INFLUENCE OF CONTRALATERAL NOISE ON DISTORTION-PRODUCT LATENCY IN HUMANS - IS THE MEDIAL OLIVOCOCHLEAR EFFERENT SYSTEM INVOLVED

To test the hypothesis of temporal modifications of cochlear responses when medial efferents are activated, otoacoustic emission latencies w ere estimated in 16 normal human subjects, in the presence and absence of a contralateral broadband noise, using measurements of the phase o f the 2f1-f2 distortion product (group latency method). Significant de crease in the latency of lower frequency (0.8-2.7 kHz) emissions was f ound in the presence of increasing levels of contralateral sound, and this effect disappeared when the primary-tone levels increased to 60 d B SPL. To ensure that effects were not attributable to mechanisms invo lving middle ear structures, susceptible to activation by contralatera l sound, latency measures were performed in seven subjects whose effer ents were severed during a vestibular neurotomy and in two subjects wi th paralyzed stapedial muscle. Results in patients were compared to th ose obtained in three surgical control patients with intact efferent b undle, and in eight other normal subjects. All the subject groups exhi bited a decrease in latency under contralateral sound except the patie nts with the severed efferent system who showed increased latencies. ( C) 1997 Acoustical Society of America. [S0001-4966(97)02909-3] PACS nu mbers: 43.64.Jb, 43.64.Wn [RDF].