Sensation and Perception - Sights + Sounds · Subliminal sensation and subliminal persuasion...

Revised by Pauline Davey Zeece, University of Nebraska-Lincoln

5Sensation and

Perception

Chapter Overview Chapter Overview

Basic concepts of sensation and perception

Vision: Sensory and perceptual processing

The nonvisual senses

Sensory interaction

ESP—Perception without sensation?

Basic concepts of sensation and perception

Vision: Sensory and perceptual processing

The nonvisual senses

Sensory interaction

ESP—Perception without sensation?

Basic Concepts of Sensation and Perception

From outer energy to inner brain activity Thresholds Thinking critically about: Subliminal sensation

and subliminal persuasion Sensory adaptation Perceptual set Context, motivation, and emotion

Sensation and Perception

Sensation

• Process by which the sensory receptors and nervous system receive and represent stimulus energies from our environment

Perception

• Process by which the brain organizes and interprets sensory information, transforming it into meaningful objects and events

Bottom-Up and Top-Down Processing

Bottom-up processing

• Analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information

Top-down processing

• Information processing guided by higher-level mental processes

• Draws on one’s experiences and expectations

What’s Going on Here?

Our sensory and perceptual processes work together to help us sort out complex images, including the hidden couple in Sandro Del-Prete’s drawing, The Flowering of Love.

Steps That Are Basic to the Sensory Systems

Receive sensory stimulation

Transform the stimulation into neural impulses

Deliver the neural information to the brain

Retrieve and Remember 1

What is the rough distinction between sensation and perception?

Absolute Threshold

Minimum stimulus energy needed to detect a particular stimulus 50 percent of the time

Subliminal: Below an individual’s absolute threshold for conscious awareness

Difference Threshold

Minimum difference between two stimuli required for detection 50 percent of the time

Individuals experience the difference threshold as a just noticeable difference (or jnd).

Weber’s law: Principle that two stimuli must differ by a constant minimum percentage to be perceived as different Exact percentage differs based on the

stimulus.

Thinking Critically

Subliminal sensation and subliminal persuasion Individuals can be affected by subliminal

sensations.Stimuli that are so weak that people do not

consciously notice them Researchers use priming to activate

unconscious associations. Individuals can evaluate a stimulus, even

when they are not consciously aware of it.


Using sound as your example, show how these concepts differ: Absolute threshold Subliminal

stimulation Difference threshold

Introduction: Sensory Adaptation

Reduced sensitivity in response to constant stimulation

Helps focus on informative changes in the environment without being distracted by background chatter

Influences perceptions of emotions

Sensory Adaptation

a. A projector mounted on a contact lens makes the projected image move with the eye.

b. At first, the person sees the whole image.

Then, as the eye grows accustomed to the unchanging stimulus, the image begins to break into fragments that fade and reappear.

Emotion Adaptation

Gaze at the angry face on the left for 20 to 30 seconds, then look at the center face (looks scared, yes?).

Then gaze at the scared face on the right for 20 to 30 seconds, before returning to the center face (now looks angry, yes?).


Why is it that after wearing shoes for a while, you cease to notice them (until questions like this draw your attention back to them)?

Perceptual Set

Mental predisposition to perceive one thing, rather than another Affects what an

individual sees, hears, tastes, and feels

Believing Is SeeingWhat do you perceive? Is this Nessie, the Loch Ness monster, or a log?

Believing Is SeeingWhat do you perceive? Is this Nessie, the Loch Ness monster, or a log?

Context, Motivation, and Emotion

Affect interpretations of a situation Context creates expectations that influence

individual perception. Motives provide energy to work toward a goal. Can cause bias in interpreting neural stimuli

Experiences, assumptions, and expectations can shape and color views of reality via top-down processing.

Figure 5.6 - Culture and Context Effects


Does perceptual set involve bottom-up or top-down processing? Why?

Vision: Sensory and Perceptual Processing

Light energy and eye structures Information processing in the eye and brain Perceptual organization Perceptual interpretation

The Wavelengths We See

Wavelengths visible to the human eye extend from the shorter waves of blue-violet light to the longer waves of red light.

Light Energy

Wavelength: Distance from the peak of one light wave to the peak of the next

Hue: Dimension of color that is determined by the wavelength of light

Intensity: Amount of energy in a light wave Influences what individuals perceive as

brightness or loudness Determined by the wave’s amplitude or height

Figure 5.10 - The Physical Properties of Waves

The Eye

The iris controls the amount of light entering the eye.

Light hits the lens in the eye after passing through the pupil.

The lens focuses the light rays into an image on the retina.

Figure 5.11 - The Eye

The Retina

Light-sensitive inner surface of the eye Contains: Receptor rods and cones Layers of neurons that begin the processing

of visual information

Figure 5.12 - The Retina’s Reaction to Light

Information Processing in the Eye and Brain

Retinal receptors Rods: Detect black, white, and grayNecessary for peripheral and twilight vision,

when cones do not respond Cones: Detect fine detail and give rise to color

sensations in daylight or well-lit conditions Optic nerve: Carries neural impulses from the eye to

the brain Blind spot: Point where the optic nerve leaves the

eye and has no receptor cells

Rods and Cones

Cones Rods

Number 6 million 120 million

Location in retina Center Periphery

Sensitivity in dim light

Low High

Color sensitivity High Low

Detail sensitivity High Low

Figure 5.14 - Pathway from the Eyes to the Visual Cortex


Some night-loving animals, such as toads, mice, rats, and bats, have impressive night vision thanks to having many more _____ (rods/cones) than _____ (rods/cones) in their retinas.

These creatures probably have very poor _____ (color/black-and-white) vision.

Cats are able to open their _____ much wider than we can, which allows more light into their eyes, so they can see better at night.

Color Processing

Young-Helmholtz trichromatic theory The retina contains three different types of color

receptors—red, green, and blue.

When stimulated in combination, these receptors can produce the perception of any color.

Opponent-process theory Opposing retinal processes enable color vision.

Opposing retinal processes include red-green, yellow-blue, and white-black.

Color Processing - Current Theory

Color processing combines the trichromatic theory and the opponent-processing theory and occurs in two stages. The retina’s red, green, and blue cones

respond in varying degrees to different color stimuli. The cones’ responses are processed by

opponent-process cells.


What are two key theories of color vision? Do they contradict each other, or do they make sense together? Explain

Feature Detectors, Part 1

Nerve cells in the brain that respond to specific features of a stimulus Include shape, angles, or movement

Pass scene specific information to other cortical areas, where more complex patterns are interpreted

Feature Detectors, Part 2

One temporal lobe area by the right ear enables a person to perceive faces. A specialized neural network helps recognize

faces from many viewpoints. Interaction between feature detectors and

supercells provides instant analyses of objects in the world around people.

Well-Developed Supercells

In the 2011 World Cup match, USA’s Abby Wambach instantly processed visual information about the positions and movements of Brazil’s defenders and goalkeeper and somehow managed to get the ball around them all and into the net.

Introduction: Parallel Processing

Processing many aspects of a problem or scene at the same time

Brain’s natural mode of information processing for many functions, including vision

Damage to neural workstations due to a stroke may render a person unable to perceive movement.

Parallel Processing

Studies of patients with brain damage suggest that the brain delegates the work of processing motion, form, depth, and color to different areas. After taking a scene apart, the brain integrates

these parts into a whole perceived image.

A Simplified Summary of Visual Information Processing

Scene

Retinal processing - Receptor rods and cones → bipolar cells → ganglion cells

Feature detection – The brain’s detector cells respond to specific features—edges, lines, and angles.

Parallel processing - Brain cell teams process combined information about color, movement, form, and depth.

Recognition – The brain interprets the constructed image based on information from stored images.

Gestalt

Refers to an organized whole

Gestalt psychologists emphasized the human tendency to integrate pieces of information into meaningful wholes.

Necker cube

Perceptual Organization

The human brain registers information about the world, filters incoming information, and constructs perceptions.

Principles in perceptual organization: Form perception Depth perception Perceptual constancy

Form Perception

Figure-ground: Organization of the visual field into objects that stand out from their surroundings

Grouping: The perceptual tendency to organize stimuli into meaningful groups Proximity Continuity Closure

Reversible Figure andGround

A classic example Is this a vase or is it

two faces?

Rules for Grouping

Illustrate how the perceived whole differs from the sum of its parts.

Also applicable for human touch perception


In terms of perception, a band’s lead singer would be considered _____ (figure/ground), and the other musicians would be considered _____ (figure/ground).

What do we mean when we say that, in perception, “the whole may exceed the sum of its parts”?

Depth Perception

Ability to see objects in three dimensions, although images that strike the retina are two-dimensional

Allows people to judge distance

Partly innate in other animals

Depth Perception: Visual Cliff

Devised by Eleanor Gibson and Richard Walk Laboratory device for testing depth perception in

infants and young animals Most infants refuse to crawl across the visual

cliff. Crawling, no matter when it begins, seems to

increase an infant's fear of heights.

Visual Cliff

Miniature cliff with a glass-covered drop-off

Helps determine whether crawling infants and newborn animals can perceive depth Even when coaxed,

infants refuse to climb onto the glass over the cliff.

Depth Cues

Binocular cue: Depends on the use of two eyes

Retinal disparity: The calculation of distance by the brain by comparing images from both eyes

Used by 3-D film makers

Monocular cue: Cue available to each eye separately

Includes relative height, relative size, interposition, relative motion, linear perspective, and light and shadow

Figure 5.22 - The Floating Finger Sausage

Figure 5.23 - Monocular Depth Cues


How do we normally perceive depth?

Motion Perception

The human brain computes motion based partly on its assumption that: Shrinking objects are moving away Enlarging objects are approaching

Humans are imperfect at motion perception. When large and small objects move at the

same speed, the large objects appear to move more slowly.

Perceptual Constancy

Perceiving objects as unchanging, even as illumination and retinal images change Objects have consistent color, brightness,

shape, and size. Color constancy Perceiving familiar objects as having

consistent color, even if changing illumination alters the wavelengths reflected by the object

Color Depends on Context

(a) Believe it or not, these three blue disks are identical in color.

(b) Remove the surrounding context and see what results.

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Lightness Constancy

The color and brightness of square A and B are the same.

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Lightness Constancy

The color and brightness of square A and B are the same.

Shape and Size Constancies

Shape constancy: Perception that the form of a familiar object is constant, even when retinas receive changing images of them

Size constancy: Perception that objects have a constant size, even when one’s distance from them varies

The Moon Illusion

The Moon looks up to 50 percent larger when near the horizon than when high in the sky.

Monocular cues to an object’s distance make the horizon Moon appear farther away. If it’s farther away, the brain assumes that it

must be larger than the Moon high in the night sky.

When the distance cues are taken away, the object will immediately shrink.

Perceptual Interpretation

According to Immanuel Kant, human beings have the innate ability to process sensory information.

John Locke argued that individuals also learn to perceive the world through their experiences. Learn to link an object’s distance with its size

Experience and Visual Perception

Research findings The effect of sensory restriction on infant cats,

monkeys, and humans suggests that there is a critical period for normal sensory and perceptual development.

In humans and other animals, sensory restrictions do not cause permanent harm later in life.

Perceptual Adaptation

Ability to adjust to changed sensory input Includes adjustments to an artificially

displaced or even inverted visual field Humans constantly adjust to changed sensory

input. Early nurture sculpts what nature has provided. Experience guides, sustains, and maintains the

pathways in the brain that enable perceptions.

Perceptual Adaptation: Hubert Dolezal

“Oops, missed,” thought researcher Hubert Dolezal as he attempted a handshake while viewing the world through inverting goggles.

The Nonvisual Senses

Hearing Touch Taste Smell Body position and movement

Hearing

Audition: Sense or act of hearing Helps individuals adapt and survive Provides information and enables

relationships Enables individuals to communicate invisiblyHearing loss is an invisible disability.

Humans are acutely sensitive to faint sounds and sound differences.

Sound Waves

Vary in shape Moving molecules of

air create waves of compressed and expanded air. Ears detect these

brief air pressure changes.

The Sounds of Music: A violin's short, fast waves create a high pitch. The longer, slower waves of a cello or bass create a lower pitch.

The Sounds of Music: A violin's short, fast waves create a high pitch. The longer, slower waves of a cello or bass create a lower pitch.

Characteristics of Sound Waves

Amplitude or height Determines the perceived loudness of sound

waves Frequency or length Number of complete wavelengths that pass a

point in a given time Pitch: A tone’s experienced highness or

lowness that depends on frequency Sound is measured in decibels.


The amplitude of a sound wave determines our perception of _____ (loudness/ pitch).

The longer the sound waves are, the _____ (lower/higher) their frequency is and the _____ (higher/lower) their pitch.

Decoding Sound Waves

Sound waves strike the eardrum, causing it to vibrate.

Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea, in the inner ear.

Ripples in the cochlea fluid bend the hair cells lining the surface, which trigger impulses in nerve cells.

Axons from these nerve cells transmit a signal to the auditory cortex.

Figure 5.26 - Transforming Sound Waves into Neural Messages

Hearing Loss

Sensorineural hearing loss

• Caused by damage to the cochlea's receptor cells or to the auditory nerves

• Called nerve deafness

Conduction hearing loss

• Caused by damage to the mechanical system that conducts sound waves to the cochlea

• Less common form of hearing loss

Locating Sounds

Two ears are better than one. Sound waves strike

one ear sooner and more intensely than the other. From this

information, the brain can compute the sound’s location.

Touch

Sense of touch - Mix of four distinct skin senses Pressure Warmth Cold Pain

Other skin sensations are variations of the basic skin senses.

The human brain influences sensory responses.

Pain

Body’s way of telling the individual that something has gone wrong

Greater number of infections and injuries when there are no warnings of pain

Reflects both bottom-up sensations and top-down cognition

Biopsychosocial event

Pain is a Gift

Ashlyn Blocker has a rare genetic mutation that prevents her from feeling pain. “Everyone in my

class asks me about it, and I say, ‘I can feel pressure, but I can’t feel pain.’ Pain!I cannot feel it!”

Biological Influences of Pain

Pain is not triggered by any one type of stimulus. Pain signals are not processed by specialized

receptors. Sensory receptors called nociceptors detect

hurtful temperatures, pressure, or chemicals. Experience of pain depends on the inherited

genes and physical characteristics. The brain sometimes misinterprets its signals

and can create pain.

Psychological Influences of Pain

Attention focused on pain is a powerful influence on human perception of pain.

Individuals seem to edit their memories of pain. Pain experienced may not be the pain that is

remembered.

Distracted from the Pain

Halfway through his lap of the 2012 Olympics 1600-meter relay, Manteo Mitchell broke one of his leg bones—and kept running.

Social-Cultural Influences of Pain

Pain is a product of an individual's attention, expectations, and culture.

Perception of pain varies with social situation and cultural traditions. Humans feel more pain when others seem to

be experiencing pain.

Pain Control Therapies

Drugs Surgery Acupuncture

Electrical stimulation Massage Exercise

Hypnosis Relaxation training

Thought distraction

Acupuncture: A Jab Well Done

Acupuncturists attempt to help people gain relief from pain by using needles on points of the patient’s body.

Built-In Pain Controls: Endorphins and Placebos

Endorphins Natural painkiller released by the brain Have a soothing effect that enables pain

reduction Placebos Help dampen the central nervous system’s

attention and responses to painful experiences

Built-In Pain Controls

Combination of endorphins and distraction Activate brain pathways that decrease pain

and increase tolerance Maximum pain relief can be obtained by: Combining a placebo and a distraction Amplifying the resulting effects from the

combination via hypnosis

Hypnosis

Social interaction where one person suggests to another that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur

Inhibits pain-related brain activity Explained by the social influence theory and the

dissociation theory Does not block the sensory input itself, but it

may block individual's attention to those stimuli

Dissociation or Social Influence?

This hypnotized woman being tested by famous researcher Ernest Hilgard showed no pain when her arm was placed in an ice bath. But when asked to

press a key if some part of her felt the pain, she did so.

To Hilgard, this was evidence of dissociation, or divided consciousness. The social influence perspective, however, maintains that people responding this way are caught up in playing the role of “good subject.”


Which of the following options has NOT been proven to reduce pain?a. Distractionb. Hypnosisc. Phantom limb sensationsd. Endorphins

Table 5.2 - The Survival Functions of Basic Tastes

Taste Indicates

Sweet Energy source

Salty Sodium essential to physiological processes

Sour Potentially toxic acid

Bitter Potential poisons

Umami Proteins to grow and repair tissue

Taste

Involves several basic sensations Sweet, sour, salty, bitter, and umami

Gives pleasure and helps people survive Can be influenced by learning and expectations Number of taste buds and taste sensitivity

decrease with age Smoking and alcohol can speed up the loss of

taste buds.

Taste: A Chemical Sense

Each bump on the top and sides of the tongue contains 200 or more taste buds.

Each bud contains a pore with 50–100 taste receptor cells.

Each receptor reacts to different types of food molecules and sends messages to the brain.

Smell: A Chemical Sense

Smell is enabled by millions of olfactory receptors that respond selectively to odors. Bypass the thalamus and directly alert the

brain Odor molecules exist in many shapes and sizes. Smell’s appeal, or the lack of it, depends partly

on learned associations. Odors can evoke strong feelings, memories, and

behaviors.

The Nose Knows

Humans have some 20 million olfactory receptors. Bloodhounds have

220 million.

Taste, Smell, and Memory

Information from the taste buds travels to an area between the frontal and temporal lobes of the brain. It registers in an area

not far from where the brain receives information from our sense of smell, which interacts with taste.


How does our system for sensing smell differ from our sensory systems for vision, touch, and taste?

Body Position and Movement

Kinesthesia System for sensing

the position and movement of individual body parts

Vestibular sense Sense of body

movement and position, including the sense of balance

These high school competitive cheer team members can thank their inner ears for the information that enables their brains to monitor their bodies’ position so expertly.


Where are kinesthetic sense and vestibular sense receptors located?

Sensory Interaction

Introduction: Sensory Interaction

Principle that one sense may influence another Smell can enhance taste, and touch can

influence it. Hearing and vision can interact.

Sensation and perception are two points on a continuum. Brain circuits that process bodily sensations

may interact with brain circuits that are responsible for cognition.

Face-to-Face

Seeing the speaker forming the words, which Apple’s FaceTime video-chat feature allows, makesthose words easier to understand for hard-of-hearing listeners.

Sensory Interaction

Embodied cognition: Influence of bodily sensations, gestures, and other states on cognitive preferences and judgments

The brain blends inputs from multiple channels. Synesthesia Condition where one sort of sensation

produces another Occurs when brain circuits for two or more

senses become joined

Table 5.3 - Summarizing the SensesSensory System

Source Receptors Key Brain Areas

Vision Light waves striking the eye Rods and cones in the retina Occipital lobes

Hearing Sound waves striking the outer ear

Cochlear hair cells in the inner ear

Temporal lobes

Touch Pressure, warmth, cold, harmful chemicals

Receptors (nociceptors), mostly in the skin, which detect pressure, warmth, cold, and pain

Somatosensory cortex

Taste Chemical molecules in the mouth

Basic tongue receptors for sweet, sour, salty, bitter, and umami

Frontal temporal lobe border

Smell Chemical molecules breathed in through the nose

Millions of receptors at top of nasal cavities

Olfactory bulb

Body position—kinesthesia

Any change in position of a body part, interacting with vision

Kinesthetic sensors in joints, tendons, and muscles

Cerebellum

Body movement—vestibular sense

Movement of fluids in the inner ear caused by head/ body movement

Hair-like receptors in the ears’ semicircular canals and vestibular sacs

Cerebellum

ESP—Perception Without Sensation?

Extrasensory Perception (ESP)

Controversial claim that perception can occur apart from sensory input

Includes three claims: Telepathy - Mind-to-mind communication Clairvoyance - Perceiving remote events Precognition - Perceiving future events

Closely linked to psychokinesis or mind over matter

ESP Research and Experiments

Most research psychologists and scientists have been skeptical of ESP claims. It is difficult to test ESP claims in a controlled,

reproducible environment. Daryl Bem conducted nine experiments that

suggested participants could anticipate future events. Critics viewed the methods as badly flawed.

Testing Psychic Powers in the British Population

Psychologists created a mind machine to see if people could influence or predict a coin toss. Using a touch-sensitive

screen, visitors to British festivals were given four attempts to call heads or tails, playing against a computer that kept score.


If an ESP event occurred under controlled conditions, what would be the next best step to confirm that ESP really exists?

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