ap psychology

AP Psychology

2.3 Sensation and Perception

Sensation• Process by which our sensory receptors

respond to light, sound, odor, textures, and taste

• Our eyes, ears, nose, tongue, and skin comprise an elaborate sensory system that receives and processes information from the environment

Sensation• Each sense organ contains specialized cells called

receptors which detect and then convert…– light waves - vision – sound waves - hearing– chemical molecules – taste, smell– pressure – touch… into neural impulses that are transmitted to the brain.

• adults totally deprived of sensory input for long periods of time– experience hallucinations – impaired efficiency in all areas of intellectual functioning

Perception• Process by which the brain actively selects,

organizes and assigns meaning to incoming neural messages sent from sensory receptors

• Example…– Sensory point of view – the American flag is a

mass of red, white, and blue colors and horizontal and vertical lines

– Perception – you interpret these splotches of color and array of lines as the American flag

Basic Principles of Sensation• Transduction– Process by which sensory receptors convert the

incoming physical energy of stimuli (ie. Light waves) into neural impulses the brain can understand

– Philip Zimbardo – “process seems so immediate and direct that it fools us into assuming the sensation of redness is characteristic of a tomato or the sensation of cold is a characteristic of ice cream”

– In reality…sensations such as “red” or “cold” occur only when neural impulses reach the brain

Transduction

Basic Principles of Sensation• Absolute Threshold– min. amount of a stimulus that an observer can

reliably detect at least 50% of the time– Anything less goes unnoticedExamples…– Vision – candle flame 30 miles (clear, dark night)– Hearing – watch ticking 20 feet away– Smell – one drop of perfume in a 3-room apartment– Taste – 1 tsp. of sugar in 2 gallons of water– Touch – a bee wing dropped on your back from a cm

Basic Principles of Sensation

• Difference Threshold– Minimal difference needed to notice a stimulus

change– aka – JND / “Just Noticeable Difference”– Example – TV volume at 50, take it down a notch

until you notice the difference

Basic Principles of Sensation• Weber’s Law– German Psychologist – Ersnt Weber (1795-1878)– Observed the JND will vary dependent on its

relation to the original stimulus– The size of the JND is proportional to the strength

of the original stimulus– Example• Weight lifter bench pressing 50 lbs would notice an

additional 5 pounds• Weight lifter bench pressing 500 lbs would not notice

an additional 5 pounds

Weber’s Law

Basic Principles of Sensation• Signal Detection Theory– Problem with traditional thresholds• Assumed if signal exceeded one’s AT, it would be

sensed / if below one’s AT, it would not• Did not account for characteristics of the perceiver

– Example – notice change in volume because that is the focus

– A new theory• No single absolute threshold• Detection is based on a combination of stimulus

intensity, background noise, and a person’s physical condition, biases, and level of motivation• EX – a soldier in wartime would detect fainter stimuli

than one in peacetime

Basic Principles of Sensation

• Signal Detection Theory cont.– When using in experiments, psychologists sort the

trials into one of four categories…– Signal is present – the person can decide that it

present or absent (called hits or misses)– Signal is absent – the person can still decide that

the signal is either present or absent (called false alarms or correct rejections)

Basic Principles of Sensation• Sensory Adaptation– Occurs when a constant stimulus is presented for

a length of time. When this happens receptors fire less frequently and the sensation often fades or disappears.

– Examples…• Jogger puts on a new pair of shoes, he or she

immediately notices the different feel. However, after going for a jog, he or she does not notice the difference• Swimmer dives into a pool, you notice the water is

chilly. However, after swimming for a while, you do not notice the water temperature

The Human Visual System

• Our most important and complex sense!• Transduces light waves into neural messages

that the brain processes into what we consciously see.

The Human Visual System• From the Cornea to the Retina…• Cornea – Light waves from the outside world first enter through– Clear membrane / protects eye / helps gather and

direct incoming light waves• Pupil– Small opening in middle of iris– Changes size to let in different amounts of light

The Human Visual System• From the Cornea to the Retina…• Iris– Colored part of the eye– Ring of muscle tissue that contracts or expands to

control the size of the pupil (respond to light and emotions)

– Sympathetic (dilate) Parasympathetic (constrict)

The Human Visual System• From the Cornea to the Retina…• Lens– Transparent structure behind the pupil that

focuses and bends light as it enters the eye– Accommodation – change in the curvature of the

lens that enables the eye to focus on objects at various distances (eye adjusts itself)


• Nearsightedness (Myopia)

• Visual acuity problem that results when the cornea and lens focus an image in the front of the retina

• As a result, distant objects appear blurry

• 25% of US population


• Farsightedness (Hyperopia)

• Visual acuity problem that results when the cornea and lens focus an image behind the retina

• As a result, objects near the eye appear blurry

• 25% of the US population


• Retina• Light-sensitive

membrane at the back of the eye

• Contains millions of sensory receptors for vision

• Transduction of light waves into neural messages occurs

The Human Visual System - Retina

Rods• Photoreceptors in the retina• Sensitive to dim light but

not to color• Allow you to see in poorly lit

environments• Cats have better night vision

than humans because they have a higher portion of rods to cones than humans

Cones• Photoreceptors in the retina• Sensitive to colors and

bright light• Concentrated in the center

of the retina (fovea)• Images that do not fall on

the fovea tend to be perceived as blurry or indistinct

The Human Visual System • Retina…• Bipolar Cells – specialized neurons that

connect rods and cones with the ganglion cells• Ganglion Cells – specialized neurons that

connect to the bipolar cells (bundled axons form the optic nerve)


• Blind Spot• Point where the optic

nerve leaves the eye there are no rods or cones

• Because there are no rods or cones, we have a tiny hole or blind spot

• Normally we are unaware because our eyes are always moving


• Visual Cortex• Optic nerve carries

visual information to • Lies in the occipital lobe

at the back of the brain


• Color Vision– Humans can identify about 7 million different

color combinations– Two color vision theories• Trichromatic or three-color theory• Opponent-process theory


• Trichromatic Theory (three-color)– Three primary colors (red, green, blue)– Any color can be created by combining light waves

of these three colors– Hermann von Helmholtz (1821-1894) proposed

that the eye must have color receptors that correspond to these primary colors• Has been proven that the retina does have cones

especially sensitive to the three primary colors

The Human Visual System• Opponent-process theory– The Trichromatic theory explains how color

processing works in cones, but not what happens in the ganglion cells and the rest of the visual system

– The ganglion cells process color in opposing pairs• Red-green / black-white / blue-yellow

– Visual cortex also encodes color in terms of these three pairs

– Explains afterimages


• Afterimage• Visual experience that

occurs after the original source of stimulation is no longer present

• Example– green, black, yellow flag– red, white, blue flag


• Color Blindness– Genetic disorder (recessive – X) that prevents an

individual from distinguishing between certain colors– Have a deficiency in their cones– Most common form is red-green deficiency (certain

pigments)– Rare to see no color at all (only about 500 reported

cases ever!!)– 1 in 10 men / very few women

The Human Auditory System

• Hearing plays a role in language development and social interactions. It also alerts us to dangerous situations

• It transduces sound waves into neural messages that the brain then processes into what we consciously hear

• aka – audition• Amplitude – loudness• Frqeuency - pitch

The Human Auditory System• Outer Ear– Pinna• Flap of skin and cartilage• Catches sound waves and channels them to the auditory

canal– Auditory Canal• Sound waves travel down and bounce into the ear drum

– Eardrum (tympanic membrane)• Tightly stretched membrane located at the end of the

auditory canal• Vibrates when hit by sound waves (match the intensity

and frequency of sound waves)

Outer Ear


• Middle Ear– Amplifies sound waves– Hammer, anvil, and stirrup• Three tiny bones• Joint action doubles the amplification of sound

– Oval Window• Stirrup transmits the amplified vibrations to oval

window• Small membrane separating the middle ear from inner

ear• Relays vibrations to the cochlea

Middle Ear

The Human Auditory System• Inner Ear– transduces sound waves into neural messages– Cochlea• Spiral-shaped, fluid filled structure that contains the

basilar membrane and hair cells• Greek word for “snail”

– Basilar membrane• Runs length of cochlea / holds hair cell receptors

– Hair cells• Sensory receptors embedded in basilar membrane• Transduce the physical vibration of sound waves into

neural impulses

Inner Ear


• Brain• As hair cells bend, they

stimulate the cells of the auditory nerve

• The auditory nerve carries the neural impulse to the thalamus and then to the temporal lobe’s auditory cortex

Distinguishing Pitch (highness/lowness)• Frequency Theory• Basilar membrane

vibrates the same frequency as sound waves

• Explains how low frequency sounds are transmitted

• Does not explain faster high frequency sounds (neurons cannot fire faster than 1000 times per second)

• Place Theory• Different frequencies

excite different hair cells at different locations along the basilar membrane

• High-frequency sounds cause max vibrations near the stirrup

• Lower-frequency sounds cause maximum vibrations at the opposite end

• Frequency Theory ^^^• Place Theory >>>

Loss of Hearing*most due to damage or old age

Conductive Deafness• Caused when the tiny bones

in the middle ear are damaged and cannot transmit sound waves

• Hearing aides can amplify sound and help overcome

Nerve (Sensorineural) Deafness• Caused by damage to the

cochlea, hair cells, or auditory nerve

• Exposure to noises such as headphones playing at full blast can damage cells and cause permanent hearing loss

• Hearing aids cannot help nerve deafness since damage to hair cells and auditory nerve is almost always irreversible

Loss of Hearing

The Chemical Sense• Smell and taste• Respond to chemical molecules rather than

forms of energy (light and sound waves)• Smell and taste receptors are located near

each other and often interact• We often have difficulty separating the two

sensations

Smell and Taste

The Chemical Senses• Smell or Olfaction– mucous membrane at the top of each nostril contain

receptor cells that absorb airborne chemical molecules– Olfactory receptors detect over 10,000 distinct smells

(flagrant flowers to leaking gas) – Receptor cells communicate neural messages to the

olfactory bulb– Unlike other sensations, impulses do not go through

the thalamus– Nerve fibers connect at the brain near the amygdala

and then to the hippocampus – limbic system (explains why smell is so closely related to vivid memories and emotions)

Olfaction

The Chemical Senses• Taste or Gustation– tongue covered with bumps called papillae– Papillae are covered with taste buds (taste buds

are also found in palate and back of throat)– Major taste sensations• Sweet, sour, salty, bitter, umami (proteins in meats)

– Least critical of senses, but plays role in survival by helping us avoid harmful substances

– Aided by smell, plays a role in enjoyment

Gustation

Skin and Body Senses• Skins Senses– Largest sense organ– Protects our internal organs, holds body fluids,

produces sensations of touch, warmth, and cold and provides essential info about pain

• Body Senses– Provide essential information about your position

and orientation in space

Skins Senses• Touch– Receptors not evenly distributed on body– i.e.. more densely concentrated in hands, face, and

lips than on leg or back– Plays role in human relationships – help

communicate feelings of support, conformity, love• Pain– Unpleasant sensation of physical discomfort or

suffering– Plays a key role in survival by warning about

potential or actual injuries

Skin Senses• Gate-control Theory of Pain– The brain regulates pain by sending signals down

the spinal cord that either open of close sensory pathways (gates)

– If the brain signals the gates to open, pain is experienced or intensified

– If the brain signals the gates to close, pain is reduced

– Psychological factors such as anxiety and fear can intensify pain while positive emotions such as laughter can help minimize pain

The Vestibular Sense• Provides a sense of balance and equilibrium• Inner ear contains receptors that are especially

important for maintaining balance• The semicircular canals are filled with fluids and

lined with hairlike receptor cells that shift in response to motion– They provide the brain with information about the

body’s posture and head positions• Vestibular and auditory systems are alike in that

both depend upon hair cells to transduce a stimulus into a neural message

Semicircular Canals

Selection

• Selecting where to direct our attention is the first step in perception

• Selective Attention and feature detectors help explain why we pay attention to some stimuli in our environment and not to other

Selective Attention

• Cognitive process of selectively concentrating on one or more aspects of the environment while filtering out or ignoring other information

• Example– Gavin is playing a new video game with his friend. He

doesn’t hear his mother call for him to come to dinner. However, he does respond when his cell phone rings because he is expecting a call from his girlfriend

Selective Attention• Perceptual Adaptation - ability of the body to adapt to an

environment by filtering out distractions. – Example - someone who lives near a train can perceptually adapt

such that they can ignore the train whistle in order to sleep at night. If someone came to visit, however, they would not have perceptually adapted to the train and would most likely not be able to sleep.

• Sensory Adaptation – decreasing responsiveness to a stimuli due to constant stimulation– Example – you felt your socks when you put them on, but you

stopped feeling them after a while• Sensory Habituation – our perception of sensations is

partially due to how focused we are on them– Example – you do not focus on your socks anymore ^^^^

Selective Attention Test #1

Selective Attention Test #2

Selective Attention• Cocktail Party Effect– being able to focus one's auditory attention on a

particular stimulus while filtering out a range of other stimuli, much the same way that a partygoer can focus on a single conversation in a noisy room

– Spotlight Effect - reading• Cocktail Party Phenomenon– situation in which one can attend to only part of a

noisy environment, yet highly pertinent stimuli such as one's own name can suddenly capture attention

Change Blindness• psychological phenomenon that occurs when

a change in a visual stimulus goes unnoticed by the observer

• Example…an individual fails to notice a difference between two images that are identical except for one change

Change Blindness Intro.

Change Blindness: Door Study

Feature Detectors

• Brain has specialized neurons called feature detectors that respond only to certain stimuli

• In occipital lobe’s visual cortex• Respond to special features of an image (angles,

lines, curves, movements)• Example … area behind ear perceives faces– Prosopagnosia – damage to this area causes inability

to detect differences in faces– Cannot recognize own face in mirror!

Gestalt Principles of Organization

• Max Wertheimer founded in early 1900s• We process sensations according to

perceptual rules• These rules create whole perceptions that are

meaningful, symmetrical, and as simple as conditions will allow

Figure-Ground Perception

• Most fundamental Gestalt Principle• Figure – main element of a scene that clearly

stands out• Ground – less distinct background of a scene• Example – on this page…the letters constitute

the figure, while the white page is the ground

Figure-Ground Perception

Similarity• There is a tendency to

perceive objects of a similar size, shape or color as a unit or figure

• Example – crowd at football game is a wide assortment of different people; you organize them into home fans, visitor fans, band members, cheerleaders

Proximity• There is a tendency to

perceive objects that are physically close to one another as a single unit

• Example – home fans and visiting fans usually group themselves on opposing sides of the stadium; you would group visiting fans into one homogenous group

Closure

• Tendency to fill in the gaps in an incomplete image

• Example – scoreboards have HOME and VISITORS on them. If it said HO E and VISI ORS, you would fill in the missing letters M and T.

Phi Phenomomenon

• Illusion movement created by presenting still pictures in rapid succession

• Example - TV

Depth Perception• Ability to perceive 3-D space and accurately

judge distance• It is possible to use sound and even smell to

judge distance, we rely heavily on vision

“Visual Cliff” Experiment• Famous experiment, Eleanor Gibson• Placed infants old enough to crawl on a Plexiglas-

topped table• Side 1 – high-contrast red-and-white check cloth

flush against the underside of the glass (appearance of solid surface)

• Side 2 – placed the same material 4-feet below the glass

• Created an illusion of “deep end” with a “visual cliff”

“Visual Cliff” Experiment

• Infants almost always refused to venture beyond the shallow side of the visual cliff

• They turned away from the “deep end” even when their mothers held a spinning toy and encouraged them to crawl forward

• Supports the conclusion that depth perception in humans is innate that emerges during infancy

Monocular (one eye) Depth Cues

• Linear Perspective• Parallel lines appear to

converge toward a vanishing point as they recede into the distance


• Aerial Perspective• Distant objects appear

hazy and blurred compared to close objects


• Relative Size• Two or more objects are

assumed to be similar in size, the object that appears larger is perceived as being close


• Motion Parallax• as you move, you use

the speed of passing objects to estimate the distance of the objects

• Example – when you are driving on an interstate, nearby poles, fences, and roadside signs seem to zip by faster than distant hills

Binocular (both eyes) Depth Cues

• Convergence• Closer the object, the

more the eyes converge, or turn inward

Binocular (both eyes) Depth Cues

• Retinal Disparity• Separation of the eyes cause different images to fall

on each retina• When two retinal images are very different, we

interpret the object as being close by.• When two retinal images are more nearly identical,

the object is perceived as being farther away• A person with only one eye lacks retinal disparity and

would have difficulty climbing an irregular set of stairs

ap psychology

Documents

neural impulses

sensory input

perceiverexample notice

sensation of cold

elaborate sensory system

incoming neural messages

stimulus changeaka jnd

sensation of redness