Temporal fine structure in cochlear implants: Preliminary speech perception results in Cantonese-speaking implant users

Conclusion: Acute comparisons between continuous interleaved sampling (CIS) and a temporal fine structure (TFS) coding strategy in Cantonese-speaking cochlear implant (CI) users did not reveal any significant differences in speech perception. Performance with the unfamiliar TFS coding strategy was on a par with CIS. Benefits of extended fine structure use observed in other studies should be investigated for tonal languages. Objectives: CIS-based stimulation strategies lack an explicit representation of fine structure, which is crucial for tonal language speech perception. The aim of this study was to assess speech recognition with a TFS coding strategy in Cantonese-speaking CI users with no prior fine structure experience. Methods: The fine structure coding strategy encodes TFS on a few apical channels, while the remaining more basal channels carry CIS stimuli. Twelve MED-EL implantees and long-term CIS users participated in a study comparing recognition for Cantonese lexical tones and CHINT sentences between CIS and fine structure stimulation. Results: Mean tone identification scores in 12 subjects were 59.2% with CIS and 59.2% with fine structure stimulation using 4 TFS channels, mean scores of CHINT sentences in 8 subjects were 54.2% with CIS and 55.9% with TFS stimulation. Differences between the two strategies were not significant for any speech test. Two additional versions of TFS strategy and pulse rates were tested in six subjects. No significant differences between strategies were found. © 2010 Informa Healthcare.link_to_subscribed_fulltex

Results from a strategy encoding temporal fine structure

Current cochlear implant stimulation strategies are widely based on the continuous interleaved sampling (CIS) paradigm. With CIS, temporal fine structure is only crudely represented in the stimulation pattern, and pitch is encoded primarily in the place of stimulation and to a limited extent in the temporal fluctuations of the channel envelopes. However, fine structure information is a crucial ingredient for the perception of music and of tonal languages, as demonstrated in studies with normal hearing subjects. In the fine structure strategy presented, “channel specific sampling sequences” (CSSS) or pulse-packages are applied to the apical electrodes, while the remaining basal electrodes carry CIS-like stimuli. The pulse sequences are triggered by the zero-crossings of the corresponding filter channel outputs and scaled with the channel envelopes. Thus, both fine time structure and envelope information are represented on CSSS channels. The new strategy has been evaluated in two experiments: In a first experiment, pitch discrimination and scaling abilities were compared for the fine structure strategy and CIS in four MED-EL implant recipients. For pure tone stimuli below 300 Hz, pitch discrimination with CIS was limited. Conversely, CSSS seems to add robust temporal cues to pitch at low frequencies, supporting better discrimination. In a second experiment, speech reception measures were taken for MEDEL implant recipients and native speakers of Cantonese Chinese in Hong Kong. Preliminary results from a pilot study showed substantial improvements in the perception of lexical tones with the fine structure strategy over CIS and triggered a more extensive survey. Data from this ongoing study will be presented. Support provided by the Christian Doppler Research Associatio

Lacustrine chalky carbonates: origin, physical properties and diagenesis (Palaeogene of the Madrid Basin, Spain)

The Palaeogene lacustrine chalky carbonates of the Madrid Basin are a peculiar type of very soft and friable carbonate facies with high porosity despite being covered by more than 800 m of sediment. Similar physical properties to those described in marine chalk reservoirs emphasize the interest in analysing and characterizing these carbonate facies within a lacustrine depositional system. Lithologically, they are calcitic and/or dolomitic poorly cemented carbonate muds with no significant amounts of skeletal debris. Clay minerals such as illite, smectite and palygorskite are present between the carbonate crystals. Palygorskite is the most common, covering the carbonate crystals and forming sheets between them. These lacustrine chalky carbonates were formed in the basinal areas of the lake as the result of inorganic carbonate precipitation and/or detrital sedimentation related to episodic reactivation of the adjacent fan systems. Their petrological, geochemical and physical properties indicate that few textural and compositional modifications occurred during diagenesis. Their main physical properties are a very low dry bulk and grain density (1.6–2.2 and 2.62 g/cm3, respectively) and medium to high porosity (10–40%) due to micropores ( 2 Am, 30%). The convergence of lacustrine sedimentation dynamics (rapid sedimentation), the original mineralogy of these calcareous lacustrine muds (relatively stable low-magnesian calcite and dolomite), the early formation of the palygorskite cement of these muds, and the retention of Mg-enriched fluids in the pore system, were decisive in the partial inhibition of calcite cementation, compaction and recrystallization. The chalky carbonates are also intercalated between impermeable littoral carbonate facies that impeded fluid flow through their pore systems