8. Other Perception

• Frequency


  How often sound waves compress. More = higher pitch. Double the number to go up an octave (yes thats how octaves work)
• Amplitude


  How much sound waves displace from the baseline. The greater the displacement, the louder the sound, which is measured in decibels (dB)
• Timbre


  Complexity of the wave form-- same fundamental frequency but difference in overtones that oscillate at a multiple of the FF
• Pure note or sine wave tone


  A sound wave without any overtone frequencies
• Pinna (auricle)


  The outer ear that acts as a funnel for sounds. It has an irregular shape that lets us detect where sounds are coming from
• Auditory canal


  Brings sounds from the pinna to the tympanic membrane (middle ear)
• Tympanic membrane (ear drum)


  0.1 mm thin membrane that is super fragile and can burst with trauma. It vibrates at exactly the same timbre, amplitude, and frequency as the incoming sounds. Represents boundary between outer and middle ear
• Ossicles


  Series of 3 bones that convey and amplify 10x the vibrational sound information from the tympanic membrane in the air-filled middle ear. Amplification is important because sound doesn't travel as well through the liquid that fills the inner ear
• Ossicles: malleus, incus, stapes
• Tensor tympani muscle connects to the malleus and the stapedius muscle connects to the stapes. When these muscles contract the ossicles move less, which decreases the intensity of loud sounds
• Acoustic reflex


  Reflex of tensing the tensor tympani and stapedius muscles to protect ourselves from loud noises. Dampens sounds by 15 dB
• Oval window


  Thin membrane attached to the stapes that connects to the main structure of the inner ear
• Vestibular labyrinth


  Hollow bone that is the main structure of the inner ear, connected to the oval window and contains the cochlea
• Cochlea


  Rolled up cone with a stiffer base that vibrates at higher frequencies than the apex. Because of this gradient different points are responsive to different frequencies
• Organ of Corti


  Specialized epithelial membrane inside of the cochlea that is the first nervous system structure that is responsible for processing physical vibrations and turning them into signals that the nervous system can interperet
• Endolymph


  High K low Na liquid similar to CSF that makes up the inner ear extracellular solution
• Stereocilia


  Mini hairs that protrude into the endolymph that are attached to the somata of hair cells embedded along the Organ of Corti (30 - a few hundred per cell)
• When a sound passes through the cochlea, the movement of the endolymph pushes around the inner cilia, which opens mechanically gated ion channels in the hair cells, allowing K+ to enter, which causes depolarization and a release of neurotransmitter
• Mechanotransduction


  The precess of physical motion leading to neural signalling (like hair cells in the cochlea)
• The length and position on the cochlea of inner hair cells determines what kinds of sounds they are sensitive to. Shorter hairs are more attuned to high pitched sounds, which are processed in the base, while the opposite is true for the apex
• Outer hair cells

  We have 3 rows of them, and they serve to amplify sounds by 20 - 80 dB as they enter the cochlea
• Conductive hearing loss


  Hearing loss as a result of changes in the auditory system up to the oval window (burst tympanic membrane, tumor in ear canal)
• Sensorineural hearing loss


  Hearing loss as a result of changes in the inner ear or neural pathway. Most common cause is noise exposure, which damages hair cells despite acoustic reflex, so older people get it as a result of more accumulated noise heard. Other causes = brain tumor or viral infection
• Hearing aid


  Device that helps filter out background noise, decrease pitch, and amplify incoming sounds
• Cochlear implant


  Surgically implanted device that receives incoming sounds and directly stimulates the auditory nerve via electrodes, bypassing the external auditory system
• Spiral ganglion


  Hair cells synapse onto these cells, whose axons make up cranial nerve VIII (auditory nerve)
• Auditory nerve (vestibulocochlear nerve)


  Cranial nerve VIII
• Superior olive


  Area of the pons that receives bilateral input from both ears. Its main job is to figure out where the noises are coming from by using interaural level difference and interaural time difference
• Cochlear nuclear complex


  Area of the rostral medulla that some auditory neurons project on which carries out some auditory processing functions
• Interaural level difference


  A difference in volume between what one ear and the other perceives based on where the sound originates, processed by neurons in the lateral superior olive
• Interaural time difference


  Assessing where a sound is coming from by the tiny differences in when the sound hits the ears (speed of sound). Processed by neurons in the medial superior olive
• Inferior colliculus (IC)


  Where information is passed on to from the superior olive. Processes things like unexpected noises so that we can react as fast as possible to them (predators)
• Medial geniculate body


  Gets info from the IC. One of the nuclei of the thalamus, which then sends signals directly to A1
• Primary auditory cortex (A1)

  Herschel's cortex
• A1


  Dorsal most part of the temporal lobe
• Tonotopically organized


  Meaning adjacent physical areas are responsible for adjacent frequencies. Many neural structures for processing sounds are organized this way
• Dual stream hypothesis also works for the auditory system: dorsal = "where" (i.e. location + recognition of language), ventral = "what" (i.e. sentence comprehension, sound recognition)
• A1 passes information to A2 and A3 which are responsible for processing sounds at a higher order
• Tinnitus


  Symptom of hearing loss or injury that results in the occasional hearing of clicking or ringing noises without ant actual stimulus
• Vestibular system


  3D compass that tells us where our head is pointed and how we should balance ourselves