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SLAC: Virtual Masking Documentation
I. Table of Contents
I. Table of Contents
II. Introduction
III. Project Partner
IV. Sound and the Ear
a. Biology of the Ear
b. Disease Pathologies
V. Masking
a. Audiograms
b. Patient History
c. Test Procedures
d. Plateau Method & Plots
VI. Project Basics
a. Getting Started With Open Source
b. Introduction to C# and Visual Studio .NET
c. C# and Visual Studio .NET Skill Session
d. Core C# and .NET Quick Reference
VII. Virtual Project Tutorials
a. Creating New Graphics
II. Introduction
The Speech Language Audiology Clinic team (part of Engineering Projects in Community Service at Purdue University) serves the M.D. Steer Audiology Clinic, located in the basement of Heavilon Hall on Purdue’s campus. Members are Purdue students from many disciplines who work in conjunction with assistant professor in Speech Language Hearing Sciences Dr. Joshua Alexander to solve the unique problems the clinic faces. Purdue academics make use of the clinic, but it also functions as a private medical facility. The widespread impact the clinic has on the community makes it a perfect organization to benefit from personalized engineering projects.
One of the projects for the spring 2011 semester will be the SLAC virtual masking project. The virtual project has been worked on close to a decade now with the first completed version being delivered in the fall 2010 semester. The goal for this group is to improve upon the delivered version of the program by adding new patient images, improving graphics, and adding randomization to current features.
The Virtual Masking Project is a simulation of a hearing loss test, from the perspective of the proctor. The software will directly benefit audiology students who are learning about the testing process and the different types of hearing loss. A real human with a certain hearing condition would be ideal to test on, but some of the conditions are rare or they won’t agree to be a subject. Thus the software will be an excellent tool for getting students exposure to many kinds of hearing loss. The basic design and functionality were previously determined by Dr. Novak and currently under the supervision of Dr. Alexander, who has a good vision of the final working version.
Specification Development
This software will be used for teaching audiology students the testing process for hearing loss through a direct simulation. Overall, the software needs to mimic the real life process as closely as possible. For the purpose that someone using our program must be able to:
· Provide a stimulus and masking
· See a patient response
· Plot a hearing assessment
· Generate a plateau plot
· Have enough data to properly determine the virtual patient’s hearing condition
· Create a report of that test for professor/TA grading
The base criteria were first determined by Dr. Novak, which were then specified by our group. Many of the previous software versions followed this blueprint. The requirements are fairly simple and have a straightforward software implementation. The requirements specified are:
· Clickable photo of a physical audiometer
· Plot-able hearing assessment graph (blank template is provided)
· A picture of a human patient (wearing stimulus device if applicable)
· Plateau Plot
· End of test review/comparison with “correct” answer and/or grade report
· Hints/info for next time
Now the goal is to improve the project with as many realistic and innovative functions that the project partner specifies until it becomes the ideal project that the project partner desires.
III. Project Partner
Our previous project partner was Dr. Robert Novak, the former head of the M.D. Steer Audiology Clinic. A new project partner, Professor Alexander, joined the SLAC team this semester. The main role that the project partner has in the virtual project is to provide feedback and suggestions of ideal functions that the project could possess. Communications with the project partner either through email or physical meetings are important to keep track of during the semester.
IV. Sound and the Ear
A. Biology of the Ear
Sound is a form of energy that moves through air, water, and other matter, in waves of pressure. Sound is the means of auditory communication, including frog calls, bird songs and spoken language. Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central nervous system that "hears". Sound waves are perceived by the brain through the firing of nerve cells in the auditory portion of the central nervous system. The ear changes sound pressure waves from the outside world into a signal of nerve impulses sent to the brain. The human ear can generally hear sounds with frequencies between 20 Hz to 20 kHz.
The outer part of the ear collects sound. This outer ear includes the pinna, the ear canal, and the tympanic membrane. This portion of the ear is vital for hearing. The outer ear does help get sound and impose filtering, but the ear canal is very important. Unless the canal is open, hearing will be dampened. The outer ear ends at the most superficial layer of the tympanic membrane. The tympanic membrane is commonly called the eardrum.
The middle ear, an air-filled cavity beginning at the inner portion of the ear drum, includes the three ear bones or ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup). The malleus has a long process (the manubrium, or handle) that is attached to the mobile portion of the eardrum. The incus is the bridge between the malleus and stapes. The stapes is the smallest named bone in the human body. The three bones are arranged so that movement of the tympanic membrane causes movement of the malleus, which causes movement of the incus, which causes movement of the stapes. When the stapes footplate pushes on the oval window, it causes movement of fluid within the cochlea (a portion of the inner ear). These ossicles function to transmit energy, facilitating the transfer of energy from acoustic energy at the eardrum to mechanical at the ossicles to hydrolic in the cochlea.
The middle ear, like the ear canal, is filled with air. Unlike the open ear canal, however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The Eustachian tube connects from the chamber of the middle ear to the back of the nasopharynx and equalizes pressure between the atmosphere and the middle ear cavity.
After that sound pressure is amplified through the middle ear, it reaches the inner ear. The inner ear, embedded in the temporal bone, is filled with fluid and contains a sensory epithelium that is lined with hair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are receptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments, triggering nerve impulses. The nerve impulses travel from the left and right ears through the eighth cranial nerve to both sides of the brain stem and up to the portion of the cerebral cortex dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe.
A conductive hearing loss refers to a hearing loss caused by an abnormality in the outer ear or the middle ear. Possible causes include a blocked ear canal, perforations in the eardrum, irregular ossicles, or fluid in the middle ear.
Sensorineural hearing loss refers to a hearing loss occurring due to abnormalities in the inner ear, along the neural path, or the auditory cortex.
B. Disease Pathologies
Presbycusis: (Older adults)
Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow older. The loss associated with presbycusis is usually greater for high frequency sounds. Presbycusis most often occurs in both ears simultaneously. Because the loss of hearing is so gradual, people with presbycusis may not realize that their hearing is diminishing, and may have trouble understanding conversation in background noise. Presbycusis is caused by cumulative factors, including repeated daily noise exposure, hereditary factors, health conditions, effects of medicine, and changes in blood supply to the ear, which all are related to aging. Presbycusis is common, affecting a third of people between 65 and 75 years, and up to half of people 75 and over. (NIDCD)
Noise-induced trauma: (More common in adults)
This refers to permanent cochlear damage from a one-time exposure to excessive sound pressure. This hearing loss commonly results from exposure to high-intensity sounds such as explosions, gun fire, and firecrackers.
Meniere’s Disease: (All ages and genders, more likely adults ages 40-60*)
A disorder of the inner ear which causes episodes of vertigo, ringing in the ears, a feeling of fullness or pressure in the ear, and fluctuating hearing loss. A low-frequency sensioneural pattern is commonly found initially, but as time goes on, it usually changes into a flat loss. Meniere’s Disease usually starts confined to one ear but it often extends to involve both ears over time. *NIDCD
Microtia with Atresia: (Present at birth)
Microtia refers to a small, abnormally shaped or absent external ear and Atresia involves an extremely narrow or absent external ear canal. It can affect one or both sides.
Otosclerosis: (More common in women, Ages 15 – 45*)
The cause of otosclerosis is unknown, but there appears to be a hereditary component. In otosclerosis, an abnormal sponge-like bone grows in the middle ear, which prevents the ear from vibrating in response to sound waves. This lack of vibration leads to hearing loss that continues to get worse with time. The hearing loss is characteristically low-frequency, with higher frequencies being affected later as the disease progresses. Otosclerosis can lead to not only conductive hearing loss, but to nerve and sensory cell loss as well, causing a sensorineural hearing loss. In addition to hearing loss, some people with otosclerosis may experience dizziness, balance problems, or tinnitus.
Otosclerosis is the most frequent cause of middle ear hearing loss in young adults, and affects about 10% of the U.S. population. It is a disorder that gets worse slowly, usually beginning in early to mid- adulthood. It is more common in women than in men. Otosclerosis usually affects both ears. Risks include pregnancy (which may trigger onset) and a family history of hearing loss. Caucasians are more susceptible than others to Otosclerosis (PubMedHealth).
*entnet.org
Otitis media: (more common in Children)
Inflammation of the middle ear characterized by the accumulation of fluid, bulging of the eardrum, pain in the ear and, drainage of purulent material into the ear canal (if the ear drum has ruptured). Otitis media is the most frequent diagnosis in sick children in the U.S., especially affecting infants and preschoolers. Almost all children have one or more bouts of otitis media before age 6. Eustachian tube dysfunction, or inability to open appropriately and equalize pressure is a common cause of otitis media. In children, the eustachian tube is shorter than in adults and is positioned at an adverse angle for appropriate opening and ventilation.
Young children with otitis media may be irritable, fussy, or have problems feeding or sleeping. Older children may complain about pain and fullness in the ear. Fever may be present in a child of any age. These symptoms are often associated with signs of upper respiratory infection, with a runny or stuffy nose or a cough.
The buildup of fluid within the middle ear can cause pain and dampens the vibrations of the eardrum, which can create a temporary low-frequency hearing loss. The treatment for acute otitis media is antibiotics usually for 7-10 days. About 10% of children do not respond within the first 48 hours of treatment. Even after antibiotic treatment, 40% of children are left with some fluid in the middle ear which can cause temporary hearing loss lasting for up to 3-6 weeks. In most children, the fluid eventually disappears on its own. Children who have recurring bouts of otitis media may have a pressure equalization tube placed into the ear to permit air pressure equalization that the Eustachian tube cannot provide.
Acoustic neuroma (tumor): (Adults)
A benign tumor that may develop on the nerves near the inner ear affecting hearing and balance. The tumor results from an overproduction of Schwann cells, which are small, sheet-like cells that normally wrap around nerve fibers and help support them. The abundance of Schwann cells press against the hearing and balance nerves, often causing gradual hearing loss, tinnitus, (ringing in the ears), and dizziness. If the tumor becomes large, it can interfere with the (VII) facial nerve, causing partial paralysis, and eventually press against nearby brain structures, becoming life-threatening. The most common first indication of an acoustic neuroma is hearing loss, which is often accompanied by tinnitus. People with acoustic neuromas sometimes report difficulties in using the phone and difficulties in perceiving the tone of a musical instrument or sound even when their hearing appears to be otherwise normal. In most cases the hearing loss is initially subtle, but worsens gradually over time until deafness occurs in the affected ear. In approximately 10% of cases the hearing loss is sudden and severe. An acoustic neuroma is suspected in someone with unilateral hearing loss or hearing loss that is less severe in one ear than the other ear (asymmetrical).
Ossicular Discontinuity: (More common in women, all ages)
As the conduction of sound from the outer ear to the inner ear is dependent on the bones of hearing or ossicles, a disruption of the ossicles will result in conductive hearing loss.
In situations such as trauma or infection, any of the ossicles may be affected.
In cases of severe head trauma, the connection between the incus and stapes, which is fragile, can be separated. In other cases, the incus bone itself is fractured producing a separation between the incus and the stapes.
With recurrent ear infections or in conditions such as cholesteatoma, the tip of the incus at its point of connection with the stapes is eroded resulting in a separation between the incus and stapes. With infection, the stapes bone itself can be eroded leaving only the platform by which it is in connection with the inner ear.
The conductive hearing loss that results from the lack of continuity of the ossicles can be surgically treated.
V. MASKING
Masking is defined as the process of introducing noise in the non-test ear (NTE) to prevent it from responding to the test signal presented in the opposite test ear (TE). The types of noises used in masking include: narrow-band noise for pure tone audiometry and speech noise for speech audiometry. Masking is necessary whenever the interaural attenuation between the test ear and non-test ear is exceeded.