Speech perception and subjective benefit in paediatric C40+ users after the upgrade to fine structure processing (FSP).

Introduction The amount of speech information available to patients with cochlear implants (CIs) is reduced by the limitations of current CI systems, which are characterised by (a) an insufficient number of effective channels imposed by the design and placement of the electrode, leading to poor frequency resolution; (b) a deficiency in the representation of the fine structure of the input signals and (c) too coarse a representation of the fundamental frequencies that are required to interpret complex sounds (Wilson et al, 2008). Recent advances in developments with cochlear implant systems have opened new listening possibilities for cochlear implant users. One of the advances is combined Electric Acoustic Stimulation (EAS) of the auditory system for persons with functional hearing in low frequencies. Using EAS, fine structure information is presented without modification in the low-frequency range (thus compensating for limitation (b)) and this fine structure information is likely to include F0 (thus compensating for limitation (c)). There are numerous studies which proved the benefit of EAS (Lorens et al. 2008; Skarzynski et al 2009) In order to transfer the benefits of EAS to patients without low frequency hearing, the Fine Structure Coding Strategy (FSP) was developed by MED-EL. The FSP strategy therefore is designed to provide improved frequency coding in the apical channels of the cochlear implant. This is achieved by providing a temporal code for frequency which is derived from zero-crossings in the band-pass filter output signals on these channels. Details on the FSP strategy can be found in Arnoldner et al. (2007). The recent release of the MAESTRO 3.0 fitting software allowed for backward compatibility, which allows users of COMBI 40+ previous generation implant utilising the CIS+ coding strategy, to be fitted with the new generation audio processor – OPUS 2, using FSP or HDCIS strategies. The CIS+ strategy is a further development of the CIS strategy (Wilson et al, 1991) in that it uses the Hilbert transform for envelope detection. The HDCIS strategy is similar in concept to the CIS+ strategy and it is available in the OPUS 2 behind-the-ear speech processor. Currently, there are no published papers reporting outcomes with FSP when implemented using the COMBI 40+ cochlear implant, probably because the MAESTRO 3 software allowing for backwards compatibility has only recently been released. Also, there are no papers outlining outcomes in children. As the number of children implanted with COMBI 40+ worldwide is substantial, it is important …