Biomedical subjects

Z M Fuzessery

Publications and source records attributed to Z M Fuzessery.

9 recordsLinked to original sources

PubMed1992

Spatial processing within the mustache bat echolocation system: possible mechanisms for optimization.

1. The directionality of an echolocation system is determined by the acoustic properties of both the emitter and receiver, i.e., by the radiation pattern of the emitted pulse and the directionally of the external ears. We measured the directionality of the echolocation system of the greater mustache bat (Pteronotus parnellii) at the 30 kHz, 60 kHz and 90 kHz harmonics of its echolocation pulse by summing, at points throughout the frontal sound field, the echo attenuation due to the spread of pulse energy and the attenuation due to the spread of pulse energy and the attenuation due to the directionality of its external ears. The pulse radiation pattern at the 3 harmonics was measured by comparing the output of a microphone moved throughout the frontal sound field against a second reference microphone at the center of the field. External ear directionality at the 3. harmonics was measured by presenting free-field sounds throughout the frontal sound field, and recording the intensity thresholds of cochlear microphonic potentials, and the intensity thresholds of monaural neurons in the inferior colliculus tuned to one of the 3 harmonics. 2. When compared with ear directionality, the echolocation system was found to be more directional for the center of the sound field in several respects. At all harmonics, attenuation of sounds originating in the peripheral part of the field was increased by 10 to 13 dB. Areas of maximum sound intensity contracted toward the center of the field. Also, the isointensity contours of the echolocation system were more radially symmetrical about the center of the field. 3. At 60 kHz, sound intensity along the azimuth within the echolocation system was nearly constant 26 degrees to either side of the center of the field. This suggests that the radiation pattern of the echolocation pulse and the directionality of the external ears complement one another to produce an acoustic environment at the center of the sound field in which stimulus intensity is stabilized to allow more effective analysis of various aspects of the echolocation target. In particular, we suggest that this intensity stabilization may allow the bat to more effectively resolve the interaural intensity differences it uses to localize prey. 4. Predictions of the azimuthal spatial tuning of binaurally sensitive neurons in the inferior colliculus within the echolocation system were compared with their spatial tuning when only ear directionality is considered.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1991

A microcomputer-controlled system for use in auditory physiology.

This report describes a digitally controlled system for use in auditory physiology in which signal generation and data acquisition are under the control of a single microcomputer. The system is designed to generate the complex waveforms required in neuroethological studies, and is able to generate these signals at frequencies of up to 160 kHz with a resolution of 1 Hz. The system is built around a commercially available digital hardware system, and augmented with custom components to enhance operation speed, precision and flexibility.

Hearing↗

PubMed1990

Determinants of horizontal sound location selectivity of binaurally excited neurons in an isofrequency region of the mustache bat inferior colliculus.

1. The monaural and binaural response properties and the horizontal sound location sensitivity of 78 binaurally excited neurons from 26 bats were examined with a combined closed-field and free-field stimulation paradigm. The aim was to determine how the response properties of these neurons shape their selectivity for auditory space. All neurons were recorded within a single, greatly enlarged isofrequency (60 kHz) region of the mustache bat's central nucleus of the inferior colliculus (ICC). In this and two companion papers (Wenstrup et al. 1988a,b) that focused on binaurally inhibited neurons in this isofrequency region, our goal was to examine the neural mechanisms for binaural processing within a single frequency channel of the primary auditory system. 2. Binaurally excited neurons were defined as either excited by monaural input from both ears or, if excited by monaural stimulation of only one ear, facilitated by binaural stimulation. Some neurons also exhibited binaural inhibition. These neurons were divided into functional classes based on their responses to monaural and binaural stimulation presented under dichotic, closed-field conditions. The following notation was used: response to contralateral stimulation (E, excitatory; O, no effect), response to ipsilateral stimulation (E, excitatory; O, no effect)/response to binaural stimulation (F, facilitatory; I, inhibitory; O, no effect). Seven functional classes were observed: EE/O, EE/F, EE/I, EE/FI, EO/F, EO/FI, and OO/F. 3. Among EE neurons, thresholds for contralateral monaural stimulation were typically lower than for ipsilateral stimulation, and response magnitudes for contralateral stimulation were typically greater. Among EO/F and EO/FI neurons, only one eye, an OE/FI neuron, was excited by ipsilateral monaural stimulation. These results suggest that contralateral input provides the dominant excitatory influence. EE/FI and EO/FI neurons, which exhibited both binaural facilitation and inhibition, were typically inhibited at interaural intensity differences (IIDs) favoring the ipsilateral ear, suggesting that ipsilateral input provides the dominant inhibitory influence. 4. Neurons were tested over the range of naturally occurring IIDs (+/- 30 dB) at intensities of -20 to 30 dB relative to threshold. The IID functions of these neurons assumed three configurations: flat, with facilitation occurring at all IIDs; stepped, with facilitation occurring over part of the IID range, and peaked, with facilitation occurring over a limited band of IIDs. The majority of cells (90%) exhibited peaked IID functions, and most of these (73%), regardless of functional class, were maximally facilitated at an IID of 0 dB. 5. Neurons differed considerably in the strength of their binaural interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1988

Binaural neurons in the mustache bat's inferior colliculus. I. Responses of 60-kHz EI units to dichotic sound stimulation.

1. Single-unit responses to closed-field, dichotic sound stimuli were obtained from EI neurons in the mustache bat's inferior colliculus; these neurons are excited by sound to the contralateral ear and inhibited by sound to the ipsilateral ear. All units were tuned to the 60-kHz component of the bat's sonar signal. The goal of the study was to describe basic features of the sensitivity to interaural intensity differences (IIDs) and sound intensity among an isofrequency population of EI neurons. The following paper describes how these features of IID sensitivity shape the response to free-field sounds. 2. Three features of IID sensitivity were considered. The inhibitory threshold (Figs. 1 and 2) described the IID at which inhibitory effects became pronounced; it was defined as the IID at which the excitatory response to contralateral sound was suppressed by 50%. Most units (68%) were inhibited at positive IID values, for which the ipsilateral (inhibitory) sound was more intense. The maximum inhibition (Figs. 1 and 3) described the strength of ipsilateral inhibition; it was defined as the percent that each unit was inhibited below its response to monaural stimulation of the contralateral ear. The majority of units (58%) were almost totally suppressed by a sufficiently intense ipsilateral sound. The IID range (Figs. 1 and 4) described the sharpness or slope of the IID cutoff; it was defined as the IID range over which the response changed from nearly unsuppressed (80% of maximum response) to near maximum suppression (20% of maximum response). Most units (71%) had IID ranges of less than or equal to 15 dB. 3. A significant correlation between the inhibitory threshold and the maximum inhibition (Fig. 5) among the sample of EI units suggests that some common neural mechanisms underlie these features of IID sensitivity. 4. The response of EI neurons to binaural stimuli was a function of sound intensity as well as IID (Fig. 7). In part, this resulted from intensity-dependent changes in properties of binaural inhibition. For most units, basic measures of IID sensitivity changed to a limited extent as the sound intensity changed.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1988

Binaural neurons in the mustache bat's inferior colliculus. II. Determinants of spatial responses among 60-kHz EI units.

1. The responses to closed-field and free-field sound stimuli were obtained from EI neurons in the 60-kHz isofrequency representation of the mustache bat's inferior colliculus. The goals of the study were 1) to examine how binaural interactions and the directional properties of the ear shape the spatial response of 60-kHz EI neurons and 2) to examine features of the spatial responses of these isofrequency neurons which may encode the location of a sound. 2. The free-field response of monaural neurons was used to describe directional effects of the head and external ears at 60 kHz. Monaural neurons were most sensitive to sounds originating 26 degrees into the contralateral field, with sharply reduced sensitivity in the ipsilateral field and the lateral extreme of the contralateral field. The interaural intensity difference (IID), computed by assuming that the ears had mirror-image directional sensitivities, was greatest for sounds between 26 and 52 degrees off the vertical midline, where IIDs typically ranged from 20 to 30 dB. These values agree well with previous measures of the directional sensitivity of the ear obtained from cochlear microphonic recordings. 3. The response of a monaural unit to closed-field stimulation was used to predict its response to free-field stimulation. This prediction agreed closely with the observed free-field response, indicating that the monaural unit's free-field response could be explained by the directional sensitivity of the contralateral ear and the unit's response as a function of contralateral sound intensity. 4. EI neurons differed in basic features of their binaural response properties, as described in a companion paper. To examine how these features of binaural inhibition shaped spatial responses, we obtained responses to free-field sounds among neurons whose binaural properties had been thoroughly characterized. We then compared the spatial response to a prediction based upon the directional properties of the ear and the sensitivity of the EI neurons to IIDs and intensity. The close agreement between the observed and predicted spatial responses in 11 of 12 EI units indicated that the spatial responses were determined largely by sensitivity to IIDs and intensity and by the directional properties of the ear. 5. EI neurons in our sample were most sensitive, and responded best, to sounds originating 26-39 degrees into the contralateral field. These spatial response features were independent of the binaural properties of EI neurons. Instead, they depended upon the directional properties of the ears at 60 kHz.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1986

Speculations on the role of frequency in sound localization.

This presentation reviews behavioral and physiological evidence suggesting that the perceived power spectrum of a sound, as modified by the external ears, provides important cues for horizontal and vertical sound localization. This spatial information is mostly likely encoded by the relative levels of excitation among the tonotopically organized hair cells of the cochlea. This suggests that the preservation of the cochlear frequency map within the central auditory system contributes an anatomical substrate for the localization of sound.

Animals↗

PubMed1985

A representation of horizontal sound location in the inferior colliculus of the mustache bat (Pteronotus p. parnellii).

Binaurally sensitive E-I neurons in the inferior colliculus are topographically organized with respect to their sensitivity to interaural intensity disparities (IIDs). IID sensitivity dictates the azimuthal position of the medial border of a neuron's spatial receptive field. A sound moving along the azimuth will result in a change in the percentage of excited neurons as receptive field borders are crossed. Percent excitation within this population may provide a neural code for horizontal sound location.

Animals↗

PubMed1985

Determinants of sound location selectivity in bat inferior colliculus: a combined dichotic and free-field stimulation study.

This study of the neural representation of sound location in the bat Pteronotus parnellii describes how the peripheral and central components of its auditory system shape the horizontal and vertical spatial selectivity of single neurons in the inferior colliculus. Pteronotus extracts spatial information from the echoes of an emitted pulse composed of four constant-frequency harmonics (30, 60, 90, and 120 kHz), each terminated by a downward frequency sweep. To quantify the intensity cues available in the echo, cochlear microphonic response thresholds were used to measure the directional selectivity of the ear and the interaural intensity level disparities (IIDs) created between ears at standardized speaker positions in the bat's frontal sound field, at frequencies in the pulse spectrum. Speaker positions where thresholds were lowest were termed the sensitive area (SA) of the ear. Positions where IID values were greater than 10 dB were termed the difference area (DA). Ear directionality exhibited a pronounced frequency dependence, both in terms of the degree of directional selectivity and the position of the SA. At the 30-kHz harmonic of the pulse, the ear was broadly directional; the SA covered most of the lower half of the ipsilateral field. The ear was highly directional at the 60- and 90-kHz harmonics. Also, the vertical position of the SA changed dramatically between 60 and 90 kHz, from the horizontal midline at 60 kHz to 40 degrees below the midline at 90 kHz. The positions of the DAs also showed a pronounced frequency dependence. The 30-kHz DA was restricted to the extreme lateral part of the frontal sound field. The 60- and 90-kHz DAs were located in the same positions as the equivalent SAs and exhibited the same difference in vertical position. The DAs of the pulse harmonics differ in both their horizontal and vertical positions; the ears thus generate pronounced binaural spectral cues, which provide two-dimensional spatial information. In the inferior colliculus, a combined paradigm of closed-field dichotic stimulation, followed by free-field stimulation, was used to document the frequency tuning and binaural response properties of single neurons and to correlate these properties with the neuron's horizontal and vertical spatial selectivity in the frontal sound field. Where a neuron responded to free-field stimulation at the lowest intensity is termed its SA. A neuron's frequency tuning primarily influenced its degree of spatial selectivity and its sensitivity in the vertical plane, reflecting the directional properties of the external ears at the neuron's best frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

Neural mechanisms of sound localization in an echolocating bat.

The mustache bat emits a three-harmonic echolocation pulse. At the external ear, large interaural intensity differences are generated only when a sound originates within a limited area of two-dimensional space, and this area is different for each pulse harmonic. As a consequence, the external ear generates pronounced binaural spectral cues containing two-dimensional spatial information. This information is encoded in the inferior colliculus by neurons tuned to one of the harmonics and sensitive to interaural intensity differences.

Acoustics↗