Training in ABR
What is the CE-Chirp® Family of Stimuli?
Description
As the name suggests the CE-Chirp® family is not a single stimulus but instead a family of short duration acoustic stimuli which can be used in evoked potential testing. They were designed with the objective of increasing the amplitude of the auditory brainstem response. Because of this the CE-Chirp® family are primarily used when measuring hearing threshold.
The CE-Chirp® family of stimuli achieves larger wave V amplitudes by providing the cochlea with optimal stimulation of the basilar membrane which results in synchronous neural firing. To understand how this works it is important to understand the anatomy and physiology of the cochlea. The cochlea is tonotopically organised so that the high frequencies are detected at the base and the low frequencies detected at the apex. This means that if all frequencies are presented to the cochlea at the same time (like with a click stimulus) the high frequency components of the stimulus will be detected by the basilar membrane first followed but the mid frequency and lastly the low frequency components. This will result in neural firing across the frequency range which is not synchronous.
A CE-Chirp® stimulus counteracts the temporal dispersion in the normal cochlea by presenting the low frequency energy content of the stimulus before the high-frequency energy. The design of the traditional CE-Chirp® is described in detail by Elberling et al. (2007a), and has the same power spectrum as a standard click ( i.e the same frequency content and the same amplitude, just a different timing relationship). In the study by Elberling and Don (2008), it was demonstrated that the CE-Chirp® ABR is up to 1.5-2.0 times larger than the corresponding click ABR in normal-hearing subjects. The practical consequence of this is that responses of a desired signal to noise ratio are obtained in a shorter test time (or that in a fixed test time, the response will have a higher signal to noise ratio) when a CE-Chirp® is used rather than a traditional click.
Since the development of the traditional CE-Chirp® in 2007, there has been much research centred on this stimulus and it has been further optimised. Firstly was the release of the Narrowband CE-Chirps® which provides a set of frequency specific stimuli at 500 Hz 1000 Hz 2000 Hz and 4000 Hz. These can be used as alternatives to tone burst stimuli. The NB CE-Chirps has been applied in several new-born hearing screening programs and for this type of hearing testing it has been demonstrated that the NB CE-Chirps are more efficient than tone burst (Ferm et al. 2013).
Lastly in 2015 the CE-Chirp® LS family was release. LS stands for level specific. Claus Elberling, the founder of the CE-Chirp® revealed that the stimulus could be further optimized for each intensity. Therefore CE-Chirp® LS was released which provides a different stimulus for each 5 dBnHL step from 0- 100 dBnHL. This means that CE-Chirp® family of stimuli now has twenty CE-Chirp LS Stimuli in addition to 4 frequency specific NB CE-Chirp LS.
Related course: An introduction to the CE-Chirp®
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