Forward-masked spatial tuning curves in cochlear implant users

• Published in: The Journal of the Acoustical Society of America Vol. 123; no. 3; pp. 1522 - 1543
• Main Authors: Nelson, David A., Donaldson, Gail S., Kreft, Heather
• Format: Journal Article
• Language: English
• Published: Woodbury, NY Acoustical Society of America 01.03.2008; American Institute of Physics
• Subjects: Adaptation, Physiological; Audiometry - instrumentation; Biological and medical sciences; Cochlear Implants; Electrodes; Hearing - physiology; Hearing Disorders; Humans; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Miscellaneous. Technology; Perceptual Masking - physiology; Prosthesis Design; Time Factors; Ultrasonic investigative techniques; Human; Prosthesis; Tuning
• ISSN: 0001-4966; 1520-8524; 1520-8524
• DOI: 10.1121/1.2836786

Forward-masked psychophysical spatial tuning curves (fmSTCs) were measured in twelve cochlear-implant subjects, six using bipolar stimulation (Nucleus devices) and six using monopolar stimulation (Clarion devices). fmSTCs were measured at several probe levels on a middle electrode using a fixed-level probe stimulus and variable-level maskers. The average fmSTC slopes obtained in subjects using bipolar stimulation ( 3.7 dB ∕ mm ) were approximately three times steeper than average slopes obtained in subjects using monopolar stimulation ( 1.2 dB ∕ mm ) . Average spatial bandwidths were about half as wide for subjects with bipolar stimulation ( 2.6 mm ) than for subjects with monopolar stimulation ( 4.6 mm ) . None of the tuning curve characteristics changed significantly with probe level. fmSTCs replotted in terms of acoustic frequency, using Greenwood's [ J. Acoust. Soc. Am. 33 , 1344-1356 ( 1961 ) ] frequency-to-place equation, were compared with forward-masked psychophysical tuning curves obtained previously from normal-hearing and hearing-impaired acoustic listeners. The average tuning characteristics of fmSTCs in electric hearing were similar to the broad tuning observed in normal-hearing and hearing-impaired acoustic listeners at high stimulus levels. This suggests that spatial tuning is not the primary factor limiting speech perception in many cochlear implant users.