SENSATION AND PERCEPTION



THE NATURE OF SENSORY PROCESSES
Sensation The process through which the senses pick up visual, auditory and other stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted


Perception The process by which sensory information is actively organized and interpreted by the brain

How do we interpret the raw data picked up by our senses?
-sight,hearing, smell, taste, balance, touch, pain

How does the body convert physical energy into nerve pulses?
-when there is sufficient energy, the receptor cell sends a coded message to brain -gentle pressure on eyes results in signal-visual pattern-hit in eye see stars

SENSORY THRESHOLD
How much sound is necessary to hear?-a watch ticking 6 meters away
How much light is necessary to see?- a candle flame 48 kilometers away on a clear night
Taste: 1 gram of salt in 500 liters H2O
Smell -1 drop perfume in three room apartment
*We all have a range of intensities;

Absolute Threshold The minimum amount of sensory stimulation that can be detected 50 % of the time

The Difference Threshold

The Difference Threshold The smallest increase or decrease in physical stimulus required to produce a difference in sensation that is noticeable 50% of the time
Just Noticeable Difference (JND) The smallest change in sensation that we can detect 50% of the time

JND- if add 2 pounds to 10 we notice but if add 2 pounds to 100 don't notice....it's relative-the greater the stimulus the greater the change necessary to notice.
SUBLIMINAL PERCEPTION Can subliminal messages in ads affect us? Can self help subliminal tapes work?
* objective tests show no measurable improvement even though when tested subjects say they improved tests don't show it. -subjects affected by label given tape for self esteem labeled memory report improved memory; however, in controlled situation subjects exposed to either honest or dishonest words later given description that could go either way report honest if previously exposed to honest or dishonest if exposed to dishonest
*no independent scientific evidence that subliminal ads or self help have significant effect.

Weber's Law The law stating that the just noticeable difference(JND) for all our senses depends on apportion or percentage of change in a stimulus rather than on a fixed amount of change


Weber's Law: The difference threshold is not the same for all senses or for all people

Signal Detection Theory The view that detection of a sensory stimulus involves both discriminating a stimulus from background noise and deciding whether the stimulus is actually present


Sensory Receptors specialized cells in sense organs that detect and respond to sensory stimuli (alight, sound, odors,etc.)and convert the stimuli to neural impulse


Transduction The process by which sensory receptors convert sensory stimulation into neural impulses


Sensory Adaptation The process of becoming less sensitive to an unchanging sensory stimulus over time

* After eating salty food what happens?
* After the perfume has been sprayed what happens? why people don't know perfume is strong -the absolute threshold rises-we can no longer detect
* a continuous odor will stimulate the smell receptors to respond only for a while

VISION

-is a most important human sense, so studied most

The Visual System -light enters eye through cornea next light passes through pupil

Cornea The transparent covering of the coloured part of the eye that bends light rays inward through the pupil

-bright light muscles of iris contract pupils to protect eye
-also helps see in bright light-dim light open pupil
-light moves from pupil through lens which focuses it on retina

Lens The transparent structure behind the iris that changes in shape as it focuses images on the retina


Retina The tissue at the back of the eye that contains the rods and cones and onto which the retinal image is projected

-light sensitive inner lining is retina
-to focus on close object muscles contract and make lens rounder --called accommodation
-to focus far muscles flatten the lens

Accommodation The changing in shape of the lens as it focuses on the retina; it becomes more spherical for near objects and flatter for far objects
Rods The light-sensitive receptors in the retina that provide vision in dim light in black, white and shades of grey
Cones The receptor cells in the retina that enable us to see colour and fine detail in adequate light, but that do not function in dim light

-directly behind lens is depressed area called fovea

Fovea small area of retina that provides the clearest and sharpest vision because it has the largest concentration of cones and no rods


-foveas is in centre of visual field-what you focus on is on fovea rest is other areas of retina

RECEPTOR CELLS -retina has receptor cells responsible for vision-rods and cones -sensitive to only a fraction of electromagnetic spectrum includes light -energies referred to by wavelength -colour shortest blue violet -longest reds

Cones concentrated in fovea (6 million cones in retina)

Rods predominate outside fovea (120 million rods in retina)-farther away from fovea less cones and rods -cones connect to bipolar cells one on one but several rods share one bipolar cell -at night you can see dimly lit object by viewing slightly from side-direct view would be fovea with cones -the greater the light the more cones are stimulated

ADAPTATION -process by which our senses adjust to different levels of stimulation -when you go from bright light to dim can see little-with time (10 min)cones become more sensitive-rods continue adapting for about 30 minutes

Dark Adaptation The eye's increasing ability to see in dim light; results partly from dilation of the pupil

-effects of dark adaptation-highway accidents-dark area in car vs illuminated road-dark on side of road ***see afterimage figure (see bottom page 82)
-visual adaptation back and forth process-eyes adjust but never adapt completely

FROM EYE TO BRAIN -rods and cones connected to bipolar cells -bipolar cells hook up to ganglion cells leading out of eye -axons of ganglion cells join to form the optic nerve

Optic Nerve The nerve that carries visual information from the retina to the brain

-single ganglion sends summary of message from large number of receptor cells -the place where axons gather to form optic nerve is blindspot-contains no receptor cells -information from left visual field goes to right hemisphere -information from right visual field goes to left hemisphere -main areas reached is occipital lobes

COLOUR VISION

Three dimensions that combine to give colour: hue, saturation, brightness

Hue The property of light commonly referred to as colour (red,blue,green,etc.) determined primarily by the wavelength of light reflected from a surface
Saturation The degree to which light waves producing a colour are the same wavelength; the purity of the colour
Brightness The dimension of visual sensation that is dependent on the intensity of light reflected from the surface and that corresponds to the amplitude of the light wave

THEORIES OF COLOUR VISION :

1.TRICHROMATIC THEORY-HERMANN VON HELMHOLTZ 1800s
-eye contains some cones sensitive to reds, some greens, some blue violet -colour comes from mixing receptors signals -but it accounts for only some colour blindness

Trichromatic Theory Theory of colour vision suggests that three are primarily 3 types of cones which are maximally sensitive to red green, or blue and that the varying levels of activity in these receptors can produce all of the colours

2. OPPONENT-PROCESS THEORY- EWALD HERING 1878
-three pairs of colour receptors: yellow-blue, red-green, black-white -explains afterimage

Opponent-process theory The theory that certain cells in the visual system increase their firing rate to signal one colour and decrease their firing rate to signal the opposing colour (red/green,yellow/blue,whit/black)
Afterimage The visual sensation that remains after a stimulus is withdrawn
Colour Blindness The ability to distinguish some or all colours in vision, resulting from a defect in cones

-contemporary research says both theories valid but at different stages

COLOUR VISION IN OTHER SPECIES -humans/primates are trichromates-can see all hues -most mammals are dichromats- reds/greens or blues/yellows -rodents monochromats-completely colourblind

HEARING SOUND

-physical stimuli that prompts sense of hearing is sound waves-changes in pressure caused by molecules of air or fluid colliding and moving apart -simplest sine wave (pure tone) from tuning fork -human ear responds to frequencies 20Hz--20,000Hz-double bass 50Hz
-sound requires a medium to move through: air, water, solid

-hearing also adapts-living in city don't hear noise

Frequency Measured in the unit hertz, the number of sound waves or cycles per second, determining the pitch of sound
Amplitude measured in decibels, the magnitude or intensity of a sound wave, determining the loudness of the sound; in vision the amplitude of a light wave affects the brightness
Decibel A unit of measurement of the intensity or loudness of a sound bases on the amplitude of a wave
Timbre The distinctive quality of a sound that distinguishes it from other sounds of the same pitch and loudness

THE EAR
-sound travels through outer ear, middle and inner ear where transmitted along Auditory nerve to brain

OUTER EAR-sound waves strike eardrum-->vibrate -tiny bones(hammer,anvil stirrup) hit in sequence -stirrup attached to membrane called oval window
-oval window vibrates to inner ear to fluid in cochlea (snail shape)
-basilar membrane contains receptor cells send message through auditory nerve--.brain -ear ear sends messages to both hemispheres of brain

Audition The sensation of hearing, the process of hearing
Outer ear The visible part of the ear, consisting of the pinna and the auditory canal
Middle Ear The portion of the ear containing ossicles which connect the eardrum to the oval window and amplify the vibrations as they travel to the inner ear
Inner Ear The innermost portion of the ear containing the cochlea, vestibular sacs, and the semicircular canals
Cochlea The snail-shaped fluid-filled organ in the inner ear that contains the hair cells (sound receptors)
Hair Cells Sensory receptors for hearing, found in cochlea

THEORIES OF HEARING

Place Theory:

-1860s German von Helmholtz-each individual pitch we hear is determined by a particular place along the basilar membrane-explains some of hearing but not for frequency below 150Hz

Place Theory The theory that sound of different frequencies or pitch cause maximum activation of hair cells at certain locations along the basilar membrane

Frequency Theory:

Frequency Theory Theory that hair cell receptors vibrate the same number of times as the sounds that reach them, accounting for the way variations in pitch are transmitted to the brain


-seems valid for low/medium frequency tones, but has a problem with high frequency tones where neurons could not fire as fast
-researchers believe that hearing is a result of both theories

SMELL

-estimates smell 10,000 x acute as taste-but also adapts-perfume not noticed by wearer PROCESS OFÊSMELL -sense of smell activated by protein in nasal gland -as we breathe fine mist of protein sprayed through duct in nose -protein binds with airborne molecules that activate receptor cells in nasal cavity -these axons go to Olfactory bulb

Olfaction The sensation of smell; the process of smell
Olfactory Epithelium A patch of tissue at the top of the nasal cavity containing 10 million receptors for smell

TASTE:
-hold nose while eating-most flavour will disappear-you will only experience 4 primary tastes: sweet sour salty bitter
-receptor cells are housed in taste buds on tips, sides, and back of tongue -tip of tongue most sensitive to sweet and salty-back most sensitive to bitter-sides most sensitive to sourness -recent studies show each area can distinguish all
-as we age taste decreases -people can identify taste in 1/10th sec -taste also experiences adaptation

Gustation The sensation of taste
Taste Buds The structures that are composed of 60-100 sensory receptors for taste
Flavour combined sensory experience of taste, smell and touch

KINESTHETIC AND VESTIBULAR SENSES SKIN SENSES
-skin receptors give rise to cutaneous sensations of pressure, temperature, and pain -cold fibres increase their firing rate as skin cools down and they slow their firing when the skin heats up -if both hot and cold stimulated at once brain reads hot-called paradoxical heat -skin sensitive-body parts differ-also adaptation-e.g. hot bath

PAIN -scientists have had difficulty finding pain receptors -people react to pain differently -our beliefs about pain affect our experience of it -athlete injured often feels no pain until later -acupuncture also release endorphins

Gate Control Theory The theory that the pain signals transmitted by slow firing nerve fibres can be blocked at the spinal gate if fast firing fibres get their message to the spinal cord first, or if the brain itself inhibits the transmission of the pain message
Endorphins Chemicals produced naturally by the pituitary gland that reduce pain and affect mood positively

 

PERCEPTION

-deciphering meaningful patterns in complex sensory information is perception

Perception The process by which sensory information is actively organized and interpreted by the brain


PERCEPTUAL ORGANIZATION

Gestalt Psychologists set out to discover principles through which we interpret sensory info
Figures: are what we attend to example red chair in white room
Ground: is what is in background not attended to-white room -figures/ground can also apply to other senses-e.g. listening to violin in orchestra- a single voice in noisy room -sometimes there are not enough cues to distinguish figure -when told you may see it- principle behind camouflage -sometimes one thing can be perceived two ways--visual -we try to fill in blanks to make meaning

Figure-ground A principle of perceptual organization where the visual field is perceived in terms of an object (figure) standing out against a background (ground)

Grouping principles:
Similarity-
objects similar are considered a unit
Proximity-
because of spacing objects considered a unit
Continuity- objects that form a continuous pattern tend to "belong" together

Closure-
the tendency to fill in the gap to produce a familiar object

PERCEPTUAL CONSTANCIES -white house looks like white house from any angle

Perceptual Constancy tendency to perceive objects maintaining stable properties as size, colour, shape, brightness despite difference in angle, lighting distance

Types of Perceptual Constancy: Size Constancy, Shape Constancy, Brightness Constancy, Colour Constancy

PERCEPTION OF DISTANCE AND DEPTH -we constantly judge distances

LOCATION OF SOUNDS
-we also draw on monaural (one ear) and binaural (two ears) cues to locate sound monaural- loud sounds are perceived as being closer than faint ones binaural- because sounds off to one side reach one ear slightly ahead, the time difference helps us make accurate judgment about distance
PERCEPTION OF MOVEMENT
-perception of movement involves both visual info from retina and messages from muscles around eye as they follow object -occasionally we think we see movement when objects are stationary
Real Movement: physical displacement of object from one position to another e.g. move head around-objects stationary -perception of real movement seems to be determined less by images moving than by how the positions of objects change in relation to a background that is perceived as stationary

Apparent Movement-when we see movement in objects that are actually standing still-stand in room dark except for tiny spot of light-stare-light appears to drift-no cues-eye muscles cause it

VISUAL ILLUSIONS -psychologists distinguish between physical and perceptual illusions physical illusions- e.g. bent appearance of stick in H2O-H20 acts like prism perceptual illusions occur because stimulus contains misleading cues that give rise to inaccurate or impossible perceptions see samples reversible and misleading cues

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copyright 2001 Karen E.Hamilton