Cochlear implants and brain machine interface (Cochlear Implant…
Cochlear implants and brain machine interface
Nature of Sounds
Air pressure creates sounds.
A number of cycles per seconds expressed in units are called hertz.
The distance between successive compressed patches is called a cycle.
Range from 20hz to 20000,
High pitch is high frequency, low frequency= low pitch
Whilst Higher intensity means louder volume whilst lower intensity means lower volume.
Peripheral auditory system
Audiotory pathway stages
Sensory neurone response
Encoding sound frequencies is through Tonotopic maps on the basilar membrane
Mechanisms of sound localisations
Interoral timing diffirence
When on ear receives the sound faster than the other sound
Interoral level differences
When one ear receives a sound first due to it being blocked by the head.
-Perilymph: Fluid in the scala vestibuli and scala tympani
-Endolymph: Fluid in scala media
Pressure at the oval window pushes the perilymph into the scala vestibuli, round window membrane which bulges out.
The response of the basilar membrane is what causes the sound
Structural properties: Wider at apex, stiffness decreases from base to apex
High frequencies -> Base
Low frequencies-> Apex
Organ of Corti and associated structures as basilar membrane moves the hair cells will bend which will open up ion channels
The voltage gated channels will move the Basilar membrane upward, reticular lamina up and stereo-cilia bends outwards
Central Audiotory Processes
Cochlear Nucleus in Brainstem
Thalamus- Medial Geniculate nucleus
Superior temporal gyrus
Primary Auditory Cortex - Axons leaving the MGN(medial geniculate nucleus) project tot the auditory cortex via internal capsule in an array, Structure of A1 and secondary auditory areas: similar to corresponding visual cortex areas.
Human audiotory cortex
MGN sends to Herrshes gyrus, but also anatomical landmark of primary Audiotory cortex
Superior temporal gyrus
Computational hub computing where and what the sound is?
Dorsal- where an object is in space and how to interact
Vestibular system - Importance for balance, equilibrium, posture, head,body and eye movement
Otolith organs-gravity and tilt: detect changes in head angle, linear acceleration macular hair cells responding to tilt.
Semicircular canals-head rotation
Use hair cells, like audiotory system to detect changes
Cochlear Implant technology
Sound like sparse input
This is due to the loss of hair cells
The electrode is usually inserted through the round window or through a hole drilled nearby (cochleostomy) in the scala tympani.
Cochlear: Social Impact
CL recipients achieves 9% of sentence recognition, recognition of 55% of monosyllabic words
Improves over time up to 1 year to interpret the sparse input
Bilateral allows for sound localisations
Types of Deafness
Prelingual -before you acquire a language, Delaying Cochlear implants delays language function
Post-lingual At a later age - showing linkage between hearing loss and dementia
Improvements in CIs
Combined electrical and acoustic stimulation for patients with residual hearings
Adaptive signal processing (noisy vs quiet environment)
Remaining gaps in prosthetic hearing
Some users have very poor speech perception
Speech recognition is much more difficult for all CL recipients in adverse noisy hearing conditions
Perception of music mains leusive
Tonal language difficulties
When there is a sensorineural hearing loss (loss of inner hair cells) but the auditory nerve is largely in tack
Brainstem implant- appropriate when there is degeneration of the audiotory nerve
Increased understanding of the nature of sensitive period for language acquisition.
The earlier the better for language outcomes
Still get benefits of CIs for prelingually deaf up to 9 years age
Cochlear LTd (AUSTRALIA)
Advanced bionics (USA)
MED-EL Austria (AUSTRIA)
Graeme clarke (Australia) and William House( USA) made the pioneering studies in 1960 and 1970s
Initial resistance from the CL and signing def community (cultural assimilation)- to young to consent.
Optic nerve stimulation
Visual Cortex sitmiation
BMI use brains signals
Use brain signal features related responses Oscillation that correspond to voluntary though to bypass disabled portions of the nervous system eg the spinal cord and coonnects directly to physical devices for communication or locomtion
Subdural electrodes over motor cortex patient can control computers
BCI invasive (surgically implanted electrode or grids or non invasive EEG,MEG,FMRI,fNIRS assistive or rehabilitation
Motor imagery the same brain are activated using imaginative actions when trying to perform a task.