Let’s look at two things with this frequency. First, the latencies of wave V. While 500 Hz gave 13-18 ms wave V latencies, at 2000 Hz they are earlier, 7-10 ms. Because the period of 2000 Hz is shorter than 500 Hz, the same two cycle rise time is shorter: the tone turns on more quickly, the response is evoked more quickly. A more basal area of the cochlea is stimulated – so we expect shorter latencies.

Next, lets look at how to read the details below the trace.
Wave 1 is the right ear testing at 60 dB nHL. Stim = inst means insert earphones. 2000_HzStape is a tone burst recommended by David Stapell’s lab. Next the number of sweeps acquired, and the number rejected due to myogenic noise contamination are shown. 2048 sweeps were averaged, and 1 was rejected. This child was sedated, so the low number of sweeps rejected is typical (and good). The rate was 27.1 tone pips per second; all of these traces were conducted using condensation polarity tone pips. PPAmp is the peak to peak amplitude of the response. If you want to learn about the residual noise and signal to noise ratio, search for David Stapell’s website and his great resources. Note, though that the proper time frame has to be analyzed for those numbers to be meaningful, and you cannot assume that the analysis regions were set correctly in these case studies. The audiologists were using visual analysis, not the computer analysis.

The gain is 100,000 times amplification, and filtering is 30-3000 Hz. That last point is important. You can obtain “prettier” ABRs by filtering it more. If you reduce the high cut to 1500 Hz, the waves would smooth out. You would remove this sort of noise. (You might also lose a little of the overall amplitude of the response.)

To reduce myogenic noise, you can filter away the low frequencies, e.g. 100-3000 Hz, but that is not a good idea when testing children, particularly with low frequency stimuli. That does reduce the broad low trough that typifies the response.

• At which intensity(s) for which ear(s) did the audiologist use fewer than 2048 sweeps per run, and why do you think she did that?