliff = Eleanor Gibson].
  • Retinal Disparity - Difference between 2 images [the greater the retinal disparity, the closer the object is].
  • Convergence - When 2 eyes move inward to see near objects and outward to see faraway objects.

Monocular CuesEdit

  • Relative Size - Objects = similar size, one that casts a smaller retinal image (smaller) is farther way.
  • Interposition - Objects that block other objects lens to be seen as closer.
  • Relative Clarity - See hazy objects farther than sharp objects.
  • Texture Gradient - Gradual change from coarse/distinct texture to be fine/indistinct texture signals increasing distance.
  • Relative Height - Perceive objects that are higher as farther away.
  • Relative Motion - As we move, objects that are actually stable may appear to move.
  • Linear Perspective - Parallel lines, such as railroad tracks, appear to meet in the distance.
  • Stroop Effect - Phenomenon that occurs when you must say the color of a word but not the name of the word.
  • Phi Phenomenon - When lights flash at a certain speed they tend to present illusions of motion (stroboscopic movement).
  • Perceptual Constancy - Perceiving objects as unchanging even as illumination and retinal images change.
  • Size-Distance Relationship - Size increases while distance decreases.
  • Perceptual Set - Mental predisposition to perceive one thing and not another.
  • ESP - The controversial claim that perception can occur apart from sensory impact.