Forward-masking patterns produced by symmetric and asymmetric pulse shapes in electric hearing.
Two forward-masking experiments were conducted with six cochlear implant listeners to test whether asymmetric pulse shapes would improve the place-specificity of stimulation compared to symmetric ones. The maskers were either cathodic-first symmetric biphasic, pseudomonophasic (i.e., with a second anodic phase longer and lower in amplitude than the first phase), or "delayed pseudomonophasic" (identical to pseudomonophasic but with an inter-phase gap) stimuli. In experiment 1, forward-masking patterns for monopolar maskers were obtained by keeping each masker fixed on a middle electrode of the array and measuring the masked thresholds of a monopolar signal presented on several other electrodes. The results were very variable, and no difference between pulse shapes was found. In experiment 2, six maskers were used in a wide bipolar (bipolar+9) configuration: the same three pulse shapes as in experiment 1, either cathodic-first relative to the most apical or relative to the most basal electrode of the bipolar channel. The pseudomonophasic masker showed a stronger excitation proximal to the electrode of the bipolar pair for which the short, high-amplitude phase was anodic. However, no difference was obtained with the symmetric and, more surprisingly, with the delayed pseudomonophasic maskers. Implications for cochlear implant design are discussed.
Macherey
Olivier
O
ExpORL, Department of Neurosciences, KU Leuven, Herestraat 49, Bus 721, 3000 Leuven, Belgium. olivier.macherey@mrc-cbu.cam.ac.uk
van Wieringen
Astrid
A
Carlyon
Robert P
RP
Dhooge
Ingeborg
I
Wouters
Jan
J
D000161:Acoustic Stimulation; D000162:Acoustics; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001307:Auditory Perception; D001309:Auditory Threshold; D003054:Cochlear Implants; D003638:Deafness / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D008875:Middle Aged; D009474:Neurons / Q000502:physiology; D010470:Perceptual Masking; D011571:Psychoacoustics; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors