My proposed research focuses on fundamental questions in hearing and the neural mechanisms employed by the brain in the processing of communication sounds. In the natural world, the auditory system extracts critical signals, such as speech, from exceedingly complex acoustic environments. This is accomplished through mechanical and neurobiological filtering processes. Some of this filtering is accomplished within the ear and auditory nerve. However, a great deal is also accomplished through complex processing in the brain, and we know comparatively little about this. A robust understanding of auditory brain function is of clear significance to a wide array of health issues, including the development of effective auditory nerve electrical stimulation paradigms and cochlear implants for the hearing impaired. I will use neurophysiological and anatomical methods to address questions about the representation of sounds in the brain. While frequency and temporal cues are both important components in communication sounds, human behavioral studies underline the salience of temporal structure in object perception (e.g. Rasch, 1978) and in source localization (e.g. Yost & Hafter, 1987). Moreover, recent studies indicate that the preservation of time-cues must be a priority in the engineering of cochlear implants (Shannon, 1990). I will concentrate on the neural representation of temporal features of sound. In many animal communication systems, temporal coding is also of preeminent importance (Myrberg et al., 1978; Michelsen et al., 1985). I have selected a vertebrate model, the mormyrid fish, on the basis of two important criteria: 1) the fish's ear is specialized for encoding temporal features of sound, lacking a sophisticated frequency analyzer as seen in the mammalian cochlea, and 2) I have shown that this fish uses temporally patterned sounds in its relatively simple acoustic communication behavior. Using extra-cellular neurophysiological recording techniques, I will examine responses to naturalistic acoustic click-trains and other temporally modulated stimuli. I will investigate the ascending auditory system, in the mesencephalon and diencephalon, with the goal of describing the neural representation of these sounds, and identifying regions where major transformations occur. Preliminary research in the mesencephalon has already revealed a number of interesting properties, including neurons which appear to be selective for particular time-intervals. Thus, the prospects for a successful study of auditory physiology and communication in this system seem good.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Hearing Research Study Section (HAR)
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Loyola University Chicago
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United States
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Suzuki, Aae; Kozloski, James; Crawford, John D (2002) Temporal encoding for auditory computation: physiology of primary afferent neurons in sound-producing fish. J Neurosci 22:6290-301
Large, Edward W; Crawford, John D (2002) Auditory temporal computation: interval selectivity based on post-inhibitory rebound. J Comput Neurosci 13:125-42
Fletcher, L B; Crawford, J D (2001) Acoustic detection by sound-producing fishes (Mormyridae): the role of gas-filled tympanic bladders. J Exp Biol 204:175-83
Kozloski, J; Crawford, J D (2000) Transformations of an auditory temporal code in the medulla of a sound-producing fish. J Neurosci 20:2400-8
Marvit, P; Crawford, J D (2000) Auditory thresholds in a sound-producing electric fish (Pollimyrus): behavioral measurements of sensitivity to tones and click trains. J Acoust Soc Am 107:2209-14
Marvit, P; Crawford, J D (2000) Auditory discrimination in a sound-producing electric fish (Pollimyrus): tone frequency and click-rate difference detection. J Acoust Soc Am 108:1819-25
Crawford, J D; Huang, X (1999) Communication signals and sound production mechanisms of mormyrid electric fish. J Exp Biol 202:1417-26
Kozloski, J; Crawford, J D (1998) Functional neuroanatomy of auditory pathways in the sound-producing fish Pollimyrus. J Comp Neurol 401:227-52
Crawford, J D; Cook, A P; Heberlein, A S (1997) Bioacoustic behavior of African fishes (Mormyridae): potential cues for species and individual recognition in Pollimyrus. J Acoust Soc Am 102:1200-12
Crawford, J D (1997) Feature-detecting auditory neurons in the brain of a sound-producing fish. J Comp Physiol A 180:439-50

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