FM Sweep Research Articles

Neural processing mechanisms in echolocating bats, correlated with differences in emitted sounds.

Bats that emit pulses containing constant wavelength (CW) components preceding an FM sweep show neural adaptations that differ conspicuously from those of bats emitting purely FM pulses. In contrast to “FM bats,” which have sharply tuned units distributed broadly throughout the range of their emitted pulses, “CW bats” have auditory systems tuned predominantly to a much smaller range corresponding to the restricted range of emitted frequencies. There is an “off”-response sharply tuned to the emitted CW frequencies. “On” response sensitivity is greater at just lower frequencies (CW component of less than 8-msec duration) or on either side of the “off”-frequency, with a null at that point (CW component of 10–20 msec or longer). The “off”-response, which is present at the level of the auditory nerve, apparently represents rebound excitation following non-neural suppression peripheral to the primary afferent fibers. It reflects a mechanism for increasing frequency discrimination and has the effect as well of enhancing response to the FM portion of the emitted pulses. High sensitivity to frequencies above that of the emitted CW, in “long CW” bats, is apparently tied to a use of the Doppler-shifted echo CW to detect and determine the angle and/or relative velocity of echo sources. CW bats show much less dramatic temporal resolution ability than FM bats, although it seems probable that the same mechanism of distance determination—measurement of elapsed time between emitted and returning FM sweeps—is used by both. CW bats, on the other hand, appear to have more units that are sharply sensitive to signal angle, showing strong binaural interaction. The consistent and conspicuous differences in neurophysiology in different species indicates not only that central analytic mechanisms are highly adaptable, but that these adaptations are important and closely tied to the types of orientation sounds used.

Comparative auditory neurophysiology of neotropical bats employing different echolocation signals

1. Five species of neotropical bats, which emit echolocation pulses different than those employed by bats previously studied, were investigated in an attempt to find corresponding differences in mechanisms of neural analysis. Evoked potentials were recorded from the posterior colliculi and more peripheral levels in anesthetized specimens. 2. Each species was found to be most sensitive in approximately the same frequency range it uses in its emitted pulses: Chilonycteris rubiginosa at 63 kc/s, Pteronotus suapurensis at 50 kc/s, Saccopteryx bilineata at 42 kc/s, Phyllostomus hastatus at 50 kc/s, and Carollia perspicillata at 80 kc/s. Sensitivity was especially sharply “tuned” in the bats employing predominantly constant frequency pulses (Chilonycteris and Saccopteryx). 3. Chilonycteris, Saccopterys and Pteronotus have prominent evoked potential responses to the end of a tone pip. In Chilonycteris and Saccopteryx these “off”-responses are extremely sharply tuned to a 2–5 kc/s frequency band centered just below the frequency of greatest sensitivity of the “on” response. The presence of an “off”-response appears to be correlated with the use of long, predominantly constant frequency pulses. 4. The rate of recovery of responsiveness following an initial signal varied, being rapid at the level of the colliculus in Phyllostomus and Carollia (100% in 2–3 msec, slight supranormal responsiveness, and no subsequent depression), also rapid in Pteronotus, (but with an unusual degree of facilitation of responsiveness at intervals of 1–2 msec, followed by 5–10 msec of deep depression), and comparatively slow in Chilonycteris and Saccopteryx (full recovery in 10 msec or more). 5. In bats using long orientation pulses which overlap with returning echoes (Chilonycteris and Saccopteryx), the “off”-responses are found to provide a more visible record of the presence of echoes and their time of arrival than do the “on”-responses. 6. Chilonycteris respond to the orientation pulses of other Chilonycteris with prominent “off”-responses, which apparently are evoked by the termination of the constant frequency portion of each pulse rather than the downward FM sweep. 7. Phyllostomus and Chilonycteris are sharply sensitive to changes in signal angle, Pteronotus is moderately so, and Saccopteryx and Carollia are relatively insensitive to angle at the level of the colliculus. In Saccopteryx and Carrollia the auditory nerve response is more sharply sensitive to angular change of the signal. 8. In several species, but most prominently in Pteronotus, large DC potentials, of the same duration as the signal, were recorded in the vicinity of the cochlea and VIII nerve. These potentials were probably “summating potentials” and sometimes showed reversal of polarity with changes in signal frequency. 9. In one preparation (Pteronotus), a DC potential was seen that was apparently contralateral in origin, had a latency 1 msec longer than the ipsilateral “summating potential”, and showed adaptation suggestive of a neural origin. It is suggested that a direct neural pathway between the two ears may exist. 10. It is concluded that species differences in response patterns are at least in part a result of evolutionary adaptation governed by the type of emitted orientation sounds employed.

Excitation and inhibition in cochlear nucleus. II. Frequency-modulated tones.

Excitation and inhibition in cochlear nucleus. II. Frequency-modulated tones.S D Erulkar, R A Butler, and G L GersteinS D Erulkar, R A Butler, and G L GersteinPublished Online:01 Jul 1968https://doi.org/10.1152/jn.1968.31.4.537MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByFM velocity selectivity in the inferior colliculus is inherited from velocity-selective inputs and enhanced by spike thresholdJoshua X. Gittelman, and Na Li1 November 2011 | Journal of Neurophysiology, Vol. 106, No. 5Facilitatory Mechanisms Shape Selectivity for the Rate and Direction of FM Sweeps in the Inferior Colliculus of the Pallid BatAnthony J. Williams, and Zoltan M. Fuzessery1 September 2010 | Journal of Neurophysiology, Vol. 104, No. 3Intracellular Recording Reveals Temporal Integration in Inferior Colliculus Neurons of Awake BatsS. V. Voytenko, and A. V. Galazyuk1 February 2007 | Journal of Neurophysiology, Vol. 97, No. 2Neural Mechanisms Underlying Selectivity for the Rate and Direction of Frequency-Modulated Sweeps in the Inferior Colliculus of the Pallid BatZoltan M. Fuzessery, Marlin D. Richardson, and Michael S. Coburn1 September 2006 | Journal of Neurophysiology, Vol. 96, No. 3Neural Processing of Amplitude-Modulated SoundsP. X. JORIS, C. E. SCHREINER, and A. REES1 April 2004 | Physiological Reviews, Vol. 84, No. 2Spectrotemporal Organization of Excitatory and Inhibitory Receptive Fields of Cat Posterior Auditory Field NeuronsWilliam C. Loftus, and Mitchell L. Sutter1 July 2001 | Journal of Neurophysiology, Vol. 86, No. 1Functional Specialization in Auditory Cortex: Responses to Frequency-Modulated Stimuli in the Cat's Posterior Auditory FieldPeter Heil, and Dexter R. F. Irvine1 June 1998 | Journal of Neurophysiology, Vol. 79, No. 6Processing of Frequency-Modulated Sounds in the Cat's Posterior Auditory FieldBiao Tian, and Josef P. Rauschecker1 May 1998 | Journal of Neurophysiology, Vol. 79, No. 5Single neurone models: oversimple, complex and reducedTrends in Neurosciences, Vol. 15, No. 11Sensitivity of neurons in cat primary auditory cortex to tones and frequency-modulated stimuli. I: Effects of variation of stimulus parametersHearing Research, Vol. 63, No. 1-2Encoding of amplitude modulation in the gerbil cochlear nucleus: II. Possible neural mechanismsHearing Research, Vol. 44, No. 2-3Spectral hyperacuity in the cat: neural response to frequency modulated tone pairsHearing Research, Vol. 41, No. 2-3Spectral characteristics of the responses of primary auditory-nerve fibers to frequency-modulated signalsHearing Research, Vol. 39, No. 1-2Sensitivity of cat primary auditory cortex (Al) neurons to the direction and rate of frequency modulationBrain Research, Vol. 327, No. 1-2Organized projection of the goldfish saccular nerve onto the Mauthner cell lateral dendriteBrain Research, Vol. 274, No. 2Responses of neurons in the inferior colliculus of the rat to AM and FM tonesHearing Research, Vol. 10, No. 3Single unit analysis of the posteroventral cochlear nucleus of the decerebrate catNeuroscience, Vol. 7, No. 8Synaptic excitation of the second and third order auditory neurons in the avian brain stemNeuroscience, Vol. 7, No. 6Audibility of short-duration tone-glides as a function of rate of frequency changeHearing Research, Vol. 7, No. 1Early auditory electric responses to fast amplitude and frequency tone glidesElectroencephalography and Clinical Neurophysiology, Vol. 51, No. 6Response Characteristics of Cochlear Nucleus Neurons to Vowel Sounds29 June 2016 | Annals of Otology, Rhinology & Laryngology, Vol. 86, No. 1Response pattern complexity of auditory cells in the cortex of unanesthetized monkeysBrain Research, Vol. 69, No. 1Unit responses in the inferior colliculus of rat to temporal auditory patterns of tone sweeps and noise burstsExperimental Neurology, Vol. 42, No. 3The physiology of auditory frequency analysisProgress in Biophysics and Molecular Biology, Vol. 28The effects of insular and temporal lesions in cats on two types of auditory pattern discriminationBrain Research, Vol. 62, No. 1Response of cat cochlear nucleus neurons to frequency and amplitude modulated tonesBrain Research, Vol. 45, No. 2Single unit responses to frequency-modulated tones and possible relationship to inhibitory effect of two-tone stimuliBrain Research, Vol. 43, No. 2 More from this issue > Volume 31Issue 4July 1968Pages 537-48 https://doi.org/10.1152/jn.1968.31.4.537PubMed5709870History Published online 1 July 1968 Published in print 1 July 1968 Metrics

Comparative Echolocation by Fishing Bats

The acoustic orientation of two species of fish-catching bats was studied as they negotiated a row of strings or fine wires extending across their flight path. Orientation sounds of Pizonyx vivesi consisted of a steep descending FM sweep lasting about 3 msec. Noctilio leporinus used 8 to 10 msec pulses composed of an initial nearly constant frequency portion followed by a descending frequency modulation. The echolocation of small wires by N. leporimis differed from that of surface fish in that during wire avoidance no nearly constant frequency or entirely FM pulses were emitted, nor was the pulse duration markedly shortened as the barrier was approached. There was extensive temporal overlap at the animal's ear of returning echoes with the emitted cries when the bat was near the barrier—a strong contrast to the apparent careful minimization of such overlap during feeding maneuvers. Noctilio increased its average pulse duration about 2 msec when confronted with a barrier of 0.21 mm, as opposed to 0.51 mm, diameter wires. Pizonyx detected these wires well before pulse-echo overlap began, but at a shorter range than did N. leporinus, suggesting the latter species may have a longer effective range of echolocation.

Results of Volume-Reverberation Tests

Reverberation tests were conducted as part of an over-all NAVAIRDEVCEN program for improving both sonar systems and the capability for predicting system effectiveness. A 15.4-kHz sound source was used to investigate volume reverberation levels as a function of source level, pulse length, and FM sweep width. Explosive sound sources were used to investigate diurnal variation and the spectral distribution of reverberation levels. The data show that the relationship between volume-reverberation level and source level is linear. An equation is empirically derived that expresses a less-than-linear dependence of volume reverberation levels on pulse length. The amplitudes of the deviations from the mean levels are shown to be lower for the FM mode than the sinusoid mode and inversely proportional to the swept bandwidth. The mean levels, however, exhibit no significant differences. Nighttime reverberation levels for the systems used are shown to be significantly higher than daytime levels.

RESPONSES OF AUDITORY CORTICAL NEURONS TO STIMULI OF CHANGING FREQUENCY.

RESPONSES OF AUDITORY CORTICAL NEURONS TO STIMULI OF CHANGING FREQUENCY.

Delay-line secondary responses in AM and FM sweep integrators

A video sweep integrator is a device for adding the successive detected radar returns of successive transmitted pulses. One type of video sweep integrator uses an ultrasonic delay line for storage and the addition is obtained by means of a closed regenerative loop operating continuously with exponential memory. Delay-line secondary, or spurious, responses result from multipath propagation through the delay line. The cumulative effect of these responses after they are recirculated in the sweep integrator may be very significant. The exact effect depends to a certain extent upon the type of modulation that is propagated through the delay line. In this paper the buildup effects of secondaries are determined for both AM and FM transmission through the delay line. With AM there is coherent buildup, which results in a secondary buildup relatively much greater than the buildup of the desired signal. With frequency modulation it is possible to alleviate the buildup effect of secondaries by introducing a small amount of hum deviation on the carrier frequency, which results in a random build-up. Experiments with FM sweep integrators confirm the expected coherent buildup without hum deviation and also confirm that random buildup occurs when the hum deviation is introduced. This paper also derives formulas for the effects of delay-line secondaries when the integrator operates with uniform or constant memory for a finite time. In this mode of operation with FM transmission through the delay line, the secondaries build up essentially noncoherently without the introduction of hum deviation.