Evaluating speech-like distortion product otoacoustic emissions: a comparison of time- and frequency-domain metrics across three datasets

Abstract

Speech-like distortion-product otoacoustic emissions (DPOAEs) allow cochlear activity to be measured during the perception of natural, continuous speech and have been used to study attentional effects in the cochlea. The technique is still young, however, and existing studies differ in stimulus design and in the metric used to quantify the emissions, which makes their results difficult to compare. Here, we reanalysed three existing datasets (106 participants, 14 stimulus types) with a common pipeline. We compared six metrics: the band power of the recording, the magnitude-squared coherence (MSC) between the recording and a DPOAE template, and four metrics derived from their complex cross-correlation, namely peak magnitude, signal-to-noise ratio (SNR), peak area and peak width. A separability index quantified how well each metric separated in-ear recordings from out-of-ear control recordings without emissions. Band power, MSC and SNR separated best, with mean separability indices of about 0.9, whereas the peak magnitude performed worst and was inverted for half of the stimulus types. Since band power does not require a DPOAE template, it serves as a sanity check of the setup rather than as evidence for an emission. The MSC was insensitive to the latency of the emission but well suited for comparisons across stimuli, whereas the cross-correlation additionally provided the latency. The emissions differed significantly between the stimulus types of the three datasets, and those below about 700 Hz were measured least reliably. We derive practical recommendations for the analysis and stimulus design of future experiments.