perception and sensation

SENSATION AND

PERCEPTION

Sensation: Receiving Messages About the World

• Sense organs• See, hear, taste, smell, touch, balance, and experience the world

• Sensory receptor cells transmit sensation

• Perception – interpreting information and forming images

• Stimulus

Sensation and Perception

Translating Messages for the Brain

• Transduction – translates one form of energy (incoming stimuli) into another (sensory information)

• Receptor cells to neural impulses


Sensory Limits: How Strong Must Messages Be?

• Threshold – lower limits

• Absolute threshold – smallest to be detected

• Difference threshold – smallest difference between 2 stimuli to be detected 50% of time

• Sensory adaptation – one’s sensitivity to a stimulus varies from time to time• Fatigue, inattention, repeated exposure


Sensory Thresholds

VisionA candle flame seen at 30 mi. on a clear, dark night

Hearing The tick of a watch under quiet conditions at 20 ft.

TasteOne teaspoon of sugar in 2 gallons of water

Smell1 drop of perfume diffused into the entire volume of a 3 room apartment

TouchThe wing of a bee falling on your cheek from a height of 1 cm

Sensory Limits: How Strong Must Messages Be?

• Weber’s law – amount of change needed for detection 50% of time is always in direct proportion to intensity of original stimulus


Stimulus – any from of energy capable of exiting the nervous system like light waves, sound waves, and the chemical energy that causes the sensation taste and smell.

Receptor – is a specialized nerve ending capable of responding to energy.Senses – mechanisms which convert stimulus energy into neutral energy.

*Five Human Senses*

1.VISIONThe organ for vision is the eye. It is stimulated by light waves that strike the retina where the photo-sensitive cells- the rod and the cones- are located. The rods and cones are the receptor for vision.

Parts of Human Eye

Structure•Globe - shaped and has a

diameter of approximately one inch.

•Composed of three coats:Sclera - the outer layer, a tough

opaque layer of connective tissue used to protect the inner structures of the eye. Helps maintain the shape of the eyeball, in front, this layer becomes the cornea which is thin and transparent.

Choroid Coat - the middle layer, a pigmented layer. It contains some of the blood vessels that supply the eye with blood. It also absorbs imperfectly focused light rays. In the front part of the eye, it becomes modified to from the iris and the cilliary blood.

Pupil – the central opening of the iris

Iris – a circular arrangement of muscles that contract and expand to change the size of the pupil depending upon the intensity of illumination called light or dark adaptation. The color of the eye is due to the pigment in the iris

Accommodation – the process when the lens become thinner to bring faraway objects into focus and thickens to focus on nearly objects.

Vision: Sensing Light• Light

• Electromagnetic radiation

• Waves - frequency

• Wavelength – determines hues seen

• Intensity – brightness

• The more wavelengths in light, the less saturated or pure its hue is


The Eye: How Does It Work?

• Light passes through cornea

• Iris regulates light through pupil into lens

• Lens held in place by ciliary muscle

• Retina has rods and cones for receptors

Fovea – center of retina

• Visual acuity – clarity and sharpness


Photoreceptors

Cones

Rods

The Eye

• Rods• Not located in fovea

• Responsible for peripheral vision

• Hundreds of times more sensitive to light than cones

• Produce images perceived with less visual acuity than cones

• Do not detect color


The Eye

• Cones• Give brain more precise information

• Code information about color

• Respond only in bright light

• Optic nerve – has no cones or rods

• Blind spot – no visual reception in optic nerve

• Optic chiasm


Dark and Light Adaptation• Dark adaptation

• Receptors receive new supply of chemicals• After 30 minutes in the dark - level of sensitivity about 100,000 times greater than in bright light

• Light adaptation• Rods and cones highly responsive – overload

• Bleaching out of receptor chemicals occurs


Defects of Vision

•Presbyopia – a special form of farsightedness which occurs with advancing age. The presbyopic person cannot focus clearly on near objects.

Presbyopia

•Farsightedness or Hyperopia

– is caused by a shortened eyeball, making the distance from the lens to the retina too short. The lens will focus at a point behind the retina. A farsighted person is able to see far objects clearly but not near ones.

•Nearsightedness or Myopia – near objects are not seen clearly but lens is unable to thin enough to bring far objects into clear focus.

•Astigmatism – a structural defect of the eye

generally caused by an irregularity in the shape of the cornea.

Color Blindness

• Affects about 8% of males, 1% of females

• Partial color blindness – difficulty distinguishing between two colors• Red-green blindness due to genetic defect

• Yellow-blue blindness due to absence of blue pigment in cones


•Colorblindness – Poor color vision can be cause by an

inherited lack of one or another of the three types of cones.

Color Blindness

2. HEARING•It is the most vital channel of interaction with the environment.•The stimuli fro hearing are soundwaves.

Three dimensions describing the sound stimulus are :

Intensity FrequencyComplexity

Hearing: Sensing Sound Waves• Audition - detection of sound waves• Frequency of cycles

• Compression – increased density of waves

• Rarefaction – reduced density of waves

• Determines pitch of sound

• Intensity measured in decibel (db) units• Prolonged exposure to over 85 db causes hearing loss

• Timbre – quality of sound


Maximum level of industrial noise considered safe

Characteristics of Sound Waves

20 40 60 80 100 1600 120 180140

Loud thunder or rock concert

Pain Pain ThresholThreshol

dd

City bus

Normal conversation

Subway

db

Noisy automobile

Absolute threshold of human hearing

Quiet office

Whisper Rocket launch

Structure of the ear.

The ear is divided into three parts:The outer ear- it is the visible

part of the ear, composed of the pinna, the auditory canal, and the tympanic membrane commonly called eardrum.

The middle ear – an air- filled chamber that is connected to the pharynx by the eustachian tube.

This connection of the middle ear to the pharynx serves to equalize the pressure on the two sides of the eardrum. The middle ear structure is composed of tree small bones or ossicles: the mallleus (hammer), the incus (anvil), and the stapes (stirrup). These bones are hanging into the system of levers, so that the movement of the eardrum is transmitted to a membrane called the oval window.

The inner ear – can find a cochlea which is a fluid- filled bony structure shaped like a snail shell. It is the organ of hearing. There are three canals in the cochlea–the cochlear canal, the tympanic canal, and the vestibular canal.

The Ear: How Does It Work?• Outer ear

• Pinna – external part of ear that collects sound

• External auditory canal – connects outer and middle ear

• Middle ear• Cardum – tympanic membrane; 1st structure

• Eardrum - outermost structure of middle ear• Passes vibration to interconnected bones (hammer, anvil,

and stirrup)


The Ear: How Does It Work?• Inner ear

• Oval window – eardrumlike structure at end of cochlea

• Round window – eardrumlike structure at other end of cochlea

• Basilar membrane – forms floor for ear’s sensory receptors

• Organ of Corti – contains hairlike receptor cells


Hearing Defects

•Conduction Deafness – deafness due to inability to transmit vibrations through the external and middle ear.

•Nerve Deafness – this kind of deafness results from damage to the nerves themselves or to the delicate parts of the cochlea.

3. SMELL

- The receptors for smell are found at the olfactory epithelium located at the very top of the nasal passages.

-They are sensitive only to gases and to volatile substances that have been dissolved in the air.

Parts of Human Nose

4. TASTEMuch of the sensation

depends on other factors-on warmth, coldness, the mild irritation caused by certain spices, and above all, on smell. When our nostrils are stuffed because of colds. Food seems almost tasteless.

The tastebuds are the receptors for taste. They respond to four qualities of taste: sweet, sour, salty, and bitter.

Chemical Senses: The Flavors and Aromas of Life

• Senses of gustation (taste) and olfaction (smell) differ from all other senses• Taste cells and papillae on tongue• Taste buds detect


Sweetness - mostly sugars Sourness - mostly acidsSaltiness - mostly saltsBitterness - toxins, chemicalsFattiness - fats

Parts of Human Tongue

Surface of tongue

Receptor cells

Pore

Bitter

Sour

Salty

Sweet and fatty

Sensory nerve fiber

Taste

Chemical Senses: The Flavors and Aromas of Life

• Olfaction• Olfactory epithelium – top of nasal cavity • Pheromone detection of sweat and urine

• Vomeronasal organ• Influence human female reproductive cycles• Inhalation of male sex hormone and mood

changes• Males may respond to sex hormones


Olfactory nerve to brain

Olfactory epithelium

Nasal cavity

5. THE SKIN SENSES

The skin has four separate senses: pain, pressure, cold, and warmth. The receptors fro the skin senses are nerve endings which come in four general forms: free nerve endings, globular bulbs, egg- shaped corpuscles, and “baskets” surrounding root hairs.

Parts of Human Skin

Body Sensations: Messages About Myself

• Orientation and movement• Vestibular organ – 2 sets of sensory structures

• Semicircular canals• Saccule and utricle

• Kinesthetic receptors – throughout body

• Skin senses• Pressure sensitivity• Temperature sensitivity


The Skin Senses Pressure

Free nerve endings

Tactile discs

hair

Specialized end bulbs

basket cell around hair

Temperature

Pain

• Nerve endings in body act as

nocioceptors• Neural messages transmitted along two

distinct pathways• Rapid – detects first pain sensation• Slow – detects second long-lasting pain

• Endorphins and endogenous morphine


Pain

• Nerve endings in body act as

nocioceptors• Pain gates regulate pain signals in 3 areas

• Brain stem – gate-control theory of pain• Spinal cord • Peripheral regulation of pain

• Phantom limbs• Up tp 70% of amputees experience this


Direction of pain message

neuro-transmitter molecules in axon of slow-pain neuron

Endorphin receptor

Axon of inhibitory pain gate neuron

endorphin

Neuron in slow-pain fiber

Inhibitory pain gate neuron

Stimulation of endorphin receptors inhibits firing of axon of slow-pain neuron

Close-up view of inhibitory pain gates

Somatosensory area of cortex

Limbric system

Area of pain gates

Pathway of fast-pain fibers

Pathway of slow-pain fibers

Gate-control theory of pain

KINESTHESISThis is the sense of bodily

movements. Its receptors are nerve endings found in muscles, tendons, and linings of joints.

EQUILIBRIUMThis is also called as the Static

Sense. Two kinds of receptors give information about movements of the head and permit a sense of balance of the body.

These are in the semicircular

canals and the vestibular canal. Both are located in the inner ear next to cochlea.

THE ORGANIC SENSEThis give s the result of the

sensitivity of the visceral and other internal organs oft he body. Among the visceral organs are the stomach, intestines, sex structure, throat, hear and lungs.

PERCEPTIONChaplin defines perception as

the process of knowing objects and objective events by means of senses. This sensory input consists of nerve impulses. They carry a sort of raw, undigested information about the environment. The individual must convert it into a meaningful information. Perception, then, is the organization of sensory input into meaningful experiences.

PERCEPTUAL CONSTANCYThe perception of an object

and all of its properties as constant and unchanging in spite of the continuously changing sensations of these properties outline the scope of object constancies. Our perceptual organization remains relatively stable even though some aspects of the pattern within the optical array undergo great changes.

ORGANIZATION IN PERCEPTION

•Figure and ground – when we perceive an object, usually one part tends to stand out while the rest seems to remain in the background. The part which stands out is called the figure and the rest of the stimulus pattern is called the ground.

Figure and Ground

Laws of Perceptual Organization

Figure-Ground

•Grouping – we are concerned more with the figure than with the ground.

*The principles of similarity – stimuli which are similar tend to be perceived as forming a group.

Similarity

*The principle of proximity – there is a tendency to

perceive stimuli which are near one another as belonging together.

*The principle of closure – when fragmentary stimuli form enough of a familiar figure, we tend to perceive the whole figure, ignoring the missing part of parts.

*The principles of continuity – stimuli which from a continuous pattern are perceived as a whole, the pattern they make generally appears as a figure apart from the ground.

ATTENTION AND PERCEPTION

Perception is selective. The

direction of perception toward selected objects is called attention. A number of stimulus conditions help determine the direction of attention

DEPTH PERCEPTION

This is the ability to see three- dimensional space and accurately judge distances. A study of perception would be incomplete without considering perceiving the third dimension- distance and depth.

Depth Perception• Retina has two-dimensional surface

• Monocular cues – perception of one eye

• Texture gradient

• Linear perspective

• Superposition

• Shadowing


– Speed of movement

– Aerial perspective

– Accommodation

– Vertical position

Depth PerceptionSensation and Perception

• Binocular cues – perception with two eyes• Convergence• Retinal disparity

• Visual Illusions• Ponzo illusion• Vertical-horizontal illusion

• Color perception– Zollner illusion– Moon illusion– Poggendorf

illusion

Perception - Depth Perception

PERSONAL FACTORS IN PERCEPTION

•Motives•Emotions•Attitudes•Frames of reference

ERRORS IN PERCEPTION

•Illusion – a perception which is common but usually considered mistaken. This is an error which depends on stimulus conditions and occur in normal individuals.

•Hallucinations – are false perceptions that occur under abnormal conditions.

1.Illusions based on relative size.

2. Illusions based on intersecting lines.

3. Ponzo illusion.

Multisensory Integration

• Integrate and interpret information from multiple senses simultaneously• Limited ability and accident occurrence

• Motivation, Emotion, and Perception• Motivation and emotions influence perception

• Past experiences influence all perceptions


THE END


perception and sensation

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