**2. Methods**

The BAER test provides an electrophysiological measure of neural responses (from the cranial nerve VIII and lower brainstem auditory nuclei) to auditory stimuli through the use of surface or subdermal electrodes. The technique is a widely used objective measure of auditory system function in humans and has also been used extensively in the auditory assessment of dogs [4].

Typically, a BAER test involves five waves occurring within 6–15 milliseconds following the evoking stimulus [3]. The fourth and fifth waves in the sequence will, occasionally merge into a single broad wave or a wave IV/V complex making identification of all the five waves difficult to define. Our experience with puppy screening and diagnostic testing in the FETCHLAB clinics is that we do see five waves most of the time. The second wave in the sequence (wave Il) is often of sufficiently small amplitude that it is masked by the background recording noise and, therefore, not readily identifiable [7, 8]. These variances in the morphology of BAER recordings are not considered unusual and likely result from an interaction between the selected electrode placement sites, acquisition parameters, and electrical transmission characteristics of the various tissues interposed between the neural generators and the electrode recording site [8].

When BAER testing is used to quantify hearing threshold levels, the most commonly used interpretation metric involves the identification of the lowest stimulus intensity at which the fifth peak in the sequence, or wave V, can be identified (the wave V threshold). This is also known as the lowest observable response level (LORL) [17].
