FineHearing™ Research
Until Fine Structure Processing, cochlear implant systems provided information regarding changes in the amplitude of a signal over time, and the timing cues were largely discarded. These amplitude changes are referred to as the “envelope” of an incoming sound; envelope coding only traces the outer edges, or outline, of a sound wave. Essentially, this provides only a two-dimensional representation of sound, although it does result in quite good speech understanding, especially in quiet environments. FineHearing™* research, however, is currently further exploring the potential of FineHearing Technology to provide even more detail, depth, and dimension to sound, particularly in relation to improving music appreciation.
Fine Structure Processing™1
In simplified terms, sound can be separated into two parts: envelope information and fine structure, or fine frequency, information. The envelope contains overall information about changes in the amplitude (intensity) of a signal over time; whereas, the fine structure contains rapidly changing details regarding the frequency (pitch) of that signal. Research with normal-hearing listeners has demonstrated that the envelope of a signal is most important for speech reception, while the fine structure is most important for pitch and music perception. Fine Structure Processing (FSP) is the first commercially released coding strategy to deliberately inform the auditory system of the actual timing of the waveform.
There are two potential ways to encode the fine structure of a sound signal using: 1) information regarding the phase (timing) and 2) information regarding the tonotopic arrangement (place) of various frequencies in the signal. FSP uses a combination of both parameters. It features a unique series of pulses called Channel Specific Sampling Sequences (CSSS) in the low frequencies, as well as Sequential Virtual Channels (also called sVC or Field Shaping) across the array. Together, these novel cues increase pitch information, which results in measurable changes in speech perception in everyday listening, as well as improved music appreciation.
| | Channel Specific Stimulation (Temporal Coding) Channel Specific Sampling Sequences (CSSS), a method of temporal coding, provides rapidly changing details regarding the frequency of a signal using cues obtained from the zero-crossing of the incoming sound wave. CSSS are groups of pulses that are presented at the exact timing of the zero-crossing. CSSS contributes to better pitch differentiation in the low frequencies. Virtual Channels Virtual Channels is a method of increasing the pitch resolution by generating pitch percepts that are intermediate to the pitches evoked at the exact location of the electrode contact. Frequency filters in the MED-EL speech processors are bell-shaped and they overlap with the bandpass filters of neighboring channels. As a result, multiple pitches between two channels can be created, allowing for more distinct and predictable pitch percepts. For a look at results found in the clinical trial of FSP in experienced adult users, click here. |
Wider Frequency Range
MED-EL has always provided cochlear implant users with the deepest electrode placement and access to the greatest number of neural elements within the cochlea. MED-EL is now investigating the potential to tonotopically match a frequency range of approximately 70Hz–8,500Hz. A wider range of frequencies should provide improved benefit for music appreciation and speech understanding in a variety of spoken languages (including complex tonal languages).
Multiple Stimulation Modes*
For the most part, current cochlear implant technology utilizes biphasic pulses and sequential stimulation to process sound. Additionally, MED-EL is exploring the potential for triphasic pulses* and simultaneous stimulation* to perpetuate future developments in speech processing. The ultimate goal is to determine the ways in which these various forms of stimulation can be utilized for new speech coding strategies and the potential benefit of such stimulation modes. PULSARci100 and SONATATI100 cochlear implants contain the electronics to generate these novel types of stimulation with future external equipment and/or software upgrades*.
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