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groove; they arc separated by less łhan 150 /im. Each tympanum is backed by a (ightly adherent iracheal sac. Sensory transduction by 30-35 sensory neurons takes place at the extreme anterior end of each tympanum. Neurophysiological and behavioral tests confirm the prediction that the auditory system lacks directionality. The advantage of a single ear in the midline is not elear, but physiological cvidence suggests that location in the deep groove inereases sensitivity by 4-6 dB. The midline car of the mantis is part of an “early waming system” affording protection from echolocating bats. Tethered flight and free flight exper-iments have shown that the mantis begins responding behaviorally within 50 ms with fuli foreleg extension and abdomen dorsiflexion; a change in flight path begins in 100-200 ms. It is hypothesized that the abdominal flexion throws the flying mantis into a stall out of which it rolls into a power dive. The maneuvers are very effective: In field trials with wild bats, normal mantises escaped capturc whencvcr attacked, while mantises deaf to the bats’ cries were almost always caught.

1:40

7AB2. Courtship communication and hearlng in an African electric flsh. John D. Crawford (Parmly Hearing Inst., Loyola Univ., 6525 N. Sheridan Rd., Chicago, IL 60626)

Among sound-producing fishes, Pollimyrus isidori is of particular interest because of its unusually large repertoire of sounds (5), and because its ears (sacculi) are specialized for sound pressure detection. Males use temporally paltemed sounds for courting females, and the male’s sonie behavior is elicited by electric signals from the female. The courtship sounds arc composed of trains of clicks, and inter-click interval (IC1) distinguishes the different sounds. The processing of these temporal features is being explored in the brain (mesencephalon) with single unit electrophysiology. The P. isidori auditory system is most sensitive to sounds in the region where amplitudę spectrum for the communication sounds peaks (235 Hz), and at a distancc of a meter from a sound-producing małe (i.e., about 20 body lengths) many neurons would be at least 20-30 dB above threshold. Most neurons are broadly tuncd (CiodB<2), and precisely represent temporal periodicities in their phase-locked activity. A subpopulation of neurons shows an inereased prob-ability of response when the ICI is close to that of one of the courtship sounds. These neurons probably play an important role in the brain’s analysis of temporal features of communication sounds. [Work supported by N1H NRSA DC00020-02 and CDR P50 DC00293-06.]

2:10

7AB3. Structure-function relationships in the auditory system of the mustache bat. Thomas J. Park (Dept. of Zoology, Univ. of Texas, Austin, TX 78712)

The mustache bat depends on interaural intensity differences (IlDs) for localizing returning sonar signals. The inferior colliculus (IC) contains many neurons that are excited by sound at one ear and inhibited by sound at the other and are thus sensitive to IIDs. These neurons were studied to determine how their response properties and spatial rcceptive fields are shaped by the convergence of inhibitory inputs from Iower centers. Inhibitory pathways (GABA-ergic and glycinergic) to the IC were identified by colocalizing a retrograde tracer injected in the IC and antibodies against putative transmitters. Glycinergic projections to the IC arise from the superior o!ivc and GABA-ergic projections from the lateral lemniscus and IC intemeurons. The effects of GA BA and glycine were then assesscd by iontophoresing agonists and antag-onists of the transmitters onto individual IC neurons while recording acoustically evoked responses. Application of GABA and glycine inhibited responding, while application of GABA and glycine receptor blockers inereased responding. Furthermore, both blockers were capable of expanding the ncuron’s recep-tive field. This result suggests that inhibition in the IC functions to “fine tune” IID-sensitive neurons by narrowing their receptive fields. (Work supported by NIH.J

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7AB4. Baleen whale vocal behavlor: A synthesis of what wc havc and have not learned. Peggy L. Edds (Dept. of Zoology, Univ. of Maryland, College Park, MD 20742)

The earliest attempt to record the sounds of a baleen whale was by Schevill and Lawrence (Science 109, 143-144 (1949)]. Since that time, a growing body of literaturę has revealed that sound production by baleen whales is quite variable, including relatively narrow-band or tonal calls, and broadband, pulsed series with variable repetition rates or complex amplitude/frequency modulations, as well as flipper slaps, taił slaps, and “noisy” underwater exhalations that appear to be communicative. Although interest in the songs of hump-back whales once dominated the field, numerous studies have documented the behavior and vocalizations of other baleen whale species. A brief revicw and synthesis of those studies will be provided, and the conccpts of "contact” calls, “song," “social sounds,” and individual variation will be considered. In addition, the limitations of acoustical censusing will be discussed. (Original research by the author was supported by ONR, AAUW, and the Cetacean Society.]

1966

J. Acoust. Soc. Am., Vol. 89, No. 4, Pt. 2, April 1991

121st Meeting: Acoustical Society of America

1966