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Our research program explores the sensory,
cognitive, and behavioral ecology of marine mammals. The approach we apply
to these areas is to study individuals in controlled and natural settings.
Experiments conducted in the laboratory allow us to generate hypotheses
about the perceptual and cognitive mechanisms that enable animals to acquire,
organize, and utilize various types of information. Observations made
in the field allow us to see how perception is translated into meaning
and action. Comparative studies in both settings help us to understand
how ecological, evolutionary, and life history factors have influenced
the sensory and cognitive capabilities of different marine mammal species.
Our laboratory research is conducted at Long Marine Lab at the University of California Santa Cruz and at the US Navy Marine Mammal Research Program at SPAWAR Systems Center in San Diego, California. At these facilities, a small group of resident seals, sea lions, and dolphins work closely with researchers in behavioral psychophysical studies. The animals are trained using operant conditioning and positive reinforcement to participate in various research procedures that involve active decision-making. The procedures themselves are either detection or discrimination tasks. For detection tasks, subjects are trained to report the presence of a signal, much like human subjects performing in sensory assessment procedures. We typically use stimuli that vary along a single dimension, such as sounds of a fixed frequency and duration that are varied in level. These signal detection procedures allow us to measure behavioral thresholds, or stimulus levels at which the subject can no longer differentiate a signal from background noise. Multiple thresholds can then be used to depict sensitivity profiles for stimuli of a given type. Examples of studies we have carried out using detection procedures include investigation of visual dark adaptation, auditory masking, and amphibious hearing capabilities in pinnipeds. For the discrimination tasks, subjects learn to differentiate between at least two alternative stimuli. Discrimination tasks can be fairly simple, where subjects choose from one of two alternatives on the basis of preference or previous experience, or they can be conditional, where the correct alternative is controlled by another stimulus known as a sample stimulus. Examples of studies we have completed using discrimination procedures include assessment of sound localization abilities, associative learning within and across sensory modalities, concept formation, and short- and long-term memory.
In the field, our interests focus on how individuals use sensory cues to communicate, forage, navigate, and avoid predation. We can combine sensitivity measures obtained in the lab with vocalization and ambient noise measurements obtained in the wild to estimate biologically significant variables such as communicative ranges, zones of masking in natural and anthropogenic noise, and directional propagation of vocal signals. These variables help us to better understand how animals such as seals and sea lions use sound and other sensory cues in social and ecological contexts. The signals produced in natural environments are generally more complex than those used in experimental situations, and various aspects of these signals—including stereotypy, redundancy, duration, frequency range, amplitude, and context—are oftentimes particularly suited to gain the attention of receivers as well as convey information about the identity, status, location, and/or the motivational state of the of the signaler. On a cognitive level, unraveling relationships between signal form and function reveals how signals acquire meaning and how they may be recognized and remembered over time.
In terms of ecological policy-making, our work has direct application to the impact of noise pollution on habitat degradation of all marine mammals, but most particularly, the pinnipeds. For example, we are interested in how exposure to noise may interfere with biologically significant activities, such as a female attending her pup or a male defending his territory during the breeding season. We believe that by evaluating the sensory abilities of marine mammals, sensible regulations can be drafted which will mitigate the impact of noise pollution (from sources including shipping traffics, oceanographic experiments, military sonar, and acoustic harassment devices) and its deleterious effects on the behavior and physiology of these diving mammals.
Finally, our work on learning, memory, concept formation, and artificial language in sea lions and other marine mammals has shown how well these animals can integrate a variety of sensory cues in order to organize perceptual information into meaningful associations and categories. These aspects of cognition are likely to be critical for the evolution of complex problem solving abilities, referential communication, and perhaps even proto-linguistic skills including syntax and semantics. Our evidence for non-verbal thinking in sea lions informs our understanding of the development of non-verbal thinking in humans such as infants, children, and language- or cognitively-impaired adults.
The
research program was developed by Dr. Ronald
J. Schusterman and his collaborators over a period of more than 40
years. The project has been based at UCSC's Long Marine Lab since 1985, and is currently headed by Dr. Colleen Reichmuth.
FOR MORE INFORMATION
Long Marine Laboratory is part of the Institute of Marine Sciences at UCSC. The Seymour Marine Discovery Center at LML offers tours and additional information about the facility and ongoing research.