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Canada (158,032)
Psychology (9,545)
PSYB65H3 (479)
Ted Petit (185)
Chapter 8

Chapter 8 detailed

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University of Toronto Scarborough
Ted Petit

Chapter 8 [HEARING AND LANGUAGE PROCESSING] Module 8.1: The Auditory System Language production was one of the first cognitive abilities to be localized in the brain The Properties of Sound Frequency rate of vibration the number of wave cycles completed per unit of time Measured in Hertz (Hz) cycles second Human ear can perceive vibrations between 20-20,000 Hz Maximally sensitive to sounds between 1000 and 4000 Hz (human voice) Codes for pitch High frequency = high pitch Low frequency = low pitch Range of frequency that an animal perceives varies widely across species Loudness corresponds to the amplitude (intensity) of the sound wave Waves of different amplitudes differ in the degree to which the high point (condensation of air) and the low point (rarefaction of air) of the wave differ from each other Measured in decibels (dB) sound pressure of a source when compared to a standard -12 intensity of 10 watts Conversation: 40-60dB Timbre complexity of sound Fourier analysis a mathematical process in which complicated sounds are broken down into simple component waves Used to compress complex sounds on computers (MPEG-1, MP3) so that the series of simple wave forms can be efficiently represented The Ear Transduction the ear detects and amplifies very subtle vibrations and transforms these vibrations into neural signals Transduction Mechanism: Sound enters funnellike outer ear, passing through the pinna (outermost visible portion of the ear) through the hole (auditory meatus) which leads to the external ear canal External ear canal amplifies vibrations and channels them to tympanic membrane (ear drum) Tympanic membrane vibrates and passes the vibration along the three bones of the middle ear: malleus, incus, stapes Collectively, the bones are referred to as ossicles Each successive bone further amplifies the vibration, and transmits the vibration through the oval window Vibration of oval window (which is attached to the stapes) causes liquid vibrations within the cochlea (filled with cochlear fluid) www.notesolution.com Chapter 8 [HEARING AND LANGUAGE PROCESSING] Vibration of cochlear fluid causes the bending of basilar membrane and tectorial membrane elicits neural activity in hair cells Hair cells are receptor cells of auditory system; connects with vestibulocochlear nerve Anatomical Divisions of the Ear: Outer Ear pinna, external ear canal Catches and amplify sound waves Middle Ear chamber between tympanic membrane and oval window Sound waves are transduced from variations in air pressure into mechanical energy that is propagated and amplified along the ossicles to the oval window Inner Ear mechanical energy is turned into neural activity Cochlea contains inner hair cells and outer hair cells o Outer hair cells outnumber inner hair cells by 3:1 o Inner hair cells serve as receptors for auditory system; only 5% of auditory nerve cells receive inputs from outer cells o Outer hair cells modulatory role; helps to tune the cochlea through contraction and relaxation Inner Hair Cells (auditory receptors) have tiny filaments at their tips cilia that are arranged in order of height Tallest cilia kinocilium When cilia move toward direction of kinocilium: Fibers are stretched, increased firing in axons of cochlea nerve When cilia move away from kinocilium (in very quiet situations): firing in cochlear nerve falls below the normal (resting) rate Organ of Corti: Hair cells + their cilia + support cells Different parts of the cochlea respond maximally to different frequencies Basilar membrane closest to oval window is quite stiff, receptors are exposed to higher frequencies Near the helicotrema (apex), the basilar membrane is more flexible, receptors are exposed to lower frequencies Efferent projections from the cochlea demonstrate different activation under different attentional conditions Inner ear functions can be affected by higher perceptual and attentional pathways Auditory Pathways Pathway #1 1. Axons of cochlear nerve form a branch of vestibulocochlear nerve which synapses on the ipsilateral cochlear nuclei 2. Pathway A: Most projects lead to ipsilateral or contralateral superior olives Projections travel ipsilaterally to the inferior colliculus www.notesolution.com
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