We developed our "Optimised" CERA test paradigm from the findings of the available literature (for details, see the page on this). However, we have taken much of this on trust and we certainly did not know whether there is any interaction between the effects of the parameters we have chosen. This study therefore addressed this issue by looking at them in isolation and in combination. Again, 24 volunteer staff are being used but only one ear is under scrutiny, at one frequency (3 kHz), at an intensity close to threshold (25 dB sensation level). In this study we hoped to identify any effect on CERA amplitude of:
varying the inter-stimulus interval of a monaurally presented stimulus
inserting a 10s stimulus-free interval half-way through the averaging process to allow an adapted response to recover
presenting the stimuli to one or other ear in a random fashion (at equal sensation level)
Results: There appeared to be no effect of any of the above on N1-P2 response amplitude.
These findings were somewhat of a surprise and disappointing - apparently suggesting that these novel stimulus presentation features that we have developed and used for many years actually bring no advantage. Still, that's the point of undertaking the research!
In fact, the results must be viewed with an important fact in mind: the nature of the experimental design was such that subjects were exposed to ever-changing stimuli over a period of about 20 minutes. Thus, there appears to be no significant short-term effect of these features. What we have not addressed in our study is whether these features offer any advantage over conventional stimulation - i.e. monotonous monaural stimulation lasting up to an hour. We suspect we would see an advantage but that's another study!
We have produced a paper on this study, Lightfoot & Kennedy (2006).