Ultrasonic Hearing Research Articles

Sensory hair cells of a fish ear: evidence of multiple types based on ototoxicity sensitivity

Sensory hair cells from the striolar region (striolar hair cells) of the utricle and the lagena of the ear of a teleost fish Astronotus ocellatus (Cuvier) ear are sensitive to gentamicin sulphate, an ototoxic drug. In contrast, sensory hair cells from outside the striolar region (extra-striolar hair cells) are not sensitive to gentamicin. These data, combined with results from studies showing different ultrastructural features and different immunoreactivity to a calcium binding protein, S-100, lead to the suggestion that there are distinguishable types of hair cells in these endorgans. These results add to the increasing evidence that classifying the sensory hair cells of fish ears only as the traditional 'vestibular type II' may be inadequate for properly understanding structure and function of the fish ear.

Human Ultrasonic Speech Perception

Bone-conducted ultrasonic hearing has been found capable of supporting frequency discrimination and speech detection in normal, older hearing-impaired, and profoundly deaf human subjects. When speech signals were modulated into the ultrasonic range, listening to words resulted in the clear perception of the speech stimuli and not a sense of high-frequency vibration. These data suggest that ultrasonic bone conduction hearing has potential as an alternative communication channel in the rehabilitation of hearing disorders.

The ultrasound‐detecting ear of the praying mantis—Form and function

Praying mantises have sensitive ultrasonic hearing mediated by a single ear located in the ventral midline of the body. The ear comprises two teardrop‐shaped tympana facing each other in a deep, longitudinal groove; they are separated by less than 150 pm. Each tympanum is backed by a tightly adherent tracheal sac. Sensory transduction by 30–35 sensory neurons takes place at the extreme anterior end of each tympanum. Neurophysiological and behavioral tests confirm the prediction that the auditory system lacks directionality. The advantage of a single ear in the midline is not clear, but physiological evidence suggests that location in the deep groove increases sensitivity by 4–6 dB. The midline ear of the mantis is part of an “early warning system” affording protection from echolocating bats. Tethered flight and free flight experiments have shown that the mantis begins responding behaviorally within 50 ms with full foreleg extension and abdomen dorsiflexion; a change in flight path begins in 100–200 ms. It is hypothesized that the abdominal flexion throws the flying mantis into a stall out of which it rolls into a power dive. The maneuvers are very effective: In field trials with wild bats, normal mantises escaped capture whenever attacked, while mantises deaf to the bats' cries were almost always caught.

Sexual dimorphism of auditory function and structure in praying mantises (Mantodea; Dictyoptera)

Sexual dimorphism of tympanate auditory systems in insects has bees described in only a few taxonomically isolated cases. However, widespread sexual dimorphism occurs in the ultrasound‐sensitive, midline ear of the praying mantis.In dimorphic species, it is always the female mantis that shows a reduction in ultrasonic hearing. The dimorphism may be mild—a difference in tuning and small reduction in sensitivity—or extreme with no evidence of audition in the female. In all but the mildest cases, the reduction in hearing is accompanied by significant anatomical divergence from the male ear structure. Two distinct metathoracic groove (‘ear’) types are linked to hearing reduction in the females.Anatomical evidence of auditory sexual dimorphism appears in 34% of the 183 mantis genera examined. The dimorphic genera are widely but non‐uniformly distributed within three of the four largest mantis families.Auditory sexual dimorphism is closely correlated with dimorphism in wing length. In general, mantises with functional wings have sensitive ultrasonic hearing while those with short wings do not. These findings support the hypothesis that ultrasonic hearing in mantises is part of a defensive system against attack by echolocating bats.

Audition in the praying mantis, Mantis religiosa L.: identification of an interneuron mediating ultrasonic hearing.

1. The praying mantis possesses a single ear located in the ventral midline of the metathorax. We have studied the mantis' auditory nervous system using both extracellular and intracellular techniques and have identified anatomically and physiologically a mirror-image pair of interneurons (MR-501-T3) in the metathoracic ganglion that mediates ultrasonic hearing. 2. MR-501-T3 is tuned broadly to ultrasound with best sensitivity (55-60 dB SPL) between 25 and 45 kHz. Its tuning matches closely that of the whole tympanal nerve. 3. The physiological responses of MR-501-T3 are characterized by: (1) a phasic-tonic firing pattern with a distinctive initial burst at 500-800 spikes/s; (2) minimum latencies of 8-12 ms; (3) no spontaneous activity; (4) sigmoid intensity response curves with a small (10 dB) dynamic range; (5) accurate coding of stimulus duration and of repetition rates up to 60 pps. 4. The ascending axon of MR-501-T3 conducts action potentials at 4 m/s, a rate comparable with some giant fiber systems. 5. MR-501-T3 shows no directional capability. Sound from right and left produce identical responses in both cells of the pair. Neither cutting one tympanal nerve nor removing one hemi-ear leads to different responses in the two cells indicating that they must receive a common input, either from the auditory afferents or from interneurons. We present evidence that the two cells are not directly connected. 6. MR-501-T3 is a large, symmetrical cell with its processes primarily in the intermediate neuropil (lateral ring tract). Its integration segment crosses the midline in the supramedian commissure, and the cell body lies dorsally near the entrance of the leg nerve. The axon travels in the dorsal lateral tract and is one of the largest (17 microns) in the connective. 7. Given the strong anatomical similarities between MR-501-T3 and the G and B cells of the locust, these cells may be homologous. 8. We present arguments based on our physiological results and existing behavioral data that MR-501-T3 is part of an ultrasonic warning/escape system in the mantis. As in moths, lacewings, and crickets, this system may provide a defense against nocturnally foraging bats.

The acoustic middle ear muscle reflex in albino rats.

The acoustic middle ear muscle reflex was studied in albino rats anesthetized with chloralose. The best frequency of the reflex and the threshold at this frequency were on average about 3 kHz and 57 dB SPL, respectively. The threshold increased as frequency increased above, and decreased below, the best frequency at a rate of about 20 dB/octave. Above about 12 kHz, the muscular response showed instability and habituation. Thresholds were similar between stapedius and tensor tympani reflexes and between ipsilateral and contralateral reflexes. The middle ear transmission loss due to the reflex was the greatest and nearly constant below about 1 kHz, where the loss was about 18 dB at the maximal stimulation. Above this frequency the loss decreased as frequency increased up to 20 kHz. Thus the reflex, unlike that in other animals, suppressed transmission over the whole range of reflex-eliciting frequencies. The transfer function of the reflex had a well damped low-pass characteristic with a cut-off frequency of about 20 Hz. From the above characteristics of the reflex, the role of the rat's tympanic muscles in improving ultrasonic hearing under ambient noises was suggested.

Echolocation for perception of the environment

Microchiropteran bats, many cetaceans, and several species of birds have independently evolved active sonar for acoustic imaging of their surroundings. Echologcating birds emit acoustic clicks at 1 to 10 kHz for orientation. Echolocation enables birds to detect wires as small as 1.0 mm in diameter, providing a perceptual acuity appropriate for obstacle avoidance and navigation. Echolocating bats comprise about 20% of all mammalian species and exhibit sophisticated adaptations of hearing which led to early success and diversity. Two classes of bat orientation signals are used for different purposes: FM sounds for target description and localization, and CF sounds for improving target detection and determining target velocity from echo Doppler shifts. These signals occur in several patterns (FM-CF, CF-FM, FM) that relate to acoustic environments. Using broad bandwidths and high frequencies (20 to 150 kHz) to exploit the superb ultrasonic hearing of mammals, bats can resolve wires as small as 0.1 mm and can perceive fine target features. Bat echolocation appears primarily adapted to acoustic constraints influencing target detection (long ranges or small targets). Cetaceans use different kinds of orientation signals; short clicks of broad bandwidth and high frequencies (10–150 kHz) being best known. These clicks, at least, seem adapted for fine resolution rather than long-range detection in the highly reverberant underwater environment. Difficulties in observing behavior and conducting experiments limit available data on cetaceans. These data indicate that fine target resolution is possible.

The influence of noise on emotional states

This review of rat sensory perception spans eight decades of work conducted across diverse research fields. It covers rat vision, audition, olfaction, gustation, and somatosensation, and describes how rat perception differs from and coincides with ours. As Nagel's seminal work (1974) implies, we cannot truly know what it is like to be a rat, but we can identify and acknowledge their perceptual biases. These primarily nocturnal rodents are extremely sensitive to light, with artificial lighting frequently causing retinal degeneration, and their vision extends into the ultraviolet. Their olfactory sensitivity and ultrasonic hearing means they are influenced by environmental factors and conspecific signals that we cannot perceive. Rat and human gustation are similar, being opportunistic omnivores, yet this sense becomes largely redundant in the laboratory, where rodents typically consume a single homogenous diet. Rat somatosensation differs from ours in their thigmotactic tendencies and highly sensitive, specialised vibrissae. Knowledge of species-specific perceptual abilities can enhance experimental designs, target resources, and improve animal welfare. Furthermore, the sensory environment has influences from neurone to behaviour, so it can not only affect the senses directly, but also behaviour, health, physiology, and neurophysiology. Research shows that environmental enrichment is necessary for normal visual, auditory, and somatosensory development. Laboratory rats are not quite the simple, convenient models they are sometimes taken for; although very adaptable, they are complex mammals existing in an environment they are not evolutionarily adapted for. Here, many important implications of rat perception are highlighted, and suggestions are made for refining experiments and housing.