Second half of final Flashcards
Physical qualities of sound waves:
Amplitude: The magnitude of displacement of a sound pressure wave.
Intensity: The amount of sound energy falling on a unit area.
Frequency: For sound, the number of times per second that a pattern of pressure repeats.
Units for measuring sound:
Hertz (Hz): A unit of measure for frequency. One Hz equals one cycle per second.
Decibel (dB): A unit of measure for the physical intensity of sound.
Psychological qualities of sound waves:
Loudness: The psychological aspect of sound related to perceived intensity or magnitude.
Pitch: The psychological aspect of sound related mainly to the fundamental frequency.
Timbre: Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar, determined by the harmonic structure of the sounds.
Sine wave, or pure tone:
One of simplest kinds of sounds
Sine wave: Waveform for which variation as a function of time is a sine function
Time taken for one complete cycle of sine wave: Period
There are 360 degrees of phase across one period
Decibel (dB)
A unit of measure for the physical intensity of sound:
Named after the inventor* of the telephone, Alexander Graham Bell.
Decibels define the difference between two sounds as the ratio between two sound pressures: dB = 20 log10 (p1/p0)
Each 10:1 sound pressure ratio equals 20 dB, and a 100:1 ratio equals 40 dB
Doubling in sound pressure corresponds to 6 dB
*Bell actually just stole the patent [citation needed]
Pure tone
A tone with a sinusoidal wave form
Complex sounds
The summation of pure tones
Most sounds in world
Complex sounds can be described by Fourier analysis
A mathematical theorem by which any sound can be divided into a set of sine waves.
Combining these sine waves will reproduce the original sound
Results can be summarized by a spectrum
Harmonic sounds with the same fundamental frequency can sound different because amplitudes of harmonics here three different instruments.
Harmonic spectra: Typically caused by simple vibrating source, (e.g., string of guitar, or reed of saxophone)
First harmonic: Fundamental frequencylowest frequency component of the sound
First harmonic: Fundamental frequency
lowest frequency component of the sound
Timbre
Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar – defined by the shape of the harmonic spectrum.
Auditory system is acutely sensitive to natural relationships between harmonics
Harmonic
Harmonic spectra: Typically caused by simple vibrating source, (e.g., string of guitar, or reed of saxophone)
First harmonic: Fundamental frequencylowest frequency component of the sound
Timbre: Psychological sensation by which listener can judge that two sounds that have same loudness and pitch are dissimilar – defined by the shape of the harmonic spectrum.
Auditory system is acutely sensitive to natural relationships between harmonics
VOICES are HARMONIC SOUNDS!
If the Fundamental is taken away from a sound, people will still HEAR IT.
Interaural time difference (ITD):
The difference in time between a sound arriving at one ear versus the other.
Medial superior olives (MSOs): First place where input converges from two ears.
ITD detectors form connections from inputs coming from two ears during first few months of life.
Azimuth
Used to describe locations on imaginary circle that extends around us, in a horizontal plane
Let’s analyze ITD:
Where would a sound source need to be located to produce maximum possible ITD?
What location would lead to minimum possible ITD?
What would happen at intermediate locations?
Medial superior olives (MSOs)
First place where input converges from two ears.
ITD detectors form connections from inputs coming from two ears during first few months of life.
Interaural level difference (ILD):
The difference in level (intensity) between a sound arriving at one ear versus the other.
Lateral superior olives (LSOs): Neurons that are sensitive to intensity differences between two ears
Excitatory connections to LSO come from ipsilateral (same side) ear
Inhibitory connections to LSO come from contralateral (opposite side) ear
ITD and ILD compared:
Low frequencies are diffracted by the head (like an ocean wave around a pylon), high frequencies are absorbed.
Low Frequencies / Timing Cues Dominate
High Frequencies / Intensity Cues Dominate
Stimuli on headphones, where ITDs pointing to the left are offset by ILDs pointing to the right, so the sound is perceived as coming from the midline.
Low Frequencies
Timing Cues Dominate
High Frequencies
Intensity Cues Dominate
Subwoofer placement is less important in a home theater setup due to our inability to accurately localize the low frequencies.
…
Cone of confusion
Regions of positions in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs)
Experiments by Wallach (1940) demonstrated this problem
THE MOST CONFUSION CONE:
ABOVE-infront-below-behind!!!
Directional transfer function:
Shape and form of pinnae helps determine localization of sound
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)
Sometimes called Head-Related Transfer Function
BINAURAL RECORDINGS
Recording through microphones inside your head, near the ear drums
Direction transfer function preserved. Then you feel sound as coming from outside of your HEAD!!
Inverse-square law
Sound intensity decreases with 1/d2 with increasing distance d in 3D space.
A sound 1 meter away is 6dB louder than 2 m
A sound 39m away is only 1dB louder then 40m
Relative amounts of direct vs. reverberant energy also help evaluate distance.
Reverberations that occur in a room can severely distort localization cues.
One strategy that listeners unconsciously employ to cope with this is to make their localization judgments instantly based on the earliest arriving waves in the onset of a sound.
This strategy is known as the precedence effect, because the earliest arriving sound wave—the direct sound with accurate localization information—is given precedence over the subsequent reflections and reverberation that convey inaccurate information.
Asymmetrical ears for localization of elevation
For example, Barn owls’ asymmetry is such that the center of the left ear flap is slightly above a horizontal line passing through the eyes and directed downward, while the center of the right ear flap is slightly below the line and directed upward.
Sound originating from below the eye level to sound louder in the left ear, while sound originating from above the eye level to sound louder in the right ear.
Shepard Tone
“Sonic Barber’s Pole” illusion.
The tone sounds as if it is continually ascends (or descends)
Consists of a superposition of sine waves separated by octaves.
Batpod™ sound effect in The Dark Knight ®
Perceptual Segregation
In complex auditory environments, humans are able to focus their attention on one source while ignoring sounds on other sources.
Perceptual segregation is often based on physical properties of a sound, but it is also facilitated by tracking the meaningful aspects of speech sounds.
Auditory Grouping Principles
- Good continuation
- Similarity of pitch
- Temporal proximity
- Similarity of timbre
- Location
Outer ear:
Sounds are first collected from environment by the pinnae
Sound waves are funneled by the pinnae into ear canal
Length and shape of ear canal enhance sound frequencies
Main purpose of canal is to insulate structure at its end: Tympanic membrane
Tympanic membrane
Eardrum; a thin sheet of skin at end of outer ear canal; it vibrates in response to sound
Common myth: Puncturing your eardrum will leave you deaf
In most cases it will heal itself
It is possible to damage it beyond repair
Earwax
Known by the medical term cerumen
Secreted in the ear canal.
Assists in cleaning and lubrication.
Provides some protection from bacteria, fungi, insects and water.
Naturally removed by the “conveyor belt” like regenerative growth process at ear drum center. (and jaw movement)
Cause of 60-80% of hearing aid faults
Middle ear:
Tympanic membrane is border between outer ear (ear canal) and middle ear
Consists of 3 tiny bones:
Ossicles, that amplify sounds
In Latin: Hammer, Anvil & Stirrup
Ossicles
Malleus, incus, stapes
smallest bones in body
Amplification provided by ossicles is essential for ability to hear faint sounds.
Stapes transmits vibrations of sound waves to oval window, another membrane which represents border between middle ear and inner ear.
Middle ear: Two muscles:
tensor tympani and stapedius
Purpose: To tense when sounds are very loud, muffling pressure changes.
However, acoustic reflex follows onset of loud sounds by about one-fifth of a second, so cannot protect against abrupt sounds, (e.g., gun shot).
Inner ear:
Fine changes in sound pressure are translated into neural signals
Function is roughly analogous to that of retina
Cochlea
Spiral structure of the inner ear containing the Organ of Corti.
Cochlea is filled with watery fluids in 3 parallel canals.
Tectorial membrane
A gelatinous structure, attached on one end, that extends into the middle canal of the ear, floating above inner hair cells and touching outer hair cells.
Vibrations cause displacement of the tectorial membrane, which bends stereocilia attached to hair cells and causes the release of neurotransmitters.
Inner and outer hair cells. 14,000 total
Inner hair cells: Convey almost all information about sound waves to brain. 3,500 total.
Outer hair cells: Convey information from brain (use of efferent fibers).
They are involved in elaborate feedback system. 10,500 total.
When stiffer, can suppress noise.
When less stiff, can tune to a given frequency.
ORGAN of CORTI
like the RETINA for the eye
COMPOSED OF HAIR CELLS and DENDRITES of auditory nerve fibers. (and a “scaffolding” of supporting cells)
STEREOCILIA
hairlike extensions on tips of hair cells that initiate the release of neurotransmitters when flexed.
The tip of each stereocilium is connected to the side of its neighbor by a tiny filament called a tip link.
Tip links open potassium channels —> depolarization
THE LARGER the amplitude of sound, THE larger the displacement of the tectorial membrane, the more neurotransmitters are released.
Mostly, place coding is due to the basilar membrane. wider towards the apex and thinner.
So, high frequencies can bend the stiffer regions of the membrane near the base and low frequencies cause greater displacement in the more felxible regions near the apex.
Firing of auditory nerve fibers into patterns of neural activity finally completes process of translating sound waves into patterns of neural activity (sensation).
Coding of amplitude and frequency in the cochlea
Amplitude: The larger the amplitude, the bigger the shear of tectorial membrane.
Place code: Tuning of different parts of cochlea to different frequencies, in which information about the particular frequency of incoming sound wave is coded by place along cochlear partition with greatest mechanical displacement.
Coin sorting machine analogy:
Smaller coins fall through smaller holes first
Quarters fall in the last hole
The Auditory Nerve (AN)
Responses of individual Auditory Nerve fibers to different frequencies are related to their place along the cochlear partition
Frequency selectivity:
Clearest when sounds are very faint
Threshold tuning curve: Map plotting thresholds of a neuron or fiber in response to sine waves with varying frequencies at lowest intensity that will give rise to a response
With faint sounds, Fibers will fire to very restricted range range.
CHARACTERISTIC frequency
frequency at which the lowest intensity sound excites AN neuron.
BOTTOMEST point of threshold tuning curve.
Rate saturation
Are AN fibers as selective for their characteristic frequencies at levels well above threshold as they are for the barely audible sounds?
To answer this, look at isointensity curves: Chart by measuring an AN fiber’s firing rate to wide range of frequencies, all presented at same intensity level.
Rate saturation: Point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate
Rate intensity function:
A map plotting firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities.
A family of isointensity curves for ONE fiber of characteristic freq. of 2000Hz
Show isointensity functions for one auditory nerve fiber
FAMILY of isointensity curves for ONE fiber of CF 2000Hz.
CONCLUSION: NEURON is VERY selective for quite sounds. Not SO MUCH FOR LOUDER SOUNDS!!!
THIS IS RATE SATURATION!!!
RATE SATURATION means:
We can NOT use a direct decoding rule like:
If a 2000 Hz Auditory Nerve fiber is firing rapidly, the sound must be 2000 Hz
Combinatorial code:
The brain uses the PATTERN of firing rates across fibers to determine frequency.
About 3,500 inner hair cell in each ear to describe each pattern.
Note the similarities with color vision
Auditory brain structures:
The auditory nerve (cranial nerve VIII) carries signals from cochlea to brain stem.
All auditory nerve fibers initially synapse in cochlear nucleus.
Superior olive, inferior colliculus, and medial geniculate nucleus all play roles in the auditory process.
COCHLEAR NUCLEUS:
the first brain stem nucleus at which afferent auditory nerve fibers synapse.
Cells here fire to onset of sounds or coincidence of firing across different frequencies.
Some use lateral inhibition to suppress nearby frequencies. (like ganglion cells On-Off).
Some, project to the superior olive
AN fibers PROJECT TO BOTH HEMISPHERES
Tonotopic organization
An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency
Maintained up to primary auditory cortex (A1)
Comparing overall structure of auditory and visual systems
Auditory system: Large proportion of processing is done before A1.
Visual system: Large proportion of processing occurs beyond V1.
Differences may be due to evolutionary
reasons:
hearing is probably an older sense than seeing.
speech (recent in evolution) is in the cortex (the newer structure).
Psychoacoustics
The study of the psychological correlates of the physical dimensions of acoustics; a branch of psychophysics
frequency —> pitch
intensity —> loudness
Audibility threshold:
A map of just equally audible tones of varying frequencies
TWO purple points: EQUAL intensity VERY DIFFERENT LOUNDNESS!
Conductive hearing loss
Caused by problems with the bones of the middle ear, (e.g., during ear infections, otitis media).
Otosclerosis: More serious type of conductive loss. Caused by abnormal growth of middle ear bones; can be remedied by surgery.
Sensorineural hearing loss
More common, most serious auditory impairment. Due to defects in cochlea or auditory nerve; when hair cells are injured, (e.g., as result of antibiotics or cancer drugs, ototoxic).
Common hearing loss: Damage to hair cells due to excessive exposure to noise.
HEARING LOSS = elevation of sound thresholds.\
However, hearing loss also means to have an inability to interpret spectral and temporal differences in signals (to use the signals) and that can happen even with sounds you can hear.
Why ear bud headphones are especially dangerous (compared to over ear headphones)
Longer battery life & more comfortable - prolonged listening sessions
Don’t block outside noise as well - higher volumes to drown out noise (7-9 decibels)
Speakers are smaller and closer to ear drum - louder at same power level
Average listening level as high as 110-120 decibels
Teens with hearing loss up 33% since 1994
American Auditory Society’s rule is 60/60
Not more than 60 minutes at 60% of the maximum volume.
Weber & Rinne hearing tests
Compare the perception of sound transmitted by air conduction to bone conduction.
Determine type of hearing loss
Conductive or Sensorineural
Patient compares the loudness of a tuning fork at multiple locations
Next to ear (air conduction)
Touching mastoid (behind ears)
Touching forehead
Ludwig van Beethoven
Partial deafness at 30. Fully at 44.
“Conversation books” recorded history
Developed severe depression
Suffered from a form of tinnitus
The perception of sound when no actual sound is present
Usually a ringing sound.
Causes include: allergies, wax, foreign objects, infections, & exposure to loud noises (gun shots)
Cochlear implants:
A microphone,
A speech processor
A transmitter and receiver/stimulator
This is NOT the same perception as normalhearing!
HORNS were better than hearing aids as they allowed people to focus on a given frequency more easily.
Harder to focus on the aspect of the sound you’re most interested, because of compression., Distracting Noise harder to filter out!
Components of Touch:
Tactile (mechanical displacement of skin)
Temperature
Pain (including itch and tickling)
Kinesthetic body sensations (where body parts are)
Proprioception: Perception mediated by kinesthetic and vestibular receptors
Somatosensation: A collective term for sensory signals from the body (also includes vestibular system)
Touch receptors: Embedded in outer layer (epidermis) and underlying layer (dermis) of skin
Multiple types of touch receptors
Each touch receptor can be categorized by 3 criteria:
- Type of stimulation to which the receptor responds
- Size of the receptive field
- Rate of adaptation (fast versus slow)
Kinesthetic receptors:
Play important role in sense of where limbs are, what kinds of movements are made:
Muscle Spindles: Convey the rate at which the muscle fibers are changing in length.
Receptors in tendons provide signals about 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
Watch BBC documentary:
Thermoreceptors:
Sensory receptors that signal information about changes in skin temperature
Two distinct populations of thermoreceptors: warmth fibers, cold fibers
Body is constantly regulating internal temperature
Thermoreceptors respond when you make contact with an object warmer or colder than your skin
Nociceptors
Sensory receptors that transmit information about noxious (painful) stimulation that causes damage or potential damage to the skin
Two groups of nociceptors:
A-delta fibers: fast transmission to brain. respond to strong pressure (crushing) and heat
initial and quick sharp burst of pain at injury time
C fibers: slower response, sustained stimulation
throbbing sensation that evolves after initial surge of pain
Benefit of pain perception:
Sensing dangerous objects (hot pots in the kitchen)
Case of “Miss C”:
Born with insensitivity to pain,
could not protect herself, did not sneeze or cough
Died at age 29 from untreated infection
This is a HUGE problem for diabetic patients, who often loose sensation of their feet and become invalids because of untreated minor injuries.
Responses to noxious stimuli can be moderated by anticipation, religious belief, prior experience, watching others respond, and excitement
Example: Wounded soldier in battle who does not feel pain until after battle
Analgesia
Decreasing pain sensation during conscious experience
Soldier in above example: Experienced effect because of endogenous opiates—chemicals released in body to block release or uptake of neurotransmitters transmitting pain sensation to brain
Endogenous opiates may be responsible for certain placebo effects
Externally produced substances have similar effect: Morphine, heroin, codeine
Remember: the more synapses the more chances we get at blocking the transmission of pain, by inhibiting the release of neurotransmitters along those synapses.
Morphine heroin and codeine DO NOT DEAL with the CAUSES of pain. Ibuprofen, aspirin, acetaminophen DO (prevent the nociceptors receptors from firing in the first place).
Gate control theory
A description of the system that transmits pain that incorporates modulating signals from the brain
Feedback circuit located in Dorsal Horn of spinal cord
Gate neurons that block pain transmission can be activated by extreme pressure, cold, or other noxious stimulation applied to another site distant from the source of pain
Touch sensations travel as far as 2 meters to get from skin and muscles of feet to brain!
Information must pass through spinal cord
(First Synapse)
Axons of various tactile receptors combine into single nerve trunks
Several nerve trunks from different areas of body
Once in spinal cord, two major pathways:
Spinothalamic (slower, evolutionary older):
heat and pain
multiple synapses = slower
Dorsal-column-medial-lemniscal (faster):
Tactile and proprioceptive information,
Fewer synapses = fast transmission
Spinothalamic pathway
Several synapses in spinal chord
Slower information transmission
Provides mechanisms for pain inhibition
DCML
Synapse in Cuneate and Gracile nuclei, then ventral posterior nucleus of thalamus, then somatosensory area 1 (S1), somatosensory area 2 (S2)
Wider axons
Fewer synapses
Faster information transmission
Used for planning and execution of fast movements
Remember that THALAMUS is mostly SHUT down during sleep, so somatosensory information about mild tactile sensations and limb movement is NOT passed to the BRAIN. You don’t notice moving or the contact with your sheets.
Touch sensations are represented somatotopically in the brain:
Primary somatosensory cortex called S1; secondary somatosensory cortex called S2
Analogous to retinotopic mapping found in vision
Adjacent areas on skin connect to adjacent areas in brain
Homunculus: Maplike representation of regions of the body in the brain
Brain contains several sensory maps of body in different areas of S1 and also in S2
How sensitive are we to mechanical pressure?
Max von Frey (Nineteenth century) developed elegant way to measure this, using carefully calibrated stimuli: Horse and human hairs.
Modern researchers: Use nylon monofilaments of varying diameters.
If you can find a hair (or pluck one from your head), try detecting a poke of your hair on your lips (easy), versus your thighs or upper arm or sole of your feet. Try your thumb or different spots on the back of your hand. You will feel differences on that surface.
Two-point touch thresholds are determined primarily by the concentration and receptive-field sizes of tactile receptors in an area of the skin
How finely can we resolve temporal details?
Two tactile pulses can be delivered over time, in a manner analogous to spatially separated two-point threshold stimuli
Touch: Sensitive to time differences of only 5 ms
Vision: Sensitive to time differences of 25 ms
Audition: Sensitive to time differences of 0.01 ms!
Haptic perception:
Knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration
Tactile agnosia:
The inability to identify objects by touch
Caused by lesions to the parietal lobe
Patient documented by Reed and Caselli (1994):
Tactile agnosia with right hand but not left hand
Could not recognize objects such as a key chain in right hand, but could with left hand or visually
\
Other sensory abilities were normal in both hands
Semicircular canals
The 3 toroidal tubes in the vestibular system that sense angular acceleration, a change in angular velocity
Source of our sense of angular motion
Otolith organs
The mechanical structures in the vestibular system that sense both linear acceleration and gravity
Source of our sense of linear velocity and gravity
The vestibular organs do not respond to constant velocity
They only respond to changes in velocity—acceleration
Push-pull symmetry
Hair cells in opposite ears respond in a complementary fashion to each other
When hair cells in the left ear depolarize, those in the analogous structure in the right ear hyperpolarize
Coding of direction in the semicircular canals
3 semicircular canals in each ear
Each canal is oriented in a different plane
Each canal is maximally sensitive to rotations perpendicular to the canal plane
Threshold estimation: What is the minimum motion needed to correctly perceive motion direction?
Magnitude estimation: Participants report how much (e.g., how many degrees) they think they tilted, rotated, or translated
Matching: Participants are tilted and then orient a line with the direction of gravity. This is done in a dark room with only the line visible to avoid any visual cues to orientation
Vestibulo-ocular reflexes
Counter-rotating the eyes to counteract head movements and maintain fixation on a target
Angular VOR: The most well-studied VOR
Example: When the head turns to the left, the eyeballs are rotated to the right to partially counteract this motion
Torsional eye movements: When the head is rolled about the x-axis, the eyeballs can be rotated a few degrees in the opposite direction to compensate
VORs are accomplished by six oculomotor muscles that rotate the eyeball
Olfaction
The sense of smell
Odors
Olfactory sensations
Odorant
Any specific aromatic chemical.
Chemical compounds
But not every chemical is an odorant
In order to be smelled, molecule must be volatile (able to float through air), and small
Olfactory epithelium:
The “retina” of the nose
Three types of cells:
Supporting cells: Provide metabolic and physical support for the olfactory sensory neurons
Basal cells: Precursor cells to olfactory sensory neurons
Olfactory sensory neurons (OSNs): The main cell type in the olfactory epithelium
OSNs are small neurons located beneath a watery mucous layer in the epithelium
Shape-pattern theory
Different scents activate different arrays of olfactory receptors in the olfactory epithelium as a function of odorant-shape to OR-shape fit.
These various arrays produce specific firing patterns of neurons in the olfactory bulb, which then determine the particular scent we perceive.
combinatorial neural code
How can we detect so many different scents if our genes only code for about 1000 olfactory receptors?
We can detect the pattern of activity across various receptor types
Intensity of odorant also changes which receptors will be activated
Weak concentrations of an odorant may not smell the same as strong concentrations of it
Specific time order of activation of OR receptors is important.
Odor mixtures
Analyses: Example from auditory mixtures. High note and low note can be played together but we can detect each individual note.
Synthesis: Example from color mixtures. Mixing red and green lights results in yellow light, but we cannot separately perceive the red and green in the yellow.
Olfaction is mostly synthesis, but analytical abilities can be trained.
Detection:
Olfactory detection thresholds: Depend on several factors.
Women: Generally lower thresholds than men, especially during ovulatory period of menstrual cycles, but their sensitivity is not heightened during pregnancy
Age: By 85, 50% of population is effectively anosmic
Professional perfumers and wine tasters can distinguish up to 100,000 odors
Professional perfumer: “Nose”
Famous example: Jacques Polge (Chanel):
Adaptation:
Sense of smell is essentially a change detector
Examples: Walking into a bakery and can only smell fresh bread for a few minutes. Someone who wears perfume every day cannot smell it and might put a lot on.
Receptor adaptation: The biochemical phenomenon that occurs after continuous exposure to an odorant, whereby the receptors stop responding to the odorant and detection ceases.
