do now: which sense would you be most willing to give up? which one would you least like to lose?

DO NOW:Which sense would you be

most willing to give up?

Which one would you least like to lose?

Unit 4: Sensation & Perception

AP Psychology Ms. Desgrosellier 11.29.2010

Key Ideasthresholds

vision

hearing (audition)

touch (somatosensation)

Chemical senses – taste (gustation) and smell (olfaction)

Gestalt organizing principles

depth perception

perceptual constancy

perceptual adaptation and perceptual set

ESP

Sensation & PerceptionHow many rectangles do you

see???

Sensation & Perception

ThEcOwgAvecOla.

Sensation & Perception

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Sensation & PerceptionSensation: the process by which you

detect physical energy from your environment and encode it as neural signals.

Perception: the process that organizes sensory input and makes it meaningful.

This is influenced by your memory, motivation, emotion, and even culture.

Sensation & PerceptionPsychophysics: the study of the

relationship between physical energy and psychological experiences.

Asks questions about our sensitivity to stimuli.

Thresholdsstimulus: a change in

environment that can be detected by sensory receptors.

absolute threshold: the weakest level of a stimulus that can be correctly detected at least half the time (50%).

ThresholdsStudied by Galanter about 50 years ago

found the following absolute thresholds:a candle flame seen at 30 miles away on

a dark clear nightthe tick of a watch under quiet

conditions at 20 feet away1 teaspoon of sugar in 2 gallons of water1 drop of perfume diffused in a three-

room apartment

Thresholdssignal detection theory:

minimum threshold changes with fatigue, attention, expectations, motivation, emotional distress, and from one person to another.

ThresholdsSubliminal stimulation:

receiving messages below one’s absolute threshold for conscious awareness.

They can have a momentary, subtle effect on thinking.

ThresholdsDifference threshold: minimum

difference between any two stimuli that a person can detect 50% of the time.

Just noticeable difference (JND): when you experience the difference threshold.

e.g. adding one penny to a container with 10 pennies is more noticeable than if it had 100 pennies in it.

ThresholdsWeber’s Law: two stimuli must differ by a

constant minimum percent (rather than a constant amount).

Sensory adaptation: when a stimulus is unchanging, you become less sensitive to the stimulus.

Allows you to focus your attention on information changes in your environment without being distracted by irrelevant data such as odors or background noises.

DO NOWIn YOUR OWN WORDS, briefly

describe the difference between sensation and perception.

Then briefly describe absolute and difference thresholds.

Transmission of Sensory Information

Sensory information of stimuli comes from millions of sensory receptors in your eyes, ears, nose, tongue, skin, muscles, joints, and tendons.

Different receptors detect different types of physical energy.


Transduction: transformation of stimulus energy to the electrochemical energy of neural impulses.

All this sensory information passes through the thalamus, EXCEPT impulses for olfaction/smell.


vision = occipital lobes

hearing = temporal lobes

smell = lower part of the frontal lobes

taste = the junction of the temporal and parietal lobes

body senses = parietal lobes

VISIONProcessed in the primary visual

cortex in the occipital lobes.

The image formed on your retina is upside down and incomplete.

Your brain fills in information and straightens out the upside down image almost immediately.

Visual Pathwaycornea: transparent, curved layer

in the front of the eye that bends incoming light rays.

normal vision: rays of light form a clear image on the retina of the eye.

Visual Pathwaynearsighted: too much curvature

of the cornea and/or lens focuses the image in front of the retina so nearby objects are seen more clearly than distant objects.

Visual Pathwayfarsighted: too little curvature of

the cornea and/or lens focuses the image behind the retina, so distant objects are seen more clearly than nearby objects.

Visual PathwayAstigmatism: caused by an

irregularity in the shape of the cornea and/or the lens. This distorts and blurs the image at the retina.

Visual Pathwayiris: colored muscle surrounding

the pupil that regulates the size of the pupil opening.

pupil: small, adjustable opening in the iris that is smaller in bright light and larger in darkness.

THE EYE

Visual Pathwaylens: structure behind the pupil

that changes shape, becoming more spherical or flatter to focus incoming rays into an image on the light-sensitive retina.

accommodation: process of changing the curvature of the lens to focus incoming rays into an image on the light-sensitive retina.

THE EYE

Visual Pathwaydark adaptation: gradual

increase in sensitivity to low levels of light when it becomes dark.

Visual Pathwayretina: light-sensitive surface in

the back of the eye containing rods and cones that transduce light energy. Also has layers of bipolar cells and ganglion cells that transmit visual information to the brain.

DO NOWBRIEFLY define the following parts

of the eye:

cornea

iris

pupil

lens

THE EYE

Visual Pathwayphotoreceptors: modified

neurons (rods and cones) that convert light energy to electrochemical neural impulses.

Visual Pathwayrods: photoreceptors that detect black,

white, and gray, and detect movement.

Necessary for peripheral and dim-light vision.

Distributed throughout the retina, except on the fovea.

lower threshold than cones and are sensitive to light and dark, as well as movement.

Visual Pathwaycones: photoreceptors that detect

color and fine detail in daylight or in bright-light conditions.

Most concentrated at the fovea of the retina, none are in the periphery.

Three kinds that are each most sensitive to a different range of wavelengths of light, which provides the basis for color vision.

Visual Pathway

Visual Pathwayfovea: small area of the retina in

the most direct line of sight where cones are most concentrated for highest visual acuity in bright light.

optic nerve: nerve formed by ganglion cell axons; carries neural impulses from the eye to the thalamus of the brain.

THE EYE

Visual Pathwayblind spot: region of the retina

where the optic nerve leaves the eye so there are no receptor cells; creates an area with no vision.

Visual PathwayOn your post-it note, draw the

following image.

Visual PathwayClose your LEFT eye and look at

the plus sign.

Move the card slowly back and forth until the dot disappears.

You have found your blind spot!

DO NOWBRIEFLY define the following

parts of the eye:

retina

rods

cones

optic nerve

Visual Pathwaybipolar cells: second layer of

neurons in the retina that transmit impulses from rods and cones to ganglion cells.

ganglion cells: third layer of neurons in the retina, whose axons converge to form the optic nerve.

Visual Pathway

Visual Pathwayacuity: ability to detect fine

details, sharpness of vision. Can be affected by small distortions in the shape of the eye.

What are some things that we have talked about that effect acuity?

Visual Pathwayfeature detectors: individual

neurons in the primary visual cortex/occipital lobes that respond to specific features of a visual stimulus.

e.g. neurons that only respond (fire) to a specific orientation of a line.

Visual PathwayIn a study, kittens were raised in

three kinds of environments:Vertical stripesHorizontal stripesNormal visual environment

Visual PathwayKittens raised in an environment

with only one line orientation only developed feature detectors for that environment!

This means they could only see ONE orientation!

Visual Pathwayparallel processing:

simultaneously analyzing different elements of sensory information, such as color, brightness, shape, etc.

Color VisionThe colors of objects you see

depend on the wavelengths of light reflected from those objects to your eyes.

Light is the visible portion of the electromagnetic spectrum.

Color Vision

Color VisionColors vary in wavelengths from

the longest (red) to the shortest (violet).

Wavelength is the distance from the top of one wave to the top of the next.

Color VisionGenerally, the more lightwaves your eyes

receive, the brighter an object appears.

If an object absorbs all the lightwaves, none reach your eyes and it appears black.

If it reflects all the lightwaves, all of them reach your eyes and it appears white.

If it reflects some of the light then we see different colors.

Color Visiontrichromatic theory: proposed

system of color vision with cones that differentially sensitive to different wavelengths of light.

Each color you see results from a specific ratio of activation among the three types of receptors.

DEMO

Color Visionopponent-process theory:

proposed system for color vision with opposing retinal processes for red-green, yellow-blue, white-black. Some retinal cells are stimulated by one of a pair and inhibited by the other.

Spanish castle demo

Color VisionBoth seem to be at work to create

color vision.

DO NOW:Take out your reading notes.

Explain the two major theories of color vision:

Trichromatic

Opponent-process

Hearing (Audition)audition: the sense of hearing.

Sound waves result from mechanical vibration of molecules from a sound source (e.g. instrument or voice).

The vibrations move outward from the source, compressing and then releasing the molecules of the air.

Hearing (Audition)amplitude: The height of the

sound wave the determines the loudness.

The bigger the amplitude, the louder the sound.

Hearing (Audition)frequency: the number of

complete wavelengths that pass a point in a given amount of time.

The wavelength is inversely proportional to the frequency.

It determines the hue of a light wave and the pitch of a sound.

Hearing (Audition)pitch: the highness or lowness of a

sound.

Shorter wavelength = higher frequency = higher pitch

Longer wavelength = lower frequency = lower pitch

We are most sensitive to frequencies that correspond to the range of human voices.

Hearing (Audition)

Hearing (Audition)timbre: the quality of a sound

determined by the purity of a waveform.

What makes a note of the same pitch and loudness sound different on different musical instruments.

DEMO

The EarOuter ear: visible part of the

ear; channels the sound waves through the auditory canal to the eardrum.

Eardrum: a tight membrane that vibrates with the waves.

The Ear

OUTER EAR(pinna)

Eardrum

outer ear canal

Middle EarMiddle ear: the chamber

between the eardrum and cochlea.

Hammer, anvil, and stirrup: a piston in the middle ear made up of containing three tiny bones that concentrate the vibrations of the eardrum on the cochlea’s oval window (membrane).

The Ear

OUTER EAR(pinna)

Eardrum/oval window

Hammer

anvil

stirrup

MIDDLE EAR

outer ear canal

The EarCochlea: a coiled, bony fluid-

filled tube in the inner ear through which sound waves trigger nerve impulses. looks like a snail!

The vibrations on the cochlea’s oval window cause vibrations that move the fluid in the tube.

The EarBasilar membrane: lined with

hair cells that are bent by the vibrations from sounds and triggers impulses in the adjacent nerve fibers that converge to form the auditory nerve.

The neural messages travel via the thalamus to the temporal lobe’s auditory cortex – and we hear!

DO NOWBriefly explain the process of

hearing, from sound waves to transduction (turning them into neural signals).

The EarAuditory nerve: axons of neurons in

the cochlea converge transmitting sound messages through the medulla, pons, and thalamus to the auditory cortex of the temporal lobe.

Semicircular canals: three fluid-filled bony channels in the inner ear. They provide information about orientation to the brain to help maintain balance.

The Ear

OUTER EAR(pinna)

Eardrum

Hammer

anvil

stirrup

cochlea

MIDDLE EAR

Basilar membrane (in the cochlea)

outer ear canal

semicircular canals

Eustachian tube

auditory nerve

INNER EAR

The Ear

Locating SoundsSound localization: the process

by which you determine the location of a sound.

With ears on both sides of our head, you can locate a sound source.

The side closest to the source of the sound hears it louder.

Locating SoundsUsing parallel processing, your brain

processes both intensity and timing differences to determine where the sound is.

It is hardest to locate a sound directly in front, behind, above, or below you because the sound hits both ears at the same time.

Demos

Determining PitchHow can you discriminate small

differences in sound frequency or pitch?

place theory: the position on the basilar membrane at which waves reach their peak depends on the frequency of a tone.

Determining PitchWorks best with high-pitched

sounds.

Waves that peak near the close end are perceived as high-pitched.

Waves that peak near the far end are interpreted as low-pitched.

Determining Pitchfrequency theory: the rate of

the neural impulses traveling up the auditory nerve matches the frequency of a tone, enabling you to sense its pitch.

Frequency theory explains well how you hear low-pitched tones.

Determining PitchIndividual neurons can only fire at a

maximum of 1,000 times per second.

A volley mechanism in which cells can alternate firing and achieve a frequency of 4,000 times per second.

The brain can read pitch from the frequency of the neural impulses.

Hearing LossConduction deafness: loss of hearing

that results when the eardrum is punctured or any of the ossicles lose their ability to vibrate. A hearing aid may restore hearing.

Nerve (sensorineural) deafness: loss of hearing that results from damage to the cochlea, hair cells, or auditory neurons. Cochlear implants may restore some hearing.

DO NOWBriefly explain one of the

theories of pitch detection.

Briefly explain how we locate sounds.

TOUCH (SOMATOSENSATION)

somatosensation: the skin sensations, or the sense of touch. Made up of four parts:touch/pressurewarmthcoldpain


These parts can combine to create different touch sensations. For example, burning is pain, warmth, and cold.

Itching is gentle stimulation of pain receptors.


Transduction of mechanical energy happens just below the surface of the skin where neural fibers carry sensory information to your spinal cord.

From your spinal cord, the signal crosses in the medulla, to the thalamus, then your somatosensory cortex in your parietal lobes.


The amount of somatosensory cortex dedicated in the brain depends on the sensitivity of that area.

This has been mapped as the somatosensory map or homunculus.

Hearing Loss


Pain follows a slower and less defined pathway, and requires a psychological and physical explanation.

gate-control theory: pain is experienced only if the pain messages can pass through a gate in the spinal cord on their route to the brain.


The gate is opened by small nerve fibers that carry pain signals, and is kept open by things like anxiety, depression, and focusing on the pain.

The gate is closed by neural activity of larger nerve fibers, which conduct most other sensory signals, or by information coming from the brain.


Massage, electrical stimulation, acupuncture, ice, and the natural release of endorphins can close the gate.

Pain is important because it alert you to injury and often prevents further damage.

BODY SENSESkinesthesis: body sense that

provides information about the position and movement of individual parts of your body with receptors in muscles, tendons, and joints.

e.g. close your eyes and touch your nose.

BODY SENSESvestibular sense: body sense of

equilibrium with hairlike receptors in semicircular canals and vestibular sac in the inner ear.

DO NOWExplain how the sense of touch

works.What are the four basic sensations

we feel

How does pain travel from our elbow to our brain?

CHEMICAL SENSESgustation: the chemical sense of

taste with receptor cells in taste buds in fungiform papillae (tissue) on the tongue, on the roof of the mouth, in the throat.

There are three kinds of tasters: nontasters, tasters, and supertasters.

Molecules must dissolved in saliva or a liquid to be sensed.

CHEMICAL SENSESFive basic taste sensations are:

sweet

sour

salty

bitter

umami (glutamate)

CHEMICAL SENSESFlavor is the interaction of

sensations of taste and odor with contributions by temperature and texture.

Babies show a preference for sweet and salty foods, both necessary for survival; and disgust for bitter and sour, which are characteristic of poisonous and spoiled food.

CHEMICAL SENSESThe pathway

for taste passes to the brainstem, thalamus, and primary gustatory cortex.

CHEMICAL SENSESOlfaction: the chemical sense of smell

with receptors in a mucous membrane on the roof of the nasal cavity.

Molecules must reach the membrane and dissolve to be sensed.

Olfactory receptors synapse immediately with neurons of the olfactory bulbs in the brain with no pathways to the thalamus.

CHEMICAL SENSESSensory information

about smell is transmitted to the hypothalamus and structures in the limbic system associated with memory and emotion, as well as the primary cortex for olfaction on the underside of the frontal lobes.

CHEMICAL SENSESThe primary olfactory cortex is

necessary for making fine distinctions among odors and using those distinctions to consciously control behavior.

PERCEPTUAL PROCESSESPerception results from the interaction

of many neuron systems, each performing a simple task.

Natural selection favors a perceptual system that is very efficient at picking up information needed for survival in a 3-D world in which there are predators, prey, competitors, and limited resources.

PERCEPTUAL PROCESSESYou brain looks for consistencies

and simplicity, making a huge number of perceptual decisions, often without your conscious awareness, in essentially two different ways of processing.

The particular stimuli you select to process greatly affect your perceptions.

AttentionThe set of processes by which you

choose from among the various stimuli bombarding your senses at any instant, allowing some to be further processed by your senses and brain.

selective attention: focused awareness of only a limited aspect of all you are capable of experiencing.

DO NOWBriefly explain our sense of

smell (from when the molecules that create an odor reach your nose).

GustationTake a small sip of the water in

the cup on your table.

Does it taste more bitter, sweet, or equally both flavors?

Sweet = nontaster

Bitter = Supertaster

Both = taster

AttentionBottom-up Processing:

information processing that begins with sensory receptors and works up to the brain’s integration of sensory information to construct perceptions.

It’s data driven.

You first sense stimuli, and then process the data to perceive.

AttentionFor example, Hubel & Weisel’s feature-

detector theory assumes that you construct perceptions of stimuli from activity in neurons of the brain that are sensitive to specific features of those stimuli, such as lines, angles, even a letter or face.

Hermann von Helmholtz’s constructivist theory maintains that we learn though experience to convert sensations into accurate perceptions.

AttentionAnne Treisman’s feature-integration

theory proposes that detection of individual features of stimuli and integration into a whole occur sequentially in two different stages.

First, detection of features involves bottom-up parallel processing.

Second, integration of features involves less automatic, partially top-down serial processing.

AttentionTop-down processing:

information processing guided by your preexisting knowledge or expectations.

It is concept driven.

Your expectations, previous experiences, interests, and biases cause different perceptions.

AttentionWhen you perceive a conflict

among senses, vision usually dominates, which is called visual capture.

This explains why you think the voice is coming from a ventriloquist’s dummy when the puppet’s mouth moves.

Attention

AttentionWhich half of the woman’s face is

in shadow?

What instrument is the man playing?

Attention

AttentionWhat rodent do you see?

What is the old man wearing on his face?

DO NOWWith your table (NOT on

paper), briefly explain the difference between top-down and bottom-up processing.

Gestalt Organizing Principles of Form

PerceptionMax Wertherimer, Kurt Koffka, and

Wolfgang Kohler studied how the mind organizes sensations into perceptions of meaningful patterns or forms, called a gestalt.

They concluded that in perception, the whole is different from, and can be greater than, the sum of its parts.

Forms are perceived as a whole.


Perceptionphi phenomenon: the illusion of

movement created by presenting visual stimuli in rapid succession.

e.g. movies

Demo


PerceptionObjects are distinct

from their surroundings (e.g. figure-ground).

visual capture: Gestalt psychologists recognized the importance of figure-ground in perception.


PerceptionThe nervous system is innately

predisposed to respond to patterns of stimuli according to rules or principles.

e.g. proximity, similarity, continuity, connectedness, closure.


Perception

Closure


Perceptionoptical or visual illusions:

discrepancies between the appearance of a visual stimulus and its physical reality.

Common examples include: reversible figures, illusory contours, the Muller-Lyer illusion, Ponzo illusion, and moon illusion.

Illusory Contours

Muller-Lyer Illusion

Ponzo illusion

moon illusion

Depth Perceptionthe ability to judge the distance of

objects.

monocular cues: clues about distance based on the image of one eye.

Depth Perceptioninterposition/overlap – when a

closer object cuts off the view of part or all of a more distant one.

Depth Perceptionrelative size – the closer of two

same-size objects casts a larger image on your retina than the farther one.

Depth Perception

Depth Perceptionrelative clarity – closer objects

appear sharper than more distant, hazy objects.

Depth Perceptiontexture gradient – closer objects

have a coarser, more distant texture than far away objects that appear more densely packed or smooth.

Depth Perceptionrelative height/elevation – The

lowest objects in our field of vision generally seem the closest.

Depth Perceptionlinear perspective – parallel

lines seem to converge in the distance.

Depth Perceptionrelative brightness – closer of

two identical objects reflects more light to your eyes.

Depth Perceptionmotion parallax – when moving,

nearby objects pass quickly while far away objects appear stationary.

Depth Perceptionaccommodation – the flexing and

relaxing of our lens.

Depth Perception

Depth Perceptionbinocular cues: clues about

distance requiring two eyes.

Binocular cues include the more important retinal disparity and convergence.

Depth PerceptionRetinal disparity: the slightly

different view the two eyes have of the same object because the eyes are a few centimeters apart.

The degree of retinal disparity decreases with distance.

With both eyes open, your brain fuses the two images, resulting in perception of depth.

Depth PerceptionConvergence: the inward turning

of the eyes that occurs when you look at an object that is close to you.

The closer the object, the more convergence.

It doesn’t work for objects beyond about 8 meters (25 feet).

Perceptual Constancy

perceiving an object as unchanging even when the immediate sensation of the object changes.


size constancy: an object appears to stay the same size despite changes in the size of the image it casts on the retina as it moves farther away or closer.


shape constancy: an object appears to maintain its normal shape regardless of the angle from which it is viewed.


brightness constancy: an object maintains a particular level of brightness regardless of the amount of light reflected from it.

However, when the context changes, the perceived brightness or color can also change.


The real shape, orientation, size, brightness, and color are perceived as remaining relatively constant even when there are significant variations in the image it projects.

Objects can be identified no matter your viewing angle, how far away it is, or how dim the lights are.

Squares A & B are the same color. Discuss with your table WHY we perceive them to

be different.

Perceptual Adaptation & Perceptual Set

You are able to adapt to changed visual input.

e.g. if you where displacement goggles and reach for an object, you will miss at first.


You are able to adapt to changed visual input.

e.g. if you where displacement goggles and reach for an object, you will miss at first.

Eventually, your vision will correct itself, even if the goggles flip your vision 180º.


Perceptual set: visual perception can also be influenced by cultural factors, assumptions, and beliefs.

e.g. For relative size to work, you must be familiar with the object and have been exposed to viewing objects in the distance.

Culture & ExperienceYour perceptual set or mental

predisposition can influence what you perceive when you look at ambiguous stimuli.

Culture & Experienceschemas: concepts or frameworks

that organize and interpret information.

They form your perceptual set.

This can account for people’s interpretations of UFOs, the Loch Ness monster, or seeing a cloud of dust in a movie.

Culture & Experience

Culture & Experience1. How many people are in the picture?

2. How many animals?

3. What is the man holding in his hands?

4. What is the woman wearing?

5. Are we looking at a circus or a costume ball?

Extrasensory PerceptionESP (extrasensory perception): the

controversial claim that perception can occur apart from sensory input.

Extrasensory Perceptionparapsychology: the study of paranormal

events that investigates claims of ESP, including:

telepathy: mind-to-mind communication

clairvoyance: perception of remote events

precognition: perception of future events

telekinesis/psychokinesis: moving remote objects through mental processes

Extrasensory PerceptionIn 1998, a National Research

Council investigation on ESP concluded that the best available evidence at that time did not support the contention that these phenomena exist.

do now: which sense would you be most willing to give up? which one would you least like to lose?

Documents

difference thresholds

sensation perception

thresholds stimulus

tac eht slide

threeroom apartment

perceptual set esp slide

sensory adaptation

following absolute thresholds