Lecture5 Flashcards
Compare the former sensory hierarchical Homogeneous Serial model to the current hierarchical Segregated Parallel model
Former - input travels from receptors to thalamus to primary sensory cortex to secondary sensory cortex to association cortex; Current - works as a feedback mechanism where there’s lots of interconnections among the senses at each level of processing
What is the role of the Pinnae?; What happens when a sound source changes its location relative to the head?
They collect sound waves & direct them to the auditory channel; also help to localise sounds - the folds selectively reflect sounds of various frequencies around the ear & into the auditory canal; Frequency profile of reflections changes offering a cue to location of the source
What does the auditory canal do?
Offers protection to the middle & inner ear
The vibrations of the tympanic membrane concentrate on what?; How much do the vibrations increase?; What does the lever action of the ossicles do?; Combined, this accounts for a 22 fold increase in what?
A very small area on the oval window; 17 fold; Amplifies the vibrations by approx. 1.3 times; The strength of vibrations hitting the tympanic membrane
How are vibrations converted into neural impulses?; Upward deflection causes…; Downward deflection causes…
Hair cells (stereo cilia) lie between the tectorial & basilar membrane (which are joined at one end) & the shear force of both membranes activate the hair cells causing a neural impulse; Hair cells to bend to the right; Hair cells to bend to the left
At auditory threshold what is the measurement of hair cell displacement?
100 picometres
What 3 processes does the auditory system use to code for different frequencies?
Frequency theory - firing rate codes directly for those frequencies; Volley theory - none can code on their own for a particular frequency but can cooperate, if each a little out of phase the sum of them can total 400hz; Place theory - depends on specific properties of basilar membrane, high frequencies travel only a short distance
What is the base of the basilar membrane tuned for?; What is the apex of the cochlear tuned for?
High frequencies (point of maximum deflection); Low frequencies (travels further)
Where is the auditory receiving area?; In order, what other auditory pathways are involved?
Temporal lobe; Cochlea, Auditory Nerve, Cochlea Nuclei, Superior Olivary Nuclei, Lateral Lemniscus, Inferior Colliculus (tectum), Medial Geniculate Nucleus (thalamus), Primary Auditory Cortex
What are Interaural Time Differences?; If sound source comes directly in the right ear how long before it reaches the left ear?
Measurable & detectable time for sound to travel across the width of the head; A few milliseconds
Explain Interaural Intensity Differences
Higher frequencies tend to bounce off objects (e.g. if a sound goes directly into right ear the intensity is less in left ear because of acoustic shadow), but lower frequencies can bend around obstacles
Explain the process of sound localisation by interaural differences with sound entering the left ear
Sound reaches the left ear first, action potential begins travelling toward Medial Superior Olive (longer path to last neuron), sound reaches right ear, action potential from right ear travels toward MSO (shorter path to first neuron), action potentials converge on an MSO neuron that responds most strongly if their arrival is coincident
If a sound source from straight ahead equally stimulates both Medial Nuclei of the Trapezoidal Body (MNTB) & completely shuts down the Lateral Superior Olive (LSO) on both sides, what occurs if sound source comes from the left?
Stronger stimulus to left ear excites left LSO, this also inhibits contralateral (right) side LSO via MNTB interneuron, excitation from left is greater than inhibition from right resulting in net excitation to higher centres, inhibition from left is greater than excitation from right resulting in net inhibition on right & no signal to higher centres
What are the 2 principles of organisation in the auditory cortex?
Columnar oragnisation (i.e. frequency columns) & Tonotopic organisation of the cochlea is preserved all the way up the auditory pathway (this results from projections from specific locations along basilar membrane)
Where does the core area lie?; What is it called?; Where does the belt area lie?; What is this called?
Inferior to the lateral fissure in the temporal lobe; Primary auditory cortex; inferior to Primary auditory cortex; Secondary auditory cortex
What does Conduction Deafness result from?; Give an example of this; What part of the system does this not involve?
Damage to the tympanic membrane & ossicles; Ossicles can become fused & no longer transmit sound vibrations from the outer ear to cochlea (mechanical process); Nervous system
What is the main feature of Sensorineural Deafness?; Deafness is…; What is this caused by?
Auditory nerve fibres are not stimulated properly; Permanent; Infection, trauma, exposure to toxic substances, loud sounds (e.g. noise pollution, headsets)
What properties does the antibiotic, Streptomycin have?; What did tuberculosis patients treated with this result in?
Ototoxic properties (ear damaging); Cochlea damage - in some cases all hair cells in the cochlea were destroyed, leading to total deafness
What is Central Deafness caused by?; What does this result in?
Brain lesions in the temporal lobes of the cortex (e.g. stroke); Loss of specific faculties, such as language processing (left lobe) or discrimination of non-language sounds (right lobe)
What does the Meaningful Sounds Identification test measure?; How do patients with left temporal damage perform on this test?; Patients with right temporal damage?
The ability to match the correct semantic meaning to a sound; Poorly; Equally to normal controls
What does the Meaningless Sounds Discrimination test measure?; How do patients with left temporal damage perform on this test?; Patients with right temporal damage?
The perceptual ability to discriminate between physically distinct sound patterns; Equally to normal controls; Poorly
