Sensation: Modules 12-14

General Psych 1February 22, 2005

Class #9

Sensation and Perception

• Sensation – The conversion of energy from the

environment into a pattern of response by the nervous system

• Perception – The active mental process or

organizing and interpreting our sensation

To use a computer concept…

• Input• Information processing• Output

Vision

• Receptors – Our sensory organs including our

eyes are packed with these– Stimuli activate receptors which then

send messages to our brain

The Stimulus Input: Light Energy

• Electromagnetic energy– Scientifically speaking, what strikes are eyes

is not color but rather pulses of electromagnetic energy that our visual system experiences as color

• Important note: – The textbook utilizes several diagrams of the

eye which illustrates many of the eye’s components

– You will only be tested on those covered in class discussions

The Eye

• In some ways, the eye functions like a camera– In both, light is admitted through a

small opening (the pupil) • The size of the pupil and therefore the

amount of light entering the eye is regulated by the iris– This muscle surrounds and dilates

(swells, expands) or contracts (shrinks or lessens) the eye

The Eye

• Accommodation – The lens (which is located behind the

pupil) will focus incoming rays by changing its curvature

– These rays are focused on a light sensitive surface called the retina – a very flexible structure

– As light passes through the eye, the lens along with the cornea focus light on the retina

– The cornea is a rigid, transparent structure

Feature Detection

• Cortical neurons that receive information from the visual cortex helping us to respond to specific features of a scene

Parallel Processing

• This is the ability to process information in parallel, or at the same time– This is in direct contrast to serial

processing where each process is done one after the other• Think of serial processing as waiting in line

at some store that only has one register• Parallel processing would have multiple

registers so that many people could be handled at the same time

Common Disorders of Vision

• Myopia – Near-sightedness– Here the focusing system is too

strong for the length of the eye – basically leading to blurry images for long distance

– About 50% of 20-year-olds– Glasses, contacts, or laser surgery

Common Disorders of Vision

• Hyperopia – Far-sightedness – The light rays from near objects

entering through the cornea and lens reach the retina before they have converged

How do we perceive color?

Geldard (1972): – How many different shades of color

are there?• Would you believe about 7 million?

Wavelengths and Color Sensations

• 3 separate aspects of sensation:– Hue

• The essential color determined by the dominant wavelength

– Saturation • This is the purity of color • The more pure the more intense • Bright colors are most pure whereas

pastels are said to be desaturated

– Brightness • This is the overall intensity of all

wavelengths

Two types of photoreceptor cells in the retina:

• Rods – Dim light

• Cones– Color

• Each cone contains structures sensitive to:– Red, green, or blue

Color Vision Theories

– Young-Helmholtz Trichromatic Theory

– Hering’s Opponent Process Theory

Young-Helmholtz Trichromatic Theory

• This theory dates back to early 1800’s– States that the retina has three types of

color receptors, each especially sensitive to one of the three primary colors

– Only when combinations of these are stimulated are other colors perceived

– Out of these three, the visual system is able to derive all other perceptible colors• For example, although we have no

receptors for yellow – if both red and green sensitive cones are stimulated then yellow is perceived

Hering’s Opponent Process Theory

• This theory was formulated in late 1800’s– This is the idea that we do not perceive color

in terms of independent colors but in terms of a system of paired opposites – not all of which are primary colors – red vs. green, yellow vs. blue, white vs. black

– So if you detect one of these colors at a particular point of the retina – you can not simultaneously detect the opposing color at the same point• You therefore, can not see a greenish-red,

or a whitish-black, or a yellowish-blue

Hering’s Opponent Process Theory

• Negative Afterimages– Hering’s theory tries to explain this experience

of seeing the paired opposite after the removal of the first

– So, if you have been looking at something red for an extended period and this is removed you will then see a green afterimage and vice versa

– This has to do with the visual system becoming fatigued

• If cells in the visual system have been stimulated too long they basically get tired and inhibited (unable to express itself and then the paired afterimage takes over – the opposite’s cells have been stimulated)

• See next slide for an example…

Color Blindness

• Malfunction of the retina– Cause: Genes – Basically, just a social inconvenience– Big gender difference…

Color Blindness

• In color-deficient individuals one of these three structures fails to function properly…– Almost all color deficient people

have either red or green deficiency

– Blue is extremely rare

Module 13: Hearing

• The Stimulus Input: Sound Waves– Air-pressure waves composed of

moving bands of compressed and expanded air…like the ripples of a pond

The Stimulus Input: Sound Waves

• Amplitude– Height of the waves determines loudness

• Frequency– Length of the waves determines the pitch

• Note: – On page 212 there is picture of ear and its

many components. Just as with the eye diagrams you are responsible for only the parts of the ear discussed in class

How do we perceive pitch?

Theories:(1) Place theory

• Presumes that we hear different pitches because sound waves of various frequencies trigger activity at different places along the cochlea's basilar membrane• Thus, the brain can determine the pitch of a sound by recognizing the place on the membrane from which it receives neural signals• Explains how we hear high-pitched sounds but fails to explain how we hear low-pitched sounds

Pitch Theories

(2) Frequency-Matching Theory • The basilar membrane vibrates with

the incoming sound wave and will trigger neural impulses to the brain

• The firing rate of a neuron in an auditory nerve matches the frequency of a sound wave – Explains how we perceive low pitches

but not high pitches

Hearing Loss

• Conduction Deafness– Problems with the mechanical system of the

ear– Results when bones connected to the eardrum

fail to transmit sound waves properly– Hearing aids often help

• Nerve Deafness– Damage to the inner ear (cochlea, hair cells,

or the auditory nerve)– Main causes: hereditary, disease, biological

changes linked to aging, prolonged exposure to ear-splitting music

Module 14: The Other Senses

• Touch• Taste• Smell• Body Position and Movement

Somatic Senses

• Touch and Temperature– Sense of touch is actually a mix

of several distinct skin senses… •Pressure•Warmth•Cold•Pain

The House of Pain

• Pain receptors – simple, bare nerve endings that send messages to the spinal cord.– A complicated mixture of sensation

and emotion (finally back to psychology!)

– No pain…no gain? Be careful…

Gate Control Theory of Pain

• Melzack and Wall (1965)– Neurological gate– May have to do with attention –

physical and psychological…•“Line drive right up the middle”

Pain Control

• Wide variety of therapies – many with a physical/psychological combo– Drugs

• Pain Killers

– Transcutaneous Electrical Nerve Stimulation (TENS)

– Acupuncture – Distraction Therapies

• Lamaze method of childbirth, etc.

Drugs – Pain Killers

• Quickest and easiest form of pain control but…

T.E.N.S.

• Replace pain impressions with massage-like sensations– Athletes, elderly among others

Acupuncture

• Used for most common ailments – backaches, headaches, arthritis, allegies, muscles aches and spasms, etc.– Shen Nung (Father of Chinese Medicine)

• Qi – Energy running through our body

• 14 main meridians– Needles bring us back to homeostasis

• Deqi – Sensation is felt (not painful)

Acupuncture

• How it relates to the Gate Control theory of Pain…

Distraction Therapies

• The “ice-water” experiments– Worthington (1983)

• Participants put into three groups– Group 1: Lamaze method used– Group 2: No instructions

– McCaul and Malott (1984)• Participants put into three groups

– Group 1: Pleasant images– Group 2: Count backwards– Group 3: No instructions

• What are experimental and control groups in above experiments?

• What are DV and IV’s???

Pain of the Phantom Limb

• Approximately 80% of amputees have some phantom limb sensations…– Sometimes, its a tingling sensation that they

feel– Others experience pain– Intensity, duration, and severity all are

variable from patient to patient

• Are they just some form of obsession neurosis stemming from the trauma of losing one's body part?

• Or is there a biological explanation for all this?

The Chemical Senses: Taste and Smell

Taste (Gustation)• Four basic sensations – sweet,

sour, salty, and bitter• Special sensitivities on tongue’s

surface:– Tip of tongue: Sweet and salty tastes– Back of tongue: Bitter tastes– Middle sides: Sour

Taste Buds and Receptors

• At least 200 taste buds50 taste receptor cells• Doesn’t take much to trigger a

response…– For example: “Can I have a taste”

• Reproduce every week

Slow decline…

• Aging factor– Taste buds and receptors start slow

decline after the age of 30

• Other factors:– Smoking– Alcohol

Sensory Interaction

• Taste is influenced by smell– Example: Bad cold

The Chemical Senses: Taste and Smell

• Smell (Olfaction)– The “intimate” sense

• Social function especially in animals– Pheromones

– Olfactory receptor cells that respond selectively• Associated with memory• Starts early – nursing infants• Peaks at 30• Most animals have more

– Bloodhounds: some reports say 2 million times the sense of smell as we do

Smell loss…

• Aging is most common cause– Usually okay until we’re 60

• Viral infections• Disease of nasal cavity• Medications, smoking,

radiation, etc.

Proprioception

• Proprioception systems provide information to the brain concerning the position of your body an what each of its parts are doing– Kinesthesia

• Tells you where the parts of your body are with respect to each other

• Helps guide our movements

– Vestibular Sense• Tells the brain about the position of your head in

space and about its general movements• Gives us our sense of balance • Keeps us from getting dizzy