Harvard Univ., 1978

Professor

Hunter Lab #306

Phone: 863-2283

Email: [email protected]

  Research Summary:

Research focuses around an analysis of neural information processing in the vertebrate auditory system, specifically as related to the processing and coding of temporal features of biologically-relevant sounds. We use the auditory system of anuran amphibians as a model system for understanding basic auditory processes, both as related to behavior and to underlying neural control. Currently three major projects are underway. One project examines behavioral sensitivity to and the neural coding of acoustic features relevant for periodicity ('pitch') perception. The frog's auditory system provides an interesting model for understanding the neural bases of periodicity extraction, because the organization of its inner ear allows separation of possible spectral and temporal codes for 'pitch' in a manner not easily achievable in other vertebrates. Currently we are quantifying the existence of parallel pathways for frequency and time processing in ascending auditory pathways, and we are conducting a series of anatomical experiments to determine how these physiological response properties are related to morphological features of these neurons. We also conduct field work on responses of frogs in their natural environments to biologically-relevant communication signals. We are interested in the role of spectral and temporal features of sounds in guiding behavior in the natural environment. Another project examines the development of sensitivity to airborne sounds across metamorphosis in anurans. Here we follow anatomically, physiologically and behaviorally those morphological rearrangements in the central auditory system that occur as the animal transforms from an aquatic (tadpole) state responsive to water currents to a terrestrial (adult) state with the ability to hear airborne sounds. In particular, we are interested in the development of time-coding processes, and in changes in the histochemical organization of the auditory brain stem across metamorphic development. A final project involves computational modeling of signal processing in the frog auditory system, particularly as related to algorithms for pitch extraction. We have developed a simple sandwich model that can account for significant portions of the ability of eighth nerve fibers to extract periodicity from complex acoustic signals, and we are currently refining this model to account for other forms of auditory perception as well.

  Publications:

Boatright-Horowitz, S.S. and Simmons, A.M. (1997) Transient deafness accompanies auditory development during metamorphosis from tadpole to frog. Proceedings of the National Academy of Sciences USA, 94, 14877-14882.

Kumaresan, V., Kang, C. and Simmons, A. M. (1998). Development and differentiation of the anuran auditory brainstem across metamorphosis: An acetylcholinesterase histochemical study. Brain, Behavior and Evolution, 52: 111-125.

Boatright-Horowitz, S. S., Cheney, C. A., and Simmons, A. M. (1999) Atmospheric and underwater propagation of bullfrog vocalizations. Bioacoustics, 9: 257-280.

Boatright-Horowitz, S.S., Garabedian, C.E., Odabashian, K. H., and Simmons, A.M. (1999)Coding of amplitude modulation in the auditory midbrain of the bullfrog (Rana catesbeiana) across metamorphosis. Journal of Comparative Physiology, 184: 219-231.

Fay, R. R. and Simmons, A.M. (1999). The sense of hearing in fishes and amphibians. In Comparative Hearing: Fish and Amphibians, A.N. Popper and R.R. Fay (Eds.). Springer Handbook of Auditory Research, Springer-Verlag, 269-318.

Simmons, A. M., and Bean, M. E. (1999). Perception of mistuned harmonics in complex sounds by the bullfrog, Rana catesbeiana. Journal of Comparative Psychology, in press.

Kaya, U., and Simmons, A. M. (1999). Advertisement calls of the tree frogs, Hyla arborea and Hyla savignyi, in Turkey. Bioacoustics, in press.

Program in Biology | Biology Undergraduate Research | Biology Undergraduate Program