High-frequency Hearing Sensitivity Research Articles

Variation in whale (Cetacea) inner ear anatomy reveals the early evolution of "specialized" high-frequency hearing sensitivity.

As fully aquatic mammals, hearing is arguably the most important sensory component of cetaceans. Increasingly, researchers have been harnessing computed tomography (CT) to investigate the details of the inner ear as they can provide clues to the hearing abilities of whales. We use microCT scans of a broad sampling of the ear bones (periotics) of primarily toothed whales (Odontoceti) to investigate the inner ear bony labyrinth shape and reconstruct hearing sensitivities among these cetaceans, including several taxa about which little is currently known. We find support for sensitivity to the lower frequency spectrum in the archaeocete Zygorhiza kochii and an early toothed mysticete cf. Aetiocetus. Oligocene odontocetes (including one from our novel dataset), stem delphinidans, and two additional species of the long-snouted eurhinodelphinids are found to have been able to hear within the narrow-band high-frequency spectrum (NBHF), which is thought to be a specialized form of hearing that evolved convergently multiple different times in extant groups to avoid predation by macroraptorial predators. Our results thus indicate that NBHF evolved as early as the Oligocene and certainly in stem delphinidans by the early Miocene, and thus may be an ancestral characteristic rather than a more recent innovation in select groups.

Erratum: High-frequency hearing sensitivity level among young adults with insulin-dependent and non-insulin diabetes mellitus

Erratum: High-frequency hearing sensitivity level among young adults with insulin-dependent and non-insulin diabetes mellitus

High-frequency hearing sensitivity does not systematically imply aversion to ultrasounds in large terrestrial mammals

ABSTRACT Crop damage and vehicle collisions caused by wild ungulates require effective deterrents. Many commercial acoustic devices use ultrasonic signals, presenting them as aversive to these animals. However, unconvincing results reported in previous studies using (non-frequency modulated) ultrasounds bring their effectiveness as deterrent signals into question. Here, we explored the deterrent effectiveness of ultrasounds in several large mammalian species that are expected to perceive these high frequencies. Specifically, we tested the effect of different ultrasonic signals on red deer, peccaries, and wolves. Animals were exposed to sequences of nine acoustic signals in the 20–30 kHz frequency range, and to a lower-pitched signal (2–3 kHz). While red deer showed no aversion to ultrasonic signals (inaudible for humans), lower frequency (audible for humans) modulations increased aversive responses. Conversely, peccaries showed strong flight responses to several ultrasonic signals. Wolves also reacted to ultrasounds but did not flee. Our study confirms that ultrasonic signals are not suitable for deterring European red deer. However, our results suggest that their effectiveness in other species should be systematically tested, without assuming that their hearing frequency range is a reliable predictor of their behavioural responses to ultrasonic signals.

Sestrin2 plays a protective role in age-related hearing loss by inhibiting NLRP3-inflammasome activity

Age-related hearing loss (ARHL) is an auditory disease characterized by gradual loss of high-frequency hearing sensitivity. Excessive reactive oxygen species trigger NLRP3-inflammasome activation that may be crucial for ARHL pathogenesis. The antioxidant factor Sestrin2 (SESN2) has been reported to be involved in the remission of oxidative stress and ARHL. However, the mechanism by which SESN2 protects auditory cells in the aging mouse cochlea remains unknown. Here, we observed that ectopic overexpression of SESN2 delayed ARHL, whereas SESN2 knockdown accelerated it. Importantly, we elucidated that SESN2 exerts a hearing-protective effect by inhibiting the production of NLRP3 by acting as a mitophagy agonist. Our study proposes a new theoretical basis for SESN2 prevention of ARHL and provides a novel therapeutic strategy for maintaining SESN2 activity in the aging cochlea.

High-Frequency Hearing Sensitivity Level among Young Adults with Insulin-Dependent and Non-Insulin-Dependent Diabetes Mellitus

Diabetes Mellitus (DM) is a metabolic disorder characterized by elevated blood sugar levels. Patients of DM body cells are exposed to excessive amounts of plasma glucose, and the symptoms reported to complicate the sensory hearing organ. Spiral ganglion atrophy, vestibulocochlear nerve myelin sheath degradation, a reduction in the number of spiral lamina nerve fibres, and thickening of the stria vascularis and small arteries capillary walls are all potential chronic auditory repercussions of diabetes. The damage to any part of the hearing mechanism can lead to hearing loss. The present study aimed to investigate the high-frequency hearing sensitivity level among young adults diagnosed with Insulin-dependent and Non-Insulin dependent Diabetes Mellitus. It is an observational study design. Totally 90 participants were included between the age range of 31–40 years and divided into three groups (Control, Insulin-dependent DM, and Non-Insulin dependent DM). Each group had 30 participants. The results indicated that the hearing sensitivity level in high frequencies decreased when compared to lower frequencies. Most of the participants were observed to have reduced hearing sensitivity from mild to moderately severe sensorineural hearing loss. The study concluded that strong evidence that hearing loss may be a sign of DM.

Speech understanding and extended high-frequency hearing sensitivity in blast-exposed veteransa).

Auditory difficulties reported by normal-hearing Veterans with a history of blast exposure are primarily thought to stem from processing deficits in the central nervous system. However, previous work on speech understanding in noise difficulties in this patient population have only considered peripheral hearing thresholds in the standard audiometric range. Recent research suggests that variability in extended high-frequency (EHF; >8 kHz) hearing sensitivity may contribute to speech understanding deficits in normal-hearing individuals. Therefore, this work was designed to identify the effects of blast exposure on several common clinical speech understanding measures and EHF hearing sensitivity. This work also aimed to determine whether variability in EHF hearing sensitivity contributes to speech understanding difficulties in normal-hearing blast-exposed Veterans. Data from 41 normal- or near-normal-hearing Veterans with a history of blast exposure and 31 normal- or near-normal-hearing control participants with no history of head injury were employed in this study. Analysis identified an effect of blast exposure on several speech understanding measures but showed no statistically significant differences in EHF thresholds between participant groups. Data showed that variability in EHF hearing sensitivity did not contribute to group-related differences in speech understanding, although study limitations impact interpretation of these results.

Auditory Brainstem Responses at 6 and 8 kHz in Infants With Normal Hearing.

Normative auditory brainstem response (ABR) data for infants and young children are available for 0.25-4 kHz, limiting clinical assessment to this range. As such, the high-frequency hearing sensitivity of infants and young children remains unknown until behavioral testing can be completed, often not until late preschool or early school ages. The purpose of this study was to obtain normative ABR data at 6 and 8 kHz in young infants. Participants were 173 full-term infants seen clinically for ABR testing at 0.4-6.7 months chronological age (M = 1.4 months, SD = 1.0), 97% of whom were ≤ 12 weeks chronological age. Stimuli included 6 and 8 kHz tone bursts presented at a rate of 27.7/s or 30.7/s using Blackman window gating with six cycles (6 kHz) or eight cycles (8 kHz) rise/fall time and no plateau. Presentation levels included 20, 40, and 60 dB nHL. The ABR threshold was estimated in 5- to 10-dB steps. As previously observed with lower frequency stimuli, ABR waveforms obtained in response to 6 and 8 kHz tone bursts decreased in latency with increasing intensity and increasing age. Latency was shorter for 8-kHz tone bursts than 6-kHz tone bursts. Data tables are presented for clinical reference for infants ≤ 4 weeks, 4.1-8 weeks, and 8.1-12 weeks chronological age including median ABR latency for Waves I, III, and V and the upper and lower boundaries of the 90% prediction interval. Interpeak Latencies I-III, III-V, and I-V are also reported. The results from this study demonstrate that ABR assessment at 6 and 8 kHz is feasible for young infants within a standard clinical appointment and provide reference data for clinical interpretation of ABR waveforms for frequencies above 4 kHz.

Sex differences in Speech and High-frequency Hearing Loss Association With Cognitive Impairment Among Older Adults

Objectives: The purpose of this study was to investigate the relationship between speech-frequency hearing loss (SFHL), high-frequency hearing loss (HFHL), and cognitive impairment (CI). Then to determine whether there are any differences in gender among older community dwellers in China. Methods: This study involved 1,012 adults aged ≥60 years (428 male; average age, 72.61±5.51 years). The participants had their hearing and cognition measured using pure tone audiometry and Mini Mental State Examination (MMSE), respectively. We used the audiometric definition of hearing loss (HL) adopted by the World Health Organization (WHO). Speech-frequencies were measured as 0.5 kHz, 1 kHz, 2 kHz, and 4 kHz; high-frequencies were measured as 4 kHz and 8 kHz. Pure tone average (PTA) was measured as hearing sensitivity. Results: Our studies demonstrated a 37.6% prevalence of HL in males and a 36.0% prevalence of HL in females. Adjusted for confounding variables, the results from a multivariate analysis showed that SFHL was associated with CI in females (OR=2.400, 95% Confidence Interval=1.313–4.385) and males (OR=2.189, 95% Confidence Interval=0.599–2.944). However, HFHL was associated with CI only in females (OR=2.943, 95% Confidence Interval=1.505–5.754). HL was associated with poorer cognitive scores (P<0.05). “Registration” (P<0.05) in MMSE was associated with speech and high-frequency hearing sensitivity. Conclusion: The associations between HL and CI varied according to gender in older community-dwellers, suggesting that different mechanisms are involved in the etiology of HL. Moreover, hearing sensitivity was negatively associated with cognition scores; therefore, early screening for HL and CI among older community-dwelling adults is advised.

Relation Between the Screening Checklist for Auditory Processing in Adults and Diagnostic Auditory Processing Test Performance.

Purpose The aim of the study was to evaluate the relationship between the Screening Checklist for Auditory Processing in Adults and the performance of older adults on a battery of diagnostic tests for auditory processing. This was done for two versions of the checklist, one answered by older individuals at risk for auditory processing disorder (APD) and the other by the family of the older adults. Method Forty-nine older adults and 34 of their family members were initially tested with the screening checklist, each being tested with the version developed for them. Approximately half of the older adults had normal pure-tone thresholds, while the others had mild-moderate hearing loss above 2 kHz. The older adults were administered tests of auditory separation/closure, auditory integration, temporal resolution, temporal patterning, and auditory memory and sequencing. Results Most of the older adults and their family members reported of the presence of auditory processing difficulties on the screening checklist. On the diagnostic test battery, many of the older adults, irrespective of their high-frequency hearing sensitivity, failed the tests measuring temporal resolution and auditory integration. The sensitivity and specificity of the checklist answered by the older individuals were 69.05% and 71.43%, respectively. On the other hand, for the checklist answered by the family members, it was 77.78% and 33.33%, respectively. The test-retest reliability of the two versions of the checklist was found to be good. Conclusions As the specificity of the checklist answered by the family members was considerably lower than that answered by the older adults, the use of the version for the latter group is recommended. However, the checklist answered by the caregivers could be used to complement information obtained from the older adults at risk for APD when the older adults are unable to give valid responses.

Extended high frequency hearing sensitivity in normal contralateral ears exposed to mastoid drill noise in patients undergoing mastoid surgery

&lt;p class="abstract"&gt;&lt;strong&gt;Background: &lt;/strong&gt;This study aimed at evaluation of extended high frequency hearing in non operated normal ear in patients undergoing mastoid surgery using otological micro drill.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Methods:&lt;/strong&gt; A hospital based prospective observational study was carried out. Patients up to 40 years of age with unilateral ear disease were recruited and divided into two groups- mastoidectomy group comprising 30 patients who underwent mastoid surgery using high speed microdrill and tympanoplasty group who underwent surgery without using microdrill. Pure tone audiometry (conventional and extended high frequency) was performed preoperatively, on 3rd and 10th postoperative day.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Results:&lt;/strong&gt; In mastoidectomy group, Air conduction thresholds in extended high frequency showed significant changes on 3rd postoperative day and showed recovery by 10th postoperative day. Recovery started by 3rd postoperative day and in majority of cases there was a complete recovery by 10th postoperative day.&lt;/p&gt;&lt;p class="abstract"&gt;&lt;strong&gt;Conclusions: &lt;/strong&gt;Otological drilling has a significant effect on the extended high frequency hearing of normal contralateral ear. Extended high frequency audiometry till 16000 Hz is a sensitive modality for evaluation to monitor these cases on post-operative follow up.&lt;/p&gt;

Effects of age and tinnitus: Limited physiological evidence and no perceptual consequence of cochlear synaptopathy

Evidence from animal models and human temporal bones has shown that cochlear synaptopathy is associated with aging. Previous work from our lab has suggested that a weakened middle-ear-muscle-reflex (MEMR) in individuals with tinnitus and normal hearing may reflect the presence of cochlear synaptopathy. In this study, we investigated effects of age and tinnitus on the MEMR strength. We also investigated the relationship between the MEMR strength and amplitudes of auditory brainstem responses (ABRs) as well as several perceptual measures that rely on precise temporal neural coding, such as amplitude-modulation detection, the detection of envelope interaural phase difference, and spatial release from speech-on-speech masking. Younger (20–30 yrs) and older (55–69 yrs) listeners with and without tinnitus and with normal or near-normal hearing were tested. We found that aging and tinnitus were associated with significant reductions in MEMR strength and ABR-based measures. However, only the MEMR-strength reduction was significant after accounting for group differences in high-frequency hearing sensitivity. No significant group differences between the older, tinnitus and control groups were found in the perceptual measures obtained in this study. Results will be discussed in terms of sensitivity of these measures to cochlear synaptopathy in humans. [Work supported by NIH grant R01 DC015987.]

Coevolution of vocal signal characteristics and hearing sensitivity in forest mammals

Although signal characteristics and sensory systems are predicted to co-evolve according to environmental constraints, this hypothesis has not been tested for acoustic signalling across a wide range of species, or any mammal sensory modality. Here we use phylogenetic comparative techniques to show that mammal vocal characteristics and hearing sensitivity have co-evolved to utilise higher frequencies in forest environments – opposite to the general prediction that lower frequencies should be favoured in acoustically cluttered habitats. We also reveal an evolutionary trade-off between high frequency hearing sensitivity and the production of calls with high frequency acoustic energy that suggests forest mammals further optimise vocal communication according to their high frequency hearing sensitivity. Our results provide clear evidence of adaptive signal and sensory system coevolution. They also emphasize how constraints imposed by the signalling environment can jointly shape vocal signal structure and auditory systems, potentially driving acoustic diversity and reproductive isolation.

Earless toads sense low frequencies but miss the high notes.

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

Factors Affecting Sentence-in-Noise Recognition for Normal Hearing Listeners and Listeners with Hearing Loss.

Background and ObjectivesDespite amplified speech, listeners with hearing loss often report more difficulties understanding speech in background noise compared to normalhearing listeners. Various factors such as deteriorated hearing sensitivity, age, suprathreshold temporal resolution, and reduced capacity of working memory and attention can attribute to their sentence-in-noise problems. The present study aims to determine a primary explanatory factor for sentence-in-noise recognition difficulties in adults with or without hearing loss.Subjects and MethodsForty normal-hearing (NH) listeners (23-73 years) and thirty-four hearing-impaired (HI) listeners (24-80 years) participated for experimental testing. For both NH and HI group, the younger, middle-aged, older listeners were included. The sentence recognition score in noise was measured at 0 dB signal-to-noise ratio. The ability of temporal resolution was evaluated by gap detection performance using the Gaps-In-Noise test. Listeners’ short-term auditory working memory span was measured by forward and backward digit spans.ResultsOverall, the HI listeners’ sentence-in-noise recognition, temporal resolution abilities, and digit forward and backward spans were poorer compared to the NH listeners. Both NH and HI listeners had a substantial variability in performance. For NH listeners, only the digit backward span explained a small proportion of the variance in their sentence-in-noise performance. For the HI listeners, all the performance was influenced by age, and their sentence-in-noise difficulties were associated with various factors such as high-frequency hearing sensitivity, suprathreshold temporal resolution abilities, and working memory span. For the HI listeners, the critical predictors of the sentence-in-noise performance were composite measures of peripheral hearing sensitivity and suprathreshold temporal resolution abilities.ConclusionsThe primary explanatory factors for the sentence-in-noise recognition performance differ between NH and HI listeners. Factors affecting sentence-in-noise recognition performance differed between NH and HI listeners. The working memory was the primary predictor of the sentence-in-noise scores for the NH individuals. In contrast, a combination of factors seemed to contributed to speech-in-noise understanding for the HI listeners. Given this, we must be careful not to generalize findings from the NH listeners to the HI individuals.

Extended high frequency audiometry in users of personal listening devices

PurposeNoise exposure leads to high frequency hearing loss. Use of Personal Listening Devices may lead to decline in high frequency hearing sensitivity because of prolonged exposure to these devices at high volume. This study explores the changes in hearing thresholds by Extended High Frequency audiometry in users of personal listening devices. Material and methodA descriptive, hospital based observational study was performed with total 100 subjects in age group of 15–30years. Subjects were divided in two groups consisting of 30 subjects (Group A) with no history of Personal Listening Devices use and (Group B) having 70 subjects with history of use of Personal Listening Devices. Conventional pure tone audiometry with extended high frequency audiometry was performed in all the subjects. ResultSignificant differences in hearing thresholds of Personal Listening Device users were seen at high frequencies (3kHz, 4kHz and 6kHz) and extended high frequencies (9kHz, 10kHz, 11kHz, 13kHz, 14kHz, 15kHz and 16kHz) with p value <0.05. Elevated hearing thresholds were observed in personal listening devices users which were directly proportional to volume and duration of usage. ConclusionIn present study no significant changes were noted in hearing thresholds in PLD users before 5years of PLD use. However, hearing thresholds were significantly increased at 3kHz, 10kHz, 13kHz in PLD users having >5years usage at high volume. Thus, it can be reasonably concluded that extended high frequencies can be used for early detection of NIHL in PLD users.

Age-related hearing loss in TrpV1 knockout mice

Several transient receptor potential (TRP) channels including TRPV1 are located on hair cell membranes. The gating mechanisms of these channels are associated with cellular stress, inflammation, and cytoplasmic uptake of aminoglycosides. Thus, TRPV1 channel may serve as a functional target that links acoustic trauma and enhanced aminoglycoside trafficking. TrpV1 mutant mice have no apparent hearing loss as young adults. Here, we assessed the hearing sensitivity of TrpV1 mutant mice (B6.129X1-Trpv1tm1Jul/J, stock #3770) by auditory brainstem responses to a broad frequency range, from 4 to 48 kHz. At 7 weeks of age, the auditory sensitivity in TrpV1 mutant mice was comparable to their heterozygous littermates. By 11 weeks of age, mutant TrpV1 mice exhibited evident high frequency hearing loss, with 30-to-40 dB elevated thresholds between 24 and 48 kHz, compared to littermate controls. At 18 weeks of age, high frequency hearing sensitivity worsened in both groups of mice, and this age-related progressive hearing loss was further expedited in TrpV1 mutant mice compared to littermate controls. Further research is required to determine the otoprotective role of TRPV1 channel in maintaining auditory sensitivity as mice age, and whether TrpV1 functionality exacerbates aminoglycoside-induced ototoxicity.

Ultrasonic hearing in frogs: inner ear morphological correlates

Three species of anuran amphibians (Odorrana tormota, O. livida and Huia cavitympanum) have recently been found to detect ultrasounds. We compared morphological data collected from the ultrasound detecting species with data from Rana pipiens, a frog with a typical anuran upper cut-off frequency of ca. 3 kHz. In addition, we examined the ears of two species of Lao torrent frogs, O. chloronota and Amolops daorum that live in acoustic environments resembling those of the ultrasonically sensitive frogs. Our results suggest that the three ultrasound-detecting species have converged on small-scale functional modifications of the basilar papilla (BP), the high-frequency hearing organ in the frog inner ear. These modifications are also seen in the ears of O. chloronota, suggesting that this species is a candidate for high-frequency hearing sensitivity. These data form the foundation for future functional work probing the physiological bases of ultrasound detection by a non-mammalian ear. Supported by NIDCD DC-002...

Inner ear morphological correlates of ultrasonic hearing in frogs

Three species of anuran amphibians (Odorrana tormota, Odorrana livida and Huia cavitympanum) have recently been found to detect ultrasounds. We employed immunohistochemistry and confocal microscopy to examine several morphometrics of the inner ear of these ultrasonically sensitive species. We compared morphological data collected from the ultrasound-detecting species with data from Rana pipiens, a frog with a typical anuran upper cut-off frequency of ∼3 kHz. In addition, we examined the ears of two species of Lao torrent frogs, Odorrana chloronota and Amolops daorum, that live in an acoustic environment approximating those of ultrasonically sensitive frogs. Our results suggest that the three ultrasound-detecting species have converged on small-scale functional modifications of the basilar papilla (BP), the high-frequency hearing organ in the frog inner ear. These modifications include: 1. reduced BP chamber volume, 2. reduced tectorial membrane mass, 3. reduced hair bundle length, and 4. reduced hair cell soma length. While none of these factors on its own could account for the US sensitivity of the inner ears of these species, the combination of these factors appears to extend their hearing bandwidth, and facilitate high-frequency/ultrasound detection. These modifications are also seen in the ears of O. chloronota, suggesting that this species is a candidate for high-frequency hearing sensitivity. These data form the foundation for future functional work probing the physiological bases of ultrasound detection by a non-mammalian ear.

High Frequency Hearing Sensitivity in Adolescent Females of a Lower Socioeconomic Status Over a Period of 24 Years (1985–2008)

To examine annually over a period of 24 years, the high frequency hearing sensitivity in different groups of urban female adolescents with a low socioeconomic status (SES) and residential foster care. Hearing screening (15 decibel [dB] hearing level ranging from 1,000 to 8,000 Hertz [Hz]) and threshold (>15 dB hearing level) records were obtained from 8,710 female adolescents (mean age, 15.8 years [range, 12-20 years]), predominantly Hispanic and African American from households with a low SES. Data related to the use of personal listening devices (PLDs), daily hours of usage, occurrence of tinnitus, and hearing thresholds between 1,000 and 8,000 Hz over an 8-year period (2001-2008) were obtained from the adolescents. High frequency hearing loss (HFHL) doubled over the 24-year period from 10.1% in 1985 to 19.2% in 2008. In comparison with the general adolescent population, this group of female adolescents presented with a higher percentage of bilateral mild or greater degrees of HFHL at two or more frequencies including 3,000, 4,000, and 6,000 Hz. Use of PLDs increased four-fold, from 18.3% (n = 68) in 2001 to 76.4% (n = 227) in 2008. Of the total number reporting tinnitus (n = 286), 99.7% (n = 285) also reported regular PLD use. A significant relationship was found between PLD use and reported tinnitus and HFHL irrespective of time of use of PLD. Increased incidence of HFHL, reported tinnitus, PLD use, and hours of daily use in at-risk female adolescents of a low SES was found. A frequency interval of 3,000-6,000 Hz should be included in hearing screening protocols to identify potentially disabling hearing loss. Hearing conservation strategies need to be developed and/or modified that target and reach at-risk children and adolescents.

No correlation of body size and high-frequency hearing sensitivity in neotropical phaneropterine katydids

We investigated the relationship between body size (weight) and hearing sensitivity in response to a high-frequency, bat-like stimulus in a number of phaneropterine katydids on BCI, Panama. These phaneropterines are nocturnal flying species and thus potential prey of various insectivorous bats on the island. We tested the prediction that larger species compensate for the disadvantage — of producing stronger echoes for searching bats — by being more sensitive to bat calls, thereby increasing safety margins towards this predator. Contrary to this prediction, larger katydids were not more sensitive. This was corroborated in neurophysiological experiments in the nocturnal rainforest, where simultaneous recordings of the T-fibre activity in response to searching bats revealed no substantial difference between small and large katydids. We offer three explanations for the lack of correlation between body size and high-frequency sensitivity in these species.