Below is the new audiogram, and then the prior audiogram is shown for comparison.

The new audiogram has this notation in the comments section: “Note: right air not masked – child too fussy to plateau; formula masking not attempted due to the conductive loss in the non-test ear.”

• How much worse is the left ear hearing, as measured by air conduction?
• How much better is the hearing by bone conduction. This may  not be due to test retest variability – why else might the bone conduction scores improve in the presence of conductive loss?
• The right ear bone conduction was not retested.  Would you expect any of the thresholds to have changed as a result of the addition of a conductive component on top of the sensorineural loss?

As noted, the right ear is not masked. That means that the right ear results might be coming from the left ear hearing the “crossover” and the right ear loss might be even worse than shown. When the child was well, the audiologist evidently had used formula masking in obtaining the masked scores. (In formula masking, one does not continually raise the noise to seek the threshold plateau, instead, one calculated level of noise is put into the ear to keep the child from hearing the test tone in the non-test ear.)

Could the air-conduction thresholds for the right ear have been formula masked with care?

A.      At 1000 Hz, the threshold by air conduction in the right ear is 100 dB HL.  Assuming that insert earphones were used, the interaural attenuation might be as little as 50 decibels; the crossed-to-the-left ear’s cochlea sound could be  ___ dB HL.  That could potentially be heard at the left cochlear.

B.     If the audiologist put in 100 dB EM (effective masking) in to the left ear, it would lose some intensity as it passes through the middle ear.  Let’s assume that it loses 40 dB of intensity – the size of the air-bone gap at 1000 Hz.  How loud is the masking noise at the left cochlea? ____ dB EM.

C.    Using your results from steps A and B above, would the noise have masked the crossed over tone?

D.    The 100 dB of effective masking noise in the left ear has the potential to cross back to the test ear (the right ear).  The noise has the same interaural attenuation value as the tone; so it could be as loud as 50 dB at the right ear cochlea.  Would having 50 dB of noise at the right cochlea change the hearing threshold results?