Audition and Zoomusicology

Audition

• Audio demo 1 at http://deutsch.ucsd.edu/psychology/pages.php?i=212
• The speech-to-song illuson is another audio demo at http://deutsch.ucsd.edu/psychology/pages.php?i=212
• A question is posed about the difference between music and speech

Music and Animals

• Music composed for Tamarins, or for humans, may be based on affiliative and threat vocalizations
• Tamarins were generally indifferent to human music
• Tamarins showed increased arousal to threat-based tamarin compositions
• Tamarins showed decreased activity and increased calm in response to affiliative tamarin compositions
• Species-specific music are most effective at eliciting behavioral responses
• There is an example of responses in tamarins elicited by species-specific music in Biology Letters, 6, 30-32 by Snowdon, C. T., Teie, D. (2010)
• Zoomusicology is the study of music-like qualities of nonhuman sound communication
• Some do not consider animal song equivalent to human music, considering music to be characteristically produced for pure enjoyment
• Questions of aesthetic preference in nonhuman animals, as well as functional attributes of human behaviors are raised
• Many elements of nonhuman animal calls and songs are similar; Intervals, "rhymes”, and phrasing
• Both learned and innate songs and calls occur in nonhuman animals
• Vocal learning is more rare among animals, like parrots, songbirds, cetaceans, elephants, and humans; these animals must be exposed to adult vocalizations to develop their own

Sound Waves

• The first sound an individual hears is the beating of their own heart
• Sound waves are periodic compressions of air, water, or other media
• The physical amplitude of sound is its intensity and correlates to the perceptual loudness
• The physical frequency of sound correlates to the perceptual pitch
• The physical complexity of sound correlates to the perceptual timbre
• Adult humans can typically perceive between 20 and 20,000 Hz and sensitivity varies among individuals
• Humans have the greatest hearing sensitivity between 2000-5,000 Hz
• Children are able to hear higher frequency sounds than older adults
• Various species can hear in different ranges as shown by a chart

Auditory Anatomy

• The pinna alters the reflections of sound waves
• The auditory canal conveys sounds toward the tympanic membrane.
• The tympanic membrane or eardrum vibrates at the frequency of the sound that struck it
• The ossicles (hammer, anvil, and stirrup or malleus, incus, & stapes) amplify the vibration and vibrate the membrane of the oval window, moving the fluid inside the cochlea
• Your pinna is unique, and differs from left to right.
• Pinnae come in varying shapes and sizes in the animal kingdom
• Birds and reptiles have different coiled shapes of the cochlea than mammals
• The auditory apparatus penetrates deep into the skull, with the cochlea sitting approximately under the eye

Auditory Transduction

• Sound waves travel along the auditory canal and strike the tympanic membrane causing it to vibrate
• The vibration causes the 3 ossicles to move, pressing the stapes into the oval window of the cochlea
• The fluid inside the cochlea begins to move, stimulating the hair cells (sensory receptors for sound), which become activated
• The hair cells generate neural impulses that travel along the auditory nerve to the brain
• The cochlea is a highly complex, chambered structure, filled with fluid
• Membranes run along the length of the cochlea's spiral shape, from the section closest to the ossicles, to the inner most portion of the spiral
• The chambers of the cochlea include the Scala vestibuli, media, and tympani
• The Scala vestibuli is a fluid-filled passage found toward the superior side of the cochlea.
• The Scala media is a fluid-filled passage of cochlea found medially
• The Scala tympani is a fluid-filled passage of cochlea found inferiorly
• Pressure moves from the scala vestibuli toward the helicotrema, then passes into the scala tympani, toward the round window
• The oval window is the flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside
• The round window is a soft area of tissue at the base of the scala tympani that releases excess pressure from vibration in the cochlea
• The helicotrema is the opening that connects the scala tympani and scala vestibuli at the apex of the cochlea
• The cochlea can be described as having a base and apex
• The cochlear base is the location of the cochlea near the oval window, where high frequency sounds displace basilar membrane maximally
• The cochlear apex is the location of the cochlea near the helicotrema, where low frequency sounds displace basilar membrane maximally
• The cochlear partition is comprised of a basilar membrane, tectorialmembrane, and organ of Corti, which are together responsible for signal transduction for sound.
• The basilar membrane is a plate of fibers that forms the base of the cochlear partition and separates the scala media and scala tympani
• The tectorial membrane is a gelatinous structure, attached on one end that extends into the middle canal of the cochlea, floating above inner hair cells and touching outer hair cells
• The organ of Corti are the cells that generate a neural signal; a structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers
• Pressure in the chambers of the cochlea travels from the oval window, through the scala vestibuli, toward the helicotrema, and then through scala tympani and then out
• Waves of pressure disturb the basilar membrane inside the scala media.
• The Basilar membrane flaps like a flag, brushing hair cells against the Tectorial membrane
• Shearing forces from the pressure below and above the scala media create a flapping movement of the cochlear partition.
• Hair cells transduce vibrations into neural signals and are covered in cilia
• They also receive input from the brain to generate active movements
• Stereocilia are hairlike extensions on tips of hair cells, and when flexed in the correct direction, they release neurotransmitters
• A tip link is a tiny filament that connects one stereocilium to its neighbor, so when pulled, they tug open an ion channel on the surface of the stereocilium

Perception of Pitch

• Place theory suggests that certain frequencies are coded at different parts of the cochlea, but this is not perfectly accurate.
• There is evidence for Place Theory in the responses of the auditory nerve fibers.
• The characteristic frequency (CF) is the frequency to which a particular auditory nerve fiber is most sensitive
• Different auditory nerve fibers have different CFs
• With rate saturation, a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate.
• Large amplitude sounds of any frequency can saturate many AN fibers at once (not just their CF).
• It happens because high amplitude sounds can stimulate nerve fibers at a wide range of frequencies
• Frequency theory and temporal coding can supplement Place Theory
• With Temporal coding tuning occurs at different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound is coded by the timing of neural firing
• Neurons have a refractory period, so humans can process around 1,000 neural impulses per second for auditory neurons.
• Vision runs much slower, with > 40 ms or 24 frames per second appearing continuous
• The Volley Principle explains that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave, but does not fire on every period
• Equal-loudness curves are a graph plotting sound pressure level against frequency for which listeners perceive constant loudness

Audition in the Wild

• Manatees are frequently injured and killed by boats
• A manatees hearing is quite good, but not at low frequencies
• Regulations that require boaters to slow down may not have the desired effect of saving manatees and driving faster is also not the solution
• Possible solution: Manatee alerting devices
• Echolocation and spatial hearing relies on information gathered from the spectral composition of sound arriving at the ears
• Experts distinguish size, shape, and materials of objects in their surroundings with echolocation

Devices that Aid Hearing

• A cochlear implant provides a sense of sound to a person who is profoundly deaf or severely hard-of-hearing
• It consists of an external microphone, processor, transmitter, and electrode array
• These do not restore perfect hearing, but can allow people to recognize warning signals and better comprehend speech sounds
• Absolute pitch is the rare ability whereby some people can accurately name or produce notes without comparison to other notes, occuring in aproximately 1/10,000 people
• Absolute pitch is more common among tonal language speakers
• It is difficult for adults to acquire even through a great deal of practice
• Relative pitch indicates that a comparison pitch is needed to judge pitch accurately
• Tone deafness is when it is difficult to perceive pitch and involves a difference between not being able to judge and not being able to produce pitch accurately