In this article results are described of a study on the effects of stimulation rate (PR), pulse duration (PW), and paired pulsatile stimulation (PPS) versus continuous interleaved sampling (CIS) on speech perception and psychophysical loudness measures.
During 3 nonconsecutive days, 27 postlingually deafened patients, implanted with either a CII or a HiRes90K with a HiFocus electrode array, were fitted with nine 12-channel strategies after a Latin-square design, systematically investigating the effect of stimulation rate (774–3868 pps/channel), PW (11–43 µsec/phase), and PPS versus CIS. Speech perception was measured in phonemes using open-set monosyllabic words. Minimum (T level) and maximum stimulation (M level) levels were measured.
In general, performance was better with CIS strategies than with PPS strategies. There was little variation in speech perception performance between the different CIS strategies. As expected, PW and rate influenced the T and M levels in a systematic way for all electrode array positions. The T levels decreased by 2.11 dB per doubling of the pulse rate, whereas the M levels were considerably less influenced (slope −0.81 dB per doubling of the rate). T levels decreased 6.46 dB per doubling of pulse width, with an associated decrease in M levels of 5.58 dB, which is expressed in a closed-set formula. Changing from CIS to PPS led to a reduction of T levels by 1.34 dB and of M levels by 1.91 dB. This reduction was superimposed on the changes caused by doubling the rate, inherent to the PPS paradigm.
CIS strategies tend to perform better than PPS strategies. PW, rate and paired stimulation have little effect on speech perception scores. However, they do have predictable and independent effects on both T and M levels for all strategies tested. The relationships found allow the improvement of the versatility of current fitting software and provide a basis to let the fitting software automatically adjust T and M levels if the PW or rate are adjusted in an existing program.