Audio Traveler AA222, Operation Manuals, Page: 17 / 141

AA222 Operation Manual Page 17
present when the Stapedius muscle is active is recorded as a
reflex. If, however, external noise was entering the ear only
during reference level measurement, and not during reflex
measurement, the level may actually be lower during the reflex,
thus resulting in a negative reflex. This is of course not a valid
measurement. The negative reflex is an extreme situation, but
noise will always distort the measurements to a certain degree
and should therefore be avoided.
Negative Onset:
It is quite common to see reflexes start out with a small negative
deflecting dip. In ears with stapedial otosclerosis this dip with an
additional dip at the end of the stimulation can be the only
reaction left from the contraction of the Stapedius muscle. Some
tumour ears have been reported to give only the negative onset,
but no further reaction.
Reflex Threshold:
For a given stimulus the lowest level that elicits a detectable
reflex. This is not an absolute measurement as no exhausting
norm exits defining stimuli and related reflex characteristics.
Therefore, differences in test setups and reflex evaluation will
produce somewhat different results. It is not uncommon to
report the reflex threshold as the intensity which produces a 1%
or 2% change in equivalent volume (Test "A" with 2%
sensitivity).
It should be noted that a visual examining of reflex test might
reveal some Stapedius muscle action, also at slightly lower
stimulus intensities. This procedure (see "Example of Popular
Fixed Intensity Reflex Test") is recommended for establishing
the absolute reflex threshold.
Generally, noise stimuli elicit reflexes at lower levels than pure
tones do.