Psychophysical tuning curves as a measure of electrode position in cochlear implant listeners

Abstract

Speech perception abilities vary widely among cochlear implant listeners. A potential source of this variability is electrode position; suboptimal placement has been associated with poorer outcomes. Insight into electrode position can be obtained via postoperative CT imaging, specifically the distance of each electrode from the modiolus. Additional information can be obtained with behavioral measures, which are sensitive to electrode position and neural integrity.Electrode-to-modiolus distance can explain some variability in behavioral thresholds; however, the relationship with psychophysical tuning curves (PTCs) has not been evaluated, which may provide a more detailed assessment of local variations in channel interaction. Four unilaterally implanted adults with the Advanced Bionics HiRes90K device participated. CT scans were obtained and image reconstructions were performed. Using a fast, sweep procedure, PTCs were collected for all available electrodes using the steered quadrupolar configuration within a forward-masking paradigm. Spread of neural excitation was quantified with the equivalent rectangular bandwidth (ERB). Preliminary data show a correlation between electrode-to-modiolus distance and the ERB of PTCs, suggesting poorer electrode placement may cause broader activation. The goal of this research is to develop a fast, non-radiologic method for estimating electrode position, which may lead to improved device programming by reducing unwanted channel interaction.