Perception Chapter 11 Sounds

Sound as Pressure Changes -condensation -rarefaction

---a sound stimulus occurs when the movements or vibrations of an object cause pressure changes in air, water or any other elastic medium that surrounds an object. -condensation=when the diaphragm of the speaker moves out, it pushes the surrounding air molecules together. It cause a slight increase in the density of molecules near the diaphragm -rarefaction=when the speaker diaphragm moves back in, air molecules spread out to fill in the increased space, causes slight decrease in air pressure ---the repeating of the process causes a pattern of alternating high and low pressure regions in the air as neighboring air molecules affect one another ---although the air pressure changes move outward from the speaker, the air molecules at each location move back and forth but stay in about the same place. What is transmitted is the pattern of increases and decreases in pressure that eventually reach the listeners ear.

Pinnae

-the structures that stick out from the sides of the head. -Helps to determine the location of sounds and is of great importance for those who wear eyeglasses.

Form Pressure Changes to Electricity

3 basic tasks during the journey. 1)delivers the sound stimulus to the receptors 2)transducers this stimulus from pressure changes into electrical signals 3) processes these electrical signals so they can indicate qualities of the sound source as pitch, loudness, timbre and location --Sound sets structures along the pathway into vibration and these vibrations of small hairlike receptors for hearing deep within the ear

Sound waves

a pattern of air pressure changes which travels through air at 340 meters per second (and through water at about 1500 meters per second)

SPL (sound pressure level)

added to indicate that the decibels were determined using the standard pressure of 20 micropascal.

Tonic map

an orderly map of frequencies along the length of the cochlea. The result shoes the idea that the apex responds best to low and the cochlea responds best to high. --More precise evidence is provided by determining neural tuning curves for auditory nerve fibers that signal activity at different places on the cochlea

Frequency Spectra

another way to represent the harmonic components of a complex tone (horizontal axis is frequency, not time) -Provide a way of indicating a complex tone's fundamental frequency and harmonics that add up to the tone's complex waveform

Higher Harmonics

are pure tones with frequencies that are whole-number multiples of the fundamental frequency. This means that the second harmonic of our complex tone has a frequency of 200x2=400Hz

Evidence for Place Theory

been confirmed by measuring the electrical response at different places along the cochlea. Placing a disc electrodes at different places along the length of the cochlea and measuring the electrical response to different frequencies resiles in a tonic map

Cochlear partition

between the upper and lower half of the cochlea. Extends almost the entire length of it from the base (near the stapes) and to its apex (at the far end).

Pitch and the Ear

can distinguish the following two types of physiological information related to stimulus frequency --timing information- the firing rate of auditory nerve fibers is related to stimulus frequency and periodicity with higher freq. causing higher firing rates 2)place information-the place on the cochlea where the maximum firing occurs is related to frequency with low frequencies causing greater firing in fibers near the base of the cochlea and high freq cause greater firing in fibers near the apex of the cochlea. -The neurons that connect to the place prisoned to the most and information is carried up to the auditory nerve to the brain...page 281

Presbycusis

caused by hair cell damage resulting from the cumulative effects over time of noise exposure, the ingestion of drugs that damage hair cells and age-related degeneration -greatest loss at high frequencies, affects males more.

Outer ear

consists of the pinna and the auditory canal. Sound waves first pass through it.

Organ of Corti

contains the hair cells, the receptors for hearing. Also the basilar membrane and the tectorial membrane which play crucial roles in the hair cells

Frequency tuning curves

each hair cell and auditory nerve fiber responds to a narrow range of frequencies. The range is indicated by each neurons ftc. The curve is determined by presenting pure tones of different frequencies and measuring the sound level necessary to cause the neuron to increase its firing above the baseline or spontaneous rate in the absence of sounds.

Harmonic

each of the components of tone

Incus

eardrum transmits the vibrations to it which in turn transmits it to the stapes.

Octave

every time we pass the same letter on the key board you go up an octave.

Hertz (Hz)

frequency, the number of cycles per second that the change in pressure repeats. 1 Hz is 1 cycle per second. Humans can here a range from 20Hz to 20000Hz. [Sound Frequency]

Malleus

hammer, is set into vibration by the eardrum to which it is attached.

Traveling wave

he found that the vibrating motion of the basilar membrane is a traveling wave like the motion that occurs when one hold an end of a rope and the other snaps it sending a wave motion.

Audibility Curve

indicates the threshold for hearing versus frequency, indicates that we can hear sounds between 20-20000HZ and that we are most sensitive at frequencies between 2000-4000Hz which happens to be the range that is most important for understanding speech

First Harmonic

is a pure tone with frequency equal to the fundamental frequency and is usually called the fundamental of the tone

Auditory Canal

is a tubelike structure about 3cm long in adults that help protect the delicate structures of the middle ear from the hazards of the outside world. --Protects tympanic membrane (eardrum) and helps keep the membrane and the structures in the middle ear at relatively constant temperature.

Inner ear

is the liquid filled cochlea, the snail like structure. The liquid inside is set into vibration by the movement of the stapes against the oval window. The most obvious feature of the uncoiled cochlea is the upper half (scala vestibule) and the lower half (scala tympani) -Cochlea is about a 2mm cylinder in diameter and 35 mm long

Loudness

is the perceptual quality most closely related to the level or amplitude of an auditory stimulus, which is expressed in decibels --One way to appreciate the importance of frequency in the perception of loudness is to consider the audibility curve

Timbre

is the quality that distinguishes between two tones that have the same loudness, pitch and duration but still sound different. -Closely related to the harmonic structure of a tone --depends on the time course of a tones attack and decay

Cochlear Implants

is used to create hearing in people with deafness caused by damage to their hair cells in the cochlea. Consists of: 1) a microphone that receives sound signals from the environment 2) a sound processor that divides the sound received by the microphone into a number of frequency bands 3)a transmitter that sends these signals to an array of 22 electrons that are implanted along the length of the cochlea. The electrodes stimulate it in different places depending on the intensities of the stimuli received.

Tone chroma

notes with the same letters have the same tone chroma. Every time we pass the same letter on the keyboard we have gone up an interval --Tones separated by octaves have the same tone chroma

Bekesy Discovers how the Basilar Membrane Vibrates

observed the vibration of the basilar membrane by boring a hole in cochleas taken from animal and human cadavers. Presented different frequencies of sound and observed the membrane;s vibration y ising a technique similar to that used to create stop-action photographs of high speed events which let him see the membranes position at different points in time.

Resonance

occurs in the auditory canal when sound waves that are reflected back from the closed end of the auditory canal interact with sound waves that are entering the canal. This interaction reinforces some of the sound's frequencies, with the frequency that is reinforced the most being determined by the length of the canal.

A pure tones

occurs when changes in air pressure occur in a pattern described by a mathematical function called sine wave. -Tones with this pattern of pressure changes are occasionally found in the environment --a person whistling or the high pitched notes produced by a flute are close to pure tones

Noise-introduced hearing loss

occurs when loud noises cause degeneration of hair cells. The loss has been observed in examinations of the cochleas of people who have worked in noisy environments and have pulled their ear structures to medical research

Sound Level

referring to decibles or sound pressure of a sound stimulus

Sound- physical definition

sound is pressure changes in the air or other medium (sound stimulus)

Sound- perceptual definitions

sound is the experience we have when we hear (sound perception)

Place theory of hearing

states that the frequency of a sound is indicated by the place along the cochlea at which nerve firing is highest. This watch place on the basilar membrane is tuned to respond best to a different frequency. The base is tuned to high frequencies the apex is tuned to low frequencies and the best frequency varies continuously along the basilar membrane between these extremes

Characteristic frequency

the arrow under each curve indicates the frequency to which the neuron is most sensitive.

Vibrations bend the hair cells

the back and forth motion of the oval window transmits vibrations to the liquid inside the cochlea which sets the basliar membrane into motion --The up and down motion create: 1) it sets the organ of Corti into an up and down vibration 2) causes the tectorial membrane to move back and forth. --The two motions mean that the tectorial membrane slides back and forward just above the inner hair cells --Resulting in the cilia hair bending, the pressure of the eaves in the liquid surrounding the cilia

Tone Attack

the buildup of sound at the beginning of the tone

Temporal Coding

the connection between the frequency of a sound stimulus and the timing of the auditory nerve fiber firing. Measurements of the pattern of firing for auditory nerve fibers indicate that phase locking occurs up to a frequency of about 5000 Hz.

Effect of the missing fundamental

the constancy of pitch, even when the fundamental or other harmonics are removed

Infant hearing

the curves for 3 and 6 months old and adults indicate that infant and adult auditory function look similar and that by 6 months, the infants threshold is within about 10 to 15 of the adult threshold. --Recognizing the mother's voice: they recognize it because they heard it in the womb.

Tone Decay

the decrease in sound at the end of the tone

Resonant frequency

the frequency reinforced the most

Auditory response area

the light green area about the audibility curve. We can hear tones that fall within that area. At intensities below the curve, we cannot hear a tone.

Frequency

the number of cycles per second that the pressure changes repeat

Cochlear Amplifier

the outer hair cells become elongated when the cilia end in one direction and contract when the bend in the other direction. The mechanical response of elongation and contraction pushes and pulls on the basilar membrane which increases the motion of the membranes and sharpens its response to specific frequencies

Tone height

the perceptual experience of increasing pitch that accompanies increases in a tone's fundamental frequency

Pitch

the perceptual quality we describe as high or low and can be defined as the property of auditor sensation in terms of which sounds may be ordered on a musical scale (also a property of speech)

Periodicity pitch

the pitch that we perceive in tones that have harmonics removed. Indicates the pitch is determined by the period or repetition rate of the sound waveform,. ----Pitch is therefore determined not by the presence of the fundamental frequency but by information like the spacing of the harmonics and the repetition rate of the waveform that is related to the fundamental frequency --Has practical consequences: what happens when you listen to someone talking to you on the phone. Even though the phone does not reproduce frequencies below 300Hz, we can hear the low pitch of a male voice that is about 100Hz fundamental frequency because of a periodicity pitch created by the higher harmonics

Phase locking

the property of firing at the same place in the sound stimulus. For high frequency tones, a nerve fire may not fire every time the pressure changes because it needs to rest after it fire. But when the fiber does fire, it fires at the same time in the sound stimulus -since many fibers respond to the tone, it is likely that if some "miss" a particular pressure change, other fibers will be firing at that time. --Therefore, when we combine the response of many fibers, each of which fires at the peak of the sound wave, the overall firing matches the frequency of the sound stimulus.

Periodic tone

the property of repetition means that this complex tone, like a pure tone is periodic. From the time scale at the bottom of the figure, we see that the tone repeats 4 times in 20 seconds

Sound Amplitude and Decibel Scale

the range of amplitudes we can encounter in the environment is extremely large which indicates the relative amplitudes of environmental sounds, ranging from a whisper to a jet taking off. --If the pressure change plotted in the middle record, in which the sine wave is about 1/2 inches high on the page, represented the amplitude associated with a sound that we can just barely hear, like a whisper. Then to plot the graph for a very loud sound like a concert.

Fundamental frequency

the repetition rate

Amplitude

the size of the pressure change

Middle ear muscles

the smallest skeletal muscles in the body. The muscles are attached to the ossicles and at very high sound levels they contract to dampen the ossicles vibration. This reduces the transmission of low frequency sounds and helps to prevent intense low frequency components from interfering with our perception at high frequencies. --Contraction of the muscle can may prevent our own vocalizations and sounds from chewing, from interfering with our perception of speech and from other people.

Ossicles

the three smallest bones in the body (malleus, incus, stapes) --helps solve the problem of vibrations having to pass from middle to inner ear. 1)by concentrating the vibration of the large tympanic membrane onto the much smaller stapes which increases the pressure by a factor of about 20. 2)by being hinged to create a lever action, an effect similar to what happens when a fulcrum is placed under a hard to that pushing down on the long end of the board makes it possible to lift a heavy weight on the short end --in patients whose ossicles have been damaged beyond surgical repair, it is necessary to increase the sound level by a factor of 10 to 50 to achieve the same hearing as functioning ones

Acoustic prism

the way the cochlea separates frequencies along its length. the cochlea separates frequencies entering the ear into activity at different places along the basilar membrane.

Equal loudness curves

these curves indicate the sound levels that create the same perception of loudness at different frequencies. The curve is determined by presenting a standard pure tone of one frequency and level and having a listener adjust the level of pure tones with frequencies across the range of hearing to match the loudness of the standard.

Cilia

thin processes that protrude from the tops or the hair cells which bend in response to pressure changes. --Inner hair cells and outer hair cells are located at different places in the organ of Corti --Human ear contains about one row of inner hair cells (3500) and about 3 rows of outer hair cells (12000) --longest row of outer hairs cells is in contact with the tectorial membrane. The cilia on the inner ear is NOT in contact with it

Bending Causes Electrical Signals

transduction involves ion flow. the flow occurs when the cilia bend. --Tip Links: structures -movement in one direction causes the tip links to stretch and this opens tiny ion channels in the membrane of the cilia which behave like trapdoors. When the ion channels are open, positively charged potassium ions flow into the cell. -When the cilia bend in the other direction, the tip links slacken and the ion channels close to the electrical signals are not generated. ---The electrical signals result in the release of neurotransmitters which diffuse across the synapse separating the inner hair cells from the auditory nerve fibers and cause these auditory nerve fibers to fire.

Stapes

transmits its vibrations to the inner ear by pushing on the membrane covering the oval window

Leisure noise

turn up volume on portable music player

Middle ear

when sound waves reach the eardrum, they set it into vibration and the vibration is transmitted to structures in the middle ear. --small cavity about 2 cc in volume that separates the outer and inner ears --outer and middle are filled with air but inner is watery so there is a low density and high density of the two. Pressure changes in the hair are transmitted poorly to the denser liquid. --If vibrations had to pass directly from the air in the middle ear to the liquid in the inner ear, less than 1 percent of the vibrations would be transmitted --FISH have no outer or inner ear

The Sounds Frequency Determines the Timing of the Electrical Signals

when the pressure increases, the cilia bend to the right, the hair cell is activated and attached auditory nerve fibers will tend to fire. --When the pressure decreases, the cilia bend to the left and no firing occurs. This means that auditory nerve fibers fire in synchrony with the rising and falling pressure of the pure tone