Demonstration of a portable system for auditory brainstem recordings based on pure tone masking difference

The auditory brainstem response (ABR) has for many years been an important research tool. It has been used in many different settings from threshold determination on subjects unable to participate in ordinary psychoacoustic testing, to diagnosing tumours on the auditory nerve. The problem with most ABR systems is that they are either big, inflexible or both. Furthermore, most systems are not portable. We have developed an ABR system based on a Tucker-Davis Technologies differential amplifier and portable digital signal processor (RM2). The differential amplifier is connected via an optical cable. This system is small, weighing less than 750 grams including batteries. It is also very flexible with a graphical pro- gramming interface that makes it possible with relative ease to modify the entire system and it is relatively inexpensive (approximately 2000 USD). We have implemented a pure tone masking difference ABR method (Ber- lin1991) The system has been developed for human ABR measurements and will be demonstrated at the symposium. To explore the possibilities of the system we have also used it to determine the audiograms for frogs (Rana temporaria, Xenopus tropicalis) and lizards (Gekko gecko). The audiogram is difficult to measure by behavioral methods since lizards and frogs cannot be conditioned to acoustical stimuli. ABR measurements are therefore the most convenient way to compare thresholds in the different species.