Glide psychophysics and related Mpeak and Speak speech performance

Speech test results have indicated that improvements in speech comprehension can be achieved by means of coding strategies with high pulse rates. A possible effect of using high rates to encode speech information is that temporal information such as formant transitions could be better represented in the resulting electrode activity. A psychophysical study involving 4 cochlear implant users was carried out to observe the effect of various carrier pulse rates on the absolute identification of stimuli with a transient electrode trajectory. Also, the duration of the trajectory was varied. The results from this study indicated, first, that the trajectory identification became progressively more difficult as the duration of the trajectory was shortened. The identification score generally deteriorated much faster at a lower rate (100 pulses per second [pps]) than at higher rates (300 and 500 pps) with decreasing transient duration. The higher two pulse rates, 300 pps and 500 pps, yielded results similar to one another for longer (500 and 300 milliseconds) transient durations, but the identification of shorter (100 and 50 milliseconds) transient durations was better at 500 pps than at 300 pps. The implication is that higher carrier pulse rates are likely to be able to transmit short transient information better than lower ones. A comparison with speech test results using the Speak (spectral peak) speech-coding strategy shows that the place of articulation feature is significantly improved when compared to the slower-rate Mpeak (Multipeak) pitch-synchronous strategy.