J Am Acad Audiol 2019; 30(08): 659-671
DOI: 10.3766/jaaa.17012
Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Bimodal Cochlear Implant Listeners’ Ability to Perceive Minimal Audible Angle Differences

Ashley Zaleski-King
*   Department of Speech and Hearing Sciences, Gallaudet University, Washington, DC
Matthew J. Goupell
†   Department of Hearing and Speech Sciences, University of Maryland College Park, College Park, MD
Dragana Barac-Cikoja
*   Department of Speech and Hearing Sciences, Gallaudet University, Washington, DC
Matthew Bakke
*   Department of Speech and Hearing Sciences, Gallaudet University, Washington, DC
› Author Affiliations
Further Information

Publication History

31 May 2018

05 June 2018

Publication Date:
25 May 2020 (online)



Bilateral inputs should ideally improve sound localization and speech understanding in noise. However, for many bimodal listeners [i.e., individuals using a cochlear implant (CI) with a contralateral hearing aid (HA)], such bilateral benefits are at best, inconsistent. The degree to which clinically available HA and CI devices can function together to preserve interaural time and level differences (ITDs and ILDs, respectively) enough to support the localization of sound sources is a question with important ramifications for speech understanding in complex acoustic environments.


To determine if bimodal listeners are sensitive to changes in spatial location in a minimum audible angle (MAA) task.

Research Design:

Repeated-measures design.

Study Sample:

Seven adult bimodal CI users (28–62 years). All listeners reported regular use of digital HA technology in the nonimplanted ear.

Data Collection and Analysis:

Seven bimodal listeners were asked to balance the loudness of prerecorded single syllable utterances. The loudness-balanced stimuli were then presented via direct audio inputs of the two devices with an ITD applied. The task of the listener was to determine the perceived difference in processing delay (the interdevice delay [IDD]) between the CI and HA devices. Finally, virtual free-field MAA performance was measured for different spatial locations both with and without inclusion of the IDD correction, which was added with the intent to perceptually synchronize the devices.


During the loudness-balancing task, all listeners required increased acoustic input to the HA relative to the CI most comfortable level to achieve equal interaural loudness. During the ITD task, three listeners could perceive changes in intracranial position by distinguishing sounds coming from the left or from the right hemifield; when the CI was delayed by 0.73, 0.67, or 1.7 msec, the signal lateralized from one side to the other. When MAA localization performance was assessed, only three of the seven listeners consistently achieved above-chance performance, even when an IDD correction was included. It is not clear whether the listeners who were able to consistently complete the MAA task did so via binaural comparison or by extracting monaural loudness cues. Four listeners could not perform the MAA task, even though they could have used a monaural loudness cue strategy.


These data suggest that sound localization is extremely difficult for most bimodal listeners. This difficulty does not seem to be caused by large loudness imbalances and IDDs. Sound localization is best when performed via a binaural comparison, where frequency-matched inputs convey ITD and ILD information. Although low-frequency acoustic amplification with a HA when combined with a CI may produce an overlapping region of frequency-matched inputs and thus provide an opportunity for binaural comparisons for some bimodal listeners, our study showed that this may not be beneficial or useful for spatial location discrimination tasks. The inability of our listeners to use monaural-level cues to perform the MAA task highlights the difficulty of using a HA and CI together to glean information on the direction of a sound source.

This study was partially supported by NIH-NIDCD Grant R01 DC014948 (M.J.G.).


  • Armstrong M, Pegg P, James C, Blamey P. 1997; Speech perception in noise with implant and hearing aid. Am J Otol 18 (6, Suppl) S140-S141
  • Aronoff JM, Freed DJ, Fisher LM, Pal I, Soli SD. 2011; The effect of different cochlear implant microphones on acoustic hearing individuals’ binaural benefits for speech perception in noise. Ear Hear 32 (04) 468
  • Bernstein JG, Goupell MJ, Schuchman GI, Rivera AL, Brungart DS. 2016; Having two ears facilitates the perceptual separation of concurrent talkers for bilateral and single-sided deaf cochlear implantees. Ear Hear 37 (03) 289
  • Brown CA. 2013; Binaural enhancement for bilateral cochlear implant users. Ear Hear 35 (05) 580-584
  • Brughera A, Dunai L, Hartmann WM. 2013; Human interaural time difference thresholds for sine tones: the high-frequency limit. J Acoust Soc Am 133 (05) 2839-2855
  • Ching TY, Dillon H. 2003; Prescribing amplification for children: adult-equivalent hearing loss, real-ear aided gain, and NAL-NL1. Trends Amplif 7 (01) 1-9
  • Ching TYC, Incerti P, Hill M. 2004; Binaural benefits for adults who use hearing aids and cochlear implants in opposite ears. Ear Hear 25: 9-21
  • Ching TYC, Van Wanrooy E, Dillon H. 2007; Binaural-bimodal fitting or bilateral implantation for managing severe to profound deafness: a review. Trends Amplif 11 (03) 161-192
  • Crew JD, Galvin III JJ, Landsberger DM, Fu QJ. 2015; Contributions of electric and acoustic hearing to bimodal speech and music perception. PLoS One 10 (03) e0120279
  • Devocht EM, Janssen AML, Chalupper J, Stokroos RJ, George EL. 2017; The benefits of bimodal aiding on extended dimensions of speech perception: intelligibility, listening effort, and sound quality. Trends Hear 21: 2331216517727900
  • Dorman MF, Gifford RH. 2010; Combining acoustic and electric stimulation in the service of speech recognition. Int J Audiol 49 (12) 912-919
  • Dorman MF, Loiselle LH, Cook SJ, Yost WA, Gifford RH. 2016; Sound source localization by normal-hearing listeners, hearing-impaired listeners and cochlear implant listeners. Audiol Neurotol 21 (03) 127-131
  • Dunn C, Tyler R, Witt S. 2005; Benefit of wearing a hearing aid on the unimplanted ear in adult users of a cochlear implant. J Speech Lang Hear Res 48: 668-680
  • Feddersen WE, Sandel TT, Teas DC, Jeffress LA. 1957; Localization of high‐frequency tones. J Acoust Soc Am 29 (09) 988-991
  • Francart T, Van den Bogaert T, Moonen M, Wouters J. 2009; a Amplification of interaural level differences improves sound localization in acoustic simulations of bimodal hearing. J Acoust Soc Am 126 (06) 3209-3213
  • Francart T, Brokx J, Wouters J. 2009; b Sensitivity to interaural time differences with combined cochlear implant and acoustic stimulation. J Assoc Res Otolaryngol 10 (01) 131-141
  • Francart T, Lenssen A, Wouters J. 2011; a Enhancement of interaural level differences improves sound localization in bimodal hearing. J Acoust Soc Am 130 (05) 2817-2826
  • Francart T, Lenssen A, Wouters J. 2011; b Sensitivity of bimodal listeners to interaural time differences with modulated single-and multiple-channel stimuli. Audiol Neurotol 16 (02) 82-92
  • Francart T, Lenssen A, Wouters J. 2014; Modulation enhancement in the electrical signal improves perception of interaural time differences with bimodal stimulation. J Assoc Res Otolaryngol 15 (04) 633-647
  • Francart T, McDermott HJ. 2013; Psychophysics, fitting, and signal processing for combined hearing aid and cochlear implant stimulation. Ear Hear 34 (06) 685-700
  • Francart T, Wouters J. 2007; Perception of across-frequency interaural level differences. J Acoust Soc Am 122 (05) 2826-2831
  • Fu QJ, Chinchilla S, Galvin JJ. 2004; The role of spectral and temporal cues in voice gender discrimination by normal-hearing listeners and cochlear implant users. J Assoc Res Otolaryngol 5 (03) 253-260
  • Fu QJ, Nogaki G, Galvin JJ. 2005; Auditory training with spectrally shifted speech: implications for cochlear implant patient auditory rehabilitation. J Assoc Res Otolaryngol 6 (02) 180-189
  • Gfeller K, Turner C, Oleson J, Zhang X, Gantz B, Froman R, Olszewski C. 2007; Accuracy of cochlear implant recipients on pitch perception, melody recognition, and speech reception in noise. Ear Hear 28: 412-423
  • Goupell MJ. 2015; Interaural envelope correlation change discrimination in bilateral cochlear implantees: effects of mismatch, centering, and onset of deafness. J Acoust Soc Am 137 (03) 1282-1297
  • Goupell MJ, Stoelb C, Kan A, Litovsky RY. 2013; Effect of mismatched place-of- stimulation on the salience of binaural cues in conditions that simulate bilateral cochlear- implant listening. J Acoust Soc Am 133 (04) 2272-2287
  • Hamzavi J, Marcel Pok S, Gstoettner W, Baumgartner WD. 2004; Speech perception with a cochlear implant used in conjunction with a hearing aid in the opposite ear. Int J Audiol 43 (02) 61-65
  • Hillenbrand J, Getty LA, Clark MJ, Wheeler K. 1995; Acoustic characteristics of American English vowels. J Acoust Soc Am 97 (05) 3099-3111
  • Kayser H, Ewert SD, Anemuller J, Rohdenburg T, Hohmann V, Kollmeier B. 2009; Database of multichannel in-ear and behind-the-ear head-related and binaural room impulse responses. EURASIP J Adv Signal Process 2009: 1-10
  • Kokkinakis K, Pak N. 2014; Binaural advantages in users of bimodal and bilateral cochlear implant devices. J Acoust Soc Am 135 (01) EL47-EL53
  • Kwon BJ. 2012; AUX: a scripting language for auditory signal processing and software packages for psychoacoustic experiments and education. Behav Res Methods 44 (02) 361-373
  • Landsberger DM, Svrakic Svrakic J, Svirsky M. 2015; The relationship between insertion angles, default frequency allocations, and spiral ganglion place pitch in cochlear implants. Ear Hear 36 (05) e207-e213
  • Lenssen A, Francart T, Brokx J, Wouters J. 2011; Bimodal listeners are not sensitive to interaural time differences in unmodulated low-frequency stimuli (L). J Acoust Soc Am 129 (06) 3457-3460
  • Litovsky RY, Jones GL, Agrawal S, van Hoesel R. 2010; Effect of age at onset of deafness on binaural sensitivity in electric hearing in humans. J Acoust Soc Am 127: 400-414
  • Macaulay EJ, Hartmann WM, Rakerd B. 2010; The acoustical bright spot and mislocalization of tones by human listeners. J Acoust Soc Am 127 (03) 1440-1449
  • Macpherson EA, Middlebrooks JC. 2002; Listener weighting of cues for lateral angle: the duplex theory of sound localization revisited. J Acoust Soc Am 111 (05) 2219-2236
  • Majdak P, Goupell MJ, Laback B. 2011; Two-dimensional localization of virtual sound sources in cochlear-implant listeners. Ear Hear 32 (02) 198-208
  • Mills AW. 1958; On the minimum audible angle. J Acoust Soc Am 30 (04) 237-246
  • Mills AW. 1959; Thresholds for interaural difference in intensity. J Acoust Soc Am 31 (06) 830
  • Morera C, Manrique M, Ramos A, Garcia-Ibanez L, Cavalle L, Huarte A, Estrada E. 2005; Advantages of binaural hearing provided through bimodal stimulation via a cochlear implant and a conventional hearing aid: a 6-month comparative study. Acta Otolaryngol 125 (06) 596-606
  • Most T, Gaon-Sivan G, Shpak T, Luntz M. 2011; Contribution of a contralateral hearing aid to perception of consonant voicing, intonation, and emotional state in adult cochlear implantees. J Deaf Stud Deaf Educ 17 (02) 244-258
  • Nittrouer S, Chapman C. 2009; The effects of bilateral electric and bimodal electric—acoustic stimulation on language development. Trends Amplif 13 (03) 190-205
  • Olson AD, Shinn JB. 2008; A systematic review to determine the effectiveness of using amplification in conjunction with cochlear implantation. J Am Acad Audiol 19 (09) 657-671
  • Potts LG, Litovsky RY. 2014; Transitioning from bimodal to bilateral cochlear implant listening: speech recognition and localization in four individuals. J Am Acad Audiol 23 (01) 79-92
  • Potts LG, Skinner MW, Litovsky RA, Strube MJ, Kuk F. 2009; Recognition and localization of speech by adult cochlear implant recipients wearing a digital hearing aid in the nonimplanted ear (bimodal hearing). J Am Acad Audiol 20 (06) 353-373
  • Sampaio AL, Araújo MF, Oliveira CA. 2011; New criteria of indication and selection of patients to cochlear implant. Int J Otolaryngol 2011: I573968
  • Schafer EC, Amlani AM, Paiva D, Nozari L, Verret S. 2011; A meta-analysis to compare speech recognition in noise with bilateral cochlear implants and bimodal stimulation. Int J Audiol 50 (12) 871-880
  • Seeber B, Baumann U, Fastl H. 2004; Localization ability with bimodal hearing aids and bilateral cochlear implants. J Acoust Soc Am 116: 1698-1709
  • Shallop JK, Arndt PL, Turnacliff KA. 1992; Expanded indications for cochlear implantation: perceptual results in seven adults with residual hearing. J Speech-Language Pathol Audiol 16 (02) 141-148
  • Shaw EAG, Vaillancourt MM. 1985; Transformation of sound-pressure level from the free field to the eardrum presented in numerical form. J Acoust Soc Am 78: 1120-1123
  • Shub DE, Carr SP, Kong Y, Colburn HS. 2008; Discrimination and identification of azimuth using spectral shape. J Acoust Soc Am 124 (05) 3132-3141
  • Stevens SS, Newman EB. 1936; The localization of actual sources of sound. Am J Psychol 48 (02) 297-306
  • Stone MA, Moore BC. 1999; Tolerable hearing aid delays. I. Estimation of limits imposed by the auditory path alone using simulated hearing losses. Ear Hear 20 (03) 352-388
  • Stone MA, Moore BC. 2003; Tolerable hearing aid delays. III. Effects on speech production and perception of across-frequency variation in delay. Ear Hear 24 (02) 175-183
  • Sucher CM, McDermott HJ. 2009; Bimodal stimulation: benefits for music perception and sound quality. Cochlear Implants Int 10 (S1) 96-99
  • Svirsky MA, Silveira A, Neuburger H, Teoh SW, Suarez H. 2004; Long-term auditory adaptation to a modified peripheral frequency map. Acta Otolaryngol 124 (04) 381-386
  • van Hoesel RJ. 2012; Contrasting benefits from contralateral implants and hearing aids in cochlear implant users. Hear Res 288 (01) 100-113
  • Veugen LC, Chalupper J, Snik AF, van Opstal AJ, Mens LH. 2016; a Matching automatic gain control across devices in bimodal cochlear implant users. Ear Hear 37 (03) 260-270
  • Veugen LC, Hendrikse MM, van Wanrooij MM, Agterberg MJ, Chalupper J, Mens LH, van Opstal AJ. 2016; b Horizontal sound localization in cochlear implant users with a contralateral hearing aid. Hear Res 336: 72-82
  • Von Ilberg CA, Baumann U, Kiefer J, Tillein J, Adunka OF. 2011; Electric-acoustic stimulation of the auditory system: a review of the first decade. Audiol Neurotol 16 (2, Suppl) 1-30
  • Wightman FL, Kistler DJ. 1992; The dominant role of low‐frequency interaural time differences in sound localization. J Acoust Soc Am 91 (03) 1648-1661
  • Zhang T, Spahr AJ, Dorman MF, Saoji A. 2013; The relationship between auditory function of non-implanted ears and bimodal benefit. Ear Hear 34: 133-141