Effects of a precursor on amplitude modulation detection are consistent with efferent feedback

The acoustic waveform of speech is characterized by slowly varying amplitude fluctuations (i.e., envelope) and an accurate representation of the envelope is essential for speech understanding. The post-cochlear representation of the contrast between peaks and valleys of the envelope (peak-to-valley contrast) may be reduced by cochlear compression. This study tested (1) whether amplitude modulation (AM) detection thresholds are consistent with cochlear compression and (2) whether the introduction of a precursor before the carrier results in improved AM thresholds, consistent with a decompressed cochlear response via the medial olivocochlear reflex (MOCR). In the no precursor condition, AM thresholds worsen at mid-levels, consistent with reduced peak-to-valley contrast from cochlear compression. In the precursor condition, AM thresholds improved at low modulation frequencies and mid-to-high levels, consistent with a reduction in cochlear amplifier gain and decompression of the cochlear input/output function...