Table 1.
Subject demographics.
Fig 1.
Block diagram illustrating the PACE (black) and TPACE (green) strategy.
Fig 2.
Model example of exponential decay of temporal masking thresholds (normalized to amplitude of 1) at two different temporal masking half-lifes T½ (0.5 ms in magenta and 1.1 ms in green).
The stimulation rate in this model example is 900 pps. At this stimulation rate, T½ of 0.5 ms or 1.1 ms leads to a decrease of the temporal masking threshold by 50% or 20% in the following frame, respectively.
Fig 3.
Stimulation patterns (electrodograms) for ACE (a), MP3000 (b) and TPACE with different values of the half-life value T½ (c-h). Current across time and electrode. Each vertical line represents the amplitude of a biphasic pulse in clinical units. Number of maxima was set to 5 in all stimulations, leading to maximum of five pulses in the same time frame. The acoustic input is an audio sample containing the word “choice”.
Fig 4.
A representative ECAP measurement of subject 2.2 on electrode 5.
The fitted exponential function (dashed line) indicates an absolute recovery period t0 = 0.52 ± 0.07 ms, the time constant τ = 1.0 ± 0.1 ms indicates the time needed to reach 63.2% of the maximal amplitude A = 104 ± 2 μV in this measurement.
Fig 5.
Speech intelligibility performance with different temporal masking half-lifes s using the HSM sentence test in noise.
The absolute performance difference between MP3000 and different TPACE conditions is presented for the first (green) and second (blue) study. Each dot shows the averaged result of each subject in the respective condition, the group median is presented as a bar in the respective group color. Speech intelligibility in noise with TPACE T½ = 0.5 ms was significantly better than MP3000 in the first study (p < 0.05; Quade test with three groups). The statistical analysis of the second study using Quade test with five groups did not show a significant difference between conditions.
Fig 6.
Individual speech intelligibility results of the second study.
The blue line presents the average result from two HSM sentence lists (circles) for each temporal masking half-life (0.4, 0.5, 0.8 and 1.1 ms). The SNR for these measurements depends on the performance of the individual patient and ranges from 15 to 5 dB SNR as stated in Table 1. The subjects are ordered in columns according to the temporal masking half-life with the best speech intelligibility (indicated by a red arrow): patients with best results without temporal masking in the first column and patients showing best speech intelligibility with temporal masking constant T½ = 0.8 ms are in the fourth row. No patients showed optimal speech intelligibility with the strongest temporal masking constant of 1.1 ms.
Fig 7.
Recovery functions t0 and τ of electrode 5 (green circles), electrode 12 (red squares) and electrode 20 (blue triangles).
Fig 8.
Relation between the ECAP recovery time t0 + τ on individual electrodes to the T½ time with the best speech intelligibility performance.
Spearman rank coefficient test results (R², p) are reported for each respective plot.
Fig 9.
Comparison between the patient performance in the clinical setting (measured with the HSM sentence test at 10 dB SNR during the yearly control visit, Table 1) and the benefit from using TPACE with a T½ of 0.5 ms.
The results of the first and second study are presented in green and blue, respectively. Regression between the clinical performance of the subject and the benefit from temporal masking was statistically significant for both studies (R² and p value are shown with the respective color in the plot).