Meisam Arjmandi1,2, Julie Arenberg1,2
1Department of Otolaryngology-Head and Neck Surgery, Harvard Medical School, Boston, MA, USA
2Audiology Division, Massachusetts Eye and Ear, Boston, MA, USA
Psychophysical tuning curves (PTCs) are effective measures to evaluate frequency selectivity in listeners with cochlear implants (CIs). We are developing a fast and reliable method to measure 5-point PTCs using acoustic stimulation via Bluetooth in CI listeners. The procedure reduces the number of measurements required by eliminating the time to measure thresholds and most comfortable listening levels for each electrode. The pure tones used for masker and probe signals matched the corner frequencies of the analysis filter bands in the processor settings such that mainly one electrode is stimulated. Rather than adaptively varying the level of the masker tone, the masker level is fixed at 56 and 46 dB SPL. Using a forward masking paradigm, the masker frequency is adaptively varied across electrode/frequencies using a two-alternative, two-interval forced choice procedure and frequency thresholds are obtained for the low and high frequency sides, relative to the probe electrode. The tip of the PTC is measured by on-frequency masking, adaptively varying the masker level. Stimuli were controlled through a custom Matlab interface with the AFC software in the background (Ewert, 2013). Data with this method was compared with the gold standard, direct electrical stimulation procedure (Kreft et al., 2019). Preliminary data from two adult CI listeners showed morphologically similar PTCs between acoustic stimulation via Bluetooth and direct electrical stimulation. We characterized PTCs using the apical, basal, and mean slopes. The measures of PTCs calculated from the Bluetooth and direct stimulation procedures were highly correlated for the apical and mean slopes (Pearson r>.9, p<.5). This new tool may be useful for rapid and reliable measurement of PTCs to evaluate frequency selectivity for individual electrode sites. Implementation is for Advanced Bionics devices, but it could be modified for other manufacturers. Developing patient-specific strategies based on PTCs to determine optimal fitting is becoming more feasible.
Acknowledgements: This work was supported by the NIH National Institute on Deafness and Other Communication Disorders Grant RO1 DC012142 (JGA).