Neuroethological studies of sensory processing
Neuroethology combines analyses at the behavioral, systems and cellular levels, and a typical neuroethological project attempts to determine the mechanism by which a class of stimulus regimes controls a given natural behavioral response. Since there is a heavy concentration on species-specific behavior, neuroethological studies of auditory specialists such as bats, owls, fish, and praying mantises can provide new insights into mechanisms used by less specialized auditory systems.
Owls, bats and insects have historically provided excellent models for linking structure and function. For example, a tremendous amount is now known at the anatomical, physiological, and modeling level, about the brain stem mechanisms in the barn owl that encode elevation and azimuth. Questions have now moved to development and how the auditory system copes with changing head size for instance. In the bat, research questions have emphasized auditory localization along the range axis, comparing psychophysical and modeling data with neurophysiological measures of object location and distance coding. Questions now center on questions of sensorimotor integration with the bat’s sonar system behaving something like an acoustic flashlight. In the final analysis, the auditory systems of these species must integrate cues from all three dimensions for object localization. Yet because they are very different, comparison of these systems should provide insight into common elements required for object localization. There is also now evidence that extraordinary temporal resolution in the "unspecialized" avian ear, well below human thresholds, may also function in the real world for object location and distance determination. Sound source identification and localization in insects, on the other hand, has evolved form different auditory processing mechanisms than found in vertebrates which provide yet a different view.
PEOPLE AND PROJECTS
Catherine E. Carr, Biology
Work at Dr Carr´s laboratory addresses the cellular basis of time coding in the auditory system, using the barn owl as a model. Temporal information is processed in the cochlear nucleus magnocellularis which projects to the nucleus laminaris, where interaural time differences (ITDs) are first computed. Since precise temporal coding is critical to the detection of ITDs, the lab is working to determine how phase-locking changes during circuit development. Physiological studies describe how ITD coding changes during development. These studies are carried out in parallel with studies of features associated with temporal coding such as the regulation of myelination and the expression of K+ channel and GluR subtypes. The Carr lab is also looking at models of ITD coding to see if specific adaptations, like changes in number of inputs, improvements in phase locking, changes in dendritic length, etc improve ITD coding. Other physiological studies in the lab address functional studies of the cochlear nucleus angularis. Well established collaborative projects include studies on ITD coding in small birds with the Dooling lab and studies on space coding in the superior colliculus of bats with the Moss lab.
ROBERT J. DOOLING, PSYCHOLOGY (C-CEBH DIRECTOR)
Prof. Dooling has recently demonstrated, both psychophysically and physiologically, that small birds have much better temporal fine structure discrimination than humans and other mammals. This information is now being applied in psychophysical studies examining the perception of environmentally induced degradation of vocalizations including smearing, reverberation, and various other changes. These studies may resolve some of the mystery of how birds locate sound sources in nature with better resolution than would be expected govern their small heads and closely spaced ears.
CYNTHIA F. MOSS, PSYCHOLOGY (C-CEBH DIRECTOR)
Prof. Moss´ research program is focused on understanding both auditory information processing and spatially-guided behavior in bats. Bats use the time delay between sonar emissions and echoes to determine target distance and integrate this information with interaural cues and spectral filtering of the pinna to form a three-dimensional representation of auditory space. Acoustic measurements of the head-related transfer function of the bat are used for models of spatial information processing and sensorimotor integration. The Moss lab is also conducting studies of the bat's adaptive motor behaviors that depend upon the spatial analysis of auditory scenes. This work now includes collaborations with the Yager lab on dynamic predator-prey interactions. Neurophysiological experiments in the Moss lab focus on the functional organization of the midbrain superior colliculus, a neural structure believed to play a role in transforming polymodal sensory information into signals relayed to brainstem structures that control appropriate orienting responses. Moss has worked closely with Catherine Carr and others in the Imaging Core to bring histological studies to bear on role of the bat SC in target identification and localizations.
DAVID D. YAGER, PSYCHOLOGY
Dr. Yager's work on insects offers a dramatic comparison. Here major research questions center on the function and evolution of sensory mechanisms in insects that can be used for the evasion of predators, such as echolocating bats. Bats produce sonar vocalizations and listen for echoes to detect, localize and track insect prey; some insect species have evolved sensory systems that respond to sonar signals and enable escape behaviors. This is something like an evolutionary arms race. Praying mantises, for example, have a cyclopean ear that is sensitive to ultrasound, and ultrasonic pulses trigger a complex, short-latency response in flying mantises. In addition, the mantis detects wind, primarily with filiform hairs on the cerci; information from both sensory modalities is carried in the CNS by giant interneurons. Part of the effort is in understanding the integration of wind and sound information which may be crucial in determining the timing, strength and nature of the insect's evasive response.
