Animal Audition: Is it Really Audiology?
Peter M. Scheifele, PhD, LCDR USN (Ret.)
“Can my dog hear? Can I do anything to help him?” At the University of Cincinnati we are finding these are quite common questions among pet owners. Normal hearing allows all of us to respond to various sound stimuli encountered on a daily basis. For safety issues and training, reduced hearing sensitivity can become a concern for the owner or dog handler. And some dog owners are concerned that their dog’s hearing loss may affect the bonding relationship they enjoy with their pet.
Just as with humans, hearing loss, or deafness, whether unilateral or bilateral, can result in a dog being unable to respond appropriately to auditory stimuli. When hearing loss is present, these animals are at greater risk for vehicular injury, bite injuries to humans, or abandonment due to behavior issues. Working dogs and their handlers rely on normal canine hearing to respond appropriately to auditory cues in potentially life-threatening situations, and therefore hearing assessment of these animals takes on a heightened importance. Canine hearing assessment is also important to identify congenital deafness, a topic of considerable interest among breeders. Congenital deafness has been reported in over 61 breeds of dogs with the highest prevalence rates noted in the Dalmatian, estimated at 20-30% followed by the Bull Terrier, English Setter, English Cocker Spaniel, Australian Cattle Dog, Norwegian Dunkerhound, and Dappled Dachshund.
Veterinary practitioners often employ behavioral testing to assess hearing in their canine patients. Behavioral hearing assessment is not an effective method to test canine hearing because the dog may respond to visual, vibrotactile or olfactory cues instead of the auditory stimulus. Behavioral tests do not test each ear independently nor identify dogs with hearing impairments at specific frequencies. Further, behavioral testing gives no information about the site or cause of the hearing impairment.
In contrast, the Auditory Brainstem Response (ABR) is an electrophysiological test used in humans and multiple animal species, including dogs, to objectively assess auditory function and estimate hearing sensitivity. In humans, ABRs are established diagnostic tools used clinically for newborn infant auditory screening and estimation of auditory sensitivity. The ABR has been referred to in the literature as a brainstem auditory evoked response (BAER), brainstem evoked response (BSER), or brainstem auditory evoked potential (BAEP). In veterinary medicine, the ABR is considered the gold standard for hearing testing. The ABR can assist in estimation of thresholds of canine hearing and be used to diagnose various forms of canine deafness. Serial ABR testing of working dogs allows progressive or acquired hearing impairments secondary to presbycusis or due to repeated sudden-intense impact noise exposure to be readily identified.
In humans, assessment of hearing sensitivity by ABR testing has universally accepted clinical norms and recording parameters, both lacking for canines assessment. Having standardized human ABRs allows testing done at one facility to be reviewed at another facility with a high degree of confidence regarding ABR value and reliability of the collected data. In addition, normative data and established protocols facilitate relatively accurate diagnoses using ABR. In veterinary medicine, the canine ABR data available in the literature lacks an established set of universally accepted clinical norms and recording parameters for canine hearing sensitivity assessment.
While many papers have been published regarding canine ABRs, there has been no universally accepted set of clinical normal criteria for dog ABRs. Current testing uses whichever norms a particular researcher or veterinarian deems fit based upon a statistical average of tests performed at their location or in collaboration with other facilities. The results are data-sets that can only be used to analyze ABRs acquired with the same stimulus and recording parameters as those used at that facility. Collaboration or discussion of ABR results among different facilities using different testing parameters prevents comparison of results. In addition, canine hearing assessments and research are often confounded when using stimuli intensity measured in dB nHL (normal hearing level) based on normal human hearing levels and using equipment which is designed for the human auditory system. An appropriate unit of measure for animal ABR stimulus levels and amplitudes should be peak equivalent sound pressure level (peSPL). Until such time that canine norms are fully established and standardized testing protocols are accepted, ABR testing of canines will continue to lack the sophistication seen in the evaluation of the human auditory system. Our laboratory is actively engaged in attaining ABR results from a wide range of breeds with varying head sizes to add to the available data requisite for the establishment of canine ABR norms.
When hearing loss is verified in a dog, either from congenital, acquired, or presbycusic origin, the clinician must work closely with the pet owner to determine what management may be needed. First and foremost, education should be provided to promote safe coexistence in the home. Dogs who do not hear well can be easily startled and may unexpectedly, and uncharacteristically of that particular animal, injure a close family member. This is, of course especially of concern when young children live in the home.
Dog owners may project onto their pets the feelings they believe they would experience with diminished hearing. It is likely that dogs are not nearly as bothered by hearing loss as one might expect as means of communication for dogs arise through other senses in addition to audition—primarily olfaction. Dogs are capable of providing high levels of love, affection, and acceptance regardless of their hearing abilities. However, some degree of communication between pet and owner remains important. Dogs are most often eager to please their owners and may be missing the communication interactions they previously enjoyed. Learning how to train a dog to respond to various manual signs or gestures can greatly improve communication between a hearing-impaired dog and its owner. The use of signs may be augmented though vibratory signals picked up through vibration collars to alert a dog or to give commands. For most dogs, safety and alternate communication methods are all that is needed.
Occasionally, dependent on residual hearing level, health of the dog and high motivation of the dog owner, amplification can be helpful. Key factors to the success of amplification for dogs are the owners’ expectation levels and a high dedication to the requisite training for success. It can take some time for a dog to recognize the benefit that may be derived from amplification, and some never do.
Beyond the Dog
Animal audiology spans more than domestic animals. In the twenty first century we are becoming more aware of the role of acoustic enrichment in the welfare of animals both in the wild and in captivity be they domestic, exotic, or agricultural. ABR testing is now routinely run on horses, exotic animals in zoos, and on marine mammals. Much of this work is related to the potential hearing loss of these animals due to noise (noise-induced hearing loss or NIHL). Growing concern over kennel noise, barn noise, and in captive habitats and the proper acoustic enrichment for the health and welfare of these animals is becoming a forefront of animal wellness.
Truly, animal audiology has reached its place among audiologists but it is not as simple as having the equipment and audiological knowledge to run ABR testing. As with human audiology, an understanding is required of otology and cochlear and neurological hearing mechanisms. The role of the audiologist is clear and beckons the beginning of a relationship between veterinarians and audiologists in the very same manner as that between MDs (ENTs) and audiologists. To this end animal audiology is taught along with veterinarians at the University of Cincinnati, with hope of this relationship coming to fruition in the coming years.
About the Author
Peter M. Scheifele is a Navy (retired) veteran. Having entered the Navy as an enlisted man he served in various ratings, ending up as a Naval Oceanographer. He began working with marine animals while in the Navy by directing the Navy Marine Mammal Technology Program at the Naval Undersea Systems Center, New London, Connecticut, specializing in marine mammal bioacoustic research. During his final ten years he worked at the Naval Underwater Systems Center in New London, Connecticut, and at Mystic Marinelife Aquarium, where he was Head Trainer. It was in this command that he received a presidential award from President Bush, Sr. for his pioneering work in dolphin bioacoustic research as it related to transducers and fetal ultrasound and was inducted into the Order of the Decibel. He retired after 23 years of active service.
He is Director and Principal Investigator and Director of the FETCHLAB (Facility for Education on and Testing of Canine Hearing and Laboratory for Animal Bioacoustics) and an Assistant Professor in the Audiology/Speech-Pathology section of the Department of Communication Sciences and Disorders in the College of Allied Health Sciences at the University of Cincinnati and the neuroscience section of the Medical Education Department of the University of Cincinnati School of Medicine. He is also an Adjunct Assistant Professor in the Communications Science Department neuroaudiology laboratory at the University of Connecticut and adjunct in the Animal Sciences Department: Animal Bioacoustics at the University of Connecticut. He specializes in neuroaudiology and electrophysiology.
Peter’s specialty regards integrated translational research into marine mammal, exotic, and companion (Canine) animal bioacoustics, specifically vocal mechanisms and hearing acuity in noise, central auditory models related to human neuroaudiology, and central auditory processing systems. Peter presently conducts research on vocalization classification and the effects of low-frequency noise on the beluga whales of the Saint Lawrence River Upper Estuary and Cook Inlet, Alaska, and canine hearing and the study of central auditory system relationships to cognitive processing in animals using electrophysiological techniques. He is also a collaborator in the study of animal vocalization processes related to stress using advanced neural computer model techniques under the Dolittle Project grant from the National Science Foundation.
Peter has been involved with human neuroaudiology research for four years and animal/marine mammal bioacoustic research and training for 30 years. His degrees are in (BS) Physics, (MS) Oceanography with an elective in Mechanical Engineering, (PhD) Bioacoustics with speech and hearing sciences minor and with a medical elective (MDr) in otolaryngology and neuroanatomy. He received his degrees from the University of Hawaii and the University of Connecticut and did his medical school at Mount Sinai School of Medicine.