© 2008 The McGraw-Hill Companies, Inc.

Chapters 5-6Sensation and PerceptionConsciousness

© 2008 The McGraw-Hill Companies, Inc.

Windows on the World

How we understand our world

Two basic processes: Sensation: Gathering

information Perception: Interpreting

information

© 2008 The McGraw-Hill Companies, Inc.

Basic Principles

Sensation The process of receiving stimulus energies from the

external environment Transduction

The process of transforming physical energy into electrochemical energy (action potential)

Perception The process of organizing and interpreting sensory

information

© 2008 The McGraw-Hill Companies, Inc.

Sensation

Sensory Receptors Specialized cells that detect and transmit

sensory information to the brain

These cells respond selectively to stimulation

Cells send signals via distinct neural pathways

© 2008 The McGraw-Hill Companies, Inc.

Figure 5-1 Sensation and Perception

Can you identify anything meaningful in these patterned shapes?

Sensation is detecting the different shapes

However, organizing it into something is the process of perception.

© 2008 The McGraw-Hill Companies, Inc.

Sensation and Perception

Look at the three boxes below. Write down what color you think each box represents.

© 2008 The McGraw-Hill Companies, Inc.

Sensation and Perception

The boxes are colored in lime, turquoise and rose.

If each student is receiving the same sensation of color from each of the boxes, then why do some students have different perceptions of the colors?

© 2008 The McGraw-Hill Companies, Inc.

Sensation

Photoreception (Vision) Detection of light

Mechanoreception (Touch) Detection of pressure, vibration, and movement

Chemoreception (Smell and Taste) Detection of chemical stimuli

© 2008 The McGraw-Hill Companies, Inc.

Absolute Thresholds Absolute threshold:

the lowest level of a stimulus detected half the time

Subliminal stimulus detected only up to 49% of the time short-lived, no long-term consequences

© 2008 The McGraw-Hill Companies, Inc.

Absolute Thresholds

Absolute thresholds can vary across individuals Limitations and variances

Age Abilities Experiences

Fatigue: Life and death implications

© 2008 The McGraw-Hill Companies, Inc.

Difference Thresholds Detection of change or

discrimination between stimuli

JND: smallest difference between two stimuli detected half the time

JNDs vary from person to person

JND’s vary by sense Ex) hearing compared to taste

© 2008 The McGraw-Hill Companies, Inc.

Difference Thresholds Weber’s Law: For a person to notice change:

A weak or a small stimulus does not require much change

Strong or large stimulus requires a proportionately greater change

Ex) 2nd vs. 80th candle on a birthday cake in a dark room

© 2008 The McGraw-Hill Companies, Inc.

Sensory Adaptation Sensory Adaptation

responsiveness to stimuli diminishes with repeated exposure

Evolutionary Value vs. Everyday Value

Smell adapts quickly Ex) Fish store or being on a farm

Vision prevents adaptation

© 2008 The McGraw-Hill Companies, Inc.

Processing Light Color is produced/created by the nervous system in

response to wavelengths Color is determined by an absorption certain wavelengths Wavelengths

Short violet Midlength green, blue, yellow Long red

Average person can discriminate about two million different colors

Photoreceptors Rods—black, white, gray (125 million) Cones—colors (7 million

© 2008 The McGraw-Hill Companies, Inc.

Signal Detection Theory

© 2008 The McGraw-Hill Companies, Inc.

Signal Detection Theory

Decision making when uncertain involves Information acquisition Criterion

Factors that shape this decision making process: Expectations (of observer) Rewards/costs associated with detecting/not

detecting

© 2008 The McGraw-Hill Companies, Inc.

Factors Affecting Perception

Attention Selective attention Cocktail party effect Novelty, size, color, movement

Stroop Effect Reading is highly practiced, automatic activity Bottom-up processing (stimulus-driven)

Sensory Adaptation

© 2008 The McGraw-Hill Companies, Inc.

Stroop Effect

© 2008 The McGraw-Hill Companies, Inc.

Perceptual Processing Bottom-up Processing

Processing of sensory info as it enters the receptors and travels to the brain Face-value interpretation

Initiated by sensory input Sensation Perception

Top-Down Processing Uses existing information (learning history) to interpret sensory

information Initiated by cognitive processing Perception Sensation

© 2008 The McGraw-Hill Companies, Inc.

Perceptual Constancy

Perceptual Constancy: The tendency to perceive objects as relatively stable despite continually changing sensory information.

Examples:

Shape, size, color, brightness

Varying distances, lighting conditions, angles

© 2008 The McGraw-Hill Companies, Inc.

Perceptual Constancy Size Constancy:

Tendency to perceive objects as same size stable in size even if viewed from a distance

© 2008 The McGraw-Hill Companies, Inc.

Perceptual Constancy

Shape Constancy:

Tendency to perceive an object as the same shape no matter from what angle it is viewed.

© 2008 The McGraw-Hill Companies, Inc.

The Mueller-Lyer IllusionIllusions

Depending on the direction of the arrow Inward or outward Two equal length lines One appears longer

© 2008 The McGraw-Hill Companies, Inc.

The Visual Cliff Experiment to test depth

perception in infants Found that infants early

on could perceive depth Older infants would not

crawl on “deep” side Younger infants showed

physiological changes

© 2008 The McGraw-Hill Companies, Inc.

Form Perception The process by which sensations are

organized into meaningful shapes and patterns.

The figure-and-ground principle brain organizes sensory input into:

a figure (the center of attention) ground (the background)

Rubin’s characteristics

“Thinglike”

In front of ground

Dominates, more memorable

© 2008 The McGraw-Hill Companies, Inc.

Laws of Grouping Similarity- Group together stimuli that are similar

Proximity-Group together stimuli that are together

Continuity-Perception of contours or straight lines as continuous

Closure- Tendency to close figures gaps in a figure and perceive it as whole.

© 2008 The McGraw-Hill Companies, Inc.

Laws of Grouping: Demos

© 2008 The McGraw-Hill Companies, Inc.

The Nature of Consciousness

What is consciousness? Our awareness of external events and internal

sensations which occurs under conditions of arousal

© 2008 The McGraw-Hill Companies, Inc.

Levels of Awareness

© 2008 The McGraw-Hill Companies, Inc.

Levels of Awareness

Higher-Level Consciousness Controlled processes

Lower-Level Consciousness Automatic processes Daydreaming

Subconscious Awareness Parallel processing

Sleep and Dreams Low levels of

consciousness

No Awareness Unconscious thought

(Freud) Non-conscious processes

© 2008 The McGraw-Hill Companies, Inc.

Sleep: Biological Rhythms

Rhythms controlled by biological clocks Annual or seasonal 28-day cycles/24-hour cycles

Circadian Rhythms

Desynchronizing the clock Jet lag Shift-work problems Insomnia

Resetting the clock Bright light Melatonin

© 2008 The McGraw-Hill Companies, Inc.

Why Do We Sleep?

Benefits of Sleep Important for physical and mental functioning

Restorative Function

Adaptive Evolutionary Function

Growth and Development

Memory

© 2008 The McGraw-Hill Companies, Inc.

Sleep Deprivation

Chronic sleep deprivation results in… Decreased alertness and cognitive performance Inability to sustain attention Less complex brain activity Adverse effects on decision making

Research indicates we should get at least 8 hours of sleep each night!

© 2008 The McGraw-Hill Companies, Inc.

Stages of Sleep

EEG measures electrical activity in the brain Awake Stage 1: light sleep

Stage 2: light sleep Sleep spindles

Stage 3: deep sleep

Stage 4: deep sleep Difficult to wake sleepers

REM sleep

© 2008 The McGraw-Hill Companies, Inc.

Stages of Sleep

© 2008 The McGraw-Hill Companies, Inc.

REM Sleep

Rapid-Eye-Movement Sleep = REM sleep Rapid eye movement; dreaming

Stage 1-4: Non-REM Sleep Lack of rapid eye movement; little dreaming

Dreams: Non-REM versus REM Sleep

Developmental Changes in REM Sleep

© 2008 The McGraw-Hill Companies, Inc.

Sleep Cycles

90-100 minutes per cycle

Sleep patterns change during the night.

Typical night 60% - Stages 1 & 2 sleep 20% - Stages 3 & 4 sleep 20% - REM sleep

© 2008 The McGraw-Hill Companies, Inc.

Sleep Disorders

Insomnia

Sleepwalking, Sleep Talking, Sleep Eating

Nightmares versus Night Terrors

Narcolepsy

Sleep Apnea

© 2008 The McGraw-Hill Companies, Inc.

Hypnosis

Hypnosis marked by Altered attention and awareness Unusual receptiveness to suggestions

Four Steps in Hypnosis1. Distractions are minimized

2. Told to concentrate on something specific

3. Told what to expect

4. Suggest events or feelings sure to occur

© 2008 The McGraw-Hill Companies, Inc.

Psychoactive Drugs

Various substances alter consciousness, modify perceptions, and change moods

Why do people take drugs?

Continued use can lead to… Tolerance Physical dependence and withdrawal Psychological dependence Addiction

© 2008 The McGraw-Hill Companies, Inc.

Critical Controversy

Medicinal uses for psychedelic drugs?

LSD

Medical Marijuana

Psychedelic Drugs, Insight, and Creativity