Sensation & Perception

“Sensation is how we take in the world around us (see, hear, feel, touch, taste, etc), and perception is how we make sense of that

world”

What is Sensation?

• The stimulus of sensory receptors and the transmission of sensory information to the central nervous system (the spinal cord and brain).

• The stimulation of senses is automatic. • Results from sources of energy such as light or

sound or from the presence of chemicals, as in smell and taste.

What is Perception?

• The psychological process through which we interpret sensory stimulation.

• Perception reflects learning, expectations, and attitudes.

• Ex: Cars down the road, football players down the field.

What is Absolute Threshold?

• The weakest amount of stimulus that can be sensed.

Absolute Thresholds for Humans Sense Stimulus Receptors ThresholdVision Electromagnetic Energy Rods and Cones in the

retinaA candle flame viewed from a distance of about 30 miles on a clear night

Hearing Sound waves Hair cells of the inner ear

The ticking of a watch from about 20 feet away in a quiet room

Smell Chemical substances in the air

Receptor cells in the nose

About one drop of perfume diffused throughout a small house

Taste Chemical substances in saliva

Taste buds on the tongue

About 1 teaspoon of sugar dissolved in 2 gallons of water

Touch Pressure on skin Nerve endings in skin The wing of a fly falling on a cheek from a distance of about 0.4 inch

Difference Threshold

• The minimum amount of difference that can be detected between two stimuli

• Black pants, headphones

Signal Detection Theory

• A method of distinguishing sensory stimuli that takes into account not only their strengths but also such elements as the setting. Your physical state, your mood, and your attitudes.

• Ex: someone who sells perfumes, parents at a recital

Sensory Adaptation

• The process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli.

• Ex: city dwellers become less aware of traffic

Vision

The most pathetic person in the world is one who has sight, but no vision”

- Helen Keller

Light• Light is electromagnetic energy, and is described in

wavelengths. • Wavelengths vary in length—some are a few inches

long, while some are miles long.• Not all light is visible to humans.• Examples of broken down wavelengths:

o Sunlight broken down through water vapor—what helps us see a rainbow.

o Sunlight broken down through glass called a prism.o Main colors of the spectrum are red, orange, yellow, green,

blue, indigo, and violet. ( ROY G. BIV)

The Human Eye

The Parts of the Human Eye

When you take a picture with a camera, light enters through an opening and is focused onto a sensitive surface—the film. Chemicals on the film are changed by the light and create a lasting impression of the image that entered the camera.

When you click the shutter button, the camera quickly switches the mirror out of the way, so the image is directed at the exposed film. The mirror is connected to the shutter timer system, so it stays open as long as the shutter is open. This is why the viewfinder is suddenly blacked out when you take a picture.

The Pupil• The amount of light that enters the eye is

determined by the size of the opening in the colored part of the eye.

• That opening is called pupil.• In the human eye, there is no black spot. • You pupil isn’t a black spot, but rather it is a hole• The size of the pupil adjusts automatically to the

amount of light entering the eye. • Pupil is also sensitive to our emotions.

Iris

• A ring of tiny muscles that control the size of the pupil (the color part of the eye)

The Lens

• Adjusts to distance of objects by changing its thickness

• Ex: finger far from nose close to nose demonstration

Retina

• The sensitive surface in the eye that acts like the film in a camera.

• Difference: retina consists of neurons, not film.

• The neurons in the retina that are sensitive to light are called photoreceptors.

Optic Nerve

• Carries the electrical impulses from the retina to the brain, where they are interpreted as visual images

Blind spot

• Area by the retina that contains no photoreceptors because that’s where the optic nerve leaves the eye.

• If we didn’t have a “blind spot” we wouldn’t be able to see anything.

Rods and Cones

• Photoreceptors in the retina contain rods and cones

• Rods: sensitive only to brightness of light. – They allow us to see black and white.

• Cones: provide color vision

Visual Acuity

• The sharpness of vision

• Determined by our ability to see visual details (in normal light)

Color Vision

• The wavelength of light determines the color• Humans with normal color vision see any color

in the visible spectrum of light• Dogs and cats see far fewer colors• Insects, birds, fish, and reptiles experience a

wide variety of colors.

The Color Circle—Complementary colors

After Images

• An afterimage of a color is its complementary color

• You perceive an afterimage when you have viewed a color for a while and then the color is removed.

• The same holds true or black and white. • Staring at one create the other.

Color blindness

• When someone has an absence of or malfunction in the cones of the retina, they have a form of color blindness

• Most common color blindness: red—green color blindness

Hearing “Blindness separates us from things, but deafness separates us from people.”

-Helen Keller

The Ear

The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.

The outer ear

• The outer ear consists of the ear canal and eardrum. Sound travels down the ear canal, striking the eardrum and causing it to move or vibrate.

The middle ear • The middle ear is a space

behind the eardrum that contains three small bones, the anvil, the stirrup, and the hammer, (called ossicles.)

• This chain of tiny bones is connected to the eardrum at one end and to an opening to the inner ear at the other end. Vibrations from the eardrum cause the ossicles to vibrate which, in turn, creates movement of the fluid in the inner ear.

The Inner Ear • Movement of the fluid in the inner ear, or cochlea, causes changes in tiny structures

called hair cells. This movement of the hair cells sends electric signals from the inner ear up the auditory nerve (also known as the hearing nerve) to the brain.

• The brain then interprets these electrical signals as sound.

DeafnessConduction Deafness

• Something goes wrong with the sound and the vibration on the way to the cochlea.

• You can replace the bones or get a hearing aid to help.

Nerve (sensorineural) Deafness

• The hair cells in the cochlea get damaged.

• Loud noises can cause this type of deafness.

• NO WAY to replace the hairs.

• Cochlea implant is possible. Pg 140)

Touch• Receptors located in

our skin.• Gate Control Theory

of Pain

Taste

• Receptor cells are located in taste buds

• Taste buds are located in papillae on the tongue

• Chemicals dissolve in saliva and activate receptors

Taste

• We have bumps on our tongue called papillae.

• Taste buds are located on the papillae (they are actually all over the mouth).

• Sweet, salty, sour and bitter.

Smell• Detecting common odors

– Odorant binding protein is released and attached to incoming molecules

– These molecules then activate receptors in the olfactory epithelium

– Axons from those receptors project directly to the olfactory bulb

Smell

• Women have a better sense of smell than men• Anosmia– Complete loss of the ability to smell

Vestibular Sense• Tells us where our

body is oriented in space.

• Our sense of balance.

• Located in our semicircular canals in our ears.

Kinesthetic Sense• Tells us where our body parts are.• Receptors located in our muscles and

joints.

Vestibular Senses

• Vestibular senses provide information about equilibrium and body position

• Fluid moves in two vestibular sacs• Vestibular organs are also responsible for

motion sickness• Motion sickness may be caused by

discrepancies between visual information and vestibular sensation

The Skin Senses

• Skin is the largest sense organ• There are receptors for pressure,

temperature, and pain• Touch appears to be important not just as a

source of information, but as a way to bond with others

Pain

• Serves as a warning about injury or other problem

• Large individual differences in pain perception• Gate control theory– Neurological “gate” in spinal cord which controls

transmission of pain to brain

Pain

• Biopsychosocial theory—pg 145– Holds that pain involves not just physical stimulus, but

psychological and social factors as well• Placebo effect– Shows that when a person believes a medication reduces

pain, their pain is often reduced even though no medication was given

– Pain relief is likely the result of endorphin release

Pain

• Alternative approaches– Hypnosis– Self-hypnosis– Accupuncture

Perception

Perceptual Organization

• Figure-ground– We perceive a

foreground object (figure) against a background (ground)

• Animals may look like the background they inhabit as a way of destroying figure-ground distinction

Perceptual Organization

• Other principles of organization– Proximity– Similarity– Closure– Continuity

Perceptual Organization

• Perceptual Constancy– Our tendency to

perceive objects as stable and unchanging despite changing sensory information

• Size constancy• Shape constancy• Brightness constancy• Color constancy

Perception of Distance and Depth

• Monocular cues – those that require only one eye– Aerial perspective– Texture gradient– Linear perspective– Motion parallax– Superposition

Perception of Distance and Depth

• Binocular cues – those that require both eyes– Retinal disparity– Convergence

Localizing Sounds• We use both monaural and

binaural cues• Loudness

– Louder sounds are perceived as being closer

• Time of arrival– Sounds will arrive at one ear

sooner than the other– This helps determine

direction of the sound

Perception of Movement

• Apparent movement– Illusion that still objects are moving

• Autokinetic illusion– Perceived motion of a single object

• Stroboscopic motion– Created by a rapid series of still pictures

• Phi phenomenon– Apparent motion created by lights flashing in

sequence

Visual Illusions

• Occur because of misleading cues in the stimulus

• Gives rise to false perceptions

Individual Differences and Culture in Perception

• Motivation– Our desires or needs shape our current

perceptions• Values• Expectations• Cognitive Style• Experience and Culture• Personality