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UIUC / Psychology / PSYC 230 / What is the meaning of hearing in psychoacoustics?

What is the meaning of hearing in psychoacoustics?

What is the meaning of hearing in psychoacoustics?


School: University of Illinois at Urbana - Champaign
Department: Psychology
Course: Perception & Sensory Processes
Professor: Lleras buetti
Term: Fall 2017
Cost: 50
Description: I uploaded all of my notes from the chapters for Exam 3. At the end I uploaded a document that has a link to a set of quizlets for every chapter for exam 3 that will be very useful as well! Good Luck!
Uploaded: 12/08/2017
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Sensory & Perception Chapter 9

What is the meaning of hearing in psychoacoustics?

 Hearing: Physiology and Psychoacoustics 

 The basics

♦ Nature of sound

♦ Anatomy and physiology of the auditory system

♦ How we perceive loudness and pitch

♦ Impairments of hearing and how to ameliorate them

What Is Sound? 

 Sounds are created when objects vibrate

♦ When an object vibrates, the molecules in the surrounding medium  start vibrating as well

♦ This causes pressure changes in the medium

♦ Same pattern, but amount of pressure decreases as the wave moves  away from the source

 Sound waves travel at a particular speed

What is sound?

♦ Depends on the medium: faster through denser substances ♦ Example: sound through air = 340 meters/second & sound through  water = 1500 meters/second

♦ Light travels a million times faster than sound (you see lightning before hearing thunder)

 Physical qualities of sound waves

♦ Amplitude of intensity: magnitude of displacement (increase or  decrease) of a sound pressure wave

 Low amplitude = quieter, high amplitude = louder If you want to learn more check out What is the proposed solution?

 Psychological quality: loudness

 Units for measuring the physical intensity of sound: decibels (dB) ♦ Frequency: for sound, the number of times per second that a pattern of pressure change repeats If you want to learn more check out What is a “protection rocket”?

 Psychological quality: pitch. Mainly related to the fundamental  frequency

What are the physical qualities of sound waves?

 Units for measuring frequency: Hertz (Hz) 1 Hz equals 1 cycle (up  and down) per second (example: 500 Hz = the wave goes up and  down 500 times per second)

 Ruben’s tube in 2D (pipe with a bunch of holes in it, pipe in  flammable gas and light in on fire) can play sounds into tube and  fire reacts differently (flow rate) Don't forget about the age old question of What are some of the biological and psychological factors that contribute to aggression?

 Human hearing uses a limited range of frequencies (Hz) and sound  pressure levels (Db)

 Humans can hear across a wide range of sound intensities ♦ Sine waves, or a pure tone: one of the simplest kinds of sounds

Sensory & Perception Chapter 9

 Sine waves aren’t common in everyday sounds because not many  vibrations in the world are so pure

∙ Most sounds in the world (human voice, bird sounds, car noises)  are complex sounds 

∙ All complex sounds can be described as combinations of sine  waves

∙ Complex sounds are best described as a spectrum that displays  how much energy is present in each of the frequencies in the  sound

♦ How to read the spectrum graph

 The combination of the bars on the spectrum graph = harmonic  spectrum

 Y axis: sound intensity (higher values = louder) If you want to learn more check out What is deontology according to kant?

 X axis: sound frequency (higher values = higher pitch). The  frequency components (blue bars) are called: harmonics. The first  harmonic is called fundamental frequency 

♦ When different instruments play the same sound, how can you tell  there are different instruments? Different harmonic spectra!  Timbre: the psychological sensation by which a listener can judge  that 2 sounds with the same loudness and pitch are dissimilar

Anatomy & Physiology of the Auditory System 


 How are sounds detected and recognized by the auditory system? ♦ Sense of hearing evolved over millions of years

♦ Many animals have very different hearing capabilities

 For instance, dogs can hear higher-frequency sounds and elephants  can hear lower-frequency sounds than humans can

 Outer ear

♦ Sounds are first collected from the environment by the pinnae ♦ Sound waves are funneled by the pinnae into the ear canal ♦ The main purpose of the ear canal is to insulate the structure at its end – the tympanic membrane or the eardrum If you want to learn more check out What is considered repetitive behavior in autism?

♦ We all have different pinnae and different ear canals. The length and  shape of the ear canal enhances certain sound frequencies ♦ Tympanic membrane or eardrum: a thin sheet of skin at the end of the  outer ear canal. Vibrates in response to sound

♦ Common myth: puncturing your eardrum will leave you deaf  In most cases it will heal itself

 However, it is still possible to damage it beyond repair

Sensory & Perception Chapter 9

 Middle ear:

♦ Tympanic membrane is border between outer ear and middle ear ♦ Consists of 3 tiny bones called Ossicles 

 Malleus, incus, stapes; smallest bones in body

 Function: to amplify sounds

♦ Stapes transmits vibrations of sound waves to oval window, another  membrane which represents border between middle ear and inner ear ♦ The Ossicles are amazing organs Don't forget about the age old question of What are the principles of choice theory?

 They amplify the sounds so they allow you to hear faint sounds  You NEED this amplification because the inner ear contains fluids  (you need strong vibrations to move them!)

 Importantly: Ossicles are also important for loud sounds ♦ The tensor tympani and stapedius are 2 muscles in the middle ear:  Purpose: to tense when sounds are very loud, muffling pressure  changes

 Acoustic reflex: when there’s a loud sound, the muscles contract. It  takes about one fifth of a second, so cannot protect against abrupt  sounds (gun shots)

 Inner Ear:

♦ Where transduction happens. Where fine changes in sound pressure  are translated into neural signals

♦ Cochlear canals and membranes

 Cochlea: spiral structure of the inner ear containing the organ of  Corti

 Cochlea is filled with watery fluids in three parallel canals ♦ The three canals of the cochlea:

 Tympanic canal: extends from round window at base of cochlea to  helicotrema at the apex

 Vestibular canal: extends from oval window at base of cochlea to  helicotrema at the apex

 Middle canal: sandwiched between the tympanic and vestibular  canals and contains the cochlear partition

♦ 3 cochlear canals are separated by membranes:

 Reissner’s membrane: separates the vestibular and middle canals in the cochlea

 Basilar membrane: plate of fibers that forms the base of the  cochlear partition and separates the middle and tympanic canals in  the cochlea  

∙ Organ of Corti: a structure on the basilar membrane of the  cochlea that is composed of hair cells and dendrites of auditory  nerve fibers

Sensory & Perception Chapter 9

∙ Where transduction happens: movements of the cochlear  partition are translated into neural signals by structures on the  organ of Corti  

∙ Hair cells in each human ear: arranged in 4 rows that run down  length of basilar membrane

∙ Organ of Corti: made of specialized neurons called hair cells ∙ Hair cells: cells that support the stereocilia which transduce  mechanical movement into neural activity

 Tectorial membrane: a gelatinous structure, attached on one end,  which extends atop organ of Corti

∙ Vibrations cause displacement of the tectorial membrane, which  bends stereocilia attached to hair cells and causes the release of  neurotransmitters

∙ Stereocilia: hair like extensions on the tips of hair cells in the  cochlea that initiate the release of neurotransmitters when they  are flexed

∙ The tip of each stereocilia is connected to the side of its neighbor by a tiny filament called a tip link: when one bends, they all  bend!

How are amplitude and frequency coded in the cochlea?  Amplitude:  

♦ Small amplitude sounds  small displacements in the cochlea  the  tectorial membrane will shear across the organ of Corti less forcefully  (hair cells will bend to a smaller degree = less NT released)

♦ Large amplitude sounds  large displacements in the cochlea  the  tectorial membrane will shear across the organ of Corti more forcefully  (hair cells will bend to a bigger degree = more NT released)

 Where is frequency coded? Where is a given frequency causing the  greatest mechanical displacement on the cochlea?

 The cochlea is like an acoustic prism in that its sensitivity spreads across  different sound frequencies along its length

♦ Base: cochlea is narrow and thick

♦ Apex: cochlea is wider and thin

♦ From base to apex = high frequencies  low frequencies ♦ Low frequency sounds: carry further than high frequency sounds  We call this tuning of different parts of the cochlea to different frequencies Place Code 

♦ Incoming sound wave with a given frequency  will cause greater  displacements on the basilar membrane at a particular location  the  brain will know the frequency because of that place code

Sensory & Perception Chapter 9

 Outer hair cells: convey info from brain. Involved in elaborate feedback  system: when stiffer, can help suppress noise. When less stiff, can tune to  a given frequency

 Inner hair cells: convey almost all info about sound waves to the brain  How is frequency coded?

♦ Thanks to cochlear place code

♦ Temporal code  

♦ When a sound of a given frequency comes in, a neuron starts finding in phase with the sound. This is called phase locking 

♦ The neuron always fires at one distinct point in the cycle of the sound  wave

♦ The firing pattern of the auditory nerve fiber carries a temporal code. If it fires 500 times in a second  500 Hz sounds

♦ Temporal coding becomes inconsistent for frequencies higher than  1000 Hz  a neuron can only produce a certain number of action  potentials per second!

♦ Luckily, we have lots of auditory nerve fibers!

♦ Their phase locking varies: they don’t fire all at the same point in the  cycle

♦ The volley principle: multiple neurons can provide the temporal code ♦ Place code of frequency on the cochlea: some areas get displaced  more than others, so the brain can tell the frequency of the sound ♦ High amplitude sounds are a problem for place coding: huge  displacements all along the cochlea!

♦ Frequency selectivity is the clearest when sounds are very faint ♦ Low intensity sounds (faint sounds) of different frequencies (low to high pitch)  auditory nerve fibers?

♦ We observe threshold tuning curves: each nerve fiber is tuned to a  different frequency

 How to read a threshold tuning curve:

♦ Find the lowest point on the curve  

♦ Read the frequency

♦ In this example, this neuron responds very strongly to a 10,000 Hz  frequency (when the sound is very faint)

♦ This neuron’s response will signal the brain that the frequency of the  sound is 10,000 Hz

♦ This is called the neuron’s characteristic frequency

♦ The rest of the red curve has higher values on the Y axis, meaning that higher intensities of sounds are needed to observe a response higher  than baseline from that neuron

 Different auditory nerve fibers have different characteristic frequencies

Sensory & Perception Chapter 9

 Real life: sounds are never presented in isolation, what happens when  more than a sound is presented to an auditory nerve fiber? ♦ When tones of similar frequencies are presented to a neuron, the rate  

of neural firing that was observed in the first tone decreases. This  phenomenon is called two-tone suppression 

♦ Similar to lateral inhibition in vision!

 Sounds in the environment aren’t always faint. What happens when  louder sounds are presented?

♦ Present the auditory nerve fibers with a given sound intensity and vary the frequency (pitch) from low to high

♦ Curves are called isointensity curves (measure dB) red curve is a faint  sound.

♦ They are measured in the same neuron

♦ As we increase the intensity of the sound, the neuron responds to a  wider range of frequencies, and stop responding selectively ♦ Rate saturation: neuron stops responding selectively to a specific  frequency

 A nerve fiber is firing as rapidly as possible and further stimulation  is incapable of increasing the firing rate

 Stereocilia can’t bend any more than this!

 What rate saturation tells us is that when the sound is not faint, the  brain cannot rely on a single neuron to determine the frequency of a sound!

 What is the solution of the hearing system then? How can we determine  the frequency on loud sounds?

♦ One hair cell has 10-30 auditory nerve fibers that have different  spontaneous firing rates  

♦ Quiet environments: high spontaneous fibers:

 Medium/high baseline firing rate (in silence)

 Sensitive to low intensity sounds

 Saturate quickly: as sound intensity is increased they lose frequency selectively (similar to rods)

♦ Noisy environments: low-spontaneous fibers

 Resting firing rate very low (< 10 spikes/second) in silence  Require higher sound intensities to start responding  

 They respond selectively to higher sound intensities (similar to  cones)

 The auditory system will look at the pattern of firing rates across all  the AN fibers to determine the frequency of the sound

Auditory Pathway

Sensory & Perception Chapter 9

 Auditory brain structures

♦ Auditory nerve fibers (cranial nerve VIII) carry signals from cochlea to  brain stem

♦ First synapse: in the cochlear nucleus

♦ Superior Olive: (brain stem) inputs from both ears converge ♦ Inferior colliculus (midbrain)

♦ Medial geniculate nucleus (thalamus)

♦ Primary auditory cortex (A1): located in the temporal lobes ♦ Belt area: a region adjacent to A1. Receives inputs from A1. Neurons  respond to more complex characteristics of sounds

♦ Parabelt area: area lateral and adjacent to the belt area. Neurons  respond to more complex characteristics of sounds, as well as to input  from other senses

♦ Tonotopic organization: in all structures along the auditory pathway  there is an orderly arrangement: neurons that respond to different  frequencies are organized anatomically in order of frequency  Starts in cochlea

 Maintained all the way through primary auditory cortex (A1) ♦ Comparing overall processing along the auditory and visual pathways:  Auditory system: large proportion of processing is done before A1  Visual system: large proportion of processing occurs beyond V1

Psychoacoustic: how do we perceive loudness and pitch?  What we covered so far:

♦ Recording auditory nerve fibers in animals

♦ Examination of basilar membrane

♦ Dissecting brain structures

 Psychoacoustics: the study of the psychological correlates of the physical  dimensions of acoustics

♦ A branch of psychophysics

♦ Frequency  pitch

♦ Intensity  loudness

 What is the relationship between the amplitude of a sound and the  loudness you experience?

♦ Loudness generally depends on amplitude, but loudness also depends  on the frequency of the sound being heard

 What is our audibility curve/threshold? The amplitude at which sound  waves are barely audible for different frequencies

 Ear loudness curves: all the points along 1 blue curve sound equally loud  to us

Sensory & Perception Chapter 9

 Temporal integration: the loudness of a sound also depends on its  duration

♦ Longer sounds are heard as being louder  

♦ The term also applies to perceived brightness, which depends on the  duration of the light

♦ Perception of loudness and brightness depends on the summation of  energy over a brief period of time. This process is called temporal  integration

 Loudness: we can detect small differences of just 1 dB (29 dB vs. 30 dB) ♦ IMPRESSIVE! (wide range of sound intensities: 0-100dB)  Frequency: humans are good at detecting small differences in frequency ♦ We are more sensitive to changes in pitch at lower frequencies than at  higher frequencies

Hearing Loss 

 Hearing can be impaired by damage to any of the structures along the  chain of auditory processing

♦ Obstructing the ear canal results in temporary hearing loss (ear plugs)  Excessive buildup of ear wax (cerumen) in ear canal

♦ Conductive hearing loss: caused by problems with the bones in the  middle ear (during infections, otitis media)

 Otosclerosis: caused by abnormal growth of middle ear bones; can  be remedied by surgery

 Most common most serious auditory impairment:

♦ Sensorineural hearing loss: due to defects in cochlea or auditory nerve; when hair cells are injured

 Some antibiotics or cancer drugs are ototoxic

 Excessive exposure to noise

 Your hair cells don’t regenerate! Protect your ears!

♦ Hearing loss: natural consequence of aging

 Young people: range of 20-20,000 Hz

 By college age: 20-15,000 Hz

 Hearing aids: earliest devices were horns; today, electronic aids ♦ Cochlear implants: a microphone, a speech processor, a transmitter  and receiver/stimulator.  

 This is NOT the same perception as normal hearing!

 Tiny flexible coils with miniature electrode contacts

Sensory & Perception Chapter 9

 Surgeons thread implants through round window toward cochlea  apex

 Tiny microphone transmits radio signals to a receiver in the scalp  Signals activate miniature electrodes at appropriate positions along  the cochlear implant

Sensory & Perception Chapter 10

Hearing in the Environment 

 Most sounds in the world are complex sounds

♦ Complex Sounds: combination of sine waves (e.g., human voices) ♦ All sound waves can be described as some combo of sine waves  (simple sounds/vibrations)

♦ All sounds are summed at the ear!

 Acoustic environments can be complicated

♦ We can have multiple sound sources in one environment  Auditory stream segregation: perceptual organization of a complex  acoustic signal into separate auditory events or streams  

 Strategies to segregate sound sources

♦ Separation on basis of sounds’ spectral or temporal qualities Harmonics



Attack and Decay


♦ Spatial separation between sounds


 Harmonic Spectrum are created by a simple vibrating source (e.g., string  of guitar, or reed of saxophone) creates unique overtones (timbre) which  helps define the sound

 Harmonic Spectra: a spectrum of sound containing only frequencies which are whole number multiples of the fundamental frequency

 Harmonics: integer multiples of the fundamental frequency  Color = Intensity

Fundamental Frequency 

 Fundamental Frequency: lowest frequency of harmonic spectrum ♦ REMEMBER frequency is related to the pitch

♦ Auditory system is very sensitive to natural relationships between  harmonics

 Missing-Fundamental Effect: when first harmonic is missing ♦ We will still hear the same pitch, even when the fundamental  frequency is missing

Auditory Stream Segregation 

 Grouping by Timbre

Sensory & Perception Chapter 10

♦ Timbre helps determine whether overlapping tones are grouped  together

♦ Tones that have increasing and decreasing frequencies or tones that  deviate from rising/falling pattern “pop out” of sequence

 Timbre: “quality” of sound perception that two sounds with same  loudness and pitch are dissimilar

 Different timbre

♦ 2 instruments with none overlapping frequencies

 Same timbre

♦ Same instrument

 Grouping by similarity

♦ Similar frequencies = same source

♦ Different frequencies = two sources

More Features of Complex Sounds 

 Attack & Decay

♦ Attack: part of a sound during which amplitude increases (onset) ♦ Decay: part of a sound during which amplitude decreases (offset)  Grouping by Onset:

♦ Sounds that start at the same time are grouped together ♦ Group harmonics into a single complex tone

♦ Rasch (1987)

 It is easier to distinguish 2 notes from one another when onset of  one precedes onset of other by very short time

 Principle of good continuation:

♦ In spite of interruptions, we still “hear” sound. The missing part is  filled-in by the auditory system

 Continuity Effect

♦ Experiments like Kluender and Jenison’s:

 Missing sounds are encoded in brain as if they were actually present – restored!


 Restoration Effects

♦ Restoration of complex sound (e.g., music, speech)

 “Higher-order” sources of info

 DEMO: phonemic restoration effect in speech

Sound Localization 

 How do you locate a sound in space?

♦ Determining distance of an object is a challenge (similar problem in  vision)

Sensory & Perception Chapter 10

♦ SOLUTION: use the difference from out 2 ears

♦ Critical for determining auditory locations

♦ Interaural time difference (ITD)

♦ Interaural level difference (ILD)

Visual vs Auditory Receptors 

 Strategies to segregate sound sources

♦ Separation on basis of sounds’ spectral or temporal qualities  Ears get different input (time & intensity (amplitude))

 Interaural time difference (ITD): the difference in time between a sound  arriving at one ear versus the other

♦ Sensitive to small differences in timing

 10 microseconds = 1 degree of sound source

 Medial Superior Olives (MSOs): 

♦ First place where input converges from 2 ears  

♦ Helps process ITDs

♦ Depends on the size of the head

♦ ITD detectors form connections to inputs coming from 2 ears during  first few months of life

♦ Mid-Pons is the structure with superior olive

 Interaural level difference (ILD): the difference in level (intensity) between a sound arriving at one ear versus the other

♦ The higher the frequency the larger the ILD

♦ Better accuracy at higher frequencies

♦ Sounds are more intense at the ear closer to sound source  ILD largest at 90 and -90 degrees, nonexistent for 0 degrees and  180 degrees

 ILD correlate with angle of sound source, but not as precise at ITD  Lateral Superior Olives (LSOs): Neurons sensitive to intensity differences  between ears

♦ Excitatory connections – ipsilateral ear

♦ Inhibitory connections – contralateral ear

 Low frequencies are localized with time disparities (ITDs) ♦ REMEMBER: Low frequencies do not have large intensity differences  (ILDs)

 Cones of Confusion: regions of space where all sounds produce the same  time and level (intensity) differences

♦ We cannot discriminate the sound source with only this information, so  we turn our head

♦ Resolving confusion:

 Move ear, head, and body relative to source

Sensory & Perception Chapter 10

 Pinnae alter sounds by location

 Sounds reverberate off of environment

 Shape and form of pinnae changes sounds from different locations  Head-related transfer function: describes how pinnae, ear canal, head and torso change intensity of sounds with different frequencies that arrive at  each ear from different locations in space (azimuth and elevation)

Direct vs Reverberant Energy 

 Relative amounts of direct vs reverberant energy also help evaluate  distance

♦ Direct energy = higher intensity

♦ Reverberant energy = smaller intensity

 How far away is a sound source?

♦ Simplest cue is the relative intensity of sound

 Inverse-square law: as distance from a source increases, the sounds’  intensity decreases faster (decrease in intensity is distance squared)  Spectral composition of sounds: higher frequencies decrease more in  energy than lower frequencies as sound waves travel (low frequencies  travel farther)

Chapter #11: Touch 


 Somatosensation: a collective term for sensory signals from the body  Touch: body sensations

♦ Mechanical displacement of the skin

♦ Pain

♦ Temperature

 Kinesthesis: where body parts are

 Proprioception: perception mediated by kinesthetic and vestibular  receptors

Touch in the Cortex

 Primary somatosensory receiving areas in the brain

♦ Motor areas

♦ Central sulcus

♦ Lateral sulcus

♦ S1 & S2

♦ Areas 5, 7

Touch Physiology

 Touch sensations are represented somatotopically in the brain: ♦ S1: primary somatosensory cortex

♦ S2: secondary somatosensory cortex

♦ Somatotopy: adjacent areas in the brain

♦ Homunculus: map-like representation of regions of the body in the  brain

 Distortions: hand is huge, torso is small

 Discontinuities: hand next to face

 Phantom Limb: sensation perceived from a physically amputated limb of  the body

♦ Face and arm/hand are close to each other

♦ Face takes over neurons

♦ Parts of brain listening to missing limbs not fully aware of altered  connections, so they attribute activity in these areas to stimulation  from missing limb


 Touch receptors: embedded on outer layer (epidermis) and underlying  layer (dermis)

♦ Multiple types of touch receptors

♦ Each touch receptor has 3 attributes:

 Type of stimulation the receptor responds to (pressure, temp, pain)  Size of the receptive field: big or small (portion of skin the receptor  responds to)

 Rate of adaptation: fast or slow (how fast it will fatigue)

 Tactile receptors

♦ “Mechanoreceptors”: respond to mechanical stimulation: pressure,  vibration, or movement

 4 types of mechanoreceptors in the skin:

∙ each receptor has a different range of responsiveness and  


Size of Receptive Field

Adaptation Rate









∙ Each receptor: different range of responsiveness

∙ Mechanoreceptors: feature sensitivity and associated function

 Primary functions: 

∙ SA 1: texture perception & pattern/form detection

∙ FA 1: low frequency vibration

∙ FA11: high frequency vibration

∙ SA11: finger position, stable grasp

 Kinesthetic receptors

♦ Other types of mechanoreceptors within muscles, tendons, and joints:  sensing where limbs are, what kinds of movements are made

 Muscle Spindle: a sensory receptor located in a muscle that senses  its tension

 Receptors in tendons signal tension in muscles attached to tendons  Receptors in joints react when joint is bent to an extreme angle

 Importance of kinesthetic receptors:

♦ Strange case of neurological patient Ian Waterman:

 Cutaneous nerves connecting Waterman’s kinesthetic  

mechanoreceptors to brain destroyed by viral infection

 Lacks kinesthetic senses, dependent on vision to tell limb positions  Illusions

♦ Pinocchio Illusion

Pain: Nociceptors

 Nociceptors: sensory receptors that transmit info about noxious (painful)  stimulation that could damage skin

♦ 2 groups of nociceptors:

 A-delta fibers: intermediate-sized, myelinated sensory nerve fibers  (rapid transmission); transmit pain and temperature signals  C fibers: narrow-diameter, unmyelinated sensory nerve fibers that  transmit pain and temperature signals

 Painful events have 2 stages:

♦ Quick sharp pain (A-delta fibers)

♦ Followed by throbbing sensation (C fibers)

♦ Difference in speeds is due to myelination

 What would happen if we had no nociceptors?

♦ Diseases: leprosy, diabetes. Loss of pain sensation (Miss C)  Benefit of pain perception:

♦ Sensing dangerous objects (sharp, hot)

♦ Case of “Miss C”

 Born with insensitivity to pain

 Did not sneeze, cough, gag, or blink reflexively

 Suffered injuries such as burning herself on radiator and biting  tongue while chewing food

 Died at age 29 from infections that could have been prevented if  she sensed pain

 How can pain be modulated?

♦ Responses to noxious stimuli can be moderated by anticipation,  religious belief, prior experience, watching others respond, and  excitement

 Ex.) wounded soldier in battle who doesn’t feel pain until after  battle

 Analgesia: decreasing pain sensation during conscious experience ♦ Endogenous opiates: chemicals released in body to block the  transmission of pain sensation to brain

♦ Externally produced substances have similar effect: morphine, heroin,  codeine

♦ Ibuprofen, aspirin, acetaminophen prevent the nociceptors from firing:  they do deal with the cause of pain  

 Gate control theory

♦ Pain signals can be modulated by the brain

♦ 1 synapse at the level of the spinal cord

♦ Gate neurons: block pain transmission in the (substantia gelatinosa of)  dorsal horn, in the spinal cord

♦ Gate neurons can be activated by counter-stimulation: 

 Extreme pressure, cold, or other noxious stimulation applied to  another site distant from the source of pain

Cognitive Aspect of Pain + Gentle Touch

 Cognitive aspects of pain

♦ Pain: generally subjective experience

♦ 2 components:

 Sensory aspects of pain (S1 & S2)

 Emotional response that accompanies it

∙ Cognitive aspect of pain

∙ Frontal cortex

♦ Hypnotic suggestions:

 Hands in hot water: you are feeling well, all is good

 Hands in lukewarm water: your hands feel terribly hot

 These suggestions modulated the activity in the anterior cingulate  cortex in the frontal cortex!

♦ Secondary pain effect:

 Emotional response associated with long-term suffering (cancer  patients undergoing chemotherapy)

 Also associated with activity in prefrontal cortex

 Pleasant/emotional touch

♦ Pleasant touch

 Mediated by unmyelinated peripheral C fibers

 Respond best to slowly moving, lightly applied forces (petting)  Processed in orbitofrontal cortex rather than S1 & S2

 Promotes endorphin responses: contribute to feelings of well-being,  confidence, and calmness

 Reduces fearfulness; beneficial effects in premature human infants

Disorders & Cool Phenomena

 Haptic Perception

♦ Tactile agnosia: the inability to identify objects by touch  Caused by lesions to the parietal lobe

 Patient documented by Reed & Caselli (1994):

∙ Tactile agnosia with right hand but not left hand

∙ Couldn’t recognize objects such as a key chain in right hand, but  could with left hand or visually  

 Remember Blindsight?

♦ Complete loss of sensory experience in the visual modality ♦ Action can still be performed towards undetected visual objects ♦ There is a similar phenomenon for the somethetic modality  Numbsense

♦ Patient J.A:

 Subcortical stroke along the somatosensory pathway

 Complete loss of all somatosensory processing on the left half of his  whole body for:

∙ Light touch, deep pressure, moving tactile stimulation, pain,  warm and cold, vibration, segment position, passive movement,  etc.

 When blindfolded, if J.A. had to guess verbally the locus of tactile  stimuli on this forearm and hand, he performed at chance

 If J.A. had to guess by pointing his performance was much better  than chance level

 Anarchic Hand: complex goal-directed movements of a hand that are  performed against the patient’s will

♦ Cannot be inhibited

♦ Anterior part of the corpus callosum

♦ Patient GP: “her left hand would take some fish bones from leftovers  and put them into her mouth…”

♦ Patient MP: problems in choosing television channels

 Alien hand: hemisomatognosia

♦ Hemi…somato…agnosia

♦ Parietal cortex and posterior part of the corpus callosum ♦ Description of Brion and Jedynak “the patient who holds his hands one  within the other behind his back doesn’t recognize the left hand as his  own)

♦ Loss of the sense of one’s own body

 Testing integration of sensory modalities

♦ Rubber hand illusion: watch video on compass

♦ Out of body experience: watch video on compass


 Thermoreceptors: sensory receptors that signal info about changes in skin temperature

♦ 2 distinct populations of thermoreceptors: warmth fibers, cold fibers ♦ Body is constantly regulating internal temperature

 Under normal conditions the skin is between 86 degrees and 96 degrees ♦ Writing this range: warmth and cold fibers do not respond much ♦ Skin temperature > 96 degrees: warmth fibers will begin to fire ♦ Skin temperature < 86 degrees: cold receptors will start firing

 Respond when you make contact with an object warmer or colder than  your skin

Tactile Sensitivity and Acuity

 How sensitive are we to mechanical pressure?

♦ Max von Frey: developed an elegant way to measure tactile sensitivity  Used horse and human hairs

 Modern researchers use nylon monofilaments of varying diameters ♦ Hairs of monofilaments of varying diameters are pressed against the  skin to see if the pressure can be sensed

 Sensitivity to mechanical pressure varies over the body ∙ Face is most sensitive

∙ Trunk and upper extremities (arms and fingers) next most  sensitive

∙ Lower extremities (thigh, calf, and foot) less sensitive

 Another approach to tactile sensitivity: what is the smallest raised  element that can be felt on an otherwise smooth surface?

♦ People can detect a bump only 1 micrometer high at 75% accuracy! ♦ Dot triggers FA1 receptors: once we touch the dot, these neurons fire  How finely can we resolve spatial details?

♦ 2-point threshold: the minimum distance at which 2 stimuli are just  perceptible as separate

♦ Like sensitivity to pressure, spatial acuity varies across the body  Extremities (fingertips, face, and toes) show the highest acuity  Tactile sensitivity is mediated by receptors having small receptive fields  (SA1 & FA1)

♦ Density of receptors: fingers > thigh

Haptic Perception

 Haptic Perception: knowledge that the world is derived from sensory  receptors in skin, muscles, tendons, and joints, usually involving active  exploration

 Perception for action: using somato-sensation to interact with the world: ♦ Grasp and manipulate objects in a stable and coordinated manner  Aligning the arrows and opening a child-proof aspirin bottle in the  dark

 If skin is anesthetized, we can no longer efficiently interact with the  world

 Action for perception: using our hands to actively explore the world of  surfaces and objects

♦ Exploratory Procedure: a stereotypical hand movement pattern used to contact objects in order to perceive their properties

♦ Each exploratory procedure is best for determining one or more object  properties

Chapter #14: Taste 

Taste Versus Flavor

 Retronasal olfactory sensations: flavor 

♦ Taste and smell woven together

♦ Flavor impoverished with stuffy nose

Anatomy & Physiology

 Olfactory epithelium, orthonasal olfaction, Retronasal olfaction  What happens when we cannot perceive taste but can still perceive smell? ♦ Patient case: damaged taste, but normal olfaction (could smell  lasagna, but it had no flavor)

♦ Similar effect in lab: Chorda tympani anesthetized with lidocaine: flavor coming from only half of the mouth

 Connection between taste & smell:

♦ Brain imaging studies: brain processes odors differently, depending on  whether they come from nose or mouth

♦ Food industry: adds sugar to intensify olfactory sensation of fruit (in  juices) (and salt to salty snacks)

♦ FDA MOVES TO REDUCE SALT AND SUGARS IN FOODS! (April 27, 2010)  Taste buds:  

♦ Create neural signals conveyed to brain by taste nerves ♦ Embedded in structures: Papillae (bumps on tongue)

♦ Each taste bud contains taste receptor cells

♦ Information is sent to brain via cranial nerves

 Papillae: 4 kinds

♦ Filiform papillae: anterior portion of tongue; without any taste function ♦ Fungiform papillae: resemble tiny mushrooms, on anterior part of  tongue, visible

♦ Foliate papillae: on sides of tongue, look like series of folds ♦ Circumvallate papillae: large circular structures

 Taste receptors: circumvallate, foliate, and fungiform papillae  Microvilli: slender projections on tips of some taste bud cells that extend  into taste pore, contain sites that bind to taste substances

The Four Basic Tastes

 Four basic tastes: salty, sour, bitter, sweet

 Salty:

♦ Salt made up of 2 particles: cation & anion

♦ Ability to perceive salt: not static

♦ Liking for saltiness is not static

♦ Gestational experiences may affect liking for saltiness

 Sour:

♦ Acidic substances

♦ At high concentrations, acids will damage both external and internal  body tissues

 Bitter:

♦ Up to 30 bitter receptors

♦ Cannot distinguish between tastes of different bitter compounds ♦ Many bitter substances are poisonous

♦ Ability to “turn off” bitter sensations – beneficial to liking certain  vegetables

♦ Bitter sensitivity is affected by hormone levels in women, intensifies  during pregnancy

 Sweet:

♦ Evoked by sugars

♦ Many different sugars that taste sweet

♦ Appetite and artificial sweeteners

 The special case of umami:

♦ Candidate for fifth basic taste

♦ Monosodium glutamate (MSG)

♦ Glutamate: important neurotransmitter

♦ Safety issues in human consumption

The Pleasure of Taste

 Hardwired affect: evidence from newborn facial expressions for different  tastes

 Specific hungers theory: the idea that a deficiency of a given nutrient will  produce craving for that nutrient

♦ Support for this theory: infant study (Davis) allowing infants to choose  their foods, resulting in healthy choices

 Chili peppers:

♦ Acquisition of chili pepper preference: depends on social influences ♦ Restriction of liking to humans

♦ Variability across individuals, depending on number of papillae ♦ Desensitization of pain through capsaicin

Genetic Variation in Taste Experience

 Fox: discovery of Phenylthiocarbamide (PTC)

♦ Bitter taste to some but not to others

 Non-tasters (1/3) vs. supertasters (genetic trait)

♦ Non-tasters: more likely to enjoy vegetables

♦ Supertasters:

 Pickier eaters!

 Suprathreshold taste and psychophysical functions

 How does perceived taste intensity vary with concentration?  Work by Stevens and his students

 Cross-modality matching: supertasters

 Health consequences:

♦ Potential links between responsivity to PROP and health:  High responsiveness  high likelihood of colon cancer and low  likelihood of cardiovascular disease (fat tastes too intense too) ♦ Evaluating food behavior in terms of sensory properties of foods  instead of nutrient content only  

 Think about the relation between your body and the world around you: ♦ We evolve to be in tune with the world

♦ The body: is it a tool or is it a temple?

♦ It’s an integral part of who you are and how you think ♦ Limits of “coding” perceptions: contrast gain adaptation is at play in  everyday emotions! No infinite sensation

 Hedonic treadmill

 Drugs

LINK TO QUIZLETS FOR EVERY CHAPTER FOR EXAM 3 https://quizlet.com/BaileyCochran216/folders/psyc230-exam-3

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