Vibrational Communication Research Articles

Vibrational communication and mating behaviour of Dichelops melacanthus (Hemiptera: Pentatomidae) recorded from loudspeaker membranes and plants

AbstractVibrational communication is important for successful mating in various stink bugs species. The vibrational signals from males and females of Dichelops melacanthus Dallas (Hemiptera: Pentatomidae) are recorded from a nonresonant substrate (i.e. a loudspeaker membrane) to characterize the temporal and spectral properties of these vibrational signals, as well as on a resonant substrate (i.e. bean plants) to obtain information about how these signals are altered when they are transmitted through the plants. On the loudspeaker membrane, D. melacanthus males and females emit only one male or one female song, respectively. However, when the insects are placed on bean leaves, a more complex repertoire is recorded, with three different songs for each sex. The first female and male songs appear to have calling functions and the third male and female songs are emitted during courtship. The second female and male songs are emitted after the first song, although their functions in mating behaviour are not clear. The identified repertoire is similar to those of other Neotropical stink bugs, starting with songs 1 and 2 and developing into song 3. Frequency modulation is observed in the female songs recorded from the loudspeaker membrane and the plants. The signals recorded from plants present higher harmonic peaks compared with the signals recorded from the loudspeaker membrane. The presence of species and sex‐specific songs during mating confirms the important role of vibrational communication in mate location and recognition. The temporal and spectral characteristic signals are influenced by the substrate used to record the songs emitted by D. melacanthus.

The role of signals of different modalities in initiating vibratory communication in Nezara viridula

Abstract Signals of different modalities are involved in the behaviour of the green stink bug, Nezara viridula (L.) (Pentatomidae, Heteroptera). Long range attraction is mediated by male pheromones, resulting in aggregation of bugs on the same plant where vibratory signals, vision and various chemical signals become important. Both males and females sing spontaneously. When both are on the plant, males start vibratory communication as often as females. Females induce the exchange of vibratory signals spontaneously or triggered by the male pheromone while males initiate the duet either spontaneously or after seeing the female. Males and females sing spontaneously and respond to signals of different modalities more often in the daylight than in the dark. Long lasting autonomous emission of the female calling song is present when triggered by the male pheromone and males respond to female calling predominantly by the emission of the courtship song.

Vibrational long-distance communication in the termitesMacrotermes natalensisandOdontotermessp.

Fungus-growing higher termites build long subterranean galleries that lead outwards from the nest to foraging sites. When soldiers are disturbed, they tend to drum with their heads against the substrate and thereby create vibrational alarm signals. The present study aimed at describing these acoustic signals, how they are elicited, produced and perceived, and how these signals propagate within the galleries and nests over long distances in two termite species of the Southern African savannah, Macrotermes natalensis and an Odontotermes sp. The signals consist of trains of pulses with a pulse repetition rate of 10-20 Hz. The galleries have physical features that promote vibrational communication and are used as channels for long-distance communication. In M. natalensis, the signal propagation velocity is ~130 m s(-1) and the signals are attenuated by ~0.4 dB per centimetre distance. Nestmates are extremely sensitive to these vibrations with a behavioural threshold amplitude of 0.012 m s(-2). Workers respond by a fast retreat into the nest and soldiers are recruited to the source of vibration. Soldiers also start to drum with a reaction time of about 0.3 s, thereby amplifying the intensity of the signal. This social long-distance communication through chains of signal-reamplifying termites results in a relatively slow propagation (1.3 m s(-1)) of the signal without decrement over distances of several metres.

Vibrational background noise in herbaceous plants and its impact on acoustic communication of small Auchenorrhyncha and Psyllinea (Homoptera)

Vibrations induced in plant stems by rain drops, wind, and mechanical activity of insects were studied under natural conditions. Wind and rain can induce high-frequency vibrations in the range up to 3–4 kHz and jamming insect signals completely. For this reason, small homopterans mostly emit their signals during the gaps between gusts of wind. In the regions where strong wind blows during most part of the day, they concentrate mainly in the places protected from the wind (dry river beds, hollows, and other depressions of the relief). Individuals of different species occurring on the same or neighboring plants usually sing alternately, i.e., demonstrate the same response to each other’s signals as to the wind-induced noise. Low-amplitude vibrations resulting from insect movements have no considerable impact on vibrational communication of Homoptera.

Responses of Diaphorina citri (Hemiptera: Psyllidae) to Conspecific Vibrational Signals and Synthetic Mimics

Abstract Mate-seeking in Diaphorina citri Kuwayama, a vector of the economically damaging huanglongbing citrus disease, typically includes male—female duetting behaviors. First, the male calls by beating his wings at ≈170–250 Hz, producing vibrations that are transmitted along the host tree branches to the female. If receptive, she immediately replies, helping to direct the searching male toward her. The duetting and searching continues until the male locates the female. Males and females are similar in size and produce wingbeat vibrations with similar temporal and spectral patterns. A study of male and female responses to playbacks of recorded and synthetic mimics of different vibrational signals on citrus plants was conducted to better understand the range of signals to which D. citri respond and potentially to co-opt or disrupt their vibrational communication. In general, both sexes responded well to a variety of 0.3–0.5-s signals that included multiple harmonics of ≈200-Hz wingbeatfrequency chirps up to ≈1,400 Hz (where a chirp is a sine wave tone that sweeps across a narrow range of frequencies). There were only minor differences in female responses to signals containing different relative amplitudes of such chirps, and males readily located sources that played these multipleharmonic signals. The results are discussed in relation to mating-signal selectivity and the potential for developing automated methods to trap male D. citri by using vibrational signals.

Palomena prasina (Hemiptera: Pentatomidae) vibratory signals and their tuning with plant substrates

Abstract Palomena prasina is interesting for the study of vibrational communication within the Pentatomid subfamily Pentatominae, because its host range is limited to woody plants, unlike the better known Nezara viridula, whose vibrational communication is commonly used as a model for the whole family. The vibrational repertoire of P. prasina was described several decades ago and is redescribed in this paper using modern methods for non-contact vibration recording. Additionally, we hypothesized that this species has retained the capacity for signal frequency variation necessary for tuning to resonance properties of various host plants of Pentatominae, but if the signals are emited in the absence of mechanical feedback, they are tuned more specifically to their native acoustic environment — woody plants. By recording live bugs signalling on different substrates and comparing spectral properties of their signals among substrates, we found that there is a match between the signals emitted on a woody branch and those emitted on a non-resonant surface, while spectral properties of signals emitted on herbaceous plants differ. Our findings provide evidence in support of the signal tuning hypothesis and shed further light on the crucial role of substrate in vibrational communication of insects.

Reproductive behaviour and vibratory communication of the neotropical predatory stink bugPodisus nigrispinus

Vibratory communication during reproductive behaviour is less well described in predatory (Asopinae) than in phytophagous (Pentatominae) stink bugs. Different steps in the mating behaviour of the predatory stink bugPodisus nigrispinus(Dallas) (Hemiptera: Pentatomidae; Asopinae) are described in the present study, together with vibratory signals emitted on artificial and natural substrate during courtship and copulation. Vibratory signals inPodisus nigrispinushave a decisive role in copulation success and are produced in both sexes by abdominal vibration and tremulation. InP. nigrispinus, one species‐specific female and two male songs, which do not show the calling function typically found in phytophagous stink bugs, are produced by abdominal vibration and are emitted during reproductive behaviour. Additionally,P. nigrispinusproduces tremulatory signals that have no species or sex specificity. Tremulatory signals emitted spontaneously on a plant as a sequence of readily repeated pulses are similar to the calling songs of the Pentatominae stink bug. These signals may carry information on the presence of a mate; however, in other behavioural contexts, they may have a different function, such as advertisement or even alarm signals. Plants transmit vibratory signals produced by both mechanisms as a low‐pass filter, increasing the amount of low‐frequency components. The results of the present study raise important questions about the interaction between chemical and vibratory signals in the mating behaviour of predatory stink bugs.

Tremulatory and Abdomen Vibration Signals Enable Communication through Air in the Stink Bug Euschistus heros

Communication by substrate-borne mechanical signals is widespread among animals but remains one of their least understood communication channels. Past studies of vibrational communication in insects have been oriented predominantly to communication during mating, showing that species- and sex-specific vibrational signals enable recognition and localization of potential mates on continuous solid substrates. No special attention has been paid to vibrational signals with less obvious specificity as well as to the possibility of vibrational communication across substrates that are not in physical contact. We aimed to reinvestigate emission of the aforementioned vibrational signals transmitted through a plant in the stink bug Euschistus heros (Pentatomidae: Pentatominae) and to check whether individuals are able to communicate across adjecent, physically separated substrates. We used laser vibrometry for registration of substrate-borne vibrational signals on a bean plant. Using two bean plants separated for 3 to 7 cm between two most adjacent leaves, we investigated the possibility of transmission of these signals through air. Our study showed that males and females of E. heros communicate using tremulatory, percussion and buzzing signals in addition to the previously described signals produced by vibrations of the abdomen. Contrary to the latter, the first three signal types did not differ between sexes or between pentatomid species. Experiments with two physically separated plants showed significant searching behaviour and localization of vibrational signals of an E. heros male or a female, in response to abdominal vibration produced signals of a pair duetting on the neighbouring plant, in comparison to control where no animals were on the neighbouring plant. We also confirmed that transmission through air causes amplitude and frequency decay of vibrational signals, which suggests high-amplitude, low-frequency tremulatory signals of these stink bugs their most plausible way of communication across discontinuous substrates.

Substrate-Borne Vibratory Communication during Courtship in Drosophila melanogaster

SummaryCourtship in Drosophila melanogaster has become an iconic example of an innate and interactive series of behaviors [1–11]. The female signals her acceptance of copulation by becoming immobile in response to a male's display of stereotyped actions. The male and female communicate via vision, air-borne sounds, and pheromones [1, 2], but what triggers the female's immobility is undetermined. Here, we describe an overlooked and important component of Drosophila courtship. Video recordings and laser vibrometry show that the male abdomen shakes (“quivers”), generating substrate-borne vibrations at about six pulses per second. We present evidence that the female becomes receptive and stops walking because she senses these vibrations, rather than as a response to air-borne songs produced by the male fluttering the wings [1, 2, 12]. We also present evidence that the neural circuits expressing the sex-determination genes fruitless and doublesex [8] drive quivering behavior. These abdominal quivers and associated vibrations, as well as their effect on female receptivity, are conserved in other Drosophila species. Substrate-borne vibrations are an ancient form of communication that is widespread in animals. Our findings in Drosophila open a door to study the neuromuscular circuitry responsible for these signals and the sensory systems needed for their reception.

Mating behaviour and vibratory signalling in non-hearing cave crickets reflect primitive communication of Ensifera.

In Ensifera, the lack of well-supported phylogeny and the focus on acoustic communication of the terminal taxa hinders understanding of the evolutionary history of their signalling behaviour and the related sensory structures. For Rhaphidophoridae, the most relic of ensiferans following morphology-based phylogenies, the signalling modes are still unknown. Together with a detailed description of their mating process, we provide evidence on vibratory signalling for the sympatric European species Troglophilus neglectus and T. cavicola. Despite their temporal shift in reproduction, the species’ behaviours differ significantly. Signalling by abdominal vibration constitutes an obligatory part of courtship in T. neglectus, while it is absent in T. cavicola. Whole-body vibration is expressed after copulation in both species. While courtship signalling appears to stimulate females for mating, the function of post-copulation signals remains unclear. Mating and signalling of both species were found to take place in most cases on bark, and less frequently on other available substrates, like moss and rock. The signals’ frequency spectra were substrate dependent, but with the dominant peak always expressed below 120 Hz. On rock, the intensity of T. neglectus courtship signals was below the species’ physiological detection range, presumably constraining the evolution of such signalling in caves. The species’ behavioural divergence appears to reflect their divergent mating habitats, in and outside caves. We propose that short-range tremulation signalling in courtship, such as is expressed by T. neglectus, represents the primitive mode and context of mechanical signalling in Ensifera. The absence of high-frequency components in the signals may be related to the absence of the crista acoustica homologue (CAH) in the vibratory tibial organ of Rhaphidophoridae. This indirectly supports the hypothesis proposing that the CAH, as an evolutionary precursor of the ear, evolved in Ensifera along the (more) complex vibratory communication, also associated with signals of higher carrier frequency.

Vibrational communication in the spatial organization of collective digging in the leaf-cutting ant Atta vollenweideri

Subterranean ant nests are structures that emerge from collective building. The mechanisms used by individual ant workers to coordinate their building behaviour are largely unknown. We discovered that isolated workers of the Chaco leaf-cutting ant Atta vollenweideri stridulate while excavating in soil, and we investigated the possibility that workers communicate via vibrational signals in the context of collective nest excavation. Workers were observed to stridulate at similar rates, not only while manipulating soil with their mandibles, but also several seconds before grabbing the material. The measured attenuation rate suggests a detectable signal range of less than 6 cm. When presented with stridulation signals in an experimental arena offering distinct locations to excavate, workers were more likely to dig close to the source than at an alternative site. The probability of a worker digging at a location increased with the intensity of the vibrational signals produced at this location. Group-level stridulatory activity was monitored in the context of nest enlargement, in which ants excavating a tunnel were allowed suddenly to break into an existing chamber. Recordings before and after having gained access to the chamber showed that workers stridulated while excavating, but gradually discontinued signal production when nest space was available. Our results indicate that beyond the previously described use of vibrational signals in the contexts of food recruitment and alarm communication, workers stridulate while engaged in nest digging and attract nestmates to join excavation activity at the same location, thus contributing to the spatial organization of collective nest building.

Evolution and Diversity of Vibrational Signals in Mantophasmatodea (Insecta)

Vibrational communication for species identification and mate location is widespread among insects. We investigated the vibrational communication signals of 13 species of the insect order Mantophasmatodea (Heelwalkers). Males and females produce percussive signals by tapping their abdomens on the substrate to locate conspecific mates. We show that male and female calls are of similar general structure but differ in temporal characteristics. Using a principal component analysis, we demonstrate that most species can be distinguished by their calls only. Mapping the calls onto an existing molecular phylogenetic tree reveals a slow diverging drift of male call pattern but no specific trend. For females, a trend from faster towards slower pulse repetition times is indicated. Two sympatric species, Karoophasma biedouwense and Viridiphasma clanwilliamense (Austrophasmatidae), exhibit very different call parameters. The latter species produces calls rather different from all other investigated species, which might hint at reproductive character displacement.

Deceptive vibratory communication: pupae of a beetle exploit the freeze response of larvae to protect themselves

It is argued that animal signals may have evolved so as to manipulate the response of receivers in a way that increases the fitness of the signallers. In deceptive communication, receivers incur costs by responding to false signals. Recently, we reported that pupae of the soil-inhabiting Japanese rhinoceros beetle Trypoxylus dichotoma produce vibratory signals to deter burrowing larvae, thereby protecting themselves. In the present study, monitoring of vibrations associated with larval movement revealed that T. dichotoma larvae remained motionless for ca 10 min when pupal vibratory signals were played back transiently (freeze response). Furthermore, pupal signals of T. dichotoma elicited a freeze response in three other scarabaeid species, whose pupae do not produce vibratory signals. This indicates that the freeze response to certain types of vibration evolved before the divergence of these species and has been evolutionarily conserved, presumably because of the fitness advantage in avoiding predators. Pupae of T. dichotoma have probably exploited pre-existing anti-predator responses of conspecific larvae to protect themselves by emitting deceptive vibratory signals.

Exploitation of Insect Vibrational Signals Reveals a New Method of Pest Management

Food production is considered to be the main source of human impact on the environment and the concerns about detrimental effects of pesticides on biodiversity and human health are likely to lead to an increasingly restricted use of chemicals in agriculture. Since the first successful field trial, pheromone based mating disruption enabled sustainable insect control, which resulted in reduced levels of pesticide use. Organic farming is one of the fastest growing segments of agriculture and with the continuously growing public concern about use of pesticides, the main remaining challenge in increasing the safety of the global food production is to identify appropriate alternative mating disruption approaches for the numerous insect pests that do not rely on chemical communication. In the present study, we show for the first time that effective mating disruption based on substrate-borne vibrational signals can be achieved in the field. When disruptive vibrational signals were applied to grapevine plants through a supporting wire, mating frequency of the leafhopper pest Scaphoideus titanus dropped to 9 % in semi-field conditions and to 4 % in a mature vineyard. The underlying mechanism of this environmentally friendly pest-control tactic is a masking of the vibrational signals used in mate recognition and location. Because vibrational communication is widespread in insects, mating disruption using substrate vibrations can transform many open field and greenhouse based farming systems.

Do different species of grass-dwelling small Auchenorrhyncha (Homoptera) have private vibrational communication channels?

Do different species of grass-dwelling small Auchenorrhyncha (Homoptera) have private vibrational communication channels?

Resonance in herbaceous plant stems as a factor in vibrational communication of pentatomid bugs (Heteroptera: Pentatomidae)

Pentatomid bugs communicate using substrate-borne vibrational signals that are transmitted along herbaceous plant stems in the form of bending waves with a regular pattern of minimal and maximal amplitude values with distance. We tested the prediction that amplitude variation is caused by resonance, by measuring amplitude profiles of different vibrational pulses transmitted along the stem of a Cyperus alternifolius plant, and comparing their patterns with calculated spatial profiles of corresponding eigenfrequencies of a model system. The measured distance between nodes of the amplitude pattern for pulses with different frequencies matches the calculated values, confirming the prediction that resonance is indeed the cause of amplitude variation in the studied system. This confirmation is supported by the resonance profile obtained by a frequency sweep, which matches theoretical predictions of the eigenfrequencies of the studied system. Signal bandwidth influences the amount of amplitude variation. The effect of both parameters on signal propagation is discussed in the context of insect vibrational communication.

Stridulation byJadera haematoloma(Hemiptera: Rhopalidae): Production Mechanism and Associated Behaviors

AbstractThe Hemiptera displays a notable diversity of vibratory communication signals across its various families. Here we describe the substrate and airborne vibrations (sounds), the mechanism of production, and associated behaviors of Jadera haematoloma Herrich-Schaeffer, a member of the family Rhopalidae. Adult males and females both produce short, stereotyped sound bursts by anterior-posterior movement of abdominal tergites I and II against a stridulitrum located on the ventral surface of the metathoracic wing. Sound bursts are produced by a single adult male or female when physically touched by another adult, and are strongly associated with being crawled on by the approaching individual, but are not produced in response to contact with other arthropods or when pinched with forceps. The propensity to produce sounds when crawled upon decreases during the mating season. These sound bursts by J. haematoloma likely are communication signals. Rhopalidae has been significantly absent from the vibratory communication literature until now. Although the sounds are produced using a mechanism common to vibratory communication systems in closely related Heteropteran Hemiptera, the sounds in these other species function primarily in courtship or in mother-daughter interactions, which suggests that the functions of stridulation and the behavioral contexts have diversified in the Heteroptera.

Effect of web-substrate on male courtship vibration transmission and female reception in web-building spiders

Event Abstract Back to Event Effect of web-substrate on male courtship vibration transmission and female reception in web-building spiders Senthurran Sivalinghem1* and Andrew Mason1 1 University of Toronto Scarborough, Ecology and Evolutionary Biology, Canada In many communication systems, the signaling environment has been shown to impose significant influence on signal characteristics, signaling behaviour, and sensory physiology. Recently, substrate-propagated vibratory communication has received increased attention, and spiders have emerged as ideal model organisms to study this mode of communication. In spiders, vibrations have been shown to play an important role during mate attraction, mate choice, mate/prey localization, and predator avoidance. Despite the purported importance of signaling substrate on vibration transmission, studies looking at the effect of substrate on the efficacy of vibration transmission have primarily focused on solid-surfaces such as small rocks, leaf and pine litter, sand, and red clay, which are generally substrates of ‘land-dwelling’ spiders. To date, however, similar studies are lacking in web-building spiders, which, unlike land-dwellers, only communicate through one substrate-type – the web – and may have signals and receptors that are adapted to the filtering and attenuation characteristics of their respective webs. Understanding these influences has important implications for understanding the function and evolution of solid substrate-borne vibratory communication. In this study, we used the Australian redback spider, Latrodectus hasselti, and the western black widow spider, L. hesperus, to examine if web-substrates influence signal characteristics and transmission properties, and receptor sensitivity. The specific goals of this study were to: 1) quantify vibration transmission properties of web-threads; 2) characterize male courtship vibrations; and 3) determine sensory physiology of vibration reception in female receivers. Vibrations (frequency sweeps from 1 to 2000 Hz) were generated with a piezoelectric actuator, and individual strands were stimulated at increasing distances. The propagated vibrations were measured using a laser Doppler vibrometer – vibrations were measured 1 cm from the female – and transfer functions were then calculated for each distance (dB gain relative to input). We then conducted mating trials and recorded and analyzed male courtship vibrations (1 cm from the female). Lastly, we conducted neurophysiological experiments. Adult females were mounted ventral side up onto a Plexiglas holder, and the front legs were mechanically vibrated at varying frequencies at varying intensities. Tungsten electrodes were inserted into the leg nerve, and extracellular nerve responses to vibrations were recorded. We determined threshold sensitivity at each frequency, and the number of action potentials as a function of stimulus intensity to obtain frequency-response and intensity-response curves, respectively. Our results contribute novel information on the influence of web-substrate on male courtship signals, and female vibration reception. These results elucidate possible functions and evolution of vibratory signals and reception in web-building spiders. Keywords: Sensory Physiology, Signal Transmission, Substrate-borne vibration Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for student poster award) Topic: Communication Citation: Sivalinghem S and Mason A (2012). Effect of web-substrate on male courtship vibration transmission and female reception in web-building spiders. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00366 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 01 May 2012; Published Online: 07 Jul 2012. * Correspondence: Mr. Senthurran Sivalinghem, University of Toronto Scarborough, Ecology and Evolutionary Biology, Toronto, Ontario, M1C 1A4, Canada, s_sen24@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Senthurran Sivalinghem Andrew Mason Google Senthurran Sivalinghem Andrew Mason Google Scholar Senthurran Sivalinghem Andrew Mason PubMed Senthurran Sivalinghem Andrew Mason Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Reproductive Biology, Mating Behavior, and Vibratory Communication of the Brown-Winged Stink Bug,Edessa meditabunda(Fabr.) (Heteroptera: Pentatomidae)

We describe different aspects of the reproductive biology, mating behavior, and vibratory communication of the pentatomidEdessa meditabunda(Fabr.). This species shows lower copulation frequency and reproductive potential with longer sexual maturation period compared to other species of pentatomids. Females with multiple mating show increased fecundity when compared with single-mated females and both increased fecundity and reduced longevity when compared with virgin females. Courtship and mating behavior and vibratory signals are typical and similar to what was observed in other species of pentatomids, except that males started the courtship. These results constitute the first paper on biology, behavior, and vibratory communication among species of the subfamily Edessinae.

Vibrational playback by means of airborne stimuli

Substrate-borne vibrational communication is a common form of communication in animals. Current contact-based playback methods limit the number of substrates that can be stimulated simultaneously and potentially change the transmission properties of the substrate. Here, we explore a solution to these limitations by broadcasting airborne stimuli onto plant substrates to impart vibrational playbacks. We demonstrate that one can effectively compensate for the filtering properties of any individual plant across a range of frequencies. We then address how well both compensated broad-band and pure-tone stimuli for one plant individual apply to other individuals across days. Variation within and between plants was similar across the range tested but was quite variable at certain frequencies. Focusing on a subset of this range, at low frequencies, responses were flat across days and pure-tone frequency stimuli in this range were consistently transmitted despite repositioning of plants relative to the loudspeaker. Our results present a potential solution to researchers interested in exposing large samples of individuals to vibrational signals but also highlight the importance of validating the use of airborne stimuli as vibrational playbacks to the particular substrate type and frequency range of interest.