Development of behavioral observation audiometry tests for companion dogs

Behavioral observational audiometry is applied to study the hearing function of preverbal children aged less than 6 months. We hypothesized that this method could be used to assess hearing threshold in untrained companion dogs. The small number of studies that examine untrained behavioral responses to sounds have not described determination of hearing threshold using this methodology. We designed and optimized a protocol for untrained dogs, performed in a soundproof booth to minimize extraneous noise influence. A handler assessed dog behavioral response to sounds played in ascending intensity on a speaker, positioned orthogonal to the dog; an ethogram was used to define the spectrum of responses. Stimuli included 5 sounds perceived to be ecologically salient to dogs (dog barks, dog whimpers, bird whistle) and 3 warble-tone sounds used in human audiology (0.5, 4, 8kHz frequency). Stimuli were pseudorandomized within each category. The first group of dogs (group 1, n=13) underwent less standardized preparation/acclimation, whereby dogs were not tested at a standard time, and were not fasted. Group 2 dogs (n=12) were fasted, tested in the early morning, and had an expanded acclimation process. Dogs responded more consistently to ecologically salient sounds, and response threshold within the spectrum of ecological sounds varied depending on frequency representation (dog bark response threshold was higher than sounds containing higher frequencies). Response thresholds to warble tone stimuli were higher than in normal humans, and responses were highly variable. Variability in responses was lower in dogs from group 2 compared with group 1. Our optimized protocol for behavioral observation audiometry using ecologically salient stimuli results in consistent testing of response threshold in untrained dogs. Future applications could include the study of the impact of aging, ear pathology, or other disease on hearing thresholds in dogs.