Training improves cochlear implant rate discrimination on a psychophysical task

AbstractA series of experiments investigated potential changes in temporal processing during the months following activation of a cochlear implant (CI) and as a function of stimulus level. Experiment 1 tested patients on the day of implant activation and two and six months later. All stimuli were presented using direct stimulation of a single apical electrode. The dependent variables were rate discrimination ratios (RDRs) for pulse trains with rates centred on 120 pulses per second (pps), obtained using an adaptive procedure, and a measure of the upper limit of temporal pitch, obtained using a pitch-ranking procedure.All stimuli were presented at their most comfortable level (MCL). RDRs decreased from 1.23 to 1.16 and the upper limit increased from 357 to 485 pps from 0 to 2 months post-activation, with no overall change from 2 to 6 months. Because MCLs and hence the testing level increased across sessions, two further experiments investigated whether the performance changes observed across sessions could be due to level differences. Experiment 2 re-tested a subset of subjects at 9 months post-activation, using current levels similar to those used at 0 months. Although the stimuli sounded softer, some subjects showed lower RDRs and/or higher upper limits at this re-test. Experiment 3 measured RDRs and the upper limit for a separate group of subjects at levels equal to 60%, 80%, and 100% of the dynamic range. RDRs decreased with increasing level. The upper limit increased with increasing level for most subjects, with two notable exceptions. Implications of the results for temporal plasticity are discussed, along with possible influences of the effects of level and of across-session learning.

Download Full-text

Effect of stimulus polarity on detection thresholds in cochlear implant users: relationships with average threshold, gap detection, and rate discrimination

10.1101/297085 ◽

2018 ◽

Cited By ~ 1

Author(s):

Robert P. Carlyon ◽

Stefano Cosentino ◽

John M. Deeks ◽

Wendy Parkinson ◽

Julie A. Arenberg

Keyword(s):

Cochlear Implant ◽

High Amplitude ◽

Gap Detection ◽

Detection Thresholds ◽

Polarity Effect ◽

Modelling Studies ◽

Neural Survival ◽

Rate Discrimination ◽

Central High ◽

Anodic Stimulation

AbstractPrevious psychophysical and modelling studies suggest that cathodic stimulation by a cochlear implant (CI) may preferentially activate the peripheral processes of the auditory nerve, whereas anodic stimulation may preferentially activate the central axons. Because neural degeneration typically starts with loss of the peripheral processes, lower thresholds for cathodic than for anodic stimulation may indicate good local neural survival. We measured thresholds for 99-pulse-per-second trains of triphasic (TP) pulses where the central high-amplitude phase was either anodic (TP-A) or cathodic (TP-C). Thresholds were obtained in monopolar mode from four or five electrodes and a total of eight ears from subjects implanted with the Advanced Bionics CI. When between–subject differences were removed, there was a modest but significant correlation between the polarity effect (TP-C threshold minus TP-A threshold) and the average of TP-C and TP-A thresholds, consistent with the hypothesis that a large polarity effect corresponds to good neural survival. When data were averaged across electrodes for each subject, relatively low thresholds for TP-C correlated with a high “upper limit” (the pulse rate up to which pitch continues to increase) from a previous study [Cosentino S, Carlyon RP, Deeks JM, Parkinson W, Bierer JA (2016) Rate discrimination, gap detection and ranking of temporal pitch in cochlear implant users. J Assoc Otolaryngol 17:371– 382]. Overall the results provide modest indirect support for the hypothesis that the polarity effect provides an estimate of local neural survival.

Download Full-text