A recent survey lists more than 100 papers utilizing the auditory evoked potential (AEP) recording technique for studying hearing in fishes. More than 95 % of these AEP-studies were published after Kenyon et al. introduced a non-invasive electrophysiological approach in 1998 allowing rapid evaluation of hearing and repeated testing of animals. First, our review compares AEP hearing thresholds to behaviorally gained thresholds. Second, baseline hearing abilities are described and compared in 111 fish species out of 51 families. Following this, studies investigating the functional significance of various accessory hearing structures  by eliminating these morphological structures in various ways are dealt with. Furthermore, studies on the ontogenetic development of hearing are summarized. The AEP-technique was frequently used to study the effects of high sound/noise levels on hearing in particular by measuring the temporary threshold shifts after exposure to various noise types . In addition, the hearing thresholds were determined in the presence of noise  in several studies, a phenomenon termed masking. Various ecological , genetic , methodical  and behavioral  factors potentially influencing hearing were investigated. Finally, the technique was successfully utilized to study acoustic communication by comparing hearing curves with sound spectra either under quiet conditions or in the presence of noise, by analyzing the temporal resolution ability of the auditory system and the detection of temporal, spectral and amplitude characteristics of conspecific vocalizations. In the modern era, interest in the questions of hearing by fishes began in 1903 Parker  and his Carassius auratus and the oscar Astronotus ocellatus.Invasive electrophysiological methods have included recording of auditory end organs , eighth nerve fibers, and neurons within the auditory brainstem and higher centers in auditory pathway  conditioning  of the many functional elements that normally determine behavior, and as such comprise an incomplete description of hearing. But how “incomplete” is the definition of hearing using these methods? What can we know about hearing, and what can’t we know using electrophysiological methods? It is certain that a physiological response is not equivalent to “an act of perceiving” sound. However, it seems likely that a physiological response from the auditory brainstem or whole auditory pathway (inner ear up to the midbrain or forebrain) could stand in for, or predict, hearing under some circumstances, such measuring the Auditory Brainstem Response (ABR) in the screening for brainstem abnormalities and consequent hearing impairment in newborn infants , and absolute sensitivity (the lowest detectable stimulus level). We assume that electrophysiological methods can be used to reasonably estimate the frequency range of hearing (what sound frequencies produce detectable responses?). This is based on our belief that significant responses from some early elements of the auditory nervous system strongly imply that they could be used by the brain to signal the presence of a sound and produce a hearing sensation. This is not certain, but it is reasonable to believe.The question of sensitivity, or the meanings of behavioral hearing thresholds versus those of electrophysiological thresholds, is much more problematic. Both behavioral and electrophysiological thresholds are properly defined statistically in terms of probabilities. However, there is no present theory of how these two very different types of thresholds relate to one another. Psychophysical thresholds have been studied for over 100 years, and the various complex factors that determine the statistical nature of the thresholds are relatively well understood , or in longitudinal studies of hearing development where the equality of behavioral and electrophysiological thresholds need not be assumed. In a limited way, they are also useful for between-species comparisons of sound thresholds and relative descriptions of the frequency range of auditory response . For these and other reasons, AEP audiometry in fishes has been popular in the literature since 1998, and has lead to renewed interest in the questions of hearing by fishes. As long as it is recognized that electrophysiological and behavioral methods do not necessarily lead to the same results, and that they are not ultimately equivalent or interchangeable descriptions of the auditory response, AEP studies on fishes should continue to grow in popularity and continue to answer fundamental questions about hearing in fishes. One of the goals of this review is to illustrate and evaluate how the AEP studies since 1998 have contributed to this rapidly growing field.Gadus morhua   detect sound pressure or can only respond to acoustic particle motion. In most cases, critical experiments to confirm pressure sensitivity have not been done in fishes without special otophysic adaptations, and it is a matter of opinion whether or not the mere presence of a swim bladder confers sound pressure sensitivity  is likely to be different from normal habitats . Because the relationship between sound pressure and particle motion in typical test tanks cannot be predicted in most cases sound pressure and particle acceleration levels should be measured at the same time. It is possible and likely that many unspecialized fishes detect particle acceleration in their natural habitat, not sound pressure, and audiometric data measured in sound pressure terms may not be appropriate.Among the more than 30,000 extant fish species, the goldfish has become by far the most popular species for studying hearing physiology. The goldfish adapts easily to various holding conditions and is therefore chosen very often by physiologists. It belongs to the otophysines a series of primarily freshwater fishes comprising the orders Cypriniformes (carps and minnows), Siluriformes (catfishes), Characiformes (characins) and Gymnotiformes (South American knifefishes) which possesses well developed hearing and sensitivity to sound pressure due to their Weberian apparatus that mechanically connects the swim bladder and inner ears  from electrophysiological thresholds. Comparisons among other species (see below) for which these data exist could tell us whether or not this hypothetical ‘factor’ is universal among fish, or is species-specific. The baseline hearing abilities of goldfish have been investigated by numerous investigators applying different behavioral Enger  or electThe behavioral audiograms in Fig. The many AEP audiograms Fig. b are genThe medians of all behavioral and all AEP data sets were calculated and shown in Fig. It is also important to note that the signals used in AEP studies are short (about 20 ms in duration) while many of the behavioral studies used long duration signals . Detection thresholds in behavioural studies have been shown to be higher when signal duration decreases in goldfish , because they lack a swim bladder, the structure that gives fish the capacity to detect sound pressure. For the little skate (family Rajidae) the audiograms are roughly similar, but with the AEP audiogram giving higher thresholds below and lower thresholds above 0.6 kHz than the behavioral audiogram , a species closely related to the goldfish, there is comparable variation threshold at best frequency among the behavioral and AEP data Fig. . There iThe two behavioral threshold estimates differ by as much as 20 dB at some frequencies, although the frequency of best hearing roughly agrees (between 0.5 and 1 kHz). The two AEP threshold estimates differ by about 25 dB at some frequencies, and the frequency of lowest thresholds vary somewhat between 0.5 and 0.8 kHz. Thus, for the carp, AEP thresholds by Amoser and Ladich  are reasIdeally, for comparative purposes behavioral and AEP-thresholds should be determined under the same acoustical conditions in the same lab. So far this was only done in the investigation by Kojima et al.  in the cHalobatrachus didactylus  is a popular species for physiological studies, primarily of its directional hearing  that enhance hearing by sound pressure detection; toadfish are thought to detect sound through the otolith organ’s direct response to acoustic particle acceleration and not to sound pressure  is also not specialized for sound pressure hearing and is likely sensitive to particle acceleration. The behavioral audiogram by Wolff  is unusuAuditory sensitivity has been measured in the red sea bream (family Sparidae) by Kojima et al.  utilizinThe oscar (family Cichlidae) is not specialized for sound pressure hearing, and thus is probably more properly described with respect to acoustic particle acceleration. Nevertheless, there is one behavioral .One generalization that arises from some of the comparisons above is that AEP measures tend to produce thresholds that are higher than the behavioral values at low frequencies, and produce lower thresholds than the behavioral thresholds at the higher frequencies. We can only be certain of this statistical tendency in the comparison between the median thresholds of six behavioral audiograms and the 10 AEP audiograms for the goldfish. Further evidence for this tendency comes from studies on the oyster toadfish Fig.  but not AEP-audiograms of 110 fish species out of 22 orders out of 51 families have been published and are dealt with in this review (see Table Families most often investigated in terms of species numbers are sciaenids or drums 11 species), cyprinids and cichlids (9 species), and pomacentrids or damselfish (8 species). The species most often chosen for investigations in AEP-studies is the goldfish (17 studies). Baseline audiograms were not the main purpose of many of these studies but were determined to investigate other issues such as the effects of accessory hearing structures, of noise exposure or masking, or of changes during ontogeny  and paddlefish Polyodon spathula (family Polyodontidae) . The former two species are likely sensitive to particle acceleration while the latter species is likely sound-pressure sensitive (Yan and Curtsinger The audiograms for the lake sturgeon ae) Fig.  (Lovell ae) Fig.  are at lRepresentatives of the family Clupeidae are specialized for sound pressure detection by virtue of an air-filled bulla adjacent to the utricle. Audiograms for these species in the region between 100 and 4,000 Hz  respond to ultrasound  have been investigated. Among the order Cypriniformes the largest number of species has been investigated in the family Cyprinidae. Audiograms gained in representatives of the family Cyprinidae reveal considerable variation Fig. . The heaCatostomus catostomus, family Catostomidae, order Cypriniformes; red piranha Pygocentrus  nattereri, family Characidae, order Characiformes; glass knifefish Eigenmannia virscens, family Sternopygidae, order Gymnotiformes) are all specialized for sound pressure detection, and they all have similar audiograms in terms of sensitivity (maximum difference 15–20 dB) and frequency range of best hearing (0.6–1 kHz).Representatives of three otophysan orders Fig.  , Esociformes (pikes) and Percopsiformes (trout-perches) are sensitive to particle acceleration, not sound pressure Fig. . This waPoeciliamexicana (family Poeciliidae), but about 30 dB less sensitivity for the lined seahorse Hippocampus erectus (family Syngnathidae).Figure Among Perciformes (perches), the most species-rich fish order, representatives of 13 (out of 160) families have been investigated Table  are probLutjanus carponotatus (family Lutjanidae), the rainbow runner Elagatis bipinnulata, and the golden trevally Gnathonodon speciosus (family Carangidae) , some large swim bladders (jewel cichlid Hemichromis guttatus) and some anterior extensions of the swim bladder contacting the inner ear (orange chromide Etroplus maculatus and Paratilapia polleni)  of Figs. Etroplus and Paratilapia . The sound pressure curves for Etroplus and Paratilapia are similarly quite sensitive at the higher frequencies. This comparison could be explained in at least two ways. The first possible explanation is that Etroplus and Paratilapia are both primarily sensitive to sound pressure and that plotting their audiograms in particle acceleration terms only reflects PALs in the tank at threshold. A second possible explanation is that these two species possess additional frequency-selective peripheral channels tuned at higher frequencies that are also activated by particle acceleration. Presently, we do not have enough experimental data to critically evaluate these two possibilities.Comparison of the SPL and PAL audiograms for pia Fig. a, b reveAmphiprion frenatus, Mediterranean damselfish Chromis chromis, yellow clownfish Amphiprion clarkii, and clown anemone fish Amphiprion ocellaris much more sensitive below about 800 Hz. However, all these species have relatively high sound pressure thresholds (>90–100 dB) and a low-pass shaped audiogram, suggesting that they are primarily sensitive to particle acceleration. Figure Members of the family Pomacentridae of Fig. Neogobius melanostomus is probably sensitive only to particle acceleration based on its high sound pressure thresholds, as is probably the Padanian goby Padogobius bonelli (formerly martensi) and the Arno goby Gobius nigricans, based on their low-frequency best hearing frequency (<100 Hz). Gobiids sometimes lack swim bladders.The Gobiidae of Fig. Trichogaster trichopterus seems unusual in having a band-pass shaped audiogram with a best frequency of 800 Hz, although it is similar to the others in having relatively good high-frequency hearing  (See “The gouramis (families Osphronemidae and Helostomatidae) of Fig. Hz) See “” sectionProtopterus annectens (family Protopteridae) of Fig. The African lungfish A comparison of hearing sensitivities in closely related species reveals a variety of trends. Hearing thresholds are either quite similar in some taxa such as catfishes . In contrast, species possessing hearing specializations such as weakly electric fish (family Mormyridae), otophysines and gouramis  had generally lower pressure thresholds than species lacking diverticulae (spot and red drum). However, the lowest sound pressure thresholds at higher frequencies  occurred in northern kingfish Menticirrhus saxatilis, a species with low hair cell densities and swim bladder that atrophies as adults , sturgeons, salmonids, pikes (Esocidae), gobiids, some cichlids, damselfish, sunfish (Centrarchidae) have best sound pressure hearing thresholds at 90 dB re 1 μPa or higher and maximal upper frequencies of 1–2 kHz Figs. , 19, 23.is Figs. , 15, 27 is Figs.  etc.. Inis Figs. , the cicery low <0 Hz. In ery low <0 Hz. In Many fish taxa possess accessory hearing structures which are thought to enhance their hearing sensitivities by extending the detectable frequency range and by lowering their hearing thresholds. This is made possible by connecting the inner ear to air-filled cavities and transmitting the oscillations of the wall of these cavities in a field of fluctuating sound pressure to the inner ears. Accessory hearing structures have developed in numerous species. Some taxa such as some holocentrids and clupeids develop anterior swim bladder horns, otophysines possess Weberian ossicles, whereas gouramis and mormyrids possess air-filled bubbles touching the inner ear without being connected to the swim bladder  from 100 Hz to 4 kHz , an otophysine family closely related to cyprinids, a second accessory hearing structure evolved in addition to Weberian ossicles. Loaches have a cranial encapsulation of the anterior part of the swim bladder and in addition special channels stretching laterally from the swim bladder to the outer body wall. These lateral trunk channels form a muscle-free window beneath the skin. Filling the lateral trunk channels with cotton/rayon stapple in the red finned loach der Fig.   resulted in an increase in thresholds between 5 and 25 dB as shown by Yan (Gouramis or labyrinth fishes (suborder Anabantoidei) possess suprabranchial air-breathing chambers which enhance their hearing sensitivity as demonstrated by Schneider  by condin by Yan  using thn by Yan . The decStegastes (formerly Eupomacentrus) partitus. Since the introduction of the AEP protocol in 1998 the ontogenetic development of hearing sensitivity has been investigated in eight species using the AEP technique, one representative of the family Clupeidae, one of the family Cyprinidae, two catfish species, one toadfish species and two perciforms. In general, hearing thresholds were given in sound pressure units but it is assumed that all fish species including those possessing hearing specialization are also particle acceleration sensitive.Due to the difficulty training or conditioning juvenile fish of a few millimeter length, just one study investigated the ontogenetic development of hearing sensitivity using behavioral techniques Kenyon . Kenyon Following the systematics by Nelson  the famiAmong otophysines the development in the zebrafish, a representative of the order Cypriniformes, and two catfish species have been studied. In the zebrafish, Higgs et al. , 2003 obSynodontis schoutedeni (family Mochokidae) larger stages showed significantly lower thresholds at frequencies below 2 kHz , the smallest juveniles had the lowest auditory thresholds. They were unable to detect frequencies higher than 2 or 3 kHz   Fig.  at 100 aIn the round goby (family Gobiidae) Belanger et al.  studied Trichopsis vittata ] afterwards. In addition, the time until fish recovered normal their hearing abilities was investigated. The second approach was to study the hearing sensitivity in the presence of noise (not after a certain period of noise exposure), a phenomenon known as masking. Masking effects are observable at much lower noise levels than effects of noise exposure, and occur in all vertebrates investigated Fay .Noise exposure can result in a temporary increase in hearing thresholds (TTS) if the noise exposure levels are high enough; this varies considerably among species. The AEP-technique has proven to be very useful for these investigations because fish could be measured repeatedly to study the degree and recovery from any TTS over short recovery periods. Different noise types have been used including white noise, ambient noise, sonar, seismic shots (the sounds from air guns used in seismic exploration) and pure tones.The majority of studies on white noise exposure were carried out in otophysines, in particular in cyprinids. The goldfish was the species most often used.Amoser and Ladich  studied Oreochromis niloticus (family Cichlidae)  Fig. b. In a sae) Fig.  found ouae) Fig. a. After ae) Fig.  Fig. 44ae) Fig.  exposed ae Fig.  Scholik and Yan  exposed Pimelodus pictus (family Pimelodidae), after exposure for 12 or 24 h at 158 dB. The catfish showed a significant rise of thresholds of up to 32 dB after exposure. Exposure duration had no effect on sensitivity. Recovery took 14 days in the pictus cat  to white noise at 142 dB for 24 h , the broad whitefish Coregonus nasus (family Coregonidae) and the lake chub Couesius plumbeus (family Cyprinidae) in the Mackenzie River Delta. Threshold shifts were found for exposed fish as compared to controls in the northern pike and lake chub, with recovery within 18 or 24 h of exposure, while there was no threshold shift in the broad whitefish . Animals were exposed to a maximum received SPL of 193 dB re 1 Pa2 for 324 or 648 s. The TTS was more pronounced in one group of rainbow trout studied (group 1) than in another group (group 2) at 400 Hz  at SPLs of 210 dB between 2.8 and 3.6 kHz. The exposure level did not affect the hearing sensitivity of rainbow trout, a species whose hearing range is lower than the MFA frequencies, and is sensitive to particle acceleration. In contrast, one cohort of channel catfish (an otophysine) showed a TTS of 4–6 dB at 2.3 kHz, but not at lower tested frequencies, whereas a second cohort showed no change. The average of the two cohorts is plotted in Fig. Halvorsen et al.  studied Oncorhynchus tshawytscha are annually transported downstream by barges in the Western USA through the federal hydropower system on the Snake and Columbia rivers. Barging noise of about 136 dB resulted in a small but significant TTS in juveniles 7 days after barging . In contrast to the impairments mentioned in the previous section, the hearing thresholds are not measured after but during the occurrence of typically much lower noise levels and spectra. Different noise types have been applied to study masking effects, in particular white noise, natural ambient noise and anthropogenic noise. An increase in the background noise caused by natural or human activity sources may render the weakest sources undetectable, and may decrease the distance at which all sources can be detected.Platydoras armatulus (family Doradidae) and the pumpkinseed sunfish Lepomis gibbosus (family Centrarchidae) at two different SPLs of uniform spectrum noise (white noise). Continuous white noise of 110 dB RMS elevated the thresholds by up to 22 dB in the goldfish and in striped Raphael catfish. White noise of 130 dB RMS elevated overall hearing thresholds up to 44 dB in both otophysines  is termed the critical masking ratio (CR) Fay . When thMasking in the sunfish Fig.  did not Pogonias chromis and Atlantic croaker (family Sciaenidae) to investigate the effect of different connections between the ear and swim bladder on noise masking effects. At the 124 dB level of white noise both species showed similar changes in auditory sensitivity. However, in the presence of the 136 dB white noise masker the black drum showed significantly greater shifts (to be expected) in auditory thresholds between 300 and 600 Hz, while the Atlantic croaker did not . The perch’s hearing thresholds were only slightly affected (mean up to 12 dB at 100 Hz) by the highest noise levels presented because it most likely lacks hearing specializations that would contribute to sound pressure sensitivity (Amoser and Ladich Gobius cruentatus (family Gobiidae). The ambient noise level was 111 dB for the toadfish and 97 dB for all other species. Data reveal that in all four species threshold shifts due to masking by ambient noise are small or insignificant, probably due to their adaptation to the ambient noise in their habitats , the brown meagre (family Sciaenidae), the Mediterranean damselfish (family Pomacentridae) and the redmouthed goby Hearing in fish is frequently masked by anthropogenic noise either when kept for aquaculture or leisure or in the field by the presence of boat/ship noise, seismic air-gun shooting, various sonars, pile driving activity, and other sources.Gutscher et al.  investigShip noise is a major anthropogenic noise source in aquatic habitats. The masking effects of ship noise have been studied in the Lusitanian toadfish, the brown meagre, the Mediterranean damselfish and the redmouthed goby. The ship noise level was 131 dB for the toadfish and 132 dB for the other species. Data reveal that the presence of ship noise decreases hearing sensitivities up to 40 dB and reduces the detectability of communication sounds  and genetic factors , ototoxic drugs (gentamicin) and comparison of different AEP-recording protocols.Fishes are ectothermic animals and their body temperature generally depends on ambient water temperature. Thus, ambient temperature might affect various physiological processes including sensory system function. Two studies applied the AEP-technique to find out if the auditory sensitivity changes with temperature in fishes. In general, an increase in sensitivity with frequency was found on all three catfish species investigated.Wysocki et al.  studied In contrast, the increase was much smaller in both Amazonian catfish species measured (stenothermic species). In the pictus cat (Pimelodidae) the hearing thresholds were maximally 7 dB higher at 30 °C as compared to 22 °C Fig.  Wysocki. In the Besides temperature, lack of visual stimuli might potentially influence hearing in fishes. A comparison revealed similar auditory sensitivity in surface and cave dwelling (blind) populations of the Atlantic molly (Poeciliidae)  and the South American bronze catfish Corydoras aeneus . Auditory thresholds did not differ for either species between normally pigmented and albinotic specimens at any frequency tested  altered evoked potential waveforms slightly but did not alter estimated threshold sensitivity  gained under various conditions  and a potential predator (bottlenose dolphin Tursiops truncatus-family Delphinidae). The authors provide evidence that the auditory system of a vocal fish, lacking accessory hearing structures, is capable of resolving fine features of con- and heterospecific vocalizations.The AEP protocol was modified by Wysocki and Ladich  to invesIn “One issue is the large variation of AEP audiograms for the same species, in particular the goldfish. This effect, however, is not peculiar to AEP studies since the same or more variation has been observed in behavioral experiments. When comparing the median goldfish audiograms from behavioral and AEP approaches we find a clear difference between these two methodical approaches. Based on the physics of the AEP technique we tentatively assume that the tendency seen in the goldfish, namely that the AEP technique gives higher thresholds at lower frequencies and lower thresholds at higher frequencies, reflects a general difference between techniques and can be expected for other species too. Because there is no second species which has been investigated as often as goldfish and because this goldfish trend cannot be seen as clearly in other species, it is impossible to quantify this effect and to derive a factor so that AEP audiograms can be transformed to closely match the behavioral data. Based on the goldfish comparison we assume that the ‘AEP effect’ is frequency dependent and that AEP curves can not simply be shifted downward to estimate the behavioral data.In view of the large variation of AEP audiograms for the goldfish, one needs to be very cautious when comparing and interpreting results for individual species gained under different conditions or from different labs. The procedure that we recommend is to carry out all measurements under identical conditions . Beyond that we recommend that every lab/beginner should measure goldfish for comparative purposes. This will give readers information on how thresholds measured in lab A potentially deviate from those gained in lab B.When measurements are carried out under the identical conditions the AEP technique is a useful tool to measure and compare different species, different stages of age, and to determine the effects of accessory hearing structures, the effects of exposure to noise and the effects of masking by various noise types, the effects of temperature etc.−2.One generalization we can make from the data reviewed here is that all species known to possess potential specializations for sound pressure detection (a gas body near or in contact with the ears) have lower sound pressure thresholds at best frequency (55–83 dB), and respond at higher frequencies (200 Hz–3 kHz at best frequency) than fishes not known to be specialized. The fishes not known to be specialized are more diverse in sensitivity and frequency range, but generally have best thresholds between 78 and 150 dB, and best frequencies of below 100 to 1 kHz. All fishes studied by measuring AEP particle acceleration threshold levels have thresholds between 30 and 70 dB re: 1 μm sThis review has identified several species, based on their AEP audiograms, that may have sound pressure sensitivity even though they have no obvious or known morphological specializations for detecting sound pressure. These include the red sea bream, the silver mojarra, the jewel cichlid, and the brown meagre, all perciformes.All future audiometric studies on fishes, except species shown to be primarily sensitive to sound pressure, should include measurements of particle acceleration level in the test tank or test environment, and audiograms expressed in terms of particle acceleration as well as sound pressure. Ideally, the acoustic impedance (ratio of sound pressure to particle velocity levels) of the test environment should be characterized and compared to the impedance of the species natural habitat in order to evaluate the measured audiogram. Wherever possible, the lab studies should be carried out in tanks with very rigid walls  to raise the impedance to near ideal levels (Halvorsen et al.


Education; people working with music, Music; and people with moderate or negligible noise exposure, Other. A fourth group included people with poorer pure tone hearing thresholds and a history of severe occupational noise, Industry. Ntotal = 193. The following hearing tests were used:The aim of the investigation was to study if dysfunctions associated to the cochlea or its regulatory system can be found, and possibly explain hearing problems in subjects with normal or near-normal audiograms. The design was a prospective study of subjects recruited from the general population. The included subjects were persons with auditory problems who had normal, or near-normal, pure tone hearing thresholds, who could be included in one of three subgroups: teachers, − pure tone audiometry with Békésy technique,− transient evoked otoacoustic emissions and distortion product otoacoustic emissions, without and with contralateral noise;− psychoacoustical modulation transfer function,− forward masking,− speech recognition in noise,− tinnitus matching.Education and Industry than for the other groups, possibly associated to the inner hair cell area. Forward masking results were significantly correlated to louder matched tinnitus. For many subjects speech recognition in noise, left ear, did not increase in a normal way when the listening level was increased. Subjects hypersensitive to loud sound had significantly better speech recognition in noise at the lower test level than subjects not hypersensitive. Self-reported stress/anxiety was similar for all groups. In conclusion, hearing dysfunctions were found in subjects with tinnitus and other auditory problems, combined with normal or near-normal pure tone thresholds. The teachers, mostly regarded as a group exposed to noise below risk levels, had dysfunctions almost identical to those of the more exposed Industry group.A questionnaire about occupations, noise exposure, stress/anxiety, muscular problems, medication, and heredity, was addressed to the participants. Forward masking results were significantly worse for  Hearing problems are not just a matter of reduced ability to recognize speech and other sounds, but also of tinnitus, abnormal sensitivity to loud sound and sound distortion. Hearing loss, as measured by pure tone audiometry, is often accompanied by tinnitus. However, tinnitus occurs without concurrent self-reported hearing loss in about 1/3rd of all casesIn a study of risk factors for tinnitus in a population 55 years and older Sindhusake et alThese days when tinnitus is being paid so much attention, it may not be provocative to claim that hearing problems can be more than, or different from, having bad pure tone thresholds. Therefore there should be a demand for diagnostic test methods for identifying or excluding dysfunctions associated to the cochlea as the origin(s) of the hearing problems. Results from such tests could form the basis for individual treatment plans.A test protocol, intended to be sufficiently sensitive to detect dysfunctions associated to minute cochlear lesions that cannot be diagnosed by routine clinical audiological tests, was developed. The protocol now consists of six auditory physiological tests, a Békésy audiogram, and a questionnaire.In a first study, with fewer tests and test subjects (n = 46), who had tinnitus and normal or near-normal hearing-thresholds, we found that certain results could be associated with certain backgroundsThe aim of the current study was to use the full test protocol to possibly identify dysfunctions associated with cochlear lesions in persons with up to moderate noise levels at work, with hearing problems, and without apparent deteriorations in the audiogram. If we found dysfunctions, would professions with different types of noise show their own characteristics?The main finding of the current study was that teachers had characteristic results for two measurements not used in the first study. Those results were similar to results from industry workers tested for comparison, although the teachers had about 20 dB better pure tone thresholds. However, there were still no characteristic features to be found for musicians.The investigation was approved by the Regional ethical review board in Stockholm, no. 04-228/4. All test subjects gave their informed consents (written) to participate in the study.Altogether 272 subjects of working age with tinnitus or other hearing problems, and not wearing a hearing aid, were tested in the study. About half of them were recruited by announcements in hearing clinics in Stockholm. The other half was recruited by an announcement at the home page of Karolinska University Hospital, and participants came from all over the country. The subjects were recruited and measured during a period of three years. There was no medical examination of the test subjects. The characterization of symptoms and exposure to e.g. noise was entirely based on the questionnaire. As it happened, very few professions were represented among these volunteers. Thus groups were formed to fit the assortment of volunteers regarding the amount and characteristics of noise exposure. It was not possible to match the participants regarding gender and age. Therefore the results should be interpreted with caution. However, some of the results have been compared with results for groups of persons of similar ages, but without hearing problems, or with internationally standardised pure tone thresholds. Reported here are results of subjects, who fulfilled the threshold criterion of having normal or near-normal hearing thresholds and who could be included in one of three groups of professions. Results of a fourth group with industrial noise and worse hearing thresholds are also reported for comparison. This study may have found dysfunctions that are characteristic for these groups before the audiogram is affected, but it will not give us a general overview of the effects of noise on hearing for these groups of professions at later stages of deterioration of the audiogram. Neither can it tell how common the detected dysfunctions are.Education; 2) people working professionally with music, the group Music; and 3) subjects with low or, in a few cases, moderate occupational noise exposure, mostly medical staff and students, the group Other. The group Other seemed the least homogenous regarding noise exposure. In these groups (1–3) pure tone thresholds on both ears had to be ≤25 dB hearing level (HL) at the frequencies 500, 1000, 1500 and 2000 Hz, and ≤40 dB HL at 4000 Hz. The average threshold at the frequencies 3000, 4000, and 6000 Hz on both ears had to be ≤35 dB HL. The threshold fence defining normality or near-normality was chosen to include the effect of normal aging for all the test subjects. At the higher frequencies it corresponds to the median thresholds of otologically normal 66 year old men with no history of undue noise exposureThe groups were: 1) teachers, with 1/3rd of them preschool teachers, forming the group Industry.For comparison a fourth group was selected 4) constituted of persons with blue-collar occupations, having audiograms with high- (and sometimes mid-) frequency hearing impairments, indicative of noise-induced hearing loss, and also having tinnitus, the group After omission of data from people not conforming to the threshold criterion or being unsuitable for the chosen groups of professions there was a total of 193 subjects, 102 men and 91 women, 18 to 66 years of age, to be analysed. The groups are presented in middle-aged reference group consisted of fifty-seven 41–60 year old subjects, all without hearing problems and with hearing thresholds no worse than the median for 50-year-old men“Normal” reference results for our methods and our equipment were used for comparison. These results were meant to be to be used in several projects. A A computer-controlled Tucker-Davis Technologies (System III) module system was used with Sennheiser HDA 200 headphones at the psychoacoustical tests, and with amplifiers plus probe systems ER-10C from Etymotic Research on both ears for the measurements of otoacoustic emissions. The HDA 200 headphones were calibrated according to ISO 389-8 and the ER-10C probe systems were calibrated in an ear simulator according to IEC 60711.The software for all the methods, for the computer and the Tucker-Davis equipment, was written in our laboratory. The TDT system was programmed to produce and present stimuli, for example the OAE stimuli and the contralateral noise, as well as collect and store the responses. However, the speech test used stored sound files for the words and their respective noise stimuli. The adaptive procedure of the speech test was controlled by the computer. All tests were performed in a sound proof audiometric test room.Basic otoscopy and tympanometry were performed. When necessary, cerumen was removed.The hearing measurements took about three and a half hours including a coffee break. All the participating subjects performed all the tests. However, individual test subjects were allowed to exclude stimulus levels they considered too high.In the intermission between the measurements the subjects were given a questionnaire. Apart from questions about age and profession there were 22 questions with two to eight response alternatives, sometimes also with a possibility of an open response. The questions regarded hearing problems, tinnitus, sensitivity to loud sounds, noise exposure at work and in their leisure time, musical activities, impulse noise incidents, military service, medication (pain relieving and tinnitus medicine), eye and hair colour, smoking, neck problems, headache, stress, and relatives with hearing problems. The questions on tinnitus and sensitivity to loud sounds had the response alternatives: never, only after a loud sound, at certain occasions, often, and constantly. The questions on headache and neck problems had only the response alternatives yes and no. The question “Do you feel stressed/anxious?” had the five response alternatives: never, seldom, sometimes, often and always. A translation of the questionnaire, including number of responses to each alternative, is presented in From the responses to the questions about profession, different types of noise exposure and exposure times, figures of noise exposure were estimated. The underlying principles for the judgements are found in Pure tone thresholds for left and right ears separately were measured at 125, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 6000, and 8000 Hz.A pulsating tone is presented. The duration is 225 ms, including attack and release times, and with a 175 ms long interval between pulses. The level of the tone is increased by 2.8 dB/s until the subject detects the tone and starts pressing the button. The level of the tone decreases with the same speed until the button is released again, etc. Thus a zigzag pattern is formed around the threshold level. The turning-points are registered by the computer. The measurement is concluded after 10 turning points. The first two turning points are not used in the calculation. The threshold is calculated as the mean value of the medians of the remaining upper and lower turning points, and presented with the resolution of 1 dB. These parameters should give high accuracy with a standard deviation of repeated measures not exceeding 1.8 dBTransient evoked otoacoustic emissions, TEOAEs, were measured at two input levels without or with contralateral noise. Normally the contralateral noise will make the efferent system controlling the outer hair cells, OHCs, reduce, suppress, the response amplitude. We measure the response correlated to the stimulus signal, but also the uncorrelated response.Clicks with the duration of 80 µs were repeated with a frequency of 50 Hz. The measurement was performed in a nonlinear mode to enhance those components in the response, which have a nonlinear dependence of the stimulus level, and to suppress the linear components. To accomplish this, the polarity of every fourth click is reversed and the sound pressure level is increased by a factor of 3. After removal of the primary click by windowing technique, the acoustical responses from 1000 clicks are averaged. The stimulus level is specified as so called peak equivalent sound pressure level, peSPL. TEOAEs were measured at 70 and 85 dB peSPL with and without contralateral masking consisting of a 70 dB SPL broadband noise. The RMS-values for the correlated and uncorrelated responses, over the interval of measurement, are used as variables in the analyses and so are the RMS-values in three different frequency areas, Low (500–2500 Hz), Mid (2500–5000 Hz), and High (5000–8000 Hz).2/f1 = 1.25, and near the measurement frequency. The measurements were performed on both ears at an input level, L, of f1 of 65 dB SPL, Lf1/Lf2 = 10 dB, nominal frequency √f1*√f2. A weak response is measured at the frequency 2f1–f2. Two measurements were done, the first one at the nominal frequency 1000 Hz and the second one at 2000 Hz. To avoid measuring in a notch of the DPOAE microstructure an automatic procedure measured at a few frequencies between 0.95 and 1.05 times the nominal frequency with an increment of 0.01 times the nominal frequency. The measurements were then performed at the frequency with the largest response. To estimate the background noise from equipment and ear, the level in narrow frequency areas below and above the response tone frequency was measured.When measuring distortion product otoacoustic emissions, DPOAEs, two stimulus tones are given, with frequencies near each other, fThe measurements were made without and with contralateral noise. We made 20 3s long measurements of the response from the two tones without contralateral noise. We calculated the individual standard deviation of these responses to test the stability.Measurements were also made with on-off noise  on the contralateral ear in order to investigate the ability of the ear to regulate the sensitivity of the other ear. The response normally decreases somewhat when the contralateral noise is on. The difference between the medians of the five off-periods and the medians of the five on-periods shows the ability and endurance of the ear to suppress the response when the noise is on.The active nonlinear process in the cochlea is mediated by the OHCs and facilitates the perception of the complex sound patterns in speech. These patterns are characterized by rapid sound variations combined with slow modulations caused by speech syllables, words and intonation. A measurement termed the psychoacoustical modulation transfer function (PMTF) reflects the functioning of the inner ear when handling slow intensity variations like those of speech. PMTF measures the thresholds of brief tones placed at the peaks or in the valleys of a fully, sinusoidally intensity-modulated, octave-band noise at various sound pressure levels centred at the test tone frequencyPMTF measurements: The measurements were performed with the brief tone, 4 ms with raised cosine flanks, first with the octave-band filtered noise at 2000 Hz, and with a modulation frequency of 2.5 Hz; and then with the octave-band filtered noise at 4000 Hz, and with a modulation frequency of 10 Hz. The noise levels were 35 to 85 dB SPL in steps of 10 dB. Initially, the threshold for the brief tone was measured without noise to familiarize the subject with the brief tone. Both ears were measured, with the left ear first. When the subject expressed tiredness or discomfort, only one ear, mostly the left ear, was measured.Typical PMTF results: peak threshold is used for the threshold of the brief tone when the tone is placed at the peak of the noise. The term valley threshold is used when the tone is placed in the valley of the noise.) For the valley threshold there is a corresponding maximum at about 65 dB SPL  we divided the PMTF curves into classes depending on the likeness to hyper-PMTF. We called them P-type, and numbered them 0 to 3. A few P-types are exemplified in Experiments on mice, using auditory brainstem responsesmiddle-aged reference group the S/N at threshold, over both ears, were −13.6 ±2.1 dB, at 70 dB SPL presentation level, and −15.5 ±2.2 dB, at 85 dB SPL. Corresponding values for the group of young women, for the left ear only, were −15.4 ±0.9 and −16.3 ±1.1 dB.The speech recognition threshold in modulated noise was measured on the self-reported worst ear. Hagermańs 5-word sentences in noise were used with the original versions of the various words stored in the computerThe subjects were asked to compare pure tones from a modified version of the Békésy audiometry program to match the pitch of their tinnitus. The level was changed in steps of 1 dB, and the frequency in steps of 1 Hz. The participants were asked to: “Try to match the frequency of the tone in the earphone with the pitch of your tinnitus. After that, match the level of the tone to that of your tinnitus”. The drawback with this method is that it is only applicable to tinnitus with a tonal character. The matching is less accurate for those perceiving their tinnitus as noise or other non-tonal sounds.The program Statistica 9.1 was used for statistical analyses. For the hearing measurements, all of them resulting in continuous variables, analysis of variances was used, often with subsequent Tukey's post hoc tests. To find relations between continuous variables linear regression with age as covariate was used. However, in analyses where age was not significant, results from ANOVAS without age as covariate are presented. For the variables from the questionnaire, with rank order variables, where no information is given in the text, Kruskal-Wallis ANOVA by ranks was used, sometimes with subsequent multiple comparisons. Other statistical tests are mentioned in Results and Discussion.Among the 193 subjects analysed, 69% had tinnitus and were also hypersensitive to loud sound, 22% had tinnitus only, 7% were only hypersensitive to loud sound and 2% had neither of these two symptoms, but felt they had difficulties hearing in noise. On a general question about hearing problems 25% answered that their hearing symptoms disturb them always: affect sleep, affect their whole life; 28% that their symptoms affect them in normal sound environments, but their tinnitus is masked by louder sounds; 25% that their symptoms affect them only in a quiet environment; 7% that they have symptoms but no problems ; 13% said they have problems, but did not specify to what extent. There was no statistical difference between the profession groups in this respect. Neither was there any difference between groups regarding hypersensitivity to loud sound.Education and Other were significantly different from the groups Music and Industry by being judged less noise exposed (p<0.05). This was the result of a Kruskal-Wallis ANOVA by ranks with estimated noise exposure as the dependent variable and with profession group as the between subjects factor. The questions referred to regarded profession, number of years working, leisure activities, and military service.Very rough estimates of noise exposure based on the individual responses to the questionnaire indicated that the groups Industry group was significantly higher than for the three other groups (p<0.01). Another group, which might have reported incidents for example with positive feedback in electronic systems, is the Music group. In our study, however, the musicians claimed that they were not using electronic amplification. This should have decreased the risk of unexpected sudden changes of the sound level. And the number of reported incidents did not differ significantly from those of the groups Education and Other.Regarding self-reported incidents with impulse noise or sudden very loud noise, a corresponding analysis showed that the exposure estimate for the Other group included mainly hospital staff, and students. Only few of the participants had been exposed to occupational noise. In those cases, they handled medical devices.The Education had significantly higher values than Industry . The Education group had significantly more self-reported tension headaches than the groups Other and Industry . The groups Education and Music had similar, slightly higher values for stress/anxiety than Industry and Other, but the differences were not significant. There were no significant differences between groups regarding pain relieving medication, eye and hair colour, smoking, and relatives with hearing problems. Tinnitus medicine was only used by ten subjects. Therefore it was not subjected to analyses. There was no difference in stress problems between the subgroups preschool teachers and other teachers.Regarding neck problems, Self-reported stress seemed to give tension headache and neck problems . Headaches and neck problems influenced the use of medication . The amount of medication was not influenced by age , gender or stress.Industry, the blue-collar group without threshold restrictions, chosen to have worse noise exposure than the other groups, was significantly different from all the other groups for left and right ears combined , Industry group the right ear was on average 2.8 dB worse than the left ear for all frequencies, but the difference was not significant. This group had worse pure tone thresholds than those of unexposed men of the same ageAn ANOVA was performed with hearing threshold as the dependent variable, with profession group as a between subjects factor, and with ear and frequency as within subjects factors. The group Education, Other and Music, and they were highly significant . However, when compensated for age they were not, and the response of the Industry group at the higher level was just marginally higher, 1.4 dB, than at the lower level. For the uncorrelated response signal, on the other hand, the Industry group showed a 6 dB higher response than Education, Other and Music . The TEOAE results of the Industry group may be explained by dysfunctional OHCs with reduced ipsilateral restraining regulation.An ANOVA with the correlated TEOAE response as the dependent variable, with profession group as between subjects factor; and with ear, stimulus level, and frequency area as within subjects independent factors; showed no significant difference between the various professions or between left and right ear. For normal ears the response increases when the stimulus level is increased from 75 to 85 dB peSPL. There was such increases of 4.4 dB for each of the groups The contralateral suppression effect was very small, the means for the groups ranging from 0.22 dB to −0.26 dB without significant differences, although age was a significant factor.Industry had a very weak mean response over frequencies, −1.9 dB SPL, which was significantly lower than the responses of the other groups .An ANOVA with the DPOAE response level without contralateral noise as the dependent variable, with profession group as between subjects factor; with ear and frequency as within subjects factors, and age as covariate, showed that the mean response level was significantly higher at 1000 Hz than at 2000 Hz, 7.5 and 3.7 dB SPL respectively (p<0.00001). There was a strongly significant age dependence (p<0.00001). From the right ear Industry had an almost 3 dB higher value of that noise in the left ear than the groups Education, Other, and Music .To estimate the background noise from equipment and ear, the level in narrow frequency areas below and above the response tone frequency was measured. A statistical analysis corresponding to the one above was performed, now with this noise level as the dependent variable. In the left ear this noise level was about 3 dB higher than in the right ear (p<0.00001). Furthermore, the group Industry had a significantly higher value, 4.0 dB, than the groups Education, Other, and Music (2.0–2.1 dB), when averaged over ears and frequencies (p<0.00005). Age had a significant influence, but compensation for age did not change any values. Thus, the group Industry differed from the other groups by low DPOAE responses on the right ear, a high noise level around the tone response on the left ear, and a large variation in the 20 measurements without contralateral noise. It looks like the DPOAE response from this group mostly consists of noise. Compare to TEOAE results.A corresponding statistical analysis was also performed with the individual standard deviation of 20 consecutive measurements as the dependent variable. Also for this standard deviation the group There was no significant influence of any of the factors ear, frequency or profession group on the suppression effect using the contralateral on-off noise. The range of suppression for the groups was 0.4 to 0.6 dB.Industry group was chosen to have a noise induced hearing loss it was a natural finding that both types of OAEs for the Industry group were marginal, unstable and considerably noisy. There were deteriorations in the contralateral regulatory system for all groups, but considerably more so in the Industry group. A few individuals in the other three groups had abnormally high emissions at some frequencies suggesting impaired ipsilateral regulatory function.As the As a whole our results regarding OAEs did not give much information, probably because most of our test subjects were middle-aged. One should keep in mind that there is a normal degradation of OAEs and regulatory efferent system with age, which may obscure for example noise induced degradation The stimulus noise levels at which the maximum values of the threshold curves were found, were used as dependent variables in a multivariate ANOVA with profession group as between subjects factor; and with peak/valley curve and frequency as within subjects factors. Those noise levels did not differ significantly between the groups. This was true for both peak and valley curves and both ears.Education group than for Other and Music . The same tendency was found on the right ear, but without statistical significance. An analysis for different types of teachers showed a tendency to higher maxima for preschool teachers than for other teachers. In this context it should be noted that a high maximum, especially on the valley curve, is one characteristic of a hyper-PMTF, Education group are caused by sudden loud sounds, they definitely indicate a reduced ability to detect short sounds in silent intervals of a complicated signal, poor temporal processing.The corresponding analyses, with the maximum value of the PMTF threshold curve on the left ear as dependent variable, showed that the maximum of the valley curve was significantly higher for the Industry group had more self-reported impulse noise incidents (p<0.01) than the other groups, this did not result in significantly more hyper-PMTFs than in the other groups. One reason may be that some of the test subjects, especially in the Industry group, could not be measured at the low levels of the modulated noise at which the characteristics of the hyper-PMTF are seen. Measurements closer to the incidents, before the characteristics in our PMTF-measurements had been obscured by further deterioration of pure tone thresholds, would have clarified if there was a hyper-PMTF. Those actually classified with P-type = 3, hyper-PMTF showed fairly flat audiogram curves. See Very few subjects with fully developed hyper-PMTFs (P-type = 3), suggesting exposure to impulse noise possibly associated to damage in the inner hair cell area Audiograms with similar hearing thresholds for all frequencies have also been observed in conscripts sent to us for measurements after severe shooting incidents, unpublished data. It is not unusual that all thresholds have positions around 10 dB HL, i.e. totally normal. This may be a warning flag when a person with normal thresholds complains of hearing problems. In experiments on chinchilla, WangIndustry, mean age 54, and Education, mean age 45, showed significantly worse forward masking mean results (over ears and levels), 19 and 21 dB threshold difference, than the about five years younger groups Music and Other, 32 and 30 dB, . These results could be compared to the threshold difference, 27 ±9 dB  for our middle-aged reference group without hearing problems. Most notable is that the median of the teachers, the Education group, 23 dB, was almost as low as the lower quartile of the middle-aged reference group, 22 dB. The lower quartile of Education was 12 dB.An ANOVA was performed with the forward masking threshold difference (difference between the thresholds of the brief tone at 5 ms and at 50 ms after the noise burst) as the dependent variable, with profession group as a between subjects factor, and with ear and level as within subjects factors. The two older groups Music and Other are as good as the median result of the (much younger) group of young women, 30 dB. WaltonOn the other hand one may note that the results of Industry group, two from Education and one from Other. Their PMTF results suggested either exposure to impulse noise or other sudden loud noise or they could not be measured at the levels of the modulated noise at which the characteristics of the hyper-PMTF are seen.If an analogy with research animals is proposed, abnormal forward masking results may indicate IHC dysfunction or radial dendrite damage, independent of OHC statusIn the speech-in-noise test some subjects regarded 85 dB SPL listening level too loud and were measured at the lower level on both ears. Three subjects found even the lower listening level too loud and did not complete any speech test at all. The resulting number of measurements on the left ear was 125 at 70 dB SPL and 83 at 85 dB SPL, and on the right ear 108 and 72, respectively. ANOVAs were performed separately for the left and right ears with the S/N threshold as the dependent variable, with profession group as a between subjects factor, and with sound level as a within subjects factor.Industry and Education were, on the left ear, significantly worse  than Music, the only group that was normal at both levels. Industry was also significantly worse than Other . However, when age was introduced as a covariate all the significant group differences disappeared. (The change in S/N at threshold per decade was 1 dB.)Industry and Education were markedly worse than the middle-aged reference group , see Other was normal at 70, but not at 85 dB SPL. Note that both the middle-aged reference group and the group of young women had considerably better results on the speech-in-noise test at the presentation level 85 dB SPL than at 70 dB SPL. Also the test groups in the current study had better results at the higher level, but the improvement was smaller due to larger deteriorations at the higher level than at the lower level.More important was that, still on the left ear, Industry's were within normal limits compared to the mean over right and left ear of our middle-aged reference group without hearing problems. However, only two subjects in Industry were tested on the right ear.On the right ear all group means except Industry had significantly louder tinnitus than Music and Other  according to the matching, but not significantly louder than Education. An ANOVA was performed with the matched tinnitus level as the dependent variable, with profession group as a between subjects factor and with ear as a within subjects factor. The group forward masking results at each of the three test levels and matched tinnitus level for both ears . This means that louder tinnitus was correlated to poor forward masking. The two groups with louder tinnitus, Industry and Education, had significantly worse forward masking results than Music and Other. That subjects with worse forward masking had louder matched tinnitus is in concordance with reports of increased gain at higher levels in the auditory system following loss of IHCsRelations between measurements were tested with linear regression. When forward masking was involved it was used as the independent variable. There were significant negative, and similar, correlations between forward masking and the speech recognition threshold in noise. The groups with the poorest forward masking results  had the worst speech recognition in noise. The correlation was strongest for both speech-in-noise levels on the right ear, and for the lower noise level on the left ear with correlations between −0.5 and −0.6 (p<0.00001) for relevant level combinations of speech-in-noise and forward masking results . For the left ear at the higher speech-in-noise level the correlation was −0.3 to −0.4 (p<0.005).There was a significant correlation between the threshold difference in Unlike the difference between the groups in the forward masking test, the differences between the groups in the speech-in-noise test were not significant when compensated for age. One may speculate that forward masking may be a basic measure of the status of receptor hair cells and a neural degeneration beyond, which has been shown to be a long-term after-effect of noise exposureforward masking results, only measured at 2000 Hz, and PMTF-results at the same frequency, indicating characteristics of the PMTF-curves concordant with hyper-PMTF (P-type = 3) or suspected hyper-PMTF (P-type = 2): Small forward masking threshold differences were accompanied by high maximum valley thresholds , and by positioning of the maximum valley thresholds at low noise level . The bond between forward masking and PMTF regarding incidents with sudden loud sound was further strengthened by the fact that high maximum valley thresholds were accompanied by positioning of the maximum valley thresholds at low noise level , both typical for the hyper-PMTF, There were strongly significant correlations between Forward masking proved to be the hearing test that showed the most revealing differences (or similarities) between persons with different professions. Therefore it was considered suitable to investigate if non-auditory factors could influence the forward masking results. Thus ANOVAs were performed with the forward masking threshold difference (difference between the thresholds of the brief tone at 5 ms and at 50 ms after the noise burst) as the dependent variable, and with ear and one non-auditory factor at a time as within subjects factors. The non-auditory factors were self-reported medication, headaches, neck problems, smoking or stress. The only non-auditory factor with a possible influence on forward masking was medication . The dose response indicates that this is not a spurious finding: The mean threshold difference for individuals taking more than 50 pain relieving tablets/year was 22 dB. For those taking 1–50 tablets/year the mean was 28 dB, and for those taking 0 tablets/year it was 29 dB. However, we have no explanation to this correlation between medication and forward masking. The fact that the Education group had forward masking results similar to the Industry group and not to the less noise exposed groups Music or Other could not be explained by this correlation, since there was no difference whatsoever in use of medication between any of the groups.Hypersensitivity to loud sound as reported in the questionnaire (no or yes response) was related to speech recognition in noise at the lower test level, 70 dB SPL, right ear . Persons, who were hypersensitive to loud sound, had a better S/N, −14.1 dB, than persons who were not so sensitive, S/N = −12.4 dB. This effect may be caused by healthy OHCs combined with ipsilateral and contralateral regulatory systems with defective restraining capacity, resulting in higher levels in the cochlea Other, consisting mainly of medical staff and students, have small deviations from results normal for their age, and that the group Industry, used for comparison, has substantial deviations in all tests. This might have been suspected from the self-estimated noise exposure including profession and other risk factors.The hearing tests in this study show, that individuals with hearing problems in the profession group Music showed the same indications, but in addition the results were very normal for the two new measurements, forward masking and speech recognition in noise. The forward masking results were even as good as the results of the (much younger) group of young women. Thus the Music-group, except a few individuals exposed to incidents, had good results regarding measurements associated to IHC-function. Musicians are acknowledged to work at sound levels at which there is a risk of NIHL according to the international standardisationIn our previous study musicians had some dysfunctions associated to damage to OHCs and the regulatory system, and a few of them showed the typical signs of incidents with sudden loud noiseEducation group showed results similar to those of the Industry group, and worse than normal for middle-aged persons, regarding forward masking, and speech recognition in noise. The self-reported tinnitus level was about the same and worse than for the other two groups. There were also PMTF-results that may be associated to exposure to sudden loud sounds. According to animal research, one may speculate that there are lesions in the inner hair cell area as referred to in the result/discussion section. Although there is an uncertainty of the location of the possible lesions, this study has clearly shown that our Education group had poor temporal processing. Regarding the location of possible lesions in the hair cell areas and the regulatory system we have based the discussions on the literature. Unfortunately there is hitherto less literature regarding inner hair cells than outer hair cells, because of physiological difficulties to measure. Our findings seem to justify more studies in this area.In contrast the Education group had been exposed to lower noise levels than the Industry and Music groups. In the questionnaire, the estimates of self-assessed noise exposure supported that assumption. However, recent results from noise measurements in preschools show that preschool teachers are exposed to considerable noise levelsOur assumption was that the participants of the Education group having worse results than the Music group could not be found in the analyses of answers to the questionnaire. Self-reported neck problems, pain relieving medication, eye and hair colour, smoking, and relatives with hearing problems were about the same in the two groups. The self-reported amounts of stress and tension headaches were slightly higher for these two groups than for the other groups.It is possible that many of the teachers may have come from soundscapes like the one described above, with noise described as troublesome but still tolerable, with several unexpected sudden changes of the sound level every working day. Other reasons for the In the study of risk factors for tinnitus in a population 55 years and older a number of extrinsic and health factors that could be linked to tinnitus were describedOur results show that persons exposed to moderate noise levels at work may run the risk of hearing dysfunction. Mean results of the 48 teachers in two measurements as well as of individual musicians and hospital staff with moderate noise exposure seem to prove that.This study may have found dysfunctions that are characteristic for these groups before the audiogram is affected, but it will not give us a general overview of the effects of noise on hearing for these groups of professions at later stages of deterioration of the audiogram. Neither can it tell how common the dysfunctions are.In this study, individuals having auditory problems and normal or near-normal hearing thresholds were divided into groups of subjects with similar noise exposure, and measured with advanced hearing tests. For each type of measurement there were individuals with abnormal results possibly indicating cochlear dysfunction.For many of the subjects these dysfunctions caused less improvement than normal when the listening level in the speech in noise test was increased. Subjects sensitive to loud noise had significantly better speech recognition in noise at the lower test level than subjects not sensitive.There were characteristic results:Teachers had results suggesting substantial dysfunction in the auditory system reflected in far worse forward masking and speech recognition in noise than a group of middle-aged without hearing problems. These results, suggesting poor temporal processing, were about equally poor as those of a group exposed to industrial noise. The latter group was tested for comparison and had about 20 dB worse pure tone thresholds. The matched tinnitus level was correlated to the forward masking results and those two groups had the loudest matched tinnitus, possibly caused by dysfunction in the inner hair cell area.Musicians showed some deficits normally associated to outer hair cells and had good results for their age at forward masking, and so did a group mainly consisting of hospital staff and students. The musicians had normal speech recognition in noise at both listening levels.The study suggests that persons exposed to occupational noise below or around risk levels may risk hearing dysfunction. Several of the teachers in this study are examples of that, possibly because of combinations of unfavourable working environment and individual susceptibility. Medication or other self-reported non-auditory factors could not explain the poor results of the teachers.Appendix S1Questionnaire. English version.(DOC)Click here for additional data file.Appendix S2Estimation of noise exposure.(DOCX)Click here for additional data file.


It is important and recommended to detect hearing loss as soon as possible. If it is found early, proper treatment may help improve hearing and reduce the negative consequences of hearing loss. In this study, we developed smartphone-based hearing screening methods that can ubiquitously test hearing. However, environmental noise generally results in the loss of ear sensitivity, which causes a hearing threshold shift (HTS). To overcome this limitation in the hearing screening location, we developed a correction algorithm to reduce the HTS effect. A built-in microphone and headphone were calibrated to provide the standard units of measure. The HTSs in the presence of either white or babble noise were systematically investigated to determine the mean HTS as a function of noise level. When the hearing screening application runs, the smartphone automatically measures the environmental noise and provides the HTS value to correct the hearing threshold. A comparison to pure tone audiometry shows that this hearing screening method in the presence of noise could closely estimate the hearing threshold. We expect that the proposed ubiquitous hearing test method could be used as a simple hearing screening tool and could alert the user if they suffer from hearing loss. The World Health Organization estimated that there were 360 million persons affected by hearing loss in 2012. Hearing loss is associated with a variety of factors. First, hearing loss is highly related to aging. Approximately one-third of persons over 65 years old have impaired hearing. This type of hearing loss is quite gradual. The chronic conditions of hearing loss possibly result in depression, loss of self-confidence, social isolation, and cognitive decline . TypicalAs many people such as smartphone users, portable music listeners, and older people are not aware of hearing loss at an initial stage, they need to periodically test their hearing. A hearing test in a clinic, called pure-tone audiometry (PTA), is performed using an audiometer system in a soundproof room. However, some people have difficulty testing their hearing in a clinic . Thus, mAs a smartphone application provides easy accessibility, people could perform a self-test anytime and anywhere in their daily life. Even though the test should be conducted in a quiet place, it is difficult to find a place as quiet as a soundproof booth. The smartphone users could run the application in a noisy environment such as a restaurant or subway terminal where the noise levels are generally between 40 to 70 dB SPL (sound pressure level). Thus, if the application test is conducted in noisy environment, the self-test system should compensate for the hearing threshold shift (HTS) resulting from background noise to estimate the real hearing level. However, no application includes such a compensation algorithm.In this study, we have developed a hearing-test application that can be used at any place regardless of environmental noise. The application automatically corrects the noise-induced HTS by measuring the environmental noise using a built-in microphone in a smartphone. We have systematically analyzed the noise-induced HTS and developed an HTS correction algorithm on the basis of the recorded noise level. This paper describes the developmental procedure of the hearing-test application that includes the HTS correction and calibration procedure using a sound-pressure-level meter. Finally, we have validated the new application by comparison with the hearing level measured using a pure tone audiometer.2.2.1.etc. The environmental sound in places such as a coffee shop or party room can be represented by babble noise. After the user chooses a noise mode, the smartphone automatically records the environmental noise over a period of 5 s using a built-in microphone , which is defined as hearing threshold. Once the “save” button is pressed, the “next” button for testing the next frequency is activated. Four frequencies are tested in the order of 1000, 500, 2000, 4000, and 1000 Hz, which is the sequence generally used in a clinic during pure-tone audiometry (➃). Because 1000 Hz is an important component in the audible-speech range, we repeated the 1000-Hz frequency test and averaged the two hearing thresholds [2.2.In this study, we have developed a mobile application based on an Android platform and tested the application using the Galaxy  smartphone. The application program was developed using Eclipse Kepler (Ver. 4.3) and the Android SDK 2.3.1 (API 9). The pure tones  were directly recorded from the clinic audiometer  using an analog-to-digital converter. Each tone has 0.03-s rising and falling times to enhance frequency specificity. We assumed that the environmental noise was either white noise or babble noise, which was composed using Matlab  and recorded at a busy street, respectively.2.3.versus the real output, they were implemented into the application.To generate the test tones, we used an earphone packed in a smartphone package. The earphone delivers a tone sound for each frequency to test the hearing threshold. Before using the earphone, we calibrated the earphone by measuring the real output using a 2-cc coupler  and sound-level meter  . The sou2.4.versus the noise level recorded by the sound-level meter for white noise (left column) and babble noise (right column). The data set was fit to the equations listed on the analysis program and found to have a significant correlation coefficient .To capture the environmental noise, a built-in smartphone microphone was used. Similar to the earphone calibration, the smartphone microphone was calibrated to provide a sound level in standard units . The sig2/s) measured by the smartphone microphone and the sound level (dB SPL) estimated as a real output value, respectively. Finally, the application could provide a physical sound level on the basis of this microphone calibration table when we measured the environmental sound using the built-in microphone.For a more precise fitting, the data set was divided into two interval groups: 20–50 dB SPL and 50–80 dB SPL. The parameters of the fitting equations are summarized in 2.5.The hearing thresholds for all frequencies  were measured using the smartphone either in the presence of noise or in a quiet environment. The noise level was varied from 30 to 80 dB SPL in 10-dB steps, and the HTS was calculated by the difference in two hearing thresholds measured in the noisy and quiet environments. Thirty-six subjects who were 20–66 years old participated in this study. Fifteen subjects in the original group were tested to quantify the HTS. The human test in this study was reviewed and approved by the Samsung Medical Center Institute Review Board .2.6.Twenty-one subjects with normal hearing and three subjects with mild hearing loss  participated in the validation of the application. They were tested with PTA and the smartphone in a soundproof room. When a subject tested their hearing with the smartphone, five different noise conditions  were presented using two loud speakers. To test the suitability of the application in real-world environments, one subject tested his hearing outside of a clinic on the street; at a café, bus stop, and public park; and inside of a bus. To assess the convenience of the application to the user, we surveyed the subjects with a questionnaire consisting of the following three questions: “Q1. How long have you used a smartphone: (1) never (2) 0–6 months (3) 6–12 months (4) 1–3 years (5) over 3 years. Q2. I think that the application is very complex to use: (1) strongly agree to (5) strongly disagree. Q3. I think that I need practice time of (1) less than 5 min (2) 5–15 min (3) 15–30 min (4) 30–60 min.”3.3.1.versus the background noise level. Either white noise (a) or babble noise (b) was presented using two loud speakers. The individual HTS  and mean of individual HTSs (black circle) were plotted as a function of noise level. As the noise level increased, the HTS increases up to 45 dB HL. The HTS for white noise is higher than that for babble noise because white noise is continuously present and produces a greater masking effect than babble noise. To estimate the HTS at a typical noise level, linear regression equations at each interval (10 dB of noise level) were computed on the basis of the mean values.i.e., the greater masking by noise in the 1000 and 2000 Hz interval is evident, presumably a result of the higher gain of the external ear.Low environmental noise (below 40 dB SPL) did not affect the HTS, whereas noise greater than 50 dB SPL resulted in a greater HTS. A comparison of HTSs from the 500 to 4000 Hz tones indicates that the 1000 and 2000 Hz tones were more masked in the presence of environmental noise. The external noise has less of an effect on the 500 and 4000 Hz pure-tone tests, 3.2.We implemented the calibration tables for the earphone and microphone and the HTS tables into the application. When starting the application, the user selects the type of environmental noise. Then, the microphone measures environmental noise over a period of 5 s. HTSs for each frequency are calculated on the basis of the environmental noise level. Next, a user begins hearing testing using the earphone. A user might control the volume up and down until the minimum sound level of the pure tone below which a person is unable to detect the sound is achieved. After finishing the testing procedure for all frequencies, the application calculates the hearing threshold by correcting the HTS from the original measured threshold. Finally, the smartphone reports the hearing threshold before and after correction on the basis of the environmental noise level.3.3.In order to evaluate the performance of the hearing-test application, we compared the hearing threshold measured by PTA and the smartphone without and with the HTS-correcting algorithm. PTA is a standard behavioral test widely used in a clinic. The hearing thresholds of three subjects were measured using PTA by an experienced audiologist, and the subjects also tested themselves using the smartphone. Before beginning the hearing test, the subjects practiced the use of the smartphone application until they became familiar with the use of the application; all participants finished their practice within 15 min. Tests were performed in a soundproof room in the presence of either white noise or babble noise  generated using two loud speakers. For statistical validation of the application, forty-two ears (from twenty-one subjects) were tested with PTA and the smartphone.Representative examples are shown in p-value of the paired test revealed how similar the threshold of the smartphone hearing test is with the PTA threshold. If the p-value is less than 0.05, there is a statistically significant difference, i.e., the threshold of the smartphone hearing test is not correct. Thus, we expected the p-value to increase after HTS correction. p-value. In each panel, environmental noise was set to 40-dB-SPL white noise, 60-dB-SPL white noise, 40-dB-SPL babble noise, and 60-dB-SPL babble noise. The p-values between the PTA data and the threshold of the smartphone hearing test with/without HTS correction were calculated. The results show an improvement  at 1000- and 2000-Hz after HTS correction. The p-value threshold to categorize the significant difference between two groups was set to 0.05. We represented the effectiveness of HTS correction using the “*” symbol in each panel if the p-value changes from a “different threshold” of no correction to a “similar threshold” of HTS correction. There was a significant improvement at 1000 and 2000 Hz for both the white- and babble-noise cases. For example, the p-value for 1000 Hz for 60-dB-SPL babble noise changed from 0.001 without HTS correction to 0.850 with HTS correction. This change indicates that the HTS correction improved the similarity of the two thresholds between PTA and the application test. As seen in i.e., the p-value changes from a “similar threshold” of no correction to a “different threshold” of HTS correction.A Wilcoxon signed rank test between the PTA results and the smartphone test was performed to validate the smartphone hearing test. As we assumed that the threshold measured by PTA is the reference data, the 3.4.The hearing thresholds were measured in a clinic by constructing a noisy environment using a loudspeaker. For a preliminary test of the compatibility of the application in real-world environments, one subject tested their hearing in various environments using the application outside the clinic of on the street; at a cafe, bus-stop, and public park; and inside of a bus. 3.5.As the advantage of the application is easy accessibility without visiting a clinic, user convenience is an important consideration. A questionnaire-based study was performed to explore the complexity of the application and procedure. 4.4.1.This study demonstrates the development of a hearing-test application and the accessibility in real-life area such as a home, restaurant, or quiet environment. The most innovative idea was the use of the built-in microphone of a smartphone to measure the noise level of the testing environment. The built-in microphone was used to capture environmental sounds. After a pure-tone hearing test was completed, the application reported the hearing thresholds for four frequencies and automatically corrected the HTS on the basis of the level of environmental noise. The preliminary evaluation showed that smartphone-based hearing screening could properly estimate the hearing threshold even in a noisy environment. Typically, HTS correction resulted in a significant improvement at 1000 and 2000 Hz in the hearing test. During the development of the application, we have considered that self-screening should be easily accessible and simple to use. The questionnaire results show that most participants thought that the application was easy to use and needed less than 15 min of practice prior to its use.4.2.More research on this topic needs to be undertaken before distributing the application for public use. In this study, we calibrated the microphone and earphone of a specific smartphone model  and an obvious concern is that the developed application may be valid only for this model. However, when we calibrated other smartphones as a preliminary step, the results showed that the calibration tables were not significantly different from those of the smartphone used in this study, but systematic calibrations for the microphone and earphone are essential to increase the accuracy in order to use the application on other models.In this application, the user was forced to select the type of environmental noise, either white noise or babble noise. Even though the application explains the selection of the noise type, it might be difficult for the user to choose the correct noise type. The user can simply choose babble noise when he/she uses the application at a restaurant, coffee shop, classroom, or indoor area; otherwise, the user can choose white noise. An improvement in the application would be achieved by using more environmental-noise categories. Furthermore, we are developing a noise-recognition algorithm that could automatically categorize the noise type so that the user does not need to choose the noise type. Although the application measured the significantly reliable hearing thresholds at 500, 1000, and 2000 Hz in a noisy environment, there was still a lack of reliable hearing thresholds for the test carried out at 4000 Hz. PTA used a headset to provide the tone sound, whereas the smartphone test used an earphone packed within the smartphone package. Thus, the effects of the concha and external auditory canal, which has a resonant frequency of approximately 2500–5000 Hz , will liDuring the validation procedure, eighteen normal-hearing and three mild-hearing-loss subjects participated. Owing to the relatively small number of subjects with hearing loss, there were still limitations for validating the performance of the hearing-loss group. Thus, further data collection using subjects with varying degrees of hearing loss as well as normal hearing is required in future research. More real-world tests are also needed to explore the statistical significance of the real-world suitability of the application.4.3.More than 360 million people around the world suffer hearing loss, and many people are exposed to noisy environments each day. As most people do not have easy access to a clinic, it is difficult to recognize the gradual loss in hearing . Thus, a