Psychophysical assessment of stimulation sites in auditory prosthesis electrode arrays

Abstract

Auditory prostheses use implanted electrode arrays that permit stimulation at many sites along the tonotopic axis of auditory neurons. Psychophysical studies demonstrate that measures of implant function, such as detection and discrimination thresholds, vary considerably across these sites, that the across-site patterns of these measures differ across subjects, and that the likely mechanisms underlying this variability differ across measures. Psychophysical and speech recognition studies suggest that not all stimulation sites contribute equally to perception with the prosthesis and that some sites might have negative effects on perception. Studies that reduce the number of active stimulation sites indicate that most cochlear implant users can effectively utilize a maximum of only about seven sites in their processors. These findings support a strategy for improving implant performance by selecting only the best stimulation sites for the processor map. Another approach is to revise stimulation parameters for ineffective sites in an effort to improve acuity at those sites. In this paper, we discuss data supporting these approaches and some potential pitfalls.

Modeling the electrode–neuron interface of cochlear implants: Effects of neural survival, electrode placement, and the partial tripolar configuration

“…In addition to threshold, across site variability in psychophysical measures has also been observed for maximum comfortable loudness and modulation detection thresholds (Pfingst et al, 2008), and forward masked spatial tuning curves (Nelson et al, 2008; Bierer and Faulkner, 2010). Ideally, such psychophysical measures could be used to infer the extent of neural degeneration, and the spatial and temporal patterns of neural activation evoked at different sites in the cochlea.…”

Fitting prelingually deafened adult cochlear implant users based on electrode discrimination performance

“…Thirdly, it is known that the amount of surviving spiral ganglion cells diminishes with a long period of profound deafness (Hardie & Shepherd, 1999). As suggested by Pfingst et al (2008), the number and condition of the activated neurons might be inferior at ''ineffective'' sites. It can be hypothesized that there are likely to be less surviving spiral ganglion cells in the basal region of the cochlea, where duration of deafness can be expected to be the longest for most subjects with prelingual extensive hearing loss.…”

“…Our objective was therefore to determine whether speech understanding performance of prelingually deafened CI users would improve when only mutually discriminable electrodes were selected for use in cochlear implant fitting. Selectively turning off electrodes related to ''ineffective sites'' in order to improve speech perception is referred to as the ''site selection strategy'' (Pfingst et al, 2008). To our knowledge, only two studies have tested speech recognition in post-lingually deafened subjects using an experimental cochlear implant program containing only discriminable electrodes.…”

Effects of electrode configuration on cochlear implant modulation detection thresholds

“…One possible strategy for optimizing processor fitting is to identify stimulation sites for which psychophysical performance is best and increasing the contributions of those sites in the processor map (Zwolan et al, 1997;Pfingst et al, 2008b;Bierer and Faulkner, 2010).…”

“…An alternative explanation of the effect of electrode configuration on detection thresholds is that the higher T levels and the larger across-site variation in T levels under bipolar stimulation might be due in large part to the effects of electrode configuration on the rate of decline in current level as a function of distance from the electrodes (Pfingst and Xu, 2004;Pfingst et al, 2008b). Variation along the electrode array in the electrode to neuron distance could account for variation in the amount of current required to reach the threshold of the target neurons.…”