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Hearing If a tree falls and no one is there, does the tree make a sound? A psychologist would answer, “There are sound waves, but there is not sound or noise. Sounds and noise are psychological experiences created by the brain in response to stimulation. Sound Sound waves – changes in pressure caused when molecules of air or fluid collide with one another and then move apart again, transmitting energy at every collision. Sine wave – what we hear as a pure tone molecule of air first contract then expand Frequency of the waves measure in cycles per second, expressed in a unit called hertz Frequency determines the pitch of the sound – how high or low it is Human ear response to frequencies from about 20 Hz to 20,000 Hz The height of the wave represented its amplitude – which with frequency, determines the perceived loudness of a sound Loudness is measures in decibels. As we grow older we lose some of our ability to hear low-intensity sounds. There are seldom pure tones produced most of the time instruments produce overtones – The complex pattern of overtones is called timbre or texture of the sound Hearing undergoes adaptation too. The Ear Hearing begins when sound waves strike the eardrum and cause it to vibrate. Three tiny bones Hammer, anvil and stirrup hit each other in sequence and carry the vibrations to the inner ear. Stirrup is attached to a membrane called the oval window. Below oval window is the round window. This equalizes the pressure in the inner each when the stirrup strikes the oval window. The vibrations are transmitted to the fluid inside the cochlea. It is divided lengthwise by the basilar membrane. Stiffer near the oval and round windows and gets more flexible toward its other end. The basilar membrane is pushed up and down rippling in response to the movement of the cochlear fluid. On top of the basilar membrane and moving in sync with it is the organ of Corti. Here messages from the sound waves finally reach the receptor cells for the sense of hearing. Thousands of tiny hair cells that are embedded in the organ of Corti. Signals are transmitted through the auditory nerve to the brain. Hearing is truly bilateral. Each ear sends messages to both cerebral hemispheres. The switching station where the nerve fibers from the ears cross over is in the medulla. The primary destinations for the auditory messages are the auditory areas in the temporal lobes of the two hemispheres. Place theory – the brain determines pitch by noting the place on the basilar membrane at which the message is strongest. Frequency theory – pitch is determined by the frequency with which hair cells in the cochlea fire Volley principle – refines frequency theory; suggests that receptors in the ear fire in sequence, with one groups responding, then the next and the third etc. Hearing disorders Damage of eardrum Small bones may not work properly Damage to basilar membrane Disease, infections and long-term exposure to loud noi8se can harm the ear Hearing aids simply amplify incoming sound Conductive hearing loss – surgery is recommended Conductive is due to a stiffening of the connections between the bones Cochlear implants can offer hope to those whose deafness is due to cochlear damage. If you have auditory nerve damage none of these things will work. Tinnitus – high pitched hum all the time. Other Senses: Amell: smell is 10,000 times as sensitive as taste Smell undergoes adaptation like other senses Two different sensory systems: Detect and discriminate among common odors Communicating sexual aggressive or territorial scent signals