PSY 150 403 CHAPTER 6 SLIDES

Sensation and

Perception

PowerPoint® Presentation by Jim Foley

Chapter 6

What we’ll sense and perceive…in this chapter:

Sense: especially vision and hearing smell, taste, touch, pain, and

awareness of body position How do the sense organs and

nervous system handle incoming sensory information?

How does the brain turn sensory information into perceptions?

Why is our style of creating perceptions better at perceiving the real world than at decoding tricky optical illusions?

Basic Principles of Sensation and

PerceptionYour brain will interpret, perceive these topics as they enter your sense organs: Sensation vs. Perception, Bottom-

Up vs. Top-Down Processing Transduction and Thresholds Sensory Adaptation Perceptual Set Context Effects on perception Emotion/Motivation effects

Sensation vs. Perception

“The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.”

“The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.”

The brain receives input

from the sensory organs.

The brain makes sense out of the

input from sensory organs.

Sensation Perception

Making sense of the world

What am I seeing?

Is that something I’ve seen before?

Bottom-up processing:

taking sensory information and then assembling and integrating it

Top-down processing:

using models, ideas, and

expectations to interpret sensory

information

Do you see a painting or a 3D

bottle?

What’s on the bottle?

Kids see eight to ten dolphins.

Why do you think kids see

something different than

adults?

Top-down Processing You may start

to see something in this picture if we give your brain some concepts to

apply: “tree”

“sidewalk”“dog”

“Dalmatian”

From Sensory Organs to the Brain

The process of sensation can be seen as three steps:

Reception--the stimulation

of sensory receptor cells by energy (sound, light, heat, etc)

Transduction-- transforming

this cell stimulation into neural impulses

Transmission--delivering this

neural information to the brain to be

processed

Thresholds

The absolute threshold: the minimum level of stimulus intensity needed to detect a stimulus half the time.

Anything below this threshold is considered

“subliminal.”

When Absolute Thresholds are not Absolute

10

Signal detection theory refers to whether or not we detect a stimulus, especially amidst background noise. This depends not just on intensity of the stimulus but on psychological factors such as the person’s experience, expectations, motivations, and alertness.

Subliminal Detection

Although we cannot learn complex knowledge from subliminal stimuli, we can be primed, and this will affect our subsequent choices.

We may look longer at the side of the paper which had just showed a nude image for an instant.

Subliminal:below our threshold for

being able to consciously detect a stimulus

Difference threshold: the minimum difference (in color, pitch, weight, temperature, etc) for a person to be able to detect the difference half the time.

Weber’s law refers to the principle that for two stimuli to be perceived as different, they must differ by a minimum percentage: 2 percent of weight 8 percent of light intensity 0.3 percent of sound wave frequency to notice a

difference in pitch. Any changes noticeable on this slide?

The “Just Noticeable Difference”

To help detect novelty in our surroundings, our senses tune out a constant stimulus, such as: a rock in your shoe the ticking of a clock

If you concentrate on keeping your eyes in one spot, you’ll see the effects, as your eyes adjust to stimuli

Visual sensory adaptation will be tested when discussing opponent-process theory.

Sensory Adaptation

Perceptual SetPerceptual set is what we expect to see, which influences what we do see. Perceptual set is an example of top-down processing .

Loch Ness monsteror a tree branch?

Flying saucersor clouds?

Perceptual set can be “primed.”

Old woman

Young woman

Ambiguous

Context Effect on Perception

Spelling test answers:

In which picture does the center dot look larger? Perception of size depends on context.

Did context affect which word you wrote?apple payor payee pairdouble pear

Effect of Emotion, Physical State, and Motivation on Perception

Experiments show that: destinations seem farther

when you’re tired. a target looks farther

when your crossbow is heavier.

a hill looks steeper with a heavy backpack, or after sad music, or when walking alone.

something you desire looks closer.

Vision, and Perceptual Organization and Interpretation

And: ESP, Perception without Sensation

Vision (Sensation): The Eye From light input to mental

images Retina and Receptors Feature Detection Parallel Processing Color Vision

Visual Organization: Form, Depth, and Motion

Perception Size, Shape, and Color

Constancy Visual Interpretation: Restored Vision Perceptual Adaptation

Topics we’ll be looking into:

The Visible

Spectrum

We encounter waves of electromagnetic radiation. Our eyes respond to some of these waves.Our brain turns these energy wave sensations into colors.

Vision: Energy, Sensation, and

Perception

Color/Hue and Brightness

We perceive the wavelength/frequency of the electromagnetic waves as color, or hue.

We perceive the height/amplitude of these waves as intensity, or brightness.

Light from the candle passes through the cornea and the pupil, and gets focused and inverted by the lens. The light then lands on the retina, where it begins the process of transduction into neural impulses to be sent out through the optic nerve.

The lens is not rigid; it can perform accommodation by changing shape to focus on near or far objects.

The Eye

The Retina

The Blind Spot

There is an area of missing information in our field of vision known as the blind spot. This occurs because the eye has no receptor cells at the place where the optic nerve leaves the eye.

To test this, walk slowly up to the screen with one eye closed and the other eye fixed on the dot, and one of the phones will disappear.

Photoreceptors: Rods and Cones When light reaches the back of the retina, it triggers

chemical changes in two types of receptor cells: Rods help us see the black and white actions in our

peripheral view and in the dark. Cones help us see sharp colorful details in bright light.

Visual Information Processing

The images we “see” are not made of light; they are made of neural signals which can be produced even by pressure on the eyeball.

The rods and cones send messages to ganglion and bipolar cells and on to the optic nerve.Once neural signals enter the optic nerve, they are sent through the thalamus to the visual cortex.

Turning Neural Signals into Images In the visual cortex are neurons called feature

detectors: they respond to certain visual aspects of the environment.

These cells in turn send information to neural networks (supercell clusters) that can perform tasks such as recognizing individual faces.

Faces

Houses

Chairs

Houses and Chairs

Feature detection areas

Parallel Processing Turning light into the mental act of seeing: light waveschemical reactionsneural impulsesfeaturesobjects

and one more step... Parallel processing: building perceptions out of sensory

details processed simultaneously in different areas of the brain. For example, a flying bird is processed as:

Visual Processing

Color Vision

Young-Helmholtz Trichromatic (Three-Color) TheoryAccording to this theory, there are three types of color receptor cones--red, green, and blue. All the colors we perceive are created by light waves stimulating combinations of these cones.

Color BlindnessPeople missing red cones or green cones have trouble differentiating red from green, and thus have trouble reading the numbers to the right.

Opponent-process theory refers to the neural process of perceiving white as the opposite of perceiving black; similarly, yellow vs. blue, and red vs. green are opponent processes.

Opponent-Process Theory Test

The dot, the dot, keep staring at the dot in the center…

Turning light waves into mental images/movies... Visual Perceptual Organization

We have perceptual processes for enabling us to organize perceived colors and lines into objects: grouping incomplete parts into gestalt wholes seeing figures standing out against background perceiving form and depth keeping a sense of shape, size, and color constancy

despite changes in visual information using experience to guide visual interpretation

Restored vision and sensory restriction Perceptual adaptation

The Role of Perception

Our senses take in the blue information on the right. However, our perceptual processes turn this into:1. a white paper with blue

circle dots, with a cube floating in front.

2. a white paper with blue circle holes, through which you can see a cube.

3. a cube sticking out to the top left, or bottom right.

4. blue dots (what cube?) with angled lines inside.

Figure-Ground Perception In most visual scenes, we pick out objects and figures,

standing out against a background. Some art muddles this ability by giving us two equal

choices about what is figure and what is “ground”:

Stepping man, or arrows?

Goblet or two faces?

Grouping: How We Make Gestalts“Gestalt” refers to a meaningful pattern/configuration, forming a “whole” that is more than the sum of its parts.Three of the ways we group visual information into “wholes” are proximity, continuity, and closure.

Grouping PrinciplesWhich ones influence perception here?

Visual Cliff: A Test of Depth PerceptionBabies seem to develop this ability at crawling age.

Even newborn animals fear the perceived cliff.

Perceiving Depth: Binocular Methods

Unlike other animals, humans have two eyes in the front of our head. This gives us retinal disparity; the two eyes have slightly different views. The more different the views are, the closer the object must be. This is used in 3D movies to create the illusion of depth, as each eye gets a different view of “close” objects.

How do we perceive depth from a 2D image?... by using monocular (needing

only one eye) cues

Monocular Cue: Interposition

Interposition: When one object appears to block the view of another, we assume that the blocking object is in a position between our eyes and the blocked object.

Monocular Cue: Relative Size

We intuitively know to interpret familiar objects (of known size) as farther away when they appear smaller.

Monocular Cues: Linear Perspective and Interposition

The flowers in the distance seem farther away because the rows converge. Our brain reads this as a sign of distance.

Tricks Using Linear

Perspective

These two red lines meet the retina as being the same size

However, our perception of distance affects our perception of length.

Monocular Cue: Relative Height

We tend to perceive the higher part of a scene as farther away.

This scene can look like layers of buildings, with the highest part of the picture as the sky.

If we flip the picture, then the black part can seem like night sky… because it is now highest in the picture.

Monocular Cues: Shading Effects

Shading helps our perception of depth. Does the middle circle bulge out or curve inward?

How about now?

Light and shadow create depth cues.

Monocular Cues: Relative Motion

When we are moving, we can tell which objects are farther away because it takes longer to pass them.

A picture of a moon on a sign would zip behind us, but the actual moon is too far for us to pass.

Perceptual Constancy

Our ability to see objects as appearing the same even under different lighting conditions, at different distances and angles, is called perceptual constancy. Perceptual constancy is a top-down process.

Examples: color and brightness constancy shape and size constancy

Color Constancy This ability to see a

consistent color in changing illumination helps us see the three sides as all being yellow, because our brain compensates for shading.

As a result, we interpret three same-color blue dots, with shades that are not adjusted for shading, as being of three different colors.

Brightness ConstancyOn this screen, squares A and B are exactly the same shade of gray. You can see this when you connect them. So why does B look lighter?

Shape ConstancyShape constancy refers to the ability to perceive objects as having a constant shape despite receiving different sensory images. This helps us see the door as a rectangle as it opens. Because of this, we may think the red shapes on screen are also rectangles.

Size Constancy We have an ability to use distance-related context

cues to help us see objects as the same size even if the image on the retina becomes smaller.

The Ames room was invented by American ophthalmologist Adelbert Ames, Jr. in 1934.

The Ames room was designed to manipulate distance cues to make two same-sized girls appear very different in size.

Visual Interpretation: Restored vision, sensory restrictionExperience shapes our visual perception People have grown up without

vision but then have surgically gained sight in adulthood. They learned to interpret depth, motion, and figure-ground distinctions, but could not differentiate shapes or even faces.

Animals raised at an early age with restrictions, e.g. without seeing horizontal lines, later seem unable to learn to perceive such lines.

We must practice our perception skills during a critical period of development, or these skills may not develop.

Being blind between ages 3 and 46 cost Mike his ability to

learn individual faces.

Perceptual Adaptation After our sensory

information is distorted, such as by a new pair of glasses or by delayed audio on a television, humans may at first be disoriented but can learn to adjust and function.

This man could learn eventually to fly an airplane wearing these unusual goggles, but here, at first, he is disoriented by having his world turned upside down.

The Nonvisual SensesThere’s more to Sensation and Perception than meets the eye

Hearing: From sound to ear to perceiving pitch and locating sounds.

Touch and Pain sensation and perception

Taste and Smell Perception of Body Position and

Movement

Hearing How do we take a sensation based on sound waves and turn it into perceptions of music, people, and actions?

How do we distinguish among thousands of pitches and voices?

Hearing/Audition: Starting with Sound

Height or intensity of

sound wave; perceived as loud and soft

(volume)

Perceived as sound quality or resonance

Length of the sound wave; perceived as high and low

sounds (pitch)

Sound Waves Reach The EarThe outer ear collects sound and funnels it to the eardrum.

In the middle ear, the sound waves hit the eardrum and move the hammer, anvil, and stirrup in ways that amplify the vibrations. The stirrup then sends these vibrations to the oval window of the cochlea.

In the inner ear, waves of fluid move from the oval window over the cochlea’s “hair” receptor cells. These cells send signals through the auditory nerves to the temporal lobe of the brain.

The Middle and Inner EarConduction Hearing Loss: when the middle ear isn’t conducting sound well to the cochlea

Sensorineural Hearing Loss: when the receptor cells aren’t sending messages through the auditory nerves

Cochlea hair cells

Preventing Hearing Loss

Exposure to sounds that are too loud to talk over can cause damage to the inner ear, especially the hair cells.

Structures of the middle and inner ear can also be damaged by disease.

Prevention methods include limiting exposure to noises over 85 decibels and treating ear infections.

Treating Hearing Loss

People with conduction hearing loss may be helped by hearing aids. These aids amplify sounds striking the eardrum, ideally amplifying only softer sounds or higher frequencies.

People with sensorineural hearing loss can benefit from a cochlear implant. The implant does the work of the hair cells in translating sound waves into electrical signals to be sent to the brain.

Loudness refers to more intense sound vibrations. This causes a greater number of hair cells to send signals to the brain.

Soft sounds only activate certain hair cells; louder sounds move those hair cells AND their neighbors.

Sound Perception: Loudness

Sound Perception: Pitch

Frequency theoryAt low sound frequencies, hair cells send signals at whatever rate the sound is received.

Place theoryAt high sound frequencies, signals are generated at different locations in the cochlea, depending on pitch. The brain reads pitch by reading the location where the signals are coming from.

How does the inner ear turn sound frequency into neural frequency?

Volley PrincipleAt ultra high frequencies, receptor cells fire in succession, combing signals to reach higher firing rates.

Sound Perception: LocalizationHow do we seem to know the location of the source of a sound? Sounds usually

reach one of our ears sooner, and with more clarity, than they reach the other ear.

The brain uses this difference to generate a perception of the direction the sound was coming from.

Other SensesWe may not have all of the sensory abilities of the shark (such as sensing the electric fields of others) or migratory birds (such as orienting by the earth’s magnetic field).

But we do have senses of: smell and taste. four different components of the sense of

touch. body/kinesthetic awareness.

Touch

Touch is valuable… for expressing

and sensing feelings.

for sharing affection, comfort, and support.

for detecting the environment in multiple ways, such as pressure, warmth, cold, and pain.

Four Components of Touch

Stroking adjacent pressure spots creates a tickle.

Adjacent cold and pressure sensations feel wet.

Adjacent warm and cold feels searing hot.

Warmth

PainCold

Pressure

Pain...what is it good for?

Pain tells the body that something has gone wrong. Pain often warns of severe injury, or even just to shift positions in a chair to keep blood flowing.

Not being able to feel pain, as in Ashley’s case, means not being able to tell when we are injured, sick, or causing damage to our bodies.

Biological Factors in Pain Perception: The Pain Circuit

Nociceptors are sensory receptors whose signals are interpreted by the brain as pain.

The pain circuit refers to signals that travel to the spinal cord, up through small nerve fibers, which then conduct pain signals to the brain.

Gate-Control TheoryThis theory hypothesizes that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain. Stimulating large nerve fibers in the spinal cord through acupuncture, massage, or electrical stimulation seems to close that gate.

EndorphinsThese hormones can be released by the body to reduce pain perception.

Phantom Limb SensationAs the brain produces false sounds (tinnitus, ear ringing) and sights (aura, lights with migraines), it can produce pain or other perception of amputated/missing arms or legs.

Biological Factors in Pain Perception

Psychological Influences on PainDistraction, such as during intense athletic competition, can limit the experience of pain.Pain and Memory Memories of pain

focus on peak moments more than duration.

Tapered pain is recalled as less painful than abruptly-ended pain.

Social and Cultural Influenceson Pain Perception

Social contagionWe feel more pain if other people are experiencing pain. This occurs either out of empathy/mirroring, or a shared belief that an experience is painful.

Cultural influencesWe may not pay attention as much to pain if we see a high level of pain endurance as the norm for our family, peer group, or culture.

Controlling/Managing/Reducing Pain Pain can be reduced through drugs, acupuncture,

electrical stimulation, exercise, hypnosis, surgery, relaxation training, and distraction.

Even the placebo effect has real influence on pain perception. When we think we are taking pain killers or receiving acupuncture, our bodies can release endorphins.

Distraction with virtual reality immersion (below) has helped burn victims manage intense pain.

Biopsychosocial Influences on Pain Perception

Examples of each influence: gate control selective

attention empathy pain

Sweet: energy source

Sour:potentially toxic acid

Umami: (savoriness)proteins to grow and repair tissue Salty: sodium

essential to physiological processes

Bitter:potential poisons

TasteOur tongues have

receptors for five different types of tastes, each of

which may have had survival functions.

Neurochemistry of Taste There are no regions of the tongue,

just different types of taste receptor cells projecting hairs into each taste bud’s pore.

These cells are easily triggered to send messages to the temporal lobe of the brain.

Burn your tongue? Receptors reproduce every week or two. But with age, taste buds become less numerous and less sensitive.

Top-down processes still can override the neurochemistry; expectations do influence taste.

Smell: Odor ReceptorsHumans have a poor sense of smell for an animal. Even so, humans have 350 different types of smell receptors allowing us to detect about 10,000 different odors.

Smell: The Shortcut Sense Sensations of smell take a

shortcut to the brain, skipping the trip through the “sensory switchboard” (thalamus) made by all the other senses.

Information from the nose goes not only to the temporal lobe but also to the limbic system, influencing memory and emotion.

Smell links lovers, parent and child, and other creatures to each other through chemistry.

Sensing Body Position and Movement

Kinesthesis (“movement feeling”): sensing the movement and position of individual body parts relative to each other.

How it works: sensors in the joints and muscles send signals that coordinate with signals from the skin, eyes, and ears

Without kinesthesis, we would need to watch our limbs constantly to coordinate movement.

Sensing Body Position and Movement Vestibular sense: the ability to sense

the position of the head and body relative to gravity, including the sense of balance.

How it works: fluid-filled chambers in the inner ear (vestibular sacs and semicircular canals) have hairlike receptors that send messages about the head’s position to the cerebellum

Vestibular sense serves as the human gyroscope, helping us to balance and stay upright.

Mixing the different senses togetherSensory interaction occurs when different senses influence each other.For example: a burst of sound makes a

dim light source more visible.

flavor is an experience not only of taste, but also of smell and texture.

seeing text or lip movement, or even feeling the puff of air from consonants, affects what words we hear.

456789Synaesthesia is a condition when perception in one sense is triggered by a sensation in a DIFFERENT sense.Some people experience synaesthesia all the time, reporting that, “the number 7 gives me a salty taste” or “rock music seems purple.”

Embodied Cognition

holding a warm mug promotes social warmth. social rejection looks like pain reception in the brain. words on a heavy clipboard seem… weighty. being ignored (cold shoulder) makes a room seem

colder. leaning left physically leaning left politically. in a foul smelling room, people were more likely to

suspect bad intentions (foul play) by others.

It’s no coincidence that we use sensation words to describe feelings. Studies seem to show that:

Embodied cognition refers to the effect of body experience on feelings, attitudes, thoughts, and judgments.

Extrasensory Perception (ESP)Extrasensory Perception (ESP) can defined, literally, as perception without sensation. Believers in ESP think that it involves getting accurate information directly to the mind, skipping the known senses.Types of ESP include: telepathy (“reading” messages from other minds). clairvoyance (“seeing” remote events). precognition (“knowing” the future).The evidence for ESP is anecdotal and controversial; people seem to notice times when predictions come true and perceptions match reality, but tend to disregard the times when they do not.

Summarizing the Senses