Sensation and Perception

Our Sensational Senses

What is the difference between sensation and perception?

What is psychophysics? How do we measure the senses? What is sensory adaptation? When do you experience sensory

overload?

Defining Sensation and Perception Sensation

The detection of physical energy emitted or reflected by physical objects.

It occurs when energy in the external environment or the body stimulates receptors in the sense organs.

The study of sensation is the study of energy.

Perception The process by which the brain

organizes and interprets sensory information.

Ambiguous Figure

Colored surface can be either the outside front surface or the inside back surface Cannot

simultaneously be both

Brain can interpret the ambiguous cues two different ways

Separate Sensations Sense receptors

Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.

Transduction: the process where physical energy is converted to electrochemical.

Sensation & Perception Processes

Why do have different senses?

Different sensorys exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain.

Synthesia A condition in which stimulation of

one sense also evokes another.

What is Psychophysics? Discipline within psychology that

quantitatively investigates the relationship between physical stimulus and the sensations and perceptions they affect.

1860-Gustav Fechner is founding father Do you remember what Wilhelm Wundt did?

He built on Fechner’s work and started his own psychological research lab!

We can measure senses by…

Absolute threshold Difference threshold Signal-detection theory

Absolute Threshold The smallest quantity of physical energy that

can be reliably detected by an observer (50% of the time in general population)

Absolute Sensory Thresholds

Vision: A single candle flame from 30 miles on a dark, clear

night Hearing:

The tick of a watch from 20 feet in total quiet Smell:

1 drop of perfume in a 6-room apartment Touch:

The wing of a bee on your cheek, dropped from 1 cm Taste:

1 tsp. Sugar in 2 gal. water

Difference Threshold The smallest difference in stimulation that

can be reliably detected by an observer when two stimuli are compared;

Also called Just Noticeable Difference (JND). Weber’s Law: JND is proportional to stimulus

intensity Greater the magnitutude of the stimulus, the

larger the difference must be to be noticed

Signal-Detection Theory A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision

process. Bias plays a role in detecting stimulus. It can be psychological or physical. (mom and her new baby)

Four Possible Outcomes on each trial in detection of stimulus Hit: signal present participant sensed it Miss: Signal present but participant did not sense it False Alarm: Signal absent but participant reported sensing it Correct Rejection: Signal absent and participant did not report it

Sensory Adaptation and Deprivation

Adaptation (Habituation) The reduction or disappearance of

sensory responsiveness when stimulation is unchanging or repetitious.

Prevents us from having to continuously respond to unimportant information (our clothes).

Deprivation The absence of normal levels of sensory

stimulation.

Sensory Overload

Overstimulation of the senses. Can use selective attention to

reduce sensory overload. Selective attention

The focusing of attention on selected aspects of the environment and the blocking out of others.

Go to Perception

Vision: What do we see? Eye, see? What makes up the eye? Why is the visual system is not a

camera? How do we see colors? How do we construct the visual world?

Vision

Most important sense (evolution) Photoreceptors gather light, send it

to neuron, occipital lobe for decoding

What We See Hue

Visual experience specified by color names and related to the wavelength of light.

Brightness Lightness and luminance; the visual

experience related to the amount of light emitted from or reflected by an object.

Saturation Vividness or purity of color; the visual

experience related to the complexity of light waves.

What We See

Hue Brightness Saturation

An Eye on the World Cornea

Protects eye and bends light toward lens.

Lens Focuses on objects

by changing shape. Iris

Controls amount of light that gets into eye.

Pupil Widens or dilates

to let in more light.

An Eye on the World Retina

Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.

This is where transduction takes place (rods and cones) Rods

Visual receptors that respond to dim light. Light and dark but no color.

Cones Visual receptors involved in color vision. Most

humans have 3 types of cones. Best in bright light, can sharply focus 5 million different shades but we only have 150 in our

language

Blind Spot

Blind Spot

At the point where the optic nerve exits the back of the eye there are no rods and cones so no receptors for vision

Head and eye movements work avoid “blind spots” in our vision

The Structures of the Retina

Why is the Visual System not a Camera?

Much visual processing is done in the brain. Some cortical cells respond to lines in

specific orientations (e.g. horizontal). Other cells in the cortex respond to other

shapes (e.g., bulls-eyes, spirals, faces). Feature-detectors

Cells in the visual cortex that are sensitive to specific features of the environment.

Hubel & Wiesel’s Experiment

How We See Colors

Trichromatic theory Opponent process theory

Trichromatic Theory

Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors:

red, blue, & green All other colors can

be derived by combining these three.

Opponent-Process Theory A competing theory of color vision, which

assumes that the visual system treats pairs of colors as opposing or antagonistic

States there are two types of cones One responds to red and green, the other to

blue and yellow, while the rods receive black and white input

As one color in each pair is excited, the other is inhibited

Afterimages

Stare at the white, what do you see?

Stare at the light bulb for 30 seconds….

Why does this happen? When you focus on the black light bulb, light

sensitive photoreceptors in your retina respond to incoming light. The longer you stare at the black light bulb, your photorecpeptors become desentitized or fatigued.

Photopigment is “bleached” by constant stimulation. The desensitization is strongest for cells viewing the brightest area and weaker for darker images.

When screen becomes white, the least depleted cells respond more strongly producing the brightest part of the after image: the glowing light bulb.

This is a negative after image. (dark areas turn light)

Test of Color Deficiency

Hearing

Do you hear what I hear? How does the ear hear? How do we construct the auditory

world?

Hearing

Sounds created by vibrations push air molecules back and forth changing air pressure.

Changes in air pressure=sine wave Frequency Theory:

Fast waves=frequency (high or low) High waves=amplitude (loud or

soft)

What We Hear Loudness

The dimension of auditory experience related to the intensity of a pressure wave.

Pitch The dimension of auditory experience related

to the frequency of a pressure wave. Place Theory: Suggests we identify pitch of

sounds according to the location of vibrations on the basilar membrane

Timbre (pronounced “TAM-bur”) The distinguishing quality of sound; the

dimension of auditory experience related to the complexity of the pressure wave.

Listen to the Hearing Test

Ultimate Hearing Test When do you stop hearing the sound? http://www.youtube.com/watch?v=igGroIcga3g

Hertz: Unit of measure for the frequency of sound

An Ear on the World

Auditory Localization

Sounds from different directions are not identical as they arrive at left and right ears

Loudness Timing Phase

The brain calculates a sound’s location by using these differences.

Virtual Barber Shop: http://www.youtube.com/watch?v=IUDTlvagjJA

Hearing is possible… When ear and brain convert sine

waves from sound Sound travels into ear, bone in the

middle ear transfers into inner ear where the sound makes fluid waves

Vibration of fluid waves stimulate tiny hairs to generate nerve impulse

Brain then analyzes sound.

Other Senses

Taste: savory sensations Smell: The sense of scents Senses of the skin The mystery of pain The environment within

Taste: Savory Sensations

Transduction: chemical molecules and saliva dissolve Papillae

Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).

Taste buds Nests of taste-receptor cells.

Taste Buds

Photograph of tongue surface (top), magnified 75 times.

10,000 taste buds line the tongue and mouth.

Taste receptors are down inside the “bud”

Children have more taste buds than adults.

Four Tastes

Four basic tastes Salty, sour, bitter and sweet.

Different people have different tastes based on: Genetics Culture Learning Food attractiveness

Smell: The Sense of Scents

Very primitive! But very useful. Close connection to memory Airborne chemical molecules enter the nose and circulate

through the nasal cavity. Vapors can also enter through the mouth and pass into

nasal cavity. Receptors on the roof of the nasal cavity detect these

molecules.

Olfactory System

Sensitivity to Touch

Gate-Control Theory of Pain Experience of pain

depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.

Neuromatrix Theory of Pain

Theory that the matrix of neurons in the brain is capable of generating pain (and other sensations) in the absence of signals from sensory nerves.

The Environment Within Kinesthesis

The sense of body position and movement of body parts; also called kinesthesia.

Equilibrium The sense of balance.

Semicircular Canals Sense organs in the inner ear, which

contribute to equilibrium by responding to rotation of the head.

What do you see?

Perception

To what extent are our perceptions of the environment accurate? Perception is the process of selecting

information from the environment and interpreting that information.

Perception brings meaning to sensation.

It produces an intrepretation of the world not a perfect representation!

Stare at the image for 30 seconds….

Which line is longer?

What picture looks like a whole room?

Feature Detectors

Still a mystery to most psychologist.

These are a bundle of cells in the brain whose purpose is to detect certain features of stimuli (such as lines, shapes, angles, movements)

Discovered by David Hubel and Torsten Wiesel.

How do we perceive the world? Attention- a process in which

consciousness is focused on particular stimuli Selective Attention – ability to focus on one

stimulus while excluding other stimuli that are present

Divided Attention – ability to respond to more than one stimulus

Cocktail Party Effect: demonstrates that attention can be divided but you can hear things that are important to you (like hearing your name in a busy room)

What do you pay attention to?

The Amazing Color Changing Card Trick

http://www.youtube.com/watch?v=voAntzB7EwE

Awareness Test http://www.youtube.com/watch?v

=Ahg6qcgoay4

How do we process stimuli?

The ability to discriminate among shapes and figures. Bottom-up processing – information

processing that beings at the stimulus and continues to higher brain centers

Top-down processing – information processing that begins in higher brain centers (what we already know) and proceeds to receptors of stimulus

Is this Top Down or Bottom Up?

The Count Censored –

http://www.youtube.com/watch?v=B-Wd-Q3F8KM Top Down Processing Example

How do we construct the visual World?

Form perception Depth and distance perception Visual constancies: When seeing is

believing Visual illusions: When seeing is

misleading

Form Perception

Gestalt principles describe the brain’s organization of sensory information into meaningful units and patterns.

Refers to recognition and identification of faces, words, shapes, melodies, etc. Feature-analysis theory – theory of pattern

perception stating that we perceive basic elements of a structure and then mentally create a complete picture

Pragnanz Theory: We see the simpliest pattern possible.

Prototypes-matching theory – patterns are identified by being compared against a set of prototypical patterns stored in memory

Form Perception (cont.) Figure-ground perception – tendency to organize that

visual field into objects (figures) that stand apart from surroundings (ground)

Closure – Filling in missing information from the perceptual array by closing in gaps

Laws of Grouping Similarity – grouping things on the basis of how similar

they are to one another Proximity – grouping things on the basis of how near

they are to one another

Figure and Ground

MC Esher Relativity

Waterfall

Tree

Depth and Distance Perception

Binocular Cues: Visual cues to depth or distance that

require the use of both eyes. Convergence: Turning inward of the

eyes, which occurs when they focus on a nearby object.

Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

Depth and Distance Perception

Monocular Cues: Accommodation

Bulging and elongating of lens Effective only for objects within 25 feet

Motion parallax – phenomenon where near objects are seen as moving more rapidly that far objects when the viewer’s head is moving

Texture gradient – texture of a surface receding in the distance changes in clarity, blurring at further distances

Linear perspective – produced by apparent converging of parallel lines in the distance

The Ames Room A specially-built room

that makes people seem to change size as they move around in it

The room is not a rectangle, as viewers assume it is

A single peephole prevents using binocular depth cues

Research suggests that the visual system is upset by redundancy

of patterns (when there is nothing apparently there).

Visual Constancies The accurate perception of objects

as stable or unchanged despite changes in the sensory patterns they produce. Shape constancy Location constancy Size constancy Brightness constancy Color constancy

Shape Constancy Even though these images cast

shadows of different shapes, we still see the quarter as round

Which line is longer?

Visual Illusions

Illusions are valuable in understanding perception because they are systematic errors.

Illusions provide hints about perceptual strategies. In the Muller-Lyer illusion (above) we tend to

perceive the line on the right as slightly longer than the one on the left.

The Ponzo Illusion Linear perspective

provides context Side lines seem to

converge Top line seems

farther away But the retinal

images of the red lines are equal!

Fooling the Eye

The cats in (a) are the same size The diagonal lines in (b) are parallel You can create a “floating fingertip frankfurter”

by holding hands as shown, 5-10” in front of face.

Perceptual Powers: Origins and Influences

Depth perception appears around 6 months of age Psychological and cultural influences on

perception We use prior experience and learning when we interpret

sensory information City dwellers vs. country dwellers will experience the

Ponzo Effect differently when around large buildings Two competing theories:

Learning Theory: Learned depth cues Innate Theory: Born with certain depth cues

Bottom Line: Perception is an interaction of nature vs. nurture

Glass surface, with checkerboard underneath at different heights

Visual illusion of a cliff Baby can’t fall

Mom stands across the gap Babies show increased

attention over deep side at age 2 months, but aren’t afraid until about the age they can crawl (Gibson & Walk, 1960)

The Visual Cliff-40 Studies

The Visual Cliff

Psychological and Cultural Influences on Perception

We are more likely to perceive something when we need it.

What we believe can affect what we perceive. Emotions, such as fear, can influence

perceptions of sensory information. Expectations based on our previous

experiences influence how we perceive the world.

Perceptual Set A habitual way of perceiving, based on expectations.

All are influenced by our culture.

Perceptual Set

What you see in the centre figures depends on the order in which you look at the figures: If you scan from the left, see an old woman If you scan from the right, see a woman’s figure

Context Effects Word Game The same physical

stimulus can be interpreted differently

We use other cues in the situation to resolve ambiguities

Is this the letter B or the number 13?

Subliminal Perception

Perceiving without awareness visual stimuli can affect your behavior

even when you are unaware that you saw it

nonconscious processing also occurs in memory, thinking, and decision making

these effects are often small, however, and difficult to demonstrate and work best with simple stimuli

Subliminal Perception

Perception versus Persuasion there is no empirical research to

support popular notions that subliminal persuasion has any effect on a person’s behavior

persuasion works best when messages, in the form of advertising or self-help tapes, are presented above-threshold, or at a supraliminal level

Extrasensory Perception

Extrasensory Perception (ESP): The ability to perceive something without

ordinary sensory information This has not been scientifically

demonstrated Three types of ESP:

Telepathy – Mind-to-mind communication Clairvoyance – Perception of remote events Precognition – Ability to see future events

Parapsychology

The study of purported psychic phenomena such as ESP and mental telepathy.

Persinger suggests that psychic phenomena are related to signs of temporal lobe epilepsy in otherwise neurologically normal individuals.

Most ESP studies produce negative findings and are not easily replicated.

Parapsychology

J. B. Rhine conducted many experiments on ESP using stimuli such as these.

Rhine believed that his evidence supported the existence of ESP, but his findings were flawed.

Quiz over Perception What is selective attention? According to feature analysis theory,

how do we identify objects that we percieve?

What is the figure ground relationship? Which Gestalt principle helps our

perception of WWWW XXX? Your mother claims she was able to

read your mind and knew you would try to sneak some food before dinner. What form of ESP might she claim?