Chapter 3 Sensation and Chapter 3 Sensation and PerceptionPerception

Sensation occurs when special Sensation occurs when special receptors in the sense organs are receptors in the sense organs are activated, allowing various forms of activated, allowing various forms of outside stimuli to become neural outside stimuli to become neural signals in the brain. This is called signals in the brain. This is called TransductionTransduction

Sensory Receptors- Specialized forms Sensory Receptors- Specialized forms of neurons that do not receive of neurons that do not receive neurotransmitters, but are neurotransmitters, but are stimulated by other forms of energystimulated by other forms of energy

Sensory ThresholdsSensory Thresholds Weber’s Law of Just noticeable Weber’s Law of Just noticeable

difference (JND)- The smallest difference (JND)- The smallest difference between two stimuli that difference between two stimuli that is detectable 50% of the timeis detectable 50% of the time– Ex. Add 1 teaspoon to 5 = 1/5 or 20%Ex. Add 1 teaspoon to 5 = 1/5 or 20%

Also 20% of 10 teaspoons it 2/10=1/5Also 20% of 10 teaspoons it 2/10=1/5

Comparisons between 2 stimuliComparisons between 2 stimuli

Absolute Threshold- Lowest level of Absolute Threshold- Lowest level of stimulation that a person can stimulation that a person can consciously detect 50% of the time consciously detect 50% of the time the stimulation is presentthe stimulation is present

Sensory Sensory Thresholds/Habituation Thresholds/Habituation and Sensory Adaptationand Sensory Adaptation Subliminal Perception- Stimuli that are Subliminal Perception- Stimuli that are

below the level of conscious awarenessbelow the level of conscious awareness Habituation- Tendency of the brain to stop Habituation- Tendency of the brain to stop

noticing constant, unchanging information noticing constant, unchanging information from the ears. Ex. Hum of air conditionerfrom the ears. Ex. Hum of air conditioner

Sensory Adaptation- Tendency of sensory Sensory Adaptation- Tendency of sensory receptor cells to become less responsive to receptor cells to become less responsive to a stimulus that is unchanging.a stimulus that is unchanging.– Pertains to sight, touch, taste and smellPertains to sight, touch, taste and smell– Feel of clothes would drive us nuts!Feel of clothes would drive us nuts!

Sensory AdaptationSensory Adaptation The eyes are different. They are The eyes are different. They are

never that adapted to what we never that adapted to what we see otherwise we would see otherwise we would eventually go blind from seeing eventually go blind from seeing things so oftenthings so often

QuizQuiz

Sight- Perceptual Sight- Perceptual Properties of LightProperties of Light Three aspects to the perception Three aspects to the perception

of light:of light:– 1. Brightness- determined by the 1. Brightness- determined by the

aptitude of the wave; how high/low aptitude of the wave; how high/low the wave isthe wave is Higher the wave=brighterHigher the wave=brighter

– 2. Color- determined by the length 2. Color- determined by the length of the waveof the wave Long wavelengths= redLong wavelengths= red

– 3. Saturation- purity of the color 3. Saturation- purity of the color determined by the purity of the determined by the purity of the wavelengthswavelengths

Structure of the EyeStructure of the Eye Cornea- clear membrane that covers Cornea- clear membrane that covers

the eyethe eye– Protects eye and focuses lightProtects eye and focuses light

Pupil- Iris hole in which light enters the Pupil- Iris hole in which light enters the eyeeye

Iris- Muscle that controls the size of Iris- Muscle that controls the size of pupil and how much light enters eyepupil and how much light enters eye

Lens- Finishes the focusing processLens- Finishes the focusing process– As lens hardens, as you age, sight gets As lens hardens, as you age, sight gets

worseworse Visual Accommodation- The change in Visual Accommodation- The change in

the thickness of the lens as the eye the thickness of the lens as the eye changes focus on far away/close objectschanges focus on far away/close objects

Structure of the EyeStructure of the Eye Retina- Last stop for light that Retina- Last stop for light that

contains 3 layers; ganglion cells, contains 3 layers; ganglion cells, bipolar cells and special cells bipolar cells and special cells (photoreceptors)(photoreceptors)– Photoreceptors respond to rods and Photoreceptors respond to rods and

conescones Rods- sensory receptors responsible for Rods- sensory receptors responsible for

non-color sensitivity to low levels of non-color sensitivity to low levels of lightlight

– Found all over the eye except the center-Found all over the eye except the center-peripheral visionperipheral vision

– All connected to one bipolar cell so the brain All connected to one bipolar cell so the brain doesn’t know exactly which rod the signal is doesn’t know exactly which rod the signal is coming from so hard to see in low lightcoming from so hard to see in low light

Structure of the EyeStructure of the Eye Cones- sensory receptors responsible Cones- sensory receptors responsible

for color and sharpness of visionfor color and sharpness of vision– Found only in center of eyeFound only in center of eye– Turn photons of light into neuron signals to Turn photons of light into neuron signals to

brainbrain– Send signals to bipolar cells that send Send signals to bipolar cells that send

signals to ganglion cellssignals to ganglion cells

Light travels through the cornea Light travels through the cornea and past the iris, through the and past the iris, through the pupil and into the lens and on to pupil and into the lens and on to the retina where it is transformed the retina where it is transformed into nerve impulsesinto nerve impulses

How the Eye WorksHow the Eye Works Dark Adaptation- Eye recovers it’s Dark Adaptation- Eye recovers it’s

ability to see when going from very ability to see when going from very bright to dark bright to dark – The brighter the light the longer to The brighter the light the longer to

readapt to darkreadapt to dark– As person gets older longer it takes to As person gets older longer it takes to

adapt to darkadapt to dark– Rods adapt to dark, but do not see Rods adapt to dark, but do not see

sharplysharply Light Adaptation- Recovery of eye’s Light Adaptation- Recovery of eye’s

sensitivity to light after being in the sensitivity to light after being in the darkdark– Cones adapt to lightCones adapt to light

Perception of ColorPerception of Color How people see colorHow people see color

– Trichromatic Theory- Three types of Trichromatic Theory- Three types of cones; red, blue and greencones; red, blue and green

– The combinations of cones and rates The combinations of cones and rates at which the neurons are fired at which the neurons are fired determine the colorsdetermine the colors

– Afterimage- vision of an object is still Afterimage- vision of an object is still seen after the object is removed seen after the object is removed from sight, though the colors are all from sight, though the colors are all wrong!wrong! Flag experimentFlag experiment

Perception of ColorPerception of Color Opponent-Process theory- Four Opponent-Process theory- Four

primary colors with cones primary colors with cones arranged in pairs; red-green and arranged in pairs; red-green and yellow-blueyellow-blue– If one color is stimulated the other is If one color is stimulated the other is

not working: when one color is seen not working: when one color is seen a lot it tires out so the other can a lot it tires out so the other can take overtake over

Color BlindnessColor Blindness 3 kinds of color blindness3 kinds of color blindness

– Monochrome= either have no cones or the Monochrome= either have no cones or the cones do not workcones do not work

See only shades of graySee only shades of gray

– Red-green= either red or green cones do Red-green= either red or green cones do not worknot work

– Blue= blue cones do not work only see Blue= blue cones do not work only see red, green and grayred, green and gray

More men are color blind than womenMore men are color blind than women Color blindness is recessiveColor blindness is recessive Men only need one recessive geneMen only need one recessive gene Y chromosome does not have the gene that Y chromosome does not have the gene that

prevents colorblindnessprevents colorblindness Women need two recessive genesWomen need two recessive genes

QuizQuiz

Hearing-Perception of Hearing-Perception of SoundSound Sound waves are the vibrations of Sound waves are the vibrations of

molecules of airmolecules of air Have the same properties as light Have the same properties as light

waveswaves Wavelengths are interpreted as Wavelengths are interpreted as

frequency or pitchfrequency or pitch Amplitude is interpreted as volumeAmplitude is interpreted as volume Purity is interpreted as timbre (pure Purity is interpreted as timbre (pure

tones)tones) Frequency is measured in Hertz (Hz)Frequency is measured in Hertz (Hz) Most accurate hearing is at 1,000 HzMost accurate hearing is at 1,000 Hz

Structure of the EarStructure of the Ear Outer EarOuter Ear

– Pinna is the outside of the ear that funnels Pinna is the outside of the ear that funnels soundsound

– Pinna is entrance to auditory canal (ear Pinna is entrance to auditory canal (ear canal) that leads to eardrumcanal) that leads to eardrum

– Tiny bones vibrate sound waves hit themTiny bones vibrate sound waves hit them Middle Ear (Hammer, Anvil, & Stirrup)Middle Ear (Hammer, Anvil, & Stirrup)

– The three tiny bones are; hammer, anvil & The three tiny bones are; hammer, anvil & stirrupstirrup

– Named for the shapes of the bonesNamed for the shapes of the bones– Stirrup vibrates a membrane covering the Stirrup vibrates a membrane covering the

opening to the inner earopening to the inner ear

Structure of the EarStructure of the Ear Inner Ear (Oval window)Inner Ear (Oval window)

– Cochlea-snail shaped structure filled Cochlea-snail shaped structure filled with fluid that vibrateswith fluid that vibrates

– Basilar membrane- in the middle of Basilar membrane- in the middle of the cochlea that houses the organ of the cochlea that houses the organ of corticorti

– Organ of corti contains receptor cells Organ of corti contains receptor cells for hearingfor hearing

– Sound waves go through pinna, Sound waves go through pinna, vibrate the eardrum, vibrates the vibrate the eardrum, vibrates the hammer, anvil & stirrup, vibrates the hammer, anvil & stirrup, vibrates the oval window, fluid in cochlea vibrates, oval window, fluid in cochlea vibrates, basilar membrane vibrates, Corti basilar membrane vibrates, Corti bends hair cells, signal sent to brain.bends hair cells, signal sent to brain.

Structure of the EarStructure of the Ear Louder the sound=stronger the Louder the sound=stronger the

vibrations=stimulates more hair vibrations=stimulates more hair cells=sound interpreted as loudcells=sound interpreted as loud

Theories of PitchTheories of Pitch Pitch- how low or high a sound isPitch- how low or high a sound is Place theory- the pitch a person Place theory- the pitch a person

hears depends on where the hair hears depends on where the hair cells that are stimulated arecells that are stimulated are

Frequency theory- Pitch depends Frequency theory- Pitch depends on how fast the basilar membrane on how fast the basilar membrane vibrates; slow=lowvibrates; slow=low

Both theories are correctBoth theories are correct– Place theory=above 1,000 HzPlace theory=above 1,000 Hz– Frequency theory=below 100 HzFrequency theory=below 100 Hz

Theories of PitchTheories of Pitch Volley Principal= After 100 Hz the Volley Principal= After 100 Hz the

auditory neurons take turns firing auditory neurons take turns firing If sound is at 300 Hz there are 3 If sound is at 300 Hz there are 3

groups of neurons at 100 Hz eachgroups of neurons at 100 Hz each

Types of Hearing Types of Hearing ImpairmentsImpairments Conduction Hearing Impairment- Conduction Hearing Impairment-

Sound not passed from eardrum to Sound not passed from eardrum to cochlea= damage to eardrum/bones-cochlea= damage to eardrum/bones-hearing aid may helphearing aid may help

Nerve Hearing Impairment- Nerve Hearing Impairment- – Inner ear, auditory pathways, or cortical Inner ear, auditory pathways, or cortical

areas are damaged.areas are damaged.– Aging, or exposure to loud noisesAging, or exposure to loud noises– Damage to the hair cells in the cochlea.Damage to the hair cells in the cochlea.– Tinnitus – ringing in one’s earsTinnitus – ringing in one’s ears