Otoacoustic emissions recorded at rapid stimulus rates

Otoacoustic emissions were evoked by clicks presented according to maximum length sequences. The analysis disentangled the overlapping responses that occur when stimuli are presented at intervals shorter than the duration of the response. Two types of sequence were used: a "monopolar" sequence in which clicks were present or absent, and a "bipolar" sequence in which both condensation and rarefaction clicks occurred. Emissions can be recorded at stimulus rates of up to 1000/sec although the amplitude of the response decreases at these rapid rates. This decrease in amplitude requires a compensatory increase in the number of stimuli to maintain the same signal-to-noise ratio. Optimal efficiency can be attained at rates between 200 and 500/sec. At these rates the emissions can be recorded in about one half the time required for conventional averaging at regular rates of 50/sec.