Lecture Notes - From Vision to Hearing PDF

** Lecture Notes: From Vision to Hearing ** ** Q: What is sound? ** ** A: It’s vibration! — it has the ability to travel through air on any other medium (think water) ** ** Fr...

** Lecture Notes: From Vision to Hearing ** ** Q: What is sound? ** ** A: It’s vibration! — it has the ability to travel through air on any other medium (think water) ** ** Frequency vs. Amplitude ** Frequency determines our sense of pitch while amplitude determines our sense of loudness. Frequency is measured in cycles per second or Hertz (Hz), amplitude is measured in decibel (dB) == A sound with a sinusoidal waveform is called a pure tone. (Think playing a singular key on the piano) == ** Complex sounds ** _ Most sounds are not pure tones! They are complex sounds (Hearing your bus arrive say for example…) _ _** Fourier transform: Decomposition (The breaking down) of a sound (or other signal) to the ** frequencies that make it up. _ == ** Example: pure tone 1 + pure tone 2 = complex sound (playing two keys on the piano, both individually are pure tones) **== A spectogram shows the frequencies that make up the sound, and how they change over time. ** ** ** ** ** Loudness: Higher decibels corresponds to louder sounds. ** _ _ ** The lowest we could hear is 0, the highest we could hear is 130 but at that point it is extremely harmful for our hearing ability. The more you are exposed to the highest decibels, the more likely will your hair cells die off. ** ** The Ear: ** The pinna collects sound & directs it down the ear canal Sound air pressure waves strikes the tympanic membrane ** ** Middle ear bones pass vibrations to the cochlea ** ** ** The Cochlea & Basilar Membrane: ** _ coiled in reality… is unwrapped to explain all parts (slides) _ ** Q: What is the Cochlea? ** ** A: The cochlea is a coiled tube that contains the basilar membrane, which tends to vibrate with sound ** waves. ** Q: What is the basilar membrane? What is its purpose? ** ** A: To summarize, sounds that arrive in the basilar membrane cause vibrations. High frequency causes ** the basal end to vibrate but not the apical end! Vice versa when it’s a low frequency, meaning it would cause the apical end to vibrate. The basilar membrane also decomposes complex sounds into the component frequencies ** All about hair cells: ** ** Q: Hair cells, what are they? what are their purpose? ** ** A: The hair cells sit on top of the basilar membrane, when the basilar membrane vibrates, they (hair ** cells) move as well. As the hair cells move that causes potassium channels to open up (reminder: this causes depolarization in the cell) Depolarization then causes neurotransmitters to release but there ** ** are no action potentials. == The auditory nerve sends signals from hair cells to the cochlear nucleus in the brainstem. ==  The louder the sound, the bigger the movement in the membrane. The amount of glutamate corresponds to frequency. If 2,000 is released, the frequency is 2,000! Please disregard in knowing the difference between the outer & inner hair cells. That is not necessary. (As this was not discussed until then.) ** What if(s)… ** 1. Q: What if a person doesn’t have the 3 bones (not necessary to know the names of these bones) ** ** that convey the vibrations from the outer ear to the cochlea? What happens then? ** A: Say there is a circumstance like this, if the person lacks the 3 bones, sound vibrations from the ** outer ear cannot be transmitted to the cochlea, resulting in conductive hearing loss. In this case, even if hair cells are present, they wouldn’t be able to receive the vibrations necessary to generate nerve impulses for hearing. The person would experience significant hearing loss or complete deafness. 2. Q: Say your hearing bone breaks, what happens then? ** ** ** A: Tears in the membranes are more common but if they break then the efficiency of your ** hearing goes down.  ** Noise & Age related hearing loss ** 1 in 3 people in the United States between the ages between of 65-74 have hearing loss. Nearly half of those older than 75 have difficulty hearing. Enhanced by excessive exposure to loud sounds. ** Additional note: When death of the hair cells occur, hair cells don’t regenerate… The more that ** die, your hearing ability decreases. (It’s so over) ** Hearing Aid vs. Cochlear Implant (Differences between both) ** _ _ Hearing Aid Cochlear Implant A small electronic device that amplifies sounds Used in complete or near complete deafness There’s 3 basic parts: Microphone, amplifier, and It bypasses / replaces hair cells to directly speaker stimulate the auditory nerve Be aware that this would only be for those who This is a more invasive procedure compare to still have some hair cells the hearing aid ** The superior olivary nucleus: ** The cochlear nuclei send information to the superior olivary nuclei Brainstem nuclei is critical for sound localization Please note that the sound location has to be computed — it’s not encoded in the peripheral receptors! Having 2 ears provides cues to localize sounds ** Additional comments: Sound will arrival on one side a bit quicker than the other side. Say someone is ** speaking from the left side, your left ear will pick it up quicker than the right side. It is not to say you won’t hear it from the right side but it will arrive quicker on the left side, it will also be louder compared to what your right side hears. #PSYCH230