This document provides an outline of key topics in sensation and perception, including: - The distinction between sensation, which is the detection of stimuli, and perception, which is the interpretation and organization of sensory information. - The stages of sensation from detection by sensory receptors to transmission to the brain. - Examples of what humans can and cannot detect with their senses. - Concepts like perceptual problems, sensory adaptation, attention, and Gestalt psychology principles of perceptual organization. - Details of the visual, auditory, olfactory, gustatory and somatosensory systems. - Phenomena such as phantom limb pain and purported extrasensory abilities.

1. Chapter Four
Sensation & Perception

2. Ch. 04 Outline, Part 1
Sensation & Perception
• Sensation & Perception
• Stages of Sensation
• What Humans Can’t Detect
• What Humans Can Detect
• Perceptual Problems
• Subliminal Stimuli
• Sensory Adaptation
• Attention
• Gestalt Psychology
• Aspects of Perceptual Organization
• Processing Sensory Data
• Vision
• Vision Properties & Problems

3. Ch. 04 Outline, Part 2
Sensation & Perception, continued
• Visual Organization
• Hearing
• Pitch & Volume
• Hearing Problems
• Smell (Olfaction)
• Taste (Gustation)
• Touch
• Pain
• Phantom Limb Pain
• Kinesthesis
• Psychics & ESP

4. Sensation & Perception
 Sensation: process of detecting, converting and transmitting raw sensory information from the external
and internal environments to the brain
o While your brain floats in complete darkness, your body is bombarded with stimuli from outside.
 Perception: process of selecting, organizing, and interpreting sensory info into meaningful patterns
o Sensing the stimuli is not enough. Our brains must receive, convert and adapt the information into meaningful
representations of the world.

5. Stages of Sensation
1. Sense: receptor cells in sensory organs detect appropriate stimuli
2. Convert: receptor cells convert stimuli (transduction) into neural impulses (action
potentials) which travel via the peripheral nervous system
3. Transmit: the message travels to the brain through different routes, allowing the
brain to differentiate physical stimuli (coding)
4. Perceive: brain assigns meaning to sensory information

6. What Humans Can’t Detect
 Ultraviolet Light
 Microwaves
 X-Rays
 Certain Frequency Sounds (dog whistles, etc..)

7. What Humans Can Detect
 We are consciously aware of only a narrow range of stimuli at one time.
o Absolute Threshold: minimum amount of stimulus (sound, light, etc…) needed to
consciously detect stimulus 50% of the time
o Difference Threshold: minimal difference in stimulus strength (sound, light, etc…) that
is detectable 50% of the time

8. Perceptual Problems
 Illusion: false or misleading perception produced by errors in the perceptual process or by actual
physical distortions.
o When perceptions do not agree with sensations.
o Illusions are NOT the same as hallucinations (false sensory experience WITHOUT external stimuli) or
delusions (false beliefs).

9. Subliminal Stimuli
 Subliminal Stimuli: stimulus below level of perception but can still be sensed by brain, used in
attempts to persuade behavior or belief
o Studies on subliminal perception flash images too quickly for conscious perception (but slowly enough
for the brain to register them at some sensory level).
o Research indicates subliminal stimuli are WEAK and don’t lead to substantial subliminal persuasion
(changes in behavior).

10. Sensory Adaptation
 Sensory Adaptation: when a constant stimulus is presented, the sensory receptors become
less sensitive and fire less frequently
o Suppose you visit a neighbor’s house with 10 cats. You smell the animals, but the owner doesn’t.
o Normally, the senses smell and touch experience sensory adaptation more often. Vision and intense
stimuli do not.

11. Attention
 Cannot pay attention to all stimuli.
 Selective Attention: paying attention to important information and filtering the rest
 Feature Detectors: specialized neurons to respond to specific stimuli, like faces
o Prosopagnosia: inability to identify person by facial features
 Habituation: decrease in responding to repeated stimulation of same stimuli; more
responsive to changes in environment
o Compliments from strangers are more exciting than from long-term partner.
o The song you HATED on first listen might grow on you (or you just hate it less).

12. Gestalt Psychology
 Gestalt Psychology: how the brain organizes sensory impressions into a “form” or “whole”
o Figure-Ground: objects are distinct from the background (example: when you see a rabbit in the grass, the rabbit is
the figure and the grass is the ground)
o Artist have manipulated this organizational system with paradoxical art.

13. Aspects of Perceptual Organization
 Depth Perception: ability to perceive 3-dimensional space using binocular and monocular cues
 Constancies Perception: perceive the environment as stable, despite changes in object’s size, shape, color
and brightness (changing size room)

14. Processing Sensory Data
 Bottom-Up Processing: raw sensory data “sent up” to the brain for higher level analysis
 Top-Down Processing: perceptual analysis starts “at the top” with expectations and knowledge driving
the process of perception
o You learn to read from bottom-up processing of letters and words.
o Now, your aiblity to raed uisng top-dwon prcessoing mkes it psosible to unedrstnad this sntenece
desipte its mnay mssiplllengis.

15. Vision
 Receptor cells in retina (rods and
cones) convert light waves into
messages sent along the optic
nerve
o Pathway for Light: Light -> Cornea -
> Pupil -> Lens -> Retina (Fovea) -
> Optic Nerve

16. Vision Properties & Problems
 Rod Receptors: manage dark adaptation – changing from
sunny to dark environment leaves you temporarily blind
(black and white)
 Cone Receptors: manage light adaptation – changing from
dark to bright environment activate cones (colors)
 Visual acuity problems result from small abnormalities in
the shape of the eye, causing the image not to be in focus
at the retina .
o Nearsightedness: image reaches focus in front of the
retina (can see near objects)
o Farsightedness: image reaches focus behind the retina
(can see far away objects)
 Presbyopia: lenses lose elasticity with age
 Blind spot : no receptor cells where the optic nerve exits
the eye

17. Visual Organization
 Color Perception
o Trichromatic Theory of Color: three “color systems”, each of which is sensitive to red,
green and blue; mixing lights of these three colors yields the full spectrum of colors
o Opponent-Process Theory: each of the color systems is sensitive to two opposing colors
(either blue or yellow, green or red, black or white)
• Afterimage: a non-specific term that refers to an image continuing to appear in one's vision after
the exposure to the original image has ceased.

18. Hearing
 Outer ear captures sound, three tiny bones in middle ear transmit eardrum’s vibration to the inner ear
where cochlea transforms waves into neural impulses.
o Pathway for Sound: Ear Drum -> Hammer -> Anvil -> Stirrup -> Cochlea

19. Pitch & Volume
 Decibels: a unit used to measure the intensity of a
sound
 Frequency: provides information about pitch of
sound
o Place Theory for Hearing: hair cells at different
locations along the cochlea’s basilar membrane are
stimulated and the location of the most stimulation
determines pitch
o Frequency Theory for Hearing: hair cells vibrate and
send nerve impulses at the same frequency as the
sounds they detect

20. Hearing Problems
 Conduction Hearing Loss (Conduction Deafness): problems with mechanics of sending sound waves to
cochlea
o Hearing aids and some surgery helps.
 Sensorineural Hearing Loss (Nerve Deafness): damage to hair cells or auditory nerve
o Result of loud noise (high decibel), disease, and biological changes; damage to receptor cells and auditory nerve
is irreversible.
o Cochlear Implants

21. Smell (Olfaction)
 Smell and taste are “chemical senses” because they use chemoreceptors
and are sensitive to chemical molecules
 Olfactory receptors in the nose transduce info from odorants (molecules
with odor) directly to olfactory bulb at base of frontal lobe, where info is
processed and sent to other brain regions.
o Olfaction is the only sensory system NOT routed through the thalamus.

22. Taste (Gustation)
 Proposed purpose of taste is to avoid poisonous foods (which are usually bitter).
o Nonpoisonous foods with good energy levels are often sweet.
 Dissolved food particles pass over papillae on the tongue and down into taste buds (taste
receptors), which transduce info to the brain.
 Taste buds are distributed all over the tongue, NOT in dedicated regions by taste (sweet,
sour, salty, bitter & umami)
 Umami: savory; sensitivity to glutamate found in meat, broth, MSG

23. Touch
 Skin’s sensory mechanisms detects pressure, temperature, and pain (various different kinds of
receptors).
 Touch receptors are most concentrated in face and hands (that’s why paper cuts hurt!).

24. Pain
 Gate Control Theory: experience of pain depends on
whether the message gets past the “gatekeeper” in the
spinal cord.
o Normally, the gate is shut and pain signals are blocked.
But when body tissue is damaged, impulses open the
gate to allow the message of pain through.
o Messages from the brain also control the gate,
allowing some to continue through pain when it should
be excruciating (athletes, military, first responders).
• Endorphins from the brain (fight or flight response),
distraction by fear or competition, and actively listening to
music (or looking at a picture) can close the gate and
reduce pain and anxiety.
• Focusing on pain amplifies it.

25. Phantom Limb Pain
 Phantom Limb Pain: when amputee continues to feel sensations (pain, tickling) in the missing limb
o Nerve cells send conflicting messages to the brain, producing “static” that is interpreted as pain.
o Prosthetic limbs and mirror visual therapy can help reduce phantom limb pain and even cure it.
• Example of Top-Down Processing

26. Kinesthesis
 Kinesthesis: provides information about body posture, orientation and movement of individual
body parts
o Independent of other senses and a major part of moving through ones environment.
o Kinesthetic receptors in muscles, joints, and tendons tell the brain what is moving, how weight is
distributed, where body parts are in relation to the whole.

27. Psychics & ESP
 Extrasensory Perception (ESP): “psychic”
perceptual abilities that supposedly go beyond
the known senses
o Examples: telepathy, clairvoyance, precognition
 Research in ESP doesn’t withstand scrutiny
because of failure to replicate findings by rival
research labs. No empirical evidence.
 Why do some believe in ESP?
o Motivation and interests influence our
perceptions, creating selective perception.
o Strong emotions about the subject mask faulty
reasoning.