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| Hearing and the effects of noise on pinnipeds
Our lab has been focused primarily on the investigation of pinniped acoustics since 1994. The main impetus for this work was growing concern about increasing levels of noise in the oceans, from sources including shipping, ocean exploration, and military operations. At the time this work was begun, relatively little was known about hearing in pinnipeds, although many species occupy particularly noisy regions close to shore. We have established auditory profiles for each of our three resident species (California sea lion, harbor seal, and northern elephant seal) by testing their hearing in air and under water at a range of different frequencies. From this information, we can generate audiograms, or hearing curves, that allow us to determine frequency ranges of hearing, regions of best hearing sensitivity, and how hearing sensitivities in different media correlate to differences in life history. To expand these auditory profiles, we examine effects of noise on hearing using two different experimental procedures. Masking experiments, which involve signal detection against a noisy background, help us to assess how the simultaneous presence of noise effects hearing, while the temporary threshold shift (TTS) experiments, which involve signal detection following exposure to a noisy background, allow us to evaluate the residual effects of noise exposure on hearing. The results of these experiments are used to generate models which predict how noise of a given intensity, duration, or character will effect the hearing of free-ranging pinnipeds. These data are useful by regulatory agencies charged with establishing policies to protect pinnipeds and other marine mammals from the damaging effects of anthropogenic noise.  top of page |
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| Neurophysiological auditory processing in
pinnipeds Our electrophysiological research, currently led by PhD candidate Jason Mulsow, focuses on evaluating auditory processing in pinnipeds at the level of the level of the brainstem. In these measurements, extremely small neural potentials are evoked in response to aerial acoustic stimuli. These auditory evoked potentials (AEPs) are recorded by small sub-dermal electrodes placed just under the subject’s skin, amplified using a high-gain bio-potential amplifier, and recorded to a laptop computer. Many aspects of pinniped hearing that are difficult to examine with traditional behavioral hearing methodologies are available for study using AEP techniques. For example, the project is currently working on the measurement of auditory sensitivity in a relatively large sample of wild California sea lions housed for rehabilitation at The Marine Mammal Center in Sausalito, California. As current data on aerial hearing in pinnipeds is limited to measurements made with a few captive subjects, we hope that this effort will also us to better understand the variability of hearing in wild California sea lion populations. Future projects will extend electrophysiological methods to other aspects of the amphibious nature of pinniped hearing, such as sound localization, and the nature of sound conduction to the pinniped inner ear. top of page |
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| Bioacoustics of southern sea otters
In 2007, our lab began an investigation into the bioacoustics of the southern sea otter, an amphibious marine mammal whose sensory biology we know surprisingly little about. Sea otters are coastal-living animals with a unique life history—while they spend nearly all of their time in the water, they carry out many important life functions at the surface. Studying sea otter sensory biology will provide us with a better understanding of their evolutionary biology and behavioral ecology, as well as the evolutionary pressures shaping underwater perception in marine mammals. This information will also be beneficial to management of critical coastal habitats. In an effort to better understand the role that sound plays in the perceptual world of sea otters, we are investigating their auditory capabilities using a behavioral approach. Led by graduate student Asila Ghoul, the main focus of this project is to measure hearing sensitivity by obtaining in-air and under-water hearing curves, or audiograms. Odin, the most recent addition to our team of research animals is currently undergoing training to participate in this behavioral hearing assessment. Once the audiograms are obtained, they will be compared to available data collected on other marine mammals (such as pinnipeds), as well as terrestrial carnivores (such as other mustelids) in order to understand better understand the hearing specializations of sea otters. top of page |
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| Cross-modal classification in California sea
lions Ron Schusterman and his past and present research groups have spent over 25 years studying the cognitive abilities of marine mammals. This area of research is concerned with how information gathered from different sensory systems is used by animals in decision-making, problem solving, learning, and memory. Our work in this area has spanned studies of artificial sign language comprehension, short- and long-term memory, discrimination learning, associative learning, and concept formation. Recently, our studies of sea lion cognition have emphasized 'equivalence' classification, or the ability to recognize relationships between stimuli that are not based on similar features, but rather, on similar function or through connections with shared associates. This cognitive skill is shared by humans, sea lions, and some birds and mammals, and is an important topic of study among human and animal psychologists. Our current research investigates the conditions under which equivalence relationships emerge between stimuli, responses and reinforcers, how equivalence relationships form across sensory modalities, and how equivalence relationships are remembered over short and long time scales. At present, we are particularly interested studying the learning mechanisms that support sensory integration between visual and auditory cues. top of page |
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| Cognitive effects of neurotoxic domoic acid
exposure on California sea lions Domoic acid (DA) is a powerful and potentially lethal neurotoxin, the cognitive effects of which are poorly understood. Produced by algal diatoms of the genus Pseudo-nitschzia, DA exposure can lead to hippocampal necrosis—which is associated with memory loss in primates and rodents—and DA exposure has been linked with a variety of neurological symptoms in California sea lions. DA is believed to be the precipitating factor in an increasingly large proportion of sea lion strandings off the California coast, and DA-producing algal blooms have grown more prevalent over the last decade, mirroring instances of DA-related stranding events. In 2007, led by graduate student Peter Cook, our lab embarked on a new line of cognitive/behavioral research: assessing the cognitive effects of naturally occurring DA toxicosis in stranded California sea lions. Specifically, we are developing a rapid behavioral assessment for DA exposure at The Marine Mammal Center—our close ally on this project and the largest marine mammal rehabilitation facility on the West Coast— and we are conducting more in-depth assays of learning and memory at our research facility at Long Marine Lab. By drawing subjects from The Marine Mammal Center we have been able to conduct the first ever marine mammal cognitive research with a large sample size. Studying wild animals that are slated for release post-study has also required our refining and designing a number of low-contact training procedures and cognitive assays that yield reliable results with a wide range of animals in a short period of time. Further, working with collaborators using MRI and other brain imaging techniques, we have access to imaging data for a large cross-set of our subjects, and we hope to pave the way for future naturalistic, non-invasive behavioral neuroscience studies. top of page |
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| Field research on elephant seal
acoustics We are interested in studying sound production, as well as sound reception, and in using our understanding of sensory systems to inform our understanding of naturally occuring behavior. Our ongoing research on northern elephant seal acoustics is conducted seasonally at Ano Nuevo State Reserve, which is located about 20 miles north of our laboratory. The general aims of this work include measuring the source levels of aerial vocalizations produced by all age and sex classes of northern elephant seals and measuring ambient noise levels in the seal rookeries during the breeding season. We are also looking at amphibious sound production by males stationed along the shoreline during the breeding season. These data provide a useful complement to our research on elephant seal hearing. The combination of our field studies with our laboratory data on elephant seal acoustics is yielding insight into intraspecific communication by allowing us to predict the distances over which an individual's calls may be detected by other seals; for example, the effective communication ranges of a mother vocalizing to her pup or an alpha male's rumbling threats directed towards a breeding rival. Additionally, we have uncovered several interesting characteristics of vocal and visual signaling in sub-adult male and adult female elephant seals, which have led us to investigate aspects of vocalization stereotypy and the influence of social context on vocal communication. top of page |
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| Vocal learning in seals and
walruses Many of our field studies deal generally with sound production and acoustic communication in pinnipeds, especially in noisy environments. However, there are some interesting aspects of sound production that are difficult to study in wild animals. Our ongoing research with captive seals at Long Marine Lab and captive walruses at Six Flags Discovery Kingdom concerns the extent to which pinnipeds are capable of vocal learning. While evidence for vocal production learning is limited in most nonhuman mammals, marine mammals appear to have a unique propensity for learning how to modify their sounds as a result of interactions with the social and physical environment. Our work involves looking at spontaneous (untrained) components of vocalizations, such as annual cycles in vocal behavior, the types of sounds emitted, and the behavioral contexts in which these sounds are produced. We also use food reinforcement and operant conditioning in order to determine how plastic these sound emissions are. Such studies help us to better understand the innate vs. learned aspects of acoustic communication in these animals. top of page |
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| Underwater wake detection and tracking by harbor
seals We are beginning some new work on a fascinating but poorly understood sensory modality--that of hydrodynamic reception--in harbor seals. This work is inspired in part by the research findings of our colleagues in Germany, who have shown that harbor seals are capable of detecting and following underwater wakes as they decay in time. We are current cooperating with partners at the University of Virginia who are tackling this research area from an engineering standpoint. Our studies with a trained seal will inform the development and fabrication of bio-inspired prototypes and instrumentation to be used for real world flow-field characterization. top of page |
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© 2009 Pinniped Cognition & Sensory
Systems Laboratory. All rights reserved. |
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