Patient's Corner

Cochlear implant manufacturers now offer a multitude of speech processing strategies in their speech processors. It is generally not known, however, which strategy will work the best for a particular patient. So, clinicians now have the option to program the patient with multiple strategies, and have the patient select the strategy they prefer. In addition, clinicians have the capability, thanks to the flexible fitting software, to change certain speech processing parameters to optimize performance.
 
    For patients fitted with the CIS strategy, clinicians can vary a number of parameters to optimize speech recognition performance for each patient. These parameters include pulse rate, pulse duration and stimulation order:
 

•  Pulse rate and pulse duration

The pulse rate defines the number of pulses per sec (pps) delivered to each electrode; pulse rates as low as 100 pulses/sec and as high as 2400 pulses/sec have been used commercially. The "optimal" pulse rate for speech recognition varies from patient to patient. Wilson et al. (1995) reported that some patients obtain a maximum performance on the 16-consonant recognition task with 833 pulses/sec and a pulse duration of 33 msecs/phase.  Other patients obtained maximum performance at different combinations of pulse rate and pulse duration (Wilson et al., 1993). Loizou et al. (2000) showed that the performance of some patients on word recognition increased monotonically from 400 pps to 2100 pps. The performance obtained at 2100 pps and with a 40-ms pulse duration, was found to be significantly higher than the performance obtained at 800 pps.
• Stimulation order

The stimulation order refers to the order with which the electrodes are stimulated.  The stimulation order can be varied to minimize possible interaction between channels. One possibility is to stimulate the electrodes in an apex-to-base order, i.e., first stimulate electrode 1, then 2, etc., and lastly, 6. This way, signals in the low frequencies (apex) are stimulated first, and signals in the high frequencies (base) are stimulated last. This apex-to-base order, however, does not minimize the spatial separation between sequentially stimulated electrodes.  Alternatively, the electrodes can be stimulated in a so called "staggered" order, i.e., 6-3-5-2-4-1, which maximizes the spatial separation between stimulated electrodes. As with the pulse rate, preference for stimulation order varies from patient to patient. Some patients prefer the apex-to-base stimulation, because they say speech sounds more natural and intelligible, while other patients prefer the staggered order stimulation.

     For patients fitted with the Nucleus’ CI24M device, clinicians have the option to select a subset of electrodes for stimulation. Research has shown that stimulating only a subset of electrodes, rather than all 22 electrodes, can produce significant benefits for some patients fitted with the CIS strategy. Plant et al. (1999) for instance, showed that some subjects preferred and performed better on word recognition with the CIS strategy when it was programmed with 8 channels than when it was programmed with 16 channels.

     For patients fitted with the Clarion device, clinicians have the option to fit the patient with the CIS, the SAS or the PPS strategies. Research has shown that some patients prefer the SAS strategy to the CIS strategy (Osberger and Fisher, 1999; Battmer et al., 1999), while other patients prefer the PPS strategy to the CIS strategy (Armstrong-Bendall et al., 1999).  In most cases, Clarion patients seem to perform better on speech recognition tasks with the strategy they prefer.

     For patients fitted with the Med-El device (COMBI 40+), clinicians now have the option to fit patients with the n-of-m strategy, in addition to the CIS strategy. Research (Ziese et al., 2000) has shown that Med-El patients performed better with the 7-of-12 strategy (operating at a higher rate) than the CIS strategy (12 channels) on monosyllabic word recognition. This is consistent with research reported by Brill et al. (1997) showing that by trading channels with higher simulation rates (i.e., by using fewer number of channels to obtain higher rates of stimulation) performance can be improved.

BIBLIOGRAPHY

Armstrong-Bendall, G., Goodrum-Clarke, K., Stollwerck, L., Nunn, T., Wei, J., Boyle P. (1999). “Clarion Paired Pulsatile Sampler (PPS): User Preference and Performance,” Conference on Implantable Auditory Prostheses, Pacific Grove, California.

Battmer, R., Zilberman, Y., Haake, P., Lenarz, T. (1999). “SAS-CIS Pilot Comparison Study in Europe,” Annals of Otology, Rhinology & Laryngology, 108, 69-73.

Brill, S., Gstottner, W., Helms, J., Ilberg, C.v., Baumgartner, W., Muller, J. and Kiefer, J. (1997). “Optimization of channel number and stimulation rate for the fast CIS strategy in the COMBI 40+,” American Journal of Otology, 18, S104-S106.

P. Loizou, O. Poroy and M. Dorman (2000). "The effect of parametric variations of cochlear implant processors on speech understanding," Journal of Acoustical Society of America, 108(2), 790-802.

Osberger, M. and Fisher, L. (1999). “SAS-CIS Preference Study in Postlingually Deafen Adults Implanted with the Clarion Cochlear Implant,” Annals of Otology, Rhinology & Laryngology, (Suppl. 177), 108(4), 74 – 79.

Plant, K., Whitford, L., Psarros, C., Vandali, A. and Clark, G. (1999). “Parameter selection and programming recommendations for the ACE and CIS speech processing strategies, 1999 Conference on Implantable Auditory Prosthesis, Pacific Grove, CA.

Wilson, B., Lawson, D. and Zerbi, M. (1993). “Speech Processors for Auditory Prostheses,” NIH Project N01-DC-2-2401, Fifth Quarterly Progress Report.
 
B. Wilson, D. Lawson, and M. Zerbi (1995). "Advances in coding strategies for cochlear implants," Advances in Otolaryngology - Head and Neck Surgery,  9, 105-129.

M. Ziese, A. Stutzel, H, von Specht, K. Begall, B. Freigang, S. Sroka and P. Nopp (2000). “Speech understanding with the CIS and n-of-m strategy in the MED-EL COMBI 40+ system,“ ORL, 62, 321-329.