Binaural hearing has been shown to support better speech perception in normal-hearing listeners than can be achieved with monaural stimulus presentation, particularly under noisy listening conditions. The purpose of this study was to evaluate whether bilateral electrical stimulation could confer similar benefits for cochlear implant listeners.
A total of 26 postlingually deafened adult patients with short duration of deafness were implanted at five centers and followed up for 1 yr. Subjects received MED-EL COMBI 40+ devices bilaterally; in all but one case, implantation was performed in a single-stage surgery. Speech perception testing included CNC words in quiet and CUNY sentences in noise. Target speech was presented at the midline (0 degrees), and masking noise, when present, was presented at one of three simulated source locations along the azimuth (−90, 0, and +90 degrees).
Benefits of bilateral electrical stimulation were observed under conditions in which the speech and masker were spatially coincident and conditions in which they were spatially separated. Both the “head shadow” and “summation” effects were evident from the outset. Benefits consistent with “binaural squelch” were not reliably observed until 1 yr after implantation.
These results support a growing consensus that bilateral implantation provides functional benefits beyond those of unilateral implantation. Longitudinal data suggest that some aspects of binaural processing continue to develop up to 1 yr after implantation. The squelch effect, often reported as absent or rare in previous studies of bilateral cochlear implantation, was present for most subjects at the 1 yr measurement interval.
The purpose of this study was to evaluate functional benefits associated with bilateral cochlear implantation. Speech perception was assessed in 26 post-lingually deafened adults receiving MED-EL COMBI 40+ devices bilaterally, with testing over one year post-implantation. Binaural stimulus presentation was superior to monaural presentation for CNC words in quiet and under several spatial configurations of CUNY sentences in noise. In most cases substantial benefit was found at the first measurement point. Binaural squelch, thought to reflect `true' binaural processing, was not reliably observed until 1 year post-implantation, suggesting that some aspects of binaural hearing may undergo prolonged development.
1Department of Otolaryngology/Head and Neck Surgery, University of North Carolina School of Medicine, Chapel Hill, North Carolina; 2Vanderbilt Bill Wilkerson Center for Otolaryngology and Communication Sciences, Vanderbilt University School of Medicine, Nashville, Tennessee; 3Department Otolaryngology/Head and Neck Surgery, University of Texas Southwestern, Dallas, Texas; 4ECHO program at Carle Foundation Hospital, Urbana, Illinois; 5Dallas Otolaryngology Associates, Dallas, Texas; 6Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, Wisconsin; 7Research Triangle Institute, Research Triangle Park, North Carolina; 8MED-EL Corporation, Innsbruck, Austria.
Address for correspondence: Emily Buss, Department of Otolaryngology/Head and Neck Surgery, Chapel Hill, NC 27599.E-mail: firstname.lastname@example.org.
Received September 16, 2006; accepted June 18, 2007.