Having proved that an occlusion effect occurs independently of a conductive loss, we then introduced background noise to assess its influence. In both instances the bone conduction thresholds improved by 15 dB. The ears were then occluded with foam “ear defenders,” which caused a 25 dB conductive impairment. Both ears were occluded with modified tympanometry earpieces (blocked with plasticine), without causing a measurable conductive loss.

Baseline binaural air and bone thresholds were obtained at 500 Hz on a subject in a soundproof audiometric booth. We conducted an experiment to determine whether the exclusion of environmental noise or the occlusion effect was responsible for Weatherall's observation. When the ear is occluded, these frequencies cannot escape and the sound seems to become louder. Some lower frequency sound, as produced by the 512 Hz tuning fork, escapes from the canal. 1-3 Sound conducted through bone causes the cochlea, the ossicular chain, and the air in the external auditory canal to vibrate. The so called occlusion effect described by Tonndorf et al in 1966 is responsible for this phenomenon.

A normal conductive mechanism is demonstrated if the sound is heard again when the ear canal is occluded. A tuning fork is placed on the skull, and the patient indicates when the sound disappears. The simulation of conductive hearing impairment by occluding the ear with a finger suggested by Weatherall is the basis of the Bing test. 1-1 Literature searches and audiological experiments were conducted. Nice little study for a neurologist, I say.Įditor-Weber's test is indeed mysterious, and the filler by Weatherall had our ear, nose, and throat department, as well as an eminent visiting professor from Glasgow, occupied for the best part of a week. You could test this by blocking your ear with one finger and the other with another material, comparing the sounds and comparing each with air. If both ears are blocked but with different materials with different conductive properties, positive results in Weber's test would localise to the side with the denser and therefore better sound conducting material. Less energy is lost, and the sound is localised to that side in Weber's test. If you have a more solid (denser) object in the ear (which would have resulted in conduction deafness (as defined by doctors) the sound conduction is actually better. The resultant sound energy to the inner ear is therefore less. The air medium in the ear, being a less efficient transmitter of sound, results in sound energy loss at the interface of bone and air. The conduction being tested is that through bone to the inner ear.

When the tuning fork is placed directly on the bone, there is no significant sound transmission from the tuning fork directly through the air.

It is, however, clear to any engineering student that bone or any denser object is a better conductor of sound than is air. This makes air a better sound conductor (when defined this way) than a solid object. The sound is normally conducted (transmitted) through the air through the external ear into the middle ear. Everything apart from the sensorineural aspect of the hearing is thought to be conductive. The word conduction is used confusingly by ear, nose, and throat surgeons and neurologists to describe normal transmission of sound from the outside world to the ear. Editor-Weatherall's mystery-a positive Weber's test in the normal ear in unilateral sensorineural hearing loss but in the affected ear in unilateral conductive hearing loss-has baffled many neurologists and ear, nose, and throat surgeons for some time I wonder whether my explanation would convince him.

Weber test ear