Sensation and Perception

Chapter 6

Sensation vs. Perception Psychophysics: The study of the relationship between physical

stimuli and our experience of them. Sensation

The experience of sensory stimulation “I see…hear…feel…smell…taste something”

Perception Creating meaningful patterns from raw sensory information “I see a cat;” “I hear footsteps” etc.

Bottom-Up Processing (DATA-DRIVEN) Beginning with stimulation of our senses, we interpret

sensory information with our brains I see a furry, 4-legged creature with a tail and identify this as

a dog Top-Down Processing (SCHEMA-DRIVEN)

Using our schemas, expectancies and past experiences, we interpret sensory information to construct deeper meaning

The dog is growling and foaming at the mouth and I realize it may have rabies so I will not approach it

Demo 1: Top-Down Processing

Based on research of Bugelski and Alampay (1961)

Examine the series of images on your worksheet. Afterwards, look at the image below and describe what you see in the space on your worksheet.

The Nature of Sensation

The Basic Process Receptor cells

Specialized cells that respond to a particular type of energy

These exist in your sense organs

Law 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 – try it!

Press on your

eyeball und you vill have a visual

experience…

YA!

Ich bin Johannes Muller!

Sensory Thresholds Absolute threshold (Demonstration #2)

The minimum amount of energy that can be detected 50% of the time

E.g. At what point can you hear the presence of a sound? Some examples for humans:

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 Sensory adaptation (Demonstration #3)

An adjustment of the senses to the level of stimulation they are receiving

Sandpaper demonstration? toothpaste/orange juice phenomenon? Distortion goggles – in springtime…

Difference threshold (Demonstration #4) The smallest change in stimulation that can be detected 50%

of the time Also called the just noticeable difference or JND e.g. At what point can you tell that the TV volume has been

raised? Weber’s Law

States that the difference threshold is detected by a constant minimum percentage of the stimulus, not a constant amount

e.g. to detect a difference in weight, the change must be 2% of the original stimulus’ weight

Subliminal Perception? We know that below threshold (subliminal) stimuli bombard

us regularly… BUT…do we respond to these 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, lasting

effect of subliminal information Priming

The often unconscious activation of certain associations for the purpose of altering perception, memory or response

Individuals flashed a pleasant or unpleasant image before viewing a photo of a person were influenced to judge the person positively if they saw a pleasant picture and negatively if unpleasant

Subliminal Research at Duke University Subliminal Advertising Experiment (Demo #5)

A Challenge to Sensory Thresholds?

Signal Detection Theory challenges the notion of the absolute threshold.

SDT is a mathematical model that predicts how and when we will detect the presence of a faint stimulus or signal There is NO single absolute threshold Detection of a stimulus depends on a person’s experience,

expectations, motivations, and fatigue.

Vision

EYE see you!

I cannot, however

Vision: Transduction and Light Energy

Transduction: Our eyes have the ability to convert one form of energy – in this case LIGHT – into messages that our brain can interpret as a visual experience

We can only see a small part of the electromagnetic spectrum (see diagram on reverse of absolute threshold)

Properties of Color and Light Energy Hue

Colors we see such as red and green

Determined by wavelength

Shorter wavelength results in blue-violet; longer results in red

Brightness “loudness” or intensity

of a color Determined by

amplitude Saturation

Vividness of a hue

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;

controls size of pupil Lens

Focuses light onto the retina Changes shape through

accommodation to help focus image on 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 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

Marker Demonstration? Stars in the sky?

Receptor Cells Bipolar cells

Receive input from receptor cells

Ganglion cells Receive input

from bipolar cells Axons of these

cells form optic nerve

Blind spot Area where

axons of ganglion cells leave the eye

NO RECEPTORS! Blind-spot demo

Click for animated visual process!

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

Thalamus relays sensory info to visual cortex in occipital lobes

Feature Detection Feature detectors are neurons in the brain that

respond to specific aspects of a stimulus: edges, lines, movements, angles Feature detectors in the visual cortex send signals to

other areas of the cortex for higher-level processing These areas – called supercell clusters – work in teams

to determine familiar patterns – such as faces (processed in the right-side of temporal lobe)

Parallel processing Our brains process multiple features of visual experience

at one and integrate these features to create our experience of vision

If parts of this integration are disrupted through damage or electromagnetic pulses, we may lose our ability to processes certain aspects of vision such as movement or lines (blindsight)

Theories of Color Vision Additive color mixing

Mixing of lights of different hues Lights, T.V., computer monitors (RGB) Lights add wavelengths

Subtractive color mixing Mixing pigments, e.g., paints Pigments absorb or subtract wavelengths

Theories of Color Vision Trichromatic theory (Young-

Helmholtz) Three different types of cones

Red Green Blue

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

Can account for some types of colorblindness

Approximately 10% of men and 1% of women have some form of “colorblindness” (sex linked trait)

Dichromats: Two colors only Monochromats: One color only Ishihara Test

Theories of Color Vision Trichromatic theory cannot explain all aspects of

color vision People with normal vision cannot see “reddish-green” or

“yellowish-blue” Red-Green colorblind people can see yellow, which

Helmholtz argues is a result of red and green cones firing – if Helmholtz is correct, how could this be?

Color afterimages? Opponent-process theory (Ewald Hering)

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

Adaptation Dark adaptation

Increased sensitivity of rods and cones in darkness

Light adaptation Decreased sensitivity of rods and cones in

bright light Afterimage

Sensory experience that occurs after a visual stimulus has been removed in response to overstimulation of receptors

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 Stomatopods have the most

complex color hyperspectral vision in the animal kingdom, allowing them to differentiate between colors that may appear the same to other human and non-human animals.

The Mantis Shrimp is a stomatopod with hyperspectral vision. Hyperspectral capabilities enable the mantis shrimp to recognize different types of coral, prey, or predators.

I’m neith

er shrimp nor mantis…I am

mantis

shrimp.

Hearing

Ear we go!

Sound We hear by transduction of

sound waves into nerve impulses.

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 Amplitude

Magnitude (height) of sound wave

Determines loudness, measured in decibels (dB)

Overtones Multiples of the basic tone

Timbre (TAM-ber) Quality of texture of sound

The Ear Outer Ear

Pinna Tympanic

Membrane (eardrum)

Middle Ear Contains three

auditory ossicles (bones)

Malleus (Hammer)

Incus (Anvil) Stapes (Stirrup)

These bones relay and amplify the incoming sound waves

Inner Ear Oval Window set in motion by

ossicles Fluid-filled Cochlea Basilar membrane set in motion by

the rippling fluid Organ of Corti sits atop the basilar

membrane and contains with cilia (hair cells) which bend as basilar membrane vibrates

Ear to Brain Cilia send nerve impulses

through the auditory nerve to the brain

Auditory nerve Connection from ear to

brain Provides information to

both sides of brain Information processed

in auditory cortex in temporal lobe

Theories of Hearing Loudness is determined by how many hair cells fire Theories of Pitch

Place theory Herman von Helmholtz (again!) 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 Accounts for high-frequency (high pitched) sounds Pattern of sequential firing determines pitch where hair cells in

teams: some fire while others go through refractory Sound Localization

Binaural cues allow us to determine source of sound Interaural Time Difference (ITD) says nearer ear picks up

sound first to provide clues about sound source Sounds directly behind us are most difficult – no visual cues

and little to no ITD.

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

Conduction hearing loss results from damage to parts of the ear itself

Sensorineural hearing loss results when there is damage to hair cells or auditory nerve

Cochlear implants can replace damaged hair cells and transduce sounds into electrical signals sent to the auditory nerve Use of the implants is debated Many advocates for the deaf argue that deafness is NOT a

disability, but rather an enhancement of other senses

The Other Senses

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

Homunculus Man Proportional representation of skin

receptor concentration The larger the part, the more

receptors/the more sensitive Demo: Skin sensitivity

“Paradoxical heat”

Remember Me?

Kinesthetic Senses Kinesthetic senses

provide information about the position and movement of body parts Stretch receptors

sense muscle stretch Golgi tendon organs

sense movement of tendons when muscle contracts and send impulses to CNS

Vestibular Senses Vestibular senses provide

information about equilibrium and head and body position Fluid moves in two

vestibular sacs and the semicircular canals

These vestibular organs are lined with hair cells that bend when fluid moves over them

Vestibular organs are also responsible for motion sickness

Motion sickness may be caused by discrepancies between visual information and vestibular sensation

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

Major pain signals (large fiber activity) can close “gate” while small ones open it

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

Alternative approaches Hypnosis and Self-hypnosis Acupuncture Thought distraction

Taste Five Basic Tastes Traditionally, taste sensations consisted of sweet, salty, sour,

and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”

Sweet Sour Salty Bitter Umami(Fresh [dead?]

Chicken)

Taste Receptor cells are

located in taste buds

Taste buds are located in papillae (“pa-PILL-ee”) on the tongue

Chemicals dissolve in saliva and activate taste receptors inside the taste buds

Taste is processed in the parietal lobe

Taste Why do we have

receptors for the tastes we do?

Evolutionary perspective on how taste receptors developed?

Other aspects of taste result from the interaction of taste and smell together, such as flavors.

Without a sense of smell, our ability to distinguish flavor vanishes!

Smell Detecting common odors

Odorant binding protein (OBP) 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

Women have a better sense of smell than men

Anosmia Complete loss of the

ability to smell

Smell, Taste and Memory The brain region for

smell (in red) is closely connected with the brain regions involved with memory (limbic system). That is why strong memories are made through the sense of smell.

Smell and Pheromones 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

T-Shirt Study?

Perception How do we

integrate our sensory experiences into something meaningful?

Gestalt principles

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:Grouping

Closure (above) : We fill in gaps to complete a whole object and assume there are three circles and two triangles in this picture.

Proximity: We group nearby things together

Similarity: We group together objects that look alike

Continuity: We tend to perceive smooth and continuous patterns over separate pieces

Connectedness: We group together things that are connected as one unit

Perception of Distance and Depth Visual Cliff revisited Binocular cues – those

that require both eyes Stereoscopic vision Retinal disparity Angle of Convergence Hotdog Finger Illusion?

Perception of Distance and Depth

Monocular cues – those that require only one eye Relative height Relative size Interposition Linear perspective Relative motion

(motion parallax) Light and shadow Texture gradient

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 (ITD)

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 without any grounding references

Stroboscopic motion Created by a rapid series of

still pictures Phi phenomenon

Apparent motion created by lights flashing in sequence

Perception of Movement

Perception of Movement

When one analyses step-by-step the gray levels next to the spokes, there are two steps where any given spoke first merges with the preceding sector on one side, then with the succeeding sector. Since in this transition the spoke’s identity is lost and thus it (seemingly) changes position, it is seen as moving. In addition, there is a Gestalt factor at play: each individual spoke only moves one single tiny step per rotation of the sectors, but each one does so at a different time. Since all spokes are grouped together, the entire spoke wheel is perceived as undergoing a continuous rotation.

Perception of MovementContrast gives the impression of stop/start movement!

Perception of Movement Spiral Illusion

Stare into the middle of the spiral After a minute, then look at a still object What happens? How can sensory adaptation explain this? This is often explained in terms of “fatigue” of

the class of neurons encoding one motion direction. It is probably more accurate to interpret this in terms of adaptation

Perceptual Organization Perceptual

Constancy Our tendency to

perceive objects as stable and unchanging despite changing sensory information

Ames Room Illusion explained

Size constancy Turnbull’s Research Is it learned?

Shape constancy Lightness constancy Color constancy

Perceptual Interpretation Sensory Deprivation and Critical Periods

Without environmental stimulation certain feature detectors may never develop

Hirsch and Spinelli’s (1970) experiment with kittens Perceptual Adaptation

Our ability to adjust to distorted perceptual circumstances Drunk goggles?

Perceptual Set Mental predisposition to perceive one thing over another Can be influences by motivation, schemas, emotions, and

experience

Perceptual Interpretation

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

We perceive what we are rewarded for!

Context Values Expectations Cognitive Style Experience and

Culture Personality

Motivation in perception: When rewarded to see sea animals, people perceived a seal; when rewarded for horses, they perceived a horse.

Midget or giant? Context shapes perception.

Extrasensory Perception Refers to extraordinary

perception such as Clairvoyance – awareness

of an unknown object or event not available to the senses

Telepathy – knowledge of someone else’s thoughts or feelings

Precognition – foreknowledge of future events

Psychokinesis – “Mind over matter”

Research has been unable to conclusively demonstrate the existence of ESP or psychokinesis

Video Links Sensation and Perception – Zimbardo’s

Discovering Psychology (27:43) Sensation and Perception 1 (13:52) and 2

(13:43) from Psychology: The Human Experience