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Chapter 8

chapter 8 psyb65

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Ted Petit

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PSYB65 – CHPT 8 Hearing and language processing The auditory system  Sound waves that are being perceived o Frequency: rate of vibration, indicated in hertz (Hz) measured in cycles per second o Human ear can only perceive vibrations between 20 and 20,000 Hz. o Humans are maximally sensitive to sounds between 1000 and 4000 Hz o The frequency of sound should not be confused with its speed, travelling 340 m per second o Sounds of different frequencies have different pitches, the higher the frequency the higher the pitch o They’re more sensitive that’s why dog whistles are silent to humans (30,000-50,000 Hz) o Loudness: the amplitude of sound waves  Waves of different amplitudes differ in the degree to which the high point (condensation of air) differ in the degree to which the high point (rarefraction of air) of the wave differ from each other  Amplitude is measured by dB (decibels) we can hear it as quiet as 1dB and a normal conversation between 2 person is around 40-60dB  Sound of 130dB produces pain o Complexity: perceived as the sound’s timbre (pure sounds of those composed of a wide variety of frequencies)  Overtones: frequencies higher than the fundamental frequency o Fourier analysis – when complicated sounds are broken down into simple component  This is used to compress sounds in a computer. Such as MP3 The ear  The outer ear: o Detects and amplifies very subtle vibrations in the air and transforming these vibrations into neural signals, a process called transduction o Sound waves enter the outer ear, passing the pinna (most outer layer of the ear) through the hole learning into the external ear canal which amplifies the vibrations and bring them into the eardrum (aka. Tympanic membrane)  The middle ear: o The tympanic membrane vibrates and passes the vibration to 3 bones. (known as ossicles)  1. Malleu  2. Incus  3. Stapes o Each other bone amplifies the wave further through the oval window  The inner ear: o Then its transferred into the cochlea through the cochlear fluid which causes a bending of both the basilar membarane and the tectorial membrane, which elicits neural activity in the hair cells, o These hair cells are the receptor cells of the auditory system, and they connect with the auditory nerve o Only 5% of the inner ear cells receive inputs from the outer cells  The outer hair plays a role in “tuning” the cochlea through contraction and relaxation  Conditioning the cochlea over a long period of time can actually increase its sensitivity to similar sounds  The inner hair cells have cilia that are arranged in order of height. When the cilium moves towards the taller ones, they stretch resulting in firing the axon of the cochlear nerve  Organ of Corti: the hair cells, the cilia and the cells  Different sections of the cochlea respond maximally to different frequencies , those closest to the oval respond to higher frequencies, those near the apex respond to lower frequencies o Tonotopic: this frequency-specific sensory organization  The function of the ears can be influenced by cognition Auditory pathways  There are 2 pathways o Eighth cranial nerve – they synapse ipsilateral cochlear nuclei. Most projections lead to the superior olives  inferior colliculus  some cross to the other side and some are projected to the medial geniculate nucleus of the thalamus  finally to the primary auditory cortex Auditory cortex  Its behind the secondary auditory cortex, located within the lateral fissure  The neurons here are highly specialized to respond to certain frequencies of sound  Is organized in a tonotopic fashion  They’re arranged in columns are those inner of the ear respond to higher frequencies  These neurons respond to narrower range of frequencies  The secondary auditory cortex: these neurons are highly sensitive to specific frequencies of sound Language systems in the brain: Models of spoken language  Language is by the frdntal lobe  Broca’s area is the 3 gyrus of the left frontal lobe – output of spoken language  Wernicke’s area: left tempora lobe posterior to the primary auditory cortex - responsible for mapping out words and sounds  These 2 areas must connect via the arcuate fasiculus to provide meaningful verbal output  Concept center: that connects both Broca’s and Wenicke’s area maps sounds to words  the angular gyrus provides a basis for visual language  spontaneous speech: produced by accessing the mappings of sounds to meanings in Wernicke’s area, projecting info to Broca’s area  sounds are not projected as meaningful words until they go through Wenicke’s area (receiving input from the primary auditory cortex)  initiation repetition- brain project meaningful “sounds images” to Broca’s area through the arculate fasciculus  WLG model- processing visual language, message is perceived through the visual system (primary and secondary visual cortices)angular gyrusproduction of sound images  This is why you hear a voice in your head  The WLG model – provides an account of many of the clinical speech disorders but it tends to oversimplify and omission Models of visual language
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