Sensation and Perception

Unit 3

Sensation and Perception

Basic concepts of Sensation

I. Sensation1. The detection of physical energy

from the environment, it is then encoded into neural signals

Occurs when energy in the external environment or the body stimulates receptors in the sense organs

2. Sensory receptors- specialized cells that detect sensory stimuli (light, sound, odors) & convert them into neural impulses

Found throughout body in eyes, ears, nose, mouth & joints & muscles

Basic concepts of Sensation

II. Thresholds1. Absolute threshold- the smallest

amount of a stimulus that a person can sensedVision The flame from a single candle flickering

about 30 miles away on a dark, clear night

Hearing The ticking of a watch placed about twenty ft. away from a listener in a quiet room

taste About one teaspoon of sugar dissolved in 2 gallons of water

smell About one drop of perfume dispersed in a small house

touch The wing of a bee falling on the cheek from about one centimeter away

Basic concepts of Sensation

2. Difference threshold (just-noticeable difference)- minimal difference in the magnitude of energy needed for people to detect a difference between stimuli (comparing) Weber’s law-Principle: difference thresholds grow withthe magnitude of thestimulus

Sensation Weber’s Constant (approximate)

Saltiness of food 1/5 (20%)

Pressure on skin 1/7

Loudness of sounds 1/10 (10%)

odor 1/20

Heaviness of weights 1/50 (2%)

Brightness of lights 1/60

Pitch of sounds 1/333

Absolute & Difference Threshold

Select a sense Design an experiment to find an

absolute threshold test the just noticeable difference for

an increase or decrease in the intensity of the stimulus.

Create a hypothesis about the intended results

Basic Concepts of Sensation

III. Signal-detection theory- detection of a stimulus depends on factors such as the intensity of the stimulus, the level of background stimulation, and the biological and physical characteristics , and expectations of the perceiver.

IV. Sensory Adaptation-process by which sensory receptors adapt to constant stimuli by becoming less sensitive to them.

V. Sensory Deprivation-absence of normal levels of sensory stimulation

VI. Sensory overload- too much stimuli

ASD

Conservative or liberal

VisionProcess by which light energy is converted into neural impulses that the brain interprets to produce the experience of sight

I. Light- physical energy in the form of electromagnetic radiation

1. Colors are caused by different wavelengths within the visible spectrum

red = longest Violet = shortest Roy G. Biv

VisionII. The Eye

1. Cornea- transparent covering on the eye’s surface through which light enters

2. Iris- regulates the size of the pupil to adjust to changes in the level of illumination

3. Pupil- allows light to enter the eye

4. Lens- focuses light rays on the retina

Accommodation-process by which the lens changes its shape (thickness) to focus images more clearly on the retina

5. Fovea- center of focus for clearer vision

Structure of the Eye

Vision

6. Retina-Neural tissue lining the back of the eyeball’s interior containing the receptors for vision; retina contains:

Photoreceptors- light-sensitive cells in the eye that register lighta) Rods- Visual receptors that are sensitive to

intensity of light (dim)b) Cones- Visual receptors involved in color vision

& fine details; humans have 3 types: blue, green, red7. Optic nerve- carries neural impulses generated by light stimulation

from the eye to the brain6. Blind spot- contains no photoreceptor cells; Place where the optic

nerve leaves the eye

Structures of the Retina

VisionIII. Color vision

2 major theories~1. Trichromatic theory- the ability to see different

colors depends on the relative activity of three types of color receptors in the eye (red, green, and blue-violet) all other colors derived by a combination

2. Opponent-process theory-assumes that the visual system treats pairs of colors as opposing or antagonistic. Opponent-process cells are inhibited by a color, and have a burst of activity when it is removed.

a) Afterimage- image remains after stimulus is removed; cones become tired

o Trichromats-people with normal color visiono Monochromats- no color visiono Dichromats- some color vision

Color vision:

HearingI. Audition (sense of hearing):

1) Travels in waves; exists only in mediums such as air, liquids, gases & solids

2) Vibration Amplitude, Pitch

3) Auditory Localization Sounds from different directions are not

identical as they arrive at left and right ears. The brain calculates a sound’s location by using these differences.

Loudness (Intensity, amplitude {height of wave}, measured in decibels)

Pitch(frequency{number of cycles per second}, hertz)

Hearing

II. The Ear: structured to capture sound waves1. Eardrum- vibrates in response to external stimuli &

transmits waves to middle ear2. Ossicles- tiny bones (hammer, anvil, & stirrup) in the

middle ear that vibrate in response to eardrum3. Cochlea- contains sensory receptors for hearing

Nerve (hair) cells- receptors that transform vibrations into neural impulses that are transmitted to the brain via the…

4. Auditory nerve- carries neural impulses from ear to brain

Hearing

HearingHow You HearWhen an object makes a noise, it sends vibrations (better known as sound waves) speeding through the air. These vibrations are then funneled into your ear canal by your outer ear. As the vibrations move into your middle ear, they hit your eardrum and cause it to vibrate as well. This sets off a chain reaction of vibrations. Your eardrum, which is smaller and thinner than the nail on your pinky finger, vibrates the three smallest bones in your body: first, the hammer, then the anvil, and finally, the stirrup.

The stirrup passes the vibrations into a coiled tube in the inner ear called the cochlea. The fluid-filled cochlea contains thousands of hair-like nerve endings called cilia. When the stirrup causes the fluid in the cochlea to vibrate, the cilia move. The cilia change the vibrations into messages that are sent to the brain via the auditory nerve. The auditory nerve carries messages from 25,000 receptors in your ear to your brain. Your brain then makes sense of the messages and tells you what sounds you are hearing.

2 types of deafness:

1. Conductive Deafness: • Caused by damage to

middle ear; prevent people from hearing sounds that aren’t loud enough

• Hearing aids provide amplification

2. Sensorineural (nerve) deafness:• Can be mild, moderate

or severe• Damage to cells or

auditory nerve in inner ear

• Cochlear implants will help “Ringing

sensation” is nerve damage

Sensorineural Deafness• Sensorineural deafness occurs when sounds of certain

frequencies are not heard.

• It is usually caused by damage to the inner ear.

• Loud sounds can destroy neurons in the ear.

• Cochlear implants can help people with sensorineural deafness.

Conductive Deafness• Conductive deafness occurs because of damage to the

middle ear, which is the part that amplifies sound.

• Hearing aids can provide for the function of the middle ear by amplifying sound.

Deafness

Chemical Senses I. Olfaction (sense of smell)

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 (olfactory hairs) on the roof of the nasal cavity detect these molecules. Intensity depends on # of receptors firing.

Passes through the olfactory nerve, olfactory bulb, to the olfactory cortex and also structures in the Limbic System (memory and emotion)

 

Chemical SensesII. Taste

1. Depends on odor, texture, & temperature; role in adaptation & survival2. Papillae (taste receptors)

1. taste buds- pores or openings on the tongue containing taste cells (receptors) inside the bud; 50 to 100 receptors/bud Regenerate in 5-10 days

2. Genetic factors, expectations, and context play a significant role in taste sensitivities and preferences

3. Five basic tastes: Sweet Salty Sour Bitter Umami

Taste1. Decrease with age2. Supertasters- 2 or

more times the taste buds,Hypersensitive, 1 in four people

3. Medium tasters4. Non-tastersALERT: receptors are actually mixed and located throughout the mouth…back of throat, roof, cheeks and tongue

Skin SensesIII. Skin Senses (largest sensory organ)

1. The senses of pressure, temperature, and pain that involve stimulation of sensory receptors in the skin

2. Pressurea) Sensory receptors at the root of body hairb) Pressure sensitivity varies throughout the body

Fingertips, lips, nose, & cheeks3. Temperature

a) Receptors are just beneath the skin (warm & cold)4. Pain

a) Pain sensitivity variesb) Prostaglandins: chemical that carries pain messages;

Aspirin productionc) Pain message sent from spinal cord to thalamus to

cerebral cortex (somatosensory cortex)

Skin Senses1. Brain generates

paina. Phantom Painb. Injured athlete

doesn’t feel painc. No Pain???

2. Gate Theorya. Only a certain

amount of information can be processed by the brain at one time

Pain Disorders Hereditary Sensory Autonomic Neuropathy

Pain and temp nerve fibers (receptors) never developed Insensitivity to pain means that the painful

stimulus is not even perceived: a patient cannot describe the intensity or type of pain.

Indifference to pain means that the patient can perceive the stimulus, but lacks an appropriate response: they will not flinch or withdraw when exposed to pain

Body Senses (Balance)1. Kinesthesis (Greek: to move & perception)- sense

that informs people about the position of their bodies

a) Sensory info is fed from receptor cells in joints, tendons and muscles to the brain

Allows for navigation, movement coordination, & feel muscle contraction; interacts with vision

2. Vestibular sense- movement, the sense that keeps us informed about balance and the position of our body in space, equilibrium, enables you to keep your balance; cerebellum, head position

a) Semicircular canals- in the inner ear; crystals; sense changes in the direction & movement of the head

Senses speed, motion and balance Dizzy

b) Vestibular sacs- fluid filled, send messages to the cerebellum

Controversies in Perception

I. Subliminal perception: perception of stimuli that are presented below the threshold of conscious awareness

Controversies in Perception

II. Parapsychology- seeks to investigate the existence and the causes of psychic abilities

A. Extrasensory perception (ESP):perception that occurs without benefit of the known senses

Psychic test #1

Psychic test #2

Ganzfeld experiment

1. Telepathy- communication of thoughts from one mind to another that occurs without using the known senses

2. Clairvoyance- ability to perceive objects and events without using the known senses

3. Precognition- ability to foretell the future

4. Psychokinesis (telekinesis)-ability to move objects by mental effort only

PerceptionPerception- process by which the brain integrates,

organizes, & interprets sensory impressions to create representations of the world

l3

Perceptual set- tendency for perception to be influenced by one’s expectations or preconceptions• context effects

Mary had a a little lamb

Perception

Perception PrinciplesI. Gestalt (whole) principles: the brain organizes

sensory information into meaningful units and patterns1. Visual field is organized into figure (shapes) and

ground (no shape) stand out from surroundings

Principles of grouping/organization:2. Proximity-things near are grouped

3. Closure- brain fills in gaps

4. Continuity- lines & patterns continue into space

PerceptionDepth Perception- see objects in 3D (visual cliff) Cues for depth: perspective, clearness, overlap,

shadow, texture1. Binocular cues: visual cues that require the use

of both eyesa) Convergence -Turning inward of the eyes,

which occurs when they focus on a nearby object

b) Retinal disparity - The slight difference in lateral separation between two objects as seen by the right and left eyes; 2 ½ in. apart

2. Monocular cues (depth): visual cues that can be used by one eye

a) Relative height, motion, size; interposition, linear perspective, light & shadow

Perception

1. Perceptual Constancy- The accurate perception of objects as stable or unchanged; context

Shape, size, color

color constancy

size constancyshape constancy

Monocular cues

PerceptionVisual Illusions• 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 inches in front of face.

Perception

I. Visual Illusions:I. The Müller-Lyer illusion