Biomedical subjects

R R Hoy

Publications and source records attributed to R R Hoy.

At least 37 records · Page 2Linked to original sources

PubMed1996

Categorical perception of sound frequency by crickets.

Partitioning continuously varying stimuli into categories is a fundamental problem of perception. One solution to this problem, categorical perception, is known primarily from human speech, but also occurs in other modalities and in some mammals and birds. Categorical perception was tested in crickets by using two paradigms of human psychophysics, labeling and habituation-dishabituation. The results show that crickets divide sound frequency categorically between attractive (<16 kilohertz) and repulsive (>16 kilohertz) sounds. There is sharp discrimination between these categories but no discrimination between different frequencies of ultrasound. This demonstration of categorical perception in an invertebrate suggests that categorical perception may be a basic and widespread feature of sensory systems, from humans to invertebrates.

Animals↗

PubMed1996

Directional hearing by mechanical coupling in the parasitoid fly Ormia ochracea.

Sound localization is a basic processing task of the auditory system. The directional detection of an incident sound impinging on the ears relies on two acoustic cues: interaural amplitude and interaural time differences. In small animals, with short interaural distances both amplitude and time cues can become very small, challenging the directional sensitivity of the auditory system. The ears of a parasitoid fly Ormia ochracea, are unusual in that both acoustic sensors are separated by only 520 microns and are contained within an undivided air-filled chamber. This anatomy results in minuscule differences in interaural time cues (ca. 2 microseconds) and no measurable difference in interaural intensity cues generated from an incident sound wave. The tympana of both ears are anatomically coupled by a cuticular bridge. This bridge also mechanically couples the tympanana, providing a basis for directional sensitivity. Using laser vibrometry, it is shown that the mechanical response of the tympanal membranes has a pronounced directional sensitivity. Interaural time and intensity differences in the mechanical response of the ears are significantly larger than those available in the acoustic field. The tympanal membranes vibrate with amplitude differences of about 12 dB and time differences on the order of 50 microseconds to sounds at 90 degrees off the longitudinal body axis. The analysis of the deflection shapes of the tympanal vibrations shows that the interaural differences in the mechanical response are due to the dynamic properties of the tympanal system and reflect its intrinsic sensitivity to the direction of a sound source. Using probe microphones and extracellular recording techniques, we show that the primary auditory afferents encode sound direction with a time delay of about 300 microseconds. Our data point to a novel mechanism for directional hearing in O. ochracea based on intertympanal mechanical coupling, a process that amplifies small acoustic cues into interaural time and amplitude differences that can be reliably processed at the neural level. An intuitive description of the mechanism is proposed using a simple mechanical model in which the ears are coupled through a flexible lever.

Acoustics↗

PubMed1996

Tympanal hearing in tachinid flies (Diptera, Tachinidae, Ormiini): the comparative morphology of an innovation.

Tympanal hearing organs have been reported only recently for Diptera. All the cases documented so far relate to parasitoid tachinid flies of the ormiine tribe. In the ormiine flies, the presence of tympanal hearing is functionally linked to their reproductive behavior. Indeed, female ormiine flies detect and localize their host, typically singing orthopterans, by hearing their calling songs. The three ormiine fly species investigated here at the comparative level share the key morphological features associated with tympanal hearing. The extent of these structural modifications becomes evident in the light of comparison with the closely related atympanate tachinid Myiopharus doryphorae. We document a series of eight characters that constitute specialized modifications of the ventral prothorax: (1) an inflation of the probasisternum, providing a rigid frame to span the large tympanal membranes; (2) an increased surface area of the prosternal membranes that constitute very thin, corrugated tympanal membranes; (3) a forked, broad presternum with tympanal pits to which the sensory organs directly attach; (4) several modifications of the tracheal system comprising the enlargement of the prosternal air sac, a supplementary tracheal tube to the prosternal air sac accompanied by a subpartioning of the spiracular atrium, and larger mesothoracic spiracles; (5) the presence of two scolopophorous chordotonal organs in the unpartitioned prosternal air sac; (6) stiff cuticular apodemes linking the chordotonal organs to the presternum; (7) reduction in size of the cervical sclerites; and (8) several structural modifications of the prosternal apophyses, creating new attachment sites for neck muscles. This comparative approach brings out differences and similarities of the homologous cuticular structures found on the ventral prothorax of both tympanate and atympanate tachinids. It is proposed that, given the degree of similarity between the ormiine hearing organs, the ormiine tribe is monophyletic, whereby all members of this tribe evolved from a common ancestor, an acoustic parasitoid of a singing orthopteran insect.

Animals↗

PubMed1996

Tympanal hearing in insects.

Specialized hearing organs, known as tympanal organs, have evolved in at least seven different orders of insects. Tympanal organs are usually defined by the presence of a tympanal membrane (or eardrum). They are backed by an air-filled space or cavity and are innervated by a chordotonal sensory organ. In some insects, however, a recognizable tympanal membrane may not be easily identified by visual inspection, yet may possess tympanal hearing organs. In insects that possess them, tympanal hearing organs may mediate the detection of predators, prey, and potential mates and rivals. Unlike the ears of vertebrates, which are localized to cranial segments, the ears of insects may be found in a bewildering variety of locations on their bodies, depending on the species. The embryological and evolutionary origins of tympanal organs are related to ancestral states as proprioceptive chordotonal organs.

Journal Article↗

PubMed1995

The tympanal hearing organ of a fly: phylogenetic analysis of its morphological origins.

A key adaptation for any parasitoid insect is the sensory modality that it uses to locate its host insect. All members of the speciose family Tachinidae (Diptera) are parasitoids, but only flies of the tribe Ormiini use acoustic cues to find their hosts. Ormiine flies are parasitoids of various genera of crickets and katydids. Gravid females of one ormiine species, Ormia ochracea, hear the reproductive calling song of male field crickets and home in on those calls to locate their hosts. While many flies possess various kinds of "ears" to detect airborne sounds, only ormiine flies have been reported to possess true tympanal hearing organs. Such organs are well-known to occur in their cricket and katydid hosts. The ormiine ear is an evolutionary innovation within Diptera. Our objective was to trace the phylogenetic origins of the tympanal hearing organ among higher flies. Since the ormiine hearing organ is a complex organ within the prothorax, we examined possible precursor structures in the prothoraces of selected Diptera. We have uncovered a suite of characters that define the ormiine ear. These characters in the prothorax include a pair of prosternal tympanal membranes, a pair of chordotonal sensory organs, and modifications of the tracheal system. We have been able to identify and trace the presumptive homologs of these ormiine characters through selected species of related Diptera, using the method of outgroup comparison.

Animals↗

PubMed1995

Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea.

An analysis is presented of the mechanical response to a sound field of the ears of the parasitoid fly Ormia ochracea. This animal shows a remarkable ability to detect the direction of an incident sound stimulus even though its acoustic sensory organs are in very close proximity to each other. This close proximity causes the arrival times of the sound pressures at the two ears to be less than 1 to 2 microseconds depending on the direction of propagation of the sound wave. The small differences in these two pressures must be processed by the animal in order to determine the incident direction of the sound. In this fly, the ears are so close together that they are actually joined by a cuticular structure which couples their motion mechanically and subsequently magnifies interaural differences. The use of a cuticular structure as a means to couple the ears to achieve directional sensitivity is novel and has not been reported in previous studies of directional hearing. An analytical model of the mechanical response of the ear to a sound stimulus is proposed which supports the claim that mechanical interaural coupling is the key to this animal's ability to localize sound sources. Predicted results for sound fields having a range of incident directions are presented and are found to agree very well with measurements.

Animals↗

PubMed1995

Ultrasound acoustic startle response in scarab beetles.

We discovered an auditory sense in a night-flying scarab beetle, Euetheola humilis, the first scarab to be shown to hear airborne sounds. In the field, beetles were captured beneath speakers broadcasting ultrasound that simulated bat echolocation pulses. Apparently, the beetles took evasive action from a potential bat predator and flew into the traps. Using another behavioral assay in laboratory studies, the beetles were sensitive to frequencies ranging from 20 to 70 kHz at levels between 60 and 70 dB SPL. One component of the behavioral response, a head roll, was graded with stimulus intensity, and the number of potentials in electromyographic recordings from muscles involved in the roll increased as stimulus intensity increased. The response latency was about 40 ms at threshold, decreasing to about 30 ms at 20 dB above threshold. The beetle's short response latency is ideally suited for predator avoidance behavior and the frequency tuning of the response suggests that it could function in evasion from insectivorous bats. The beetle's acoustic sensitivity is remarkably similar to that of other night-flying insects showing ultrasound-induced startle and it should provide these scarab beetles with a similar advance warning of predation risk.

Acoustic Stimulation↗

PubMed1995

The role of neurohormonal octopamine during 'fight or flight' behaviour in the field cricket Gryllus bimaculatus.

Octopamine has been called the 'fight or flight' hormone of insects. We tested this hypothesis by measuring octopamine levels in the haemolymph of field crickets after fighting, flying, courting and escape behaviours. Octopamine levels in the cricket Gryllus bimaculatus increased during aggressive (agonistic) behaviour from baseline levels of 4.5 +/- 2.1 pg microliters-1 haemolymph to 24.3 +/- 15.2 pg microliters-1 haemolymph, regardless of whether the cricket won or lost the encounter. Octopamine levels also increased after 5 min of flying (to 44.6 +/- 22.3 pg microliters-1) and during courtship. However, crickets did not exhibit an increase in their haemolymph octopamine levels after performing an escape run. Therefore, neurohormonal octopamine shows some, but not all, of the characteristics that would be expected if it were a component of a nonspecific 'arousal' system. Rather, octopamine may be released as a neurohormone to prepare the animal for a period of extended activity or to assist the animal in recovering from a period of increased energy demand. Antennal contact with conspecifics may provide a sensory cue that results in the release of octopamine into the haemolymph.

Aggression↗

PubMed1994

Frequency as a releaser in the courtship song of two crickets, Gryllus bimaculatus (de Geer) and Teleogryllus oceanicus: a neuroethological analysis.

1. The courtship behavior of male field crickets, Gryllus bimaculatus (De Geer) and Teleogryllus oceanicus, is a complex, multimodal behavioral act that involves acoustic signals (a courtship song; Fig. 1A, B). The dominant frequency is 4.5 kHz for T. oceanicus song (Fig. 1A) and 13.5 kHz for G. bimaculatus (Fig. 1B). 2. When courting males are deprived of their courtship song by wing amputation, their courtship success declines markedly but is restored when courting is accompanied by tape-recordings of their courtship songs or a synthetic courtship song with only the dominant frequency of the natural song; other naturally occurring frequency components are ineffective for restoring mating success (Figs. 4, 5). 3. It has been suggested that an identified auditory interneuron, AN2, plays a critical role in courtship success. Chronic recordings of AN2 in an intact, tethered female show that AN2's response to the natural courtship song and synthesized songs at 4.5 and 13.5 kHz is similar in T. oceanicus. By contrast, in G. bimaculatus, AN2's response to the natural courtship song and synthesized song at 13.5 kHz, but not at 4.5 kHz, is similar (Fig. 2,3). 4. In behavioral experiments, playback of a 30 kHz synthetic courtship song in G. bimaculatus does not restore courtship success, yet this same stimulus elicits as strong a response from AN2 as does the normal courtship song (Fig. 6). Thus, contrary to earlier work by others, we conclude AN2 is not, by itself, a critical neural link in the courtship behavior of these two species of crickets.

Acoustic Stimulation↗

PubMed1994

The tympanal hearing organ of the parasitoid fly Ormia ochracea (Diptera, Tachinidae, Ormiini).

Tympanate hearing has evolved in at least 6 different orders of insects, but had not been reported until recently in the Diptera. This study presents a newly discovered tympanal hearing organ, in the parasitoid tachinid fly, Ormia ochracea. The hearing organ is described in terms of external and internal morphology, cellular organization of the sensory organ and preliminary neuroanatomy of the primary auditory afferents. The ear is located on the frontal face of the prothorax, directly behind the head capsule. Conspicuously visible are a pair of thin cuticular membranes specialized for audition, the prosternal tympanal membranes. Directly attached to these membranes, within the enlarged prosternal chamber, are a pair of auditory sensory organs, the bulbae acusticae. These sensory organs are unique among all auditory organs known so far because both are contained within an unpartitioned acoustic chamber. The prosternal chamber is connected to the outside by a pair of tracheae. The cellular anatomy of the fly's scolopophorous organ was investigated by light and electron microscopy. The bulba acustica is a typical chordotonal organ and it contains approximately 70 receptor cells. It is similar to other insect sensory organs associated with tympanal ears. The similarity of the cellular organization and tympanal morphology of the ormiine ear to the ears of other tympanate insects suggests that there are potent constraints in the design features of tympanal hearing organs, which must function to detect high frequency auditory signals over long distances. Each sensory organ is innervated by a branch of the frontal nerve of the fused thoracic ganglia. The primary auditory afferents project to each of the pro-, meso-, and metathoracic neuropils. The fly's hearing organ is sexually dimorphic, whereby the tympanal membranes are larger in females and the spiracles larger in males. The dimorphism presumably reflects differences in the acoustic behavior in the two sexes.

Animals↗

PubMed1993

Demonstration of the precedence effect in an insect.

Field crickets are interesting models for study of auditory phenomena because they solve many of the same acoustic problems as humans, but with simpler nervous systems. Previous work in this lab and others has investigated sound localization, frequency and temporal pattern discrimination, habituation and dishabituation, and categorical perception. This paper demonstrates the precedence effect in crickets, using a standard two-pulse paradigm with a directional escape response to ultrasound. When two pulses of ultrasound are presented form opposite sides with a delay between, crickets respond only to the first pulse for delays of approximately 4 to 75 ms. For delays of 0 to 2 ms, the direction of response is variable (the first wave front does not have precedence); for delays over approximately 75 ms, crickets respond directionally to each of the two pulses. Some neural correlates of the precedence effect were studied by using this paradigm during recordings from a bilateral pair of ascending second-order auditory interneurons known to initiate ultrasound avoidance. There are no ipsilateral-contralateral differences in their responses that could account for the precedence effect; such interactions in the brain must be involved instead. This seems to be the first test of precedence effect in a nonmammal.

Acoustics↗

PubMed1992

The evolutionary convergence of hearing in a parasitoid fly and its cricket host.

Parasitism is a widespread and diverse life strategy that connects species throughout the animal kingdom. Female parasitoid flies of the genus Ormia must find a specific cricket host on which to deposit their parasitic maggots. To reproduce, female flies must perform the same task as female crickets: find a singing male cricket. These flies have evolved a unique hearing organ that allows them to detect and locate singing male crickets. Through evolutionary convergence, these flies possess a hearing organ that much more resembles a cricket's ear than a typical fly's ear, allowing these parasitoids to take advantage of the sensory ecological niche of their host.

Acoustic Stimulation↗

PubMed1992

Temperature coupling in cricket acoustic communication. I. Field and laboratory studies of temperature effects on calling song production and recognition in Gryllus firmus.

Temperature effects on calling song production and recognition were investigated in the North American field cricket, Gryllus firmus. Temporal parameters of field-recorded G. firmus calling song are strongly affected by temperature. Chirp rate and syllable rate increase, by factors of 4 and 2, respectively, as linear functions of temperature over the range in which these animals sing in the field (12 degrees-30 degrees C). Temperature affects syllable duration to a lesser extent, and does not influence calling song carrier frequency. Female phonotactic preference, measured on a spherical treadmill in the laboratory, also changes with temperature such that warmer females prefer songs with faster chirp and syllable rates. Best phonotaxis, measured as accuracy of orientation to the sound source, and highest walking velocity, occur in response to temperature-matched songs at 15 degrees, 21 degrees, and 30 degrees C. Experiments under semi-natural conditions in an outdoor arena revealed that females perform phonotaxis at temperatures as low as 13 degrees C. Taken together, the song and phonotaxis data demonstrate that this communication system is temperature coupled. A strategy is outlined by which temperature coupling may be exploited to test hypotheses about the organization of neural networks subserving song recognition.

Animal Communication↗

PubMed1992

Temperature coupling in cricket acoustic communication. II. Localization of temperature effects on song production and recognition networks in Gryllus firmus.

Acoustic communication in Gryllus firmus is temperature-coupled: temperature induces parallel changes in male calling song temporal pattern, and in female preference for song. Temperature effects on song production and recognition networks were localized by selectively warming head or thorax or both head and thorax of intact crickets, then eliciting aggression song production (males) or phonotaxis to synthetic calling song (females). Because male song is produced by a thoracic central pattern generator (CPG), and because head ganglia are necessary for female song recognition, measurements of female phonotaxis under such conditions may be used to test the following competing hypotheses about organization of the song recognition network: 1. A set of neurons homologous to the male song CPG exist in the female, and are used as a template that determines preferred values of song temporal parameters for song pattern recognition (the common neural elements hypothesis), and 2. temporal pattern preference is determined entirely within the head ganglia. Neither selective warming of the head nor of the thorax was effective in changing female song preference, but simultaneous warming of head and thorax shifted preference toward a faster song in most preparations, as did warming the whole animal by raising ambient temperature. These results suggest that phonotactic preference for song temporal pattern is plurisegmentally determined in field crickets. Selective warming experiments during aggression song production in males revealed that syllable period is influenced but not completely determined by thoracic temperature; head temperature is irrelevant. The song CPG appears to receive some rate-setting information from outside the thoracic central nervous system.

Acoustic Stimulation↗

PubMed1992

Multisegmental analyses of acoustic startle in the flying cricket (Teleogryllus oceanicus): kinematics and electromyography.

Tethered, flying Australian field crickets (Teleogryllus oceanicus) stimulated with ultrasound respond with a rapid, short-latency turn from the sound source. We analyzed the kinematics of two behavioral components of this acoustic startle response and recorded electromyograms from the muscles involved in producing them. The two behavior patterns studied were the swing of the metathoracic leg, which has been shown to elicit a short-latency turn, and a lateral swing of the antennae, for which a direct role in steering has not been demonstrated. The kinematic data showed that when a pulse of ultrasound was presented to one side of the animal (1) the contralateral metathoracic leg abducted and elevated, while the ipsilateral leg remained in place, (2) both antennae swung laterally, but the contralateral antenna moved farther than the ipsilateral antenna, (3) increases in stimulus intensity elicited larger movements of the leg and contralateral antenna, while the ipsilateral antenna showed little sensitivity to stimulus intensity, and (4) for the leg, the latency to the onset of the swing decreased and the duration of the movement increased with increasing stimulus intensity. Electromyograms were recorded from the leg abductor M126 and two antennal muscles: the medial scapo-pedicellar muscle M6 and the lateral scapo-pedicellar muscle M7. M7 moves the antenna laterally, M6 moves it medially. Upon stimulation with ultrasound (1) both M126 and M7 showed increasing spike activity with increasing intensity of the ultrasound stimulus, (2) M126 showed a decrease in latency to the first spike and an increase in the duration of spike activity with increasing stimulus intensity, (3) latencies for M6 and M7 were not correlated with stimulus intensity, but M7 had significantly shorter latencies than M6 and the contralateral M7 had significantly shorter latencies than the ipsilateral M7, and (4) the ipsilateral M126 spiked in response to ultrasound in 6 of the 10 animals tested. In these cases, however, latency to the first spike was substantially longer, and the spike frequency was lower than for the muscle's response to contralateral stimuli. We attempt to correlate these electromyogram data with the kinematic data and relate them to the relevance of the two behavior patterns to the execution of an escape response.

Acoustic Stimulation↗

PubMed1991

Ultrasonic startle behavior in bushcrickets (Orthoptera; Tettigoniidae).

1. In the present work, we show that in flight, bushcrickets not previously known to respond to ultrasound alter their flight course in response to ultrasonic stimuli. Such stimuli elicit in flying Neoconocephalus ensiger an extension of the front and middle legs along the body and a rapid closure of all 4 wings (Fig. 1). This is a short latency acoustic startle response to ultrasound, consistent with acoustic startle responses of other insects. 2. The percentage of trials on which acoustic startle responses were elicited was maximum (90%) for sound frequencies ranging from 25 to at least 60 kHz. No acoustic startle response was observed at frequencies of 5 or 10 kHz (Fig. 2). The threshold for the response was roughly 76 dB between 25 to 60 kHz (Fig. 2) and the behavioral latency was 45 ms (Fig. 3). Recordings from flight muscles show that they cease discharging during the acoustic startle response (Fig. 4). 3. The characteristics of the acoustic startle response match those of an auditory interneuron called the T-neuron. The frequency sensitivity of this neuron is greatest for sound frequencies ranging from 13 to 60 kHz (Fig. 6). Moreover, we found that the neuron produces many more spikes to ultrasound (30 kHz) of increasing intensities than to a conspecific communication sound, whose dominant frequency is 14 kHz (Fig. 7).

Acoustic Stimulation↗

PubMed1991

Habituation of the ultrasound-induced acoustic startle response in flying crickets.

The ultrasound-induced negative phonotactic response of tethered, flying Australian field crickets habituates to repeated stimuli. Using the magnitude of the metathoracic leg's swing during a series of ultrasonic stimuli as a measure of habituation, we show that: (1) the response declines exponentially; (2) the response recovers spontaneously; (3) repeated trials produce more rapid and stronger habituation; (4) successive stimuli presented more rapidly produce more rapid and stronger habituation; (5) a weaker stimulus intensity produces more rapid and stronger habituation; (6) the habituation shows stimulus generalization (i.e. the response is similar for different ultrasonic frequencies); (7) a novel stimulus produces dishabituation; and (8) the effect of the dishabituating stimulus habituates after repeated trials. These findings place habituation of cricket negative phonotaxis in the context described for habituation in mammals.

Animals↗

PubMed1990

Ultrasound sensitive neurons in the cricket brain.

1. The aim of this study was to identify neurons in the brain of the cricket, Teleogryllus oceanicus, that are tuned to high frequencies and to determine if these neurons are involved in the pathway controlling negative phonotaxis. In this paper we describe, both morphologically and physiologically, 20 neurons in the cricket brain which are preferentially tuned to high frequencies. 2. These neurons can be divided into two morphological classes: descending brain interneurons (DBINs) which have a posteriorly projecting axon in the circumesophageal connective and local brain neurons (LBNs) whose processes reside entirely within the brain. All the DBINs and LBNs have processes which project into one common area of the brain, the ventral brain region at the border of the protocerebrum and deutocerebrum. Some of the terminal arborizations of Int-1, an ascending ultrasound sensitive interneuron which initiates negative phonotaxis, also extend into this region. 3. Physiologically, ultrasonic sound pulses produce 3 types of responses in the DBINs and LBNs. (1) Seven DBINs and 6 LBNs are excited by ultrasound. (2) Ongoing activity in one DBIN and 5 LBNs is inhibited by ultrasound, and (3) one cell, (LBN-ei), is either excited or inhibited by ultrasound depending on the direction of the stimulus. 4. Many of the response properties of both the DBINs and LBNs to auditory stimuli are similar to those of Int-1. Specifically, the strength of the response, either excitation or inhibition, to 20 kHz sound pulses increases with increasing stimulus intensity, while the response latency generally decreases. Moreover, the thresholds to high frequencies are much lower than to low frequencies. These observations suggest that the DBINs and LBNs receive a majority of their auditory input from Int-1. However, the response latencies and directional sensitivity of only LBN-ei suggest that it is directly connected to Int-1. 5. The response of only one identified brain neuron, DBIN8, which is inhibited by 20 kHz sound pulses, is facilitated during flight compared to its response at rest. This suggests that suppression of activity in DBIN8 may be associated with ultrasound-induced negative phonotactic steering responses in flying crickets. The other DBINs and LBNs identified in this paper may also play a role in negative phonotaxis, and possibly in other cricket auditory behaviors influenced by ultrasonic frequencies.

Action Potentials↗