title: Masking patterns for monopolar and phantom electrode stimulation in cochlear implants.
abstract: Phantom electrode (PE) stimulation consists of out-of-phase stimulation of two electrodes. When presented at the apex of the electrode array, phantom stimulation is known to produce a lower pitch sensation than monopolar (MP) stimulation on the most apical electrode. The ratio of the current between the primary electrode (PEL) and the compensating electrode (CEL) is represented by the coefficient σ, which ranges from 0 (monopolar) to 1 (full bipolar). The exact mechanism by which PE stimulation produces a lower pitch sensation is unclear. In the present study, unmasked and masked thresholds were obtained using a forward masking paradigm to estimate the spread of current for MP and PE stimulation. Masked thresholds were measured for two phantom electrode configurations (1) PEL = 4, CEL = 5 (lower pitch phantom) and (2) PEL = 4, CEL = 3 (higher pitch phantom). The unmasked thresholds were subtracted from the masked thresholds to obtain masking patterns which were normalized to their peak. The masking patterns reveal (1) differences in the spread of excitation that are consistent with the direction of pitch shift produced by PE stimulation, and (2) narrower spread of electrical excitation for PE stimulation relative to MP stimulation.
authors.affiliation: Research and Technology group, Advanced Bionics, LLC, 28515 Westinghouse Place, Valencia CA 91355, USA. AniketS@advancedbionics.com
authors.forename: Aniket A
authors.initials: AA
authors.lastname: Saoji
authors.forename: David M
authors.initials: DM
authors.lastname: Landsberger
authors.forename: Monica
authors.initials: M
authors.lastname: Padilla
authors.forename: Leonid M
authors.initials: LM
authors.lastname: Litvak
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001307:Auditory Perception; D001309:Auditory Threshold; D019929:Cochlear Implantation / Q000295:instrumentation*; D003054:Cochlear Implants; D012048:Correction of Hearing Impairment / Q000523:psychology*; D004558:Electric Stimulation; D006801:Humans; D008875:Middle Aged; D010470:Perceptual Masking; D019986:Persons with Hearing Disabilities / Q000523:psychology / Q000534:rehabilitation*; D010898:Pitch Perception; D011474:Prosthesis Design; D011571:Psychoacoustics