• Sensation: – is the stimulation of sensory receptors and the

transmission of sensory information to the central nervous system.

• Perception: – is an active process in which sensations are organized

and interpreted to form an inner representation of the world.

• Five Senses:– Vision– Hearing– Smell– Taste– Touch

• the weakest amount of a stimulusthat a person can distinguish fromno stimulus at all 50% of the time.

Examples of Absolute ThresholdVision: candle flame viewed from about

30 miles on a clear, dark night.

Hearing: a watch ticking from about 20 feet away in a quiet room.

Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.

Smell: about one drop of perfume diffused throughout a small house (1 part in 500 million).

Touch: the pressure of the wing of a fly falling on a cheek from a distance of about 0.4 inch.

Gustav Fechner

• Brain cells that respond to different aspects of features of a scene (e.g. angles, vertical, horizontal).

• The sensory process of adjustment. – Sensitization (Positive adaptation)

Becoming more sensitive to stimulation.

– Desensitization (Negative adaptation)

Becoming less sensitive to stimulation.

VisioVisionn

• More than half of our brain’s cerebralcortex is devoted to visual functions.

• Light– All forms of electromagnetic energy moves in waves.

• Visible light at about 400 billionths of a meter in length (violet) to 700 billionths of a meter (red).

• Radio waves extend for miles.• Cosmic rays: wavelengths are only a few trillionths of an inch

long.– Sir Isaac Newton discovered the prism that could break

light into different colors. Colors of the spectrum include:

• Red, orange, yellow, green, blue, indigo, violet (Roy G. Biv)• The wavelength of visible light determines the color or hue.

• Light first passes through the transparent cornea. • The amount of light that is allowed to enter is

controlled by the muscle called the iris (the colored part of the eye).

• The actual opening in the iris is called the pupil.• The lens adjusts to the image by changing its

thickness. The thickness permits a clear image of the object to be projected onto the retina.

Figure 4.2 The Human Eye. In both the eye and a camera, light enters through a narrow opening and is projected onto a sensitive surface. In the eye, the photosensitive surface is called the retina, and information concerning the changing images on the retina is transmitted to the brain. The retina contains photoreceptors called rods and cones. Rods and cones transmit sensory input back through the bipolar neurons to the ganglion neurons. The axons of the ganglion neurons form the optic nerve, which transmits sensory stimulation through the brain to the visual cortex of the occipital lobe.

The Human Eye

The retina – consists of cells called photoreceptors that are

sensitive to light (photosensitive). – The retina contains several layers of cells; the rods and

cones, bipolar cells, and ganglion cells. All of these are neurons.

– The rods and cones respond to light with chemical changes that create neural impulses that are picked up by the bipolar cells. These then activate the ganglion cells.

– The axons of the million or so ganglion cells in our retina ultimately converge to form the optic nerve.

– The optic nerve conducts sensory input to the visual area of the occipital lobe.

Rods and Cones– About 125 million rods and 6.4 million cones are distributed

across the retina. – Rods allow us to see

in black and white.– Cones provide

color vision.

Nearsighted: People who have to be unusually close to a distant object to discriminate its details.

Farsighted: People who see distant objects clearly but have difficulty focusing on nearby objects.

PresbyopiaWith age ( 30s to mid 40s) the lenses start to grow brittle, making it more difficult to accommodate to, or focus on, objects.

Dark adaptation: the process of adjusting to lower lighting conditions.

Light adaptation Adapting to brighter lighting takes place much more

rapidly.

dilated constricted

• The wavelength of light determines its color or hue.

• The value of color is its degree of lightness or darkness.

• Saturation refers to how intense a color appears.• Warm and Cold Colors.

– Colors on the green-blue side of the color wheel are considered to be cool in temperature.

– Colors on the yellow-red side are considered to be warm.

Complementary Colors.The colors across from one another on the color wheel are complementary.

Afterimages.Persistent sensations of color arefollowed by perception of the complimentary color when thefirst color is removed.

Theories of color visionOur ability to perceive color depends on the eye’s transmission of different messages to the brain when lights with different wavelengths stimulate the cones in the retina.

Figure 4.6 The Color Wheel. A color wheel can be formed by bending the colors of the spectrum into a circle and placing complementary colors across from one another. When lights of complementary colors such as yellow and violet-blue are mixed, they dissolve into neutral gray. The afterimage of a color is its complement.

Color Wheel

Visual PerceptionVisual Perception

Trichromatic Theory (Young-Helmholtz theory)

– Young found that he could create any color from the visible spectrum by varying the intensities of three lights: red, green, and blue-violet.

– Helmholtz suggested that the retina in the eye must have three different types of color photoreceptors or cones.

Opponent-Process theory (Ewald Hering)

– Hering proposed that there are three types of color receptors but they don’t respond just to red, green and blue-violet.

– They are pairs including red-green; blue-yellow; and a type that perceives differences in brightness.

– These pairs of receptors are what make afterimages possible.

Afterimage

Muller-Lyer

Are the vertical lines equal in length?

Hering-Helmholtz

Are the horizontal lines straight or curved?

• If you can discriminate among the colors of the visible spectrum, you have normal color vision and are labeled a trichromat.

• People who are totally color blind are called monochromats.

• Partially color-blind people are called dichromats.

• Visual perception – is the process by which we organize or make sense of

the sensory impressions caused by the light that strikes our eyes.

• Gestalt psychologists refer to closure as being – the integration of disconnected pieces of information

into a meaningful whole

• Gestalt psychologists are interested in the way we integrate bits and pieces of sensory stimulation into meaningful wholes. – Wertheimer discovered many rules that we use to do

this called the laws of perceptual organization.

• Figure-Ground Perception.– When figure-ground relationships are ambiguous, or

capable of being interpreted in various ways, our perceptions tend to be unstable, shifting back and forth.

Figure 4.13 The Rubin Vase. A favorite drawing used by psychologists to demonstrate figure–ground perception. Part A is ambiguous, with neither the vase nor the profiles clearly the figure or the ground. In part B, the vase is the figure; in part C, the profiles are.

The Rubin Vase

Figure 4.14 Necker Cube. Ambiguity in the drawing of the cube makes perceptual shifts possible. Therefore, the darker tinted surface can become either the front or back of the cube.

Necker Cube

• Other Gestalt Rules for Organization:– Proximity – Similarity – Continuity – Common Fate

• Visual perception of movement is based on change of position relative to other objects.

• Types of apparent movement (illusions of movement). – The Autokinetic Effect

• is the tendency to perceive a stationary point of light as moving in a dark room.

– Stoboscopic Motion • is what makes motion pictures possible.

– The Phi Phenomenon • occurs as the on-off process of lights is perceived as

movement.

• Monocular Cues: cues that can be perceived by one eye. – Perspective:

• distances between far off objects appear to be smaller than equivalent distances between nearby objects.

– Relative size: • the fact that distant objects look smaller than nearby objects of

the same size.

– Clearness of an object: • We sense more details of nearby objects.

– Interposition: • Nearby objects can block our view of more distant objects.• Interposition is placing of one object in front of another.

Figure 4.17 The Effects of Interposition. The four circles are all the same size. Which circles seem closer? The complete circles or the circles with chunks bitten out of them?

Effects of Interposition

• Monocular Cues continued. . .– Shadows:

opaque objects block light and produce shadows giving us a relationship to the source of light

– Texture Gradient: close objects are perceived as having rougher textures

– Motion Parallax: the tendency of objects to seem to move backward or forward as a function of their distance

Figure 4.18 Shadowing as a Cue for Depth. Shadowing makes the circle on the right look three-dimensional.

Shadowing as a cue for depth

• Binocular Cues: cues that can be perceived by both eyes. – Retinal disparity:

• The difference between projected images (e.g. different angles). • Closer objects have greater retinal disparity.

– Convergence: • Causes feelings of tension in the eye muscles and provides

another binocular cue for depth.

• Size constancy: – Allows us to perceive objects to be the same size even when viewed

from different distances.– Experiences teach us about perspective.

• Color constancy: – The tendency to perceive objects as retaining their color even though

lighting conditions may alter their appearance.

• Brightness constancy: – similar to color constancy.

• Shape constancy: – The tendency to perceive objects as maintaining their shape, even if

we look at them from different angles so that the shape of their image on the retina changes dramatically.

Figure 4.19 Brightness Constancy. The orange squares within the blue squares are the same hue, yet the orange within the dark blue square is perceived as brighter. Why?

Brightness Consistency

Figure 4.20 Shape Constancy. When closed, this door is a rectangle. When open, the retinal image is trapezoidal. But because of shape constancy, we still perceive it as rectangular.

Shape Constancy

HearingHearing

• Sound or auditory stimulation, travels through the air like waves.– The changes in air pressure are vibrations that approach your ears

in waves. – The human ear is sensitive to sound waves with frequencies

from 20 to 20,000 cycles per second.

• Pitch and Loudness– Pitch of a sound is determined by its frequency -- number of

cycles per second as expressed in the unit hertz (Hz). – Loudness of a sound roughly corresponds

• to the height or amplitude of sound waves and • is expressed in decibels (dB).

Decibel Ratingsof Familiar Sounds

Zero dB is the threshold of hearing.

You may suffer hearing loss if you have prolonged exposure to sounds of 85 to 90 dB.

Decibel Ratings

The ear has three parts: the outer ear, middle ear, and the inner ear.

• The outer ear is shaped to funnel sound waves to the eardrum.

• The eardrum is a thin membrane that vibrates in response to sound waves and thereby transmits them to the middle and inner ears.

• Middle ear functions as an amplifier. – The three small bones are called the hammer, anvil, and stirrup.

• Inner ear converts vibrations to electronic signals– The cochlea is a snail shaped structure. – Inside the cochlea are receptor cells called hair cells that dance

in response to vibrations. – Their movements generate neural impulses which are sent to

the brain via the auditory nerve.

• A sound that is louder in the right ear is perceived as coming from the right.

• Both loudness and the sequence in which the sounds reach the ears provide directional cues.

• More than 1 in 10 Americans has a hearing impairment, and 1 in 100 cannot hear at all.

• Two major types of deafness are conductive and sensorineural deafness.

Conductive deafness: • stems from damage to the structures of the middle ear.

Sensorineural deafness: • stems from damage to the structures of the inner ear, most

often the loss of hair cells, or damage to the auditory nerve.

Smell & TasteSmell & Taste

Smell– An odor is a sample of the substance being sensed.

• Odors are detected by sites on receptor neurons in the olfactory membrane high in each nostril.

• Their firing transmits information about odors to the brain via the olfactory nerve.

– The sense of smell adapts rapidly to odors such that we lose awareness of them.

Taste– Four primary taste qualities: sweet, sour, salty, and

bitter.

– Food flavor depends on its odor, texture, temperature as well as taste.

– Taste cells are receptor neurons located on taste buds.

• Humans have approximately 10,000 taste buds most of which are located on the edge and back of your tongue.

• Taste cells reproduce rapidly enough to renew themselves weekly.

The Skin SensesThe Skin Senses

• The skin senses include touch, pressure, warmth, cold, and pain.

• Touch and Pressure: – Active touching involves reception of information

concerning not only touch per se but also pressure, temperature, and feedback from the muscles involved in movements of our hands.

– Psychophysicists use methods such as the two-point threshold to assess sensitivity to pressure.

• Sensory nerve endings are more densely packed in the fingertips and face than in other locations.

• Temperature– The receptors for temperature are neurons located just

beneath the skin.

Sensation & Sensation & PerceptionPerception

and Virtual realityand Virtual reality

• Hard research does not support the existence of ESP.Nonetheless, 60% of Americans believe that some people have psychic powers or ESP.

• Examples of ESP phenomena:– Precognition – see into the future

– Psychokinesis – moving objects with your mind

– Telepathy – mind reading

– Clairvoyance - ability to gain information about an object, person, location through means other than the known human senses.

• Rhine studied ESP for several decades with the conclusion that some people might have some degree of ESP. – Ganzfeld Procedure. – File drawer problem.

• People who have demonstrated ESP with one researcher have failed to do so with another researcher.

• Not one person has emerged who can reliably show psi communication from one occasion to another and from one researcher to another.

• A Gallup survey of 2,002 adults in the U.S. showed that 89% experience pain at least once a month.

• Pain means that something is wrong in the body. – Pain is adaptive.– There are no nerve endings for pain in the brain. – Postaglandins (substance P) facilitate transmission of the

pain message to the brain and heighten circulation to the injured area.

– Other aspects influence pain:– Visual and other sensory inputs tell us what is happening

and influence the cognitive interpretation of the situation.

• Phantom Limb Pain.Seems to involve activation of nervesin the stump of the missing limb.

• Gate Theory.The nervous system can process only a limited amount of stimulation at a time.

• Acupuncture.Research has shown that acupuncture stimulates nerves that reach the hypothalamus and may also result in the release of endorphins.

• Modern Psychological Methods for Coping with Pain.– The primary treatment has been chemical;

pain-killing drugs.

– Accurate Information: Knowledge of medical proceduresreduces stress.

– Distraction and Fantasy:Diverting attention from pain helps many cope with it.

– Hypnosis has been used to reduce chronic pain, as an anesthetic in dentistry, childbirth, even in some forms of surgery.

• Modern Psychological Methods for Coping with Pain.– Relaxation Training and Biofeedback.– Coping with Irrational Beliefs.– Other methods.

• Sense of commitment. • Supportive social networks help as well.

Biofeedback