Chapter 8

Sensation and Perception

Section 1

Sensation

What is Sensation?

• Sensation- what occurs when a stimulus activates a receptor.

• Perception- the organization of sensory information into meaningful experiences

• Pyschophysics- the study of the relationships between sensory experiences and the physical stimuli that cause them

Threshold

• Absolute threshold- is the weakest amount of a stimulus that a person can detect half the time

• Difference threshold- the smallest change in a physical stimulus that can be detected half the time

Sensory Differences and Ratios

• Just noticeable difference (JND)- the smallest increase or decrease in the intensity of a stimulus that a person is able to detect half of the time.

• Weber’s law: the principle that for any change in a stimulus to be detected, a constant proportion of that stimulus must be added or subtracted.

Sensory Differences and Ratios

• Some senses produce huge increases in sensation in response to a small amount of energy

Sensory Adaptation

• Senses are tuned to change when exposed to stimuli

• People have the ability to adapt to stimulation in the environment– Adjusting to a dark movie theatre

• Allows us to notice differences in sensations and react to the challenges of different or changing stimuli

Signal-Detection Theory

• Is the study of people’s tendencies to make correct judgments in detecting the presence of a stimuli.

• Detection thresholds- involve recognizing some stimulus against a background of competing stimuli.

Two types of processing stimuli or signals

• Preattentive process- method for extracting information automatically and simultaneously when presented with stimuli.

• Attentive process- is a procedure that considers only one part of the stimuli presented at a time.

Section 2

The Senses

The Senses

• Vision

• Hearing

• Taste

• Smell

• Touch

• Skin senses– Vestibular– Kinesthetic

Vision

• Most studied of all senses

• Pupil- the opening in the iris that regulates the amount of light entering the eye

• Lens- a flexible, elastic, transparent structure in the eye that changes its shape to focus light on the retina

Vision

• Retina- the innermost coating of the back of the eye, containing the light-sensitive receptor cells– Rods & cones are responsible for changing

light energy into neuronal impulses

• Optic nerve- the nerve that carries impulses from the retina to the brain

Light

• Is a form of electromagnetic radiation

• Electromagnetic spectrum is made up of:– Radio waves– Microwaves– Infrared radiation– Ultraviolet rays– X-rays– Gamma rays

Light

• Visible light only makes up a small portion of the electromagnetic spectrum

• Passing sunlight through a spectrum breaks the light into a rainbow of colors, each color having a different wavelength

Color Deficiency

• If a person’s cones don’t function correctly, the person is color-deficient

• Fewer people have trouble between red and green than yellow and blue

• 8% of American men and 1% of American women are color blind/color deficient

Binocular Fusion

• Is the process of combining the images received from the two eyes into a single, fused image

• Retinal disparity- is the differences between the images stimulating each eye

• Depth perception– Large retinal disparity means object is nearby– Small retinal disparity means object is distant

Nearsightedness and Farsightedness

• Long eyeball usually means you are nearsighted– You can see objects close to you, but objects

in the distance are blurry

• Short eyeball usually means you are farsighted– You can see distant objects clear, but up-

close objects are blurry

Hearing

• Depends on the vibration of sound waves in the air

• Auditory nerve- is the nerve that carries impulses from the inner ear to the brain, resulting in the perception of sound

• Loudness- determined by amplitude – Higher the amplitude, the louder the sound– Decibels- sound-pressure energy

Hearing

• Pitch- based on sound wave frequency– Low frequency- deep bass sounds– High frequency- shrill squeaks

• You can find the source of a sound when both ears work together

The Pathway of Sound

• Outer ear– Receives sound waves and directs sounds

through the auditory canal

• Middle ear- air-filled cavity– 3 bones (hammer, anvil, and stirrup) are

linked to the ear drum on one end and the cochlea

The Pathway of Sound

• Inner ear– Cochlea makes up the inner ear– Bony tube that contains fluids and neurons– Pressure makes the liquid inside move– Tiny hairs in the cochlea pick up motion which

are attached to sensory cells– These cells turn the sound vibrations into

neuronal impulses, which are sent to the brain

Deafness

• Conduction deafness- occurs when something hinders motion through the outer or middle ear or when bones of the middle ear become rigid and cannot carry sounds inward– Usually helped with a hearing aid

Deafness

• Sensorineural- occurs from damage to the cochlea, hair cells, or auditory neurons– Can be helped by a cochlear implant– Cochlear implant- is a miniature electronic

device surgically implanted

Balance

• Vestibular system- three semicircular canals that provide the sense of balance, located in the inner ear and connected to the brain by a nerve

• Over-stimulation of the vestibular sense will make you dizzy and possibly motion sick

Smell and Taste

• Known as chemical senses because their receptors are sensitive to chemical molecules

• Olfactory nerve- the nerve that carries smell impulses from the nose to the brain

• Liquid chemicals must stimulate receptors in the taste buds for you to taste something

The Skin Senses

• Skin provides the brain with four kinds of information about the environment:– Pressure– Warmth– Cold– Pain

• Pressure varies from place to place on the skin

The Skin Senses

• Pressure sensations can serve as protection

• Many things that can produce pain:– Scratches, punctures, heat, and cold

• Pain makes it possible for you to prevent damage to your body

Perceptions of Pain

• Two types of pain sensation– sharp- localized pain you may feel

immediately after an injury – Dull- generalized pain you may feel later

• Gate control theory of pain- we can lessen some pains by shifting our attention away from the pain impulses or by sending other signals to complete with the pain signals

The Body Senses

• Kinesthesis- The sense of movement and body position– Comes from receptors in and near the

muscles, tendons, and joints– Without kinesthetic sensations your

movements would be jerky and uncoordinated

Section 3

Perception

Perception

• Is when the brain receives information from the senses and organizes and interprets it into meaningful experiences

• Goes beyond our reflexive behavior

• Allows us to confront changes in our environment

Principles of Perceptual Organization

• Gestalt- is the experience that comes from organizing bits and pieces of information into meaningful wholes

• Psychologists have tried to identify principles the brain uses to construct perceptions– Proximity, continuity, similarity, simplicity,

closure

Figure-ground Perception

• Is the ability to discriminate properly between a figure and its background.

• Two dimensional objects are heard to tell the figure from the ground

• These are important in hearing and vision

• In music:– The melody becomes the figure, the rest of

the music becomes the background

Perceptual Inference

• Is the phenomena of filling in the gaps in what our senses tell us is known

• Usually automatic and unconscious

• Differs by our experiences

Learning to Perceive

• Something people learn to do

• Active involvement in the environment is important for accurate perception

• Is influenced by our needs, beliefs, and expectations

• Perceptual set- prepares you to see what you want to see

Subliminal Perception

• Subliminal messages: brief auditory or visual messages that are presented below the absolute threshold

• Subliminal perception: the ability to notice stimuli that affect only the unconscious mind

• The Hidden Persuaders by Vance Packard believed advertisers were using subliminal advertising in 1957.

Depth Perception

• Being able to recognize distances and 3-D

• Is being developed as an infant

• Study:– Babies would not crawl of the edge of a table,

they realized the difference; so they believe depth perception is developing as an infant

Monocular Depth Cues

• Cues that can be used with a single eye– Size of an object– Relative height– Interposition- overlapping of images– Light and shadows– Texture-density gradient

• Motion parallax- is the apparent movement of stationary objects relative to one another that occurs when the observer changes postion

Monocular Cues

• Linear perspective- parallel lines converge when stretched into the distance

• Relative motion– Objects nearby seem to be moving in the

opposite direction when focusing on a distant object

Binocular Depth Cues

• Depend on the existence or movement of both eyes

• Retinal disparity- each eye occupies a different position, each eye receives a different image

Constancy

• The tendency to perceive certain objects in the same way regardless of changing angle, distance, or lighting

Illusions

• Perceptions that misrepresent physical stimuli

• Perceptual cues are distorted so our brains cannot interpret:– Space, size, and depth cues

Extrasensory Perception

• Is an ability to gain information by some means other than the ordinary senses

• Four types of ESP– Clairvoyance- is perceiving objects or information

without sensory input– Telepathy- involves reading someone else’s mind or

transferring one’s thoughts– Psychokinesis- moving objects through purely mental

effort– Precognition is the ability to foretell event

Extrasensory Perception

• Intense personal experience that can be scientifically validated

• J.B. Rhine- parapsychologist that has been studying ESP since the early 1900s

Source:

• Kasschau, Richard, A. Understanding Psychology. McGraw-Hill, Glencoe, New York, New York, 2008.