Sensation and Perception

If a tree falls in the woods and no one is around to hear it, does it make a sound?

Sensation vs. Perception

• Sensation– The experience of sensory stimulation– “I see…hear…feel…smell…taste something”– Raw sensory information

• Perception– The process of creating meaningful patterns from

raw sensory information – “I see a cat;” “I hear footsteps” etc. – Forms the foundation of consciousness

The Nature of Sensation

The Basic Process

• Is the same for most senses:

1. Energy stimulates receptor cell in one of the sense organs

2. If stimulus is strong enough, a signal is sent by receptor through sensory nerves (we know what these are) to appropriate area of cerebral cortex (we also know what this is)

The Basic Process

• Receptor cells– Specialized cells that respond to a particular type of energy– These exist in your sense organs

• Doctrine of specific nerve energies (Muller)– One-to-one relationship between stimulation of a specific

nerve and the resulting sensory experience– For example, applying pressure with your finger to your

eye results in a visual experience because they are visual receptors– try it!

How does the brain differentiate between variations of same sensory mode????

• Aka, how do we know the difference between an ambulance siren and a song on our ipod (they’re both sounds and stimulate the same organ, no?)

• Answer: Different stimuli affect:1. How many neurons fire2. Which neurons are activated or inhibited3. The rate at which the neurons fire

• This information acts as a code for your brain to crack.

Sensory Thresholds

• Absolute threshold– The minimum amount of energy that can be

detected 50% of the time– If the responders can identify a sound 50% of the

time they hear it, that’s the absolute threshold– E.g. At what point can you hear the presence of a

sound? (Watch example)

Absolute Thresholds

• Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water

• Smell: 1 drop of perfume diffused throughout a three-room apartment

• Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch)

• Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions

• Vision: a candle flame seen from 50km (30 miles) on a clear, dark night

Sensory thresholds

• Difference threshold– The smallest change in stimulation that can be detected

50% of the time– Also called the just noticeable difference– e.g. At what point can you tell that the TV volume has

been raised?

Sensory Thresholds• Weber’s Law

– States that the difference threshold is a constant proportion of the specific stimulus

– Senses vary in their sensitivity to changes in stimulation

– Example: Would you feel an additional 5 points on each side of barbell when you’re benching 200 lbs? What if you’re benching 100?

Sensory Thresholds

• Sensory adaptation– An adjustment of the senses to the level of stimulation

they are receiving– Car radio blasting?– Toothpaste/orange juice (ice cream/soda) phenomenon?

• “sweet” taste buds adapt (become less sensitive)– Other examples?– Perfume, Swimming/Baths, etc.

Subliminal Perception

• The notion that we may respond to stimuli that are below our level of awareness

• Research shows that the effect only occurs in controlled laboratory studies

• Research outside the laboratory shows no significant effect of subliminal information– Subliminal Research@Duke University– Subliminal Advertising Experiment– Subliminal McDonald's Advertisement

Extrasensory Perception

• Refers to extraordinary perception such as– Clairvoyance – awareness of an unknown object

or event– Telepathy – knowledge of someone else’s

thoughts or feelings– Precognition – foreknowledge of future events

• Research has been unable to conclusively demonstrate the existence of ESP

Vision

The Visual System

• Cornea • Transparent protective

coating over the front of the eye

• Pupil• Small opening in the iris

through which light enters the eye

• Iris• Colored part of the eye

The Visual System

• Lens• Focuses light onto the

retina

• Retina• Lining of the eye

containing receptor cells that are sensitive to light

• Fovea• Center of the visual field

Receptor Cells

• Cells in the retina that are sensitive to light• Visual receptors are called rods and cones

Receptor Cells

• Rods– About 120 million rods– Respond to light and

dark– Very sensitive to light– Provide our night vision

• Cones– About 8 million cones– Respond to color as well

as light and dark– Work best in bright light– Found mainly in the

fovea

Receptor Cells

• Bipolar cells– Receive input from

receptor cells

• Ganglion cells– Receive input from

bipolar cells

• Blind spot– Area where axons of

ganglion cells leave the eye

Adaptation

• Dark adaptation– Increased sensitivity of rods and cones in darkness

• Light adaptation– Decreased sensitivity of rods and cones in bright

light• Afterimage

– Sense experience that occurs after a visual stimulus has been removed

From Eye to Brain

• Optic nerve• Made up of axons of

ganglion cells• carries neural messages

from each eye to brain

• Optic chiasm• Point where part of each

optic nerve crosses to the other side of the brain

Color Vision

• Properties of color– Hue – refers to colors such as red and green– Saturation – refers to the vividness of a hue– Brightness – the nearness of a color to white

Theories of Color Vision

• Additive color mixing– Mixing of lights of different hues– Lights, T.V., computer monitors (RGB)

• Subtractive color mixing– Mixing pigments, e.g., paints

Theories of Color Vision

• Trichromatic theory– Three different types of cones

• Red• Green• Blue-violet

– Experience of color is the result of mixing of the signals from these receptors

– Can account for some types of colorblindness

Forms of Colorblindness• Approximately 10% of

men and 1% of women have some form of colorblindness

• Dichromats– People who are

blind to either red-green or blue-yellow

• Monochromats– People who see no

color at all, only shades of light and dark

Theories of Color Vision

• Trichromatic theory cannot explain all aspects of color vision– People with normal vision cannot see “reddish-

green” or “yellowish-blue”– Color afterimages

Theories of Color Vision

• Opponent-process theory– Three pairs of color receptors

• Yellow-blue• Red-green• Black-white

– Members of each pair work in opposition– Can explain color afterimages

• Both theories of color vision are valid

Color Vision in Other Species

• Other species see colors differently than humans

• Most other mammals are dichromats• Rodents tend to be monochromats, as are

owls who have only rods• Bees can see ultraviolet light

Hearing

Sound

• Sound waves• Changes in pressure

caused by molecules of air moving

• Frequency• Number of cycles per

second in a wave, measured in Hertz (Hz)

• Frequency determines pitch

Sound

• Amplitude– Magnitude (height) of

sound wave– Determines loudness,

measured in decibels (dB)

• Overtones– Multiples of the basic

tone• Timbre

– Quality of texture of sound

The Ear

• Eardrum• Middle ear

– Contains three small bones; the hammer, anvil, and stirrup

– These bones relay and amplify the incoming sound waves

The Ear

• Oval window– Membrane between

middle ear and inner ear• Cochlea

– Part of inner ear containing fluid that vibrates

– This causes the basilar membrane to vibrate

The Ear

• Basilar membrane– Membrane in the

cochlea which contains receptor cells, called hair cells

• Auditory nerve – Connection from ear to

brain– Provides information to

both sides of brain

Theories of Hearing

• Place theory– Pitch is determined by location of vibration along

the basilar membrane• Frequency theory

– Pitch is determined by frequency hair cells produce action potentials

– Volley Principle• Pattern of sequential firing determines pitch

Hearing Disorders

• About 28 million people have some form of hearing damage in the U.S.

• Can be caused by– Injury– Infections– Explosions– Long-term exposure to loud noises

The Other Senses

Smell

• Detecting common odors– Odorant binding protein

is released and attached to incoming molecules

– These molecules then activate receptors in the olfactory epithelium

– Axons from those receptors project directly to the olfactory bulb

Smell

• Women have a better sense of smell than men• Anosmia

– Complete loss of the ability to smell

Smell

• Pheromones– Used by animals as a form of communication– Provides information about identity– Also provides information about sexual receptivity

• Pheromones stimulate the vomeronasal organ (VNO)• Information from the VNO is sent to a special part of

the olfactory bulb used for pheromonal communication

Taste

• Four basic tastes– Sweet– Salty– Sour– Bitter

• Recent discovery of fifth taste– Umami

Taste

• Receptor cells are located in taste buds

• Taste buds are located in papillae on the tongue

• Chemicals dissolve in saliva and activate receptors

The Other Senses

Kinesthetic Senses

• Kinesthetic senses provide information about speed and direction of movement– Stretch receptors sense muscle stretch and

contraction– Golgi tendon organs sense movement of tendons

Vestibular Senses

• Vestibular senses provide information about equilibrium and body position

• Fluid moves in two vestibular sacs• Vestibular organs are also responsible for

motion sickness• Motion sickness may be caused by

discrepancies between visual information and vestibular sensation

The Skin Senses

• Skin is the largest sense organ• There are receptors for pressure,

temperature, and pain• Touch appears to be important not just as a

source of information, but as a way to bond with others

The Skin Senses

• Homunculus Man• Proportional

representation of skin receptor concentration

• The larger the part, the more receptors/the more sensitive

Pain• Serves as a warning about injury or other

problem• Large individual differences in pain perception• Gate control theory

– Neurological “gate” in spinal cord which controls transmission of pain to brain

Wahhhh, mommyyy

Pain

• Biopsychosocial theory– Holds that pain involves not just physical stimulus, but

psychological and social factors as well

• Placebo effect– Shows that when a person believes a medication reduces

pain, their pain is often reduced even though no medication was given

– Pain relief is likely the result of endorphin release

Pain

• Alternative approaches– Hypnosis– Self-hypnosis– Accupuncture

Perception

Perceptual Organization

• Figure-ground– We perceive a

foreground object (figure) against a background (ground)

• Animals may look like the background they inhabit as a way of destroying figure-ground distinction

Perceptual Organization

• Other principles of organization– Proximity– Similarity– Closure– Continuity

Perceptual Organization

• Perceptual Constancy– Our tendency to

perceive objects as stable and unchanging despite changing sensory information

• Size constancy• Shape constancy• Brightness constancy• Color constancy

Perception of Distance and Depth• Monocular cues – those

that require only one eye– Aerial perspective (far-

fuzzy)– Texture gradient (far-

less textured)– Linear perspective- (lines

come together at horizon)

– Motion parallax (objects in background move in direction of our head)

– Superposition

Perception of Distance and Depth

• Binocular cues – those that require both eyes– Retinal disparity– Convergence– Tennis bals

Localizing Sounds

• We use both monaural and binaural cues

• Loudness– Louder sounds are

perceived as being closer• Time of arrival

– Sounds will arrive at one ear sooner than the other

– This helps determine direction of the sound

Perception of Movement

• Apparent movement- Illusion that still objects are moving– Autokinetic illusion

• Perceived motion of a single object– Stroboscopic motion

• Created by a rapid series of still pictures– Phi phenomenon

• Apparent motion created by lights flashing in sequence– Induced movement

• Car next to you moves without you being aware

Visual Illusions

• Occur because of misleading cues in the stimulus

• Gives rise to false perceptions

Individual Differences and Culture in Perception

• Motivation– Our desires or needs shape our current

perceptions• Values- Things we value are larger• Expectations• Cognitive Style• Experience and Culture- dog differences at

dog show• Personality- cup is half full?

The Stroop Effect!!!Trial 1

1. Blue2. Yellow3. Red 4. Green5. Green6. Purple7. Orange 8. Black

9. Yellow10.Blue11.Pink12.Purple13.Green14.Blue 15.Red16.Blue

The Stroop Effect!!!!Trial 2

1. Blue2. Yellow3. Red 4. Green5. Green6. Purple7. Orange 8. Black

9. Yellow10.Blue11.Pink12.Purple13.Green14.Blue 15.Red16.Blue

Philosophy or Psychology?!• So...if a tree falls in the forest, and no one is there to hear it, does it make a sound?

When a tree falls, it produces a physical change detectable by the human ear, but "sound" is not a physical entity.Rather, it is the psychological interpretation of a physical entity, a phenomenon created by our brains. Since no one is present in the forest to hear the tree falling, there is no brain to "create" the sound. Technically speaking, then, a tree falling in the forest with no human there to observe it, makes no sound. A change in air pressure occurred, in a range humans can detect, but that change is not "sound" until it is detected and perceived by an observer.

If a red apple is growing on a tree in the forest and no one is there to see it, is the apple still red?

Like the falling tree question, the answer is still no. The apple will still reflect light at about 700nm, but without someone there to see it, it does not have "colour." Colour is created by the workings of our visual system.

Which image is produced by our rods? Cones?