Since the inception of modern audiometry, infrequent but persistent instances show a patient responding consistently at the lowest audiometric setting. These thresholds have been marked using the standard symbols.
The Massachusetts Eye and Ear Infirmary Department of Audiology (MEEI) began reexamining these occurrences after the recent description of Superior Semicircular Canal Dehiscence and other "third-window" phenomena, where hyper-sensitivity to bone conduction is seen (c.f. Rosowski, et al. Otology and Neurotology 25(3):323-32). MEEI started using an extension of the standard symbols consisting of an upward arrow for designating "Response at Limit" ( Fig. 1 [PDF]).
Besides capturing the fact that these are not standard thresholds (found by ascending), they indicate the use of a more sensitive crossover value for the calculation of masking. Since neither bone nor contralateral air can be lower than the limit, there are no instances of masked air conduction.
MEEI Senior Engineer Peter Marciniak has also developed an alternative symbol for responses found using speakers. It consists of two "F"'s facing in opposite directions from the center of the frequency line. These stand for "field" (sound, not free) and seem to effectively convey the impression that the response is not ear-specific ( Fig. 2 [PDF]).
By making this symbol out of two "F's," it can be separated into right and left to indicate, for example, that the contralateral ear was plugged or masked with an insert (see sidebar [PDF]).
These symbols are one recent result of a wider, 15-year effort at MEEI to develop software that assists the audiologist during testing (as opposed to that developed elsewhere which does a test automatically). For example, the masking calculation mentioned above is continually updated in real time and supports the audiologist in the use of minimal effective masking in every situation as it arises.
These symbols represent new exploratory developments and are not part of the ASHA standard symbol set (ASHA, 1990; 32(Suppl. 2) p. 25-30). In particular, there is a current recommendation for sound field symbols ("S") that is widely accepted. If the developments presented here seem useful to audiologists generally, a further process of discussion and committee evaluation may be warranted. Until then, they are offered as "something new under the sun" for the clinical audiogram.
For a link to ASHA information on Manual Pure Tone audiometry, go to ASHA's Guidelines for Manual Pure-Tone Threshold Audiometry.