Today’s audiological functional diagnostics is based on a variety of hearing tests, whose large number takes account of the variety of malfunctions of a complex sensory organ system and the necessity to examine it in a differentiated manner and at any age of life. The objective is to identify nature and origin of the hearing loss and to quantify its extent as far as necessary to dispose of the information needed to initiate the adequate medical  treatment or the provision with technical hearing aids or prostheses. Moreover, audiometry provides the basis for the assessment of impairment and handicap as well as for the calculation of the degree of disability. In the present overview, the current state of the method inventory available for practical use is described, starting from basic diagnostics over to complex special techniques. The presentation is systematically grouped in subjective procedures, based on psychoacoustic exploration, and objective methods, based on physical measurements: preliminary hearing tests, pure tone threshold, suprathreshold processing of sound intensity, directional hearing, speech understanding in quiet and in noise, dichotic hearing, tympanogram, acoustic reflex, otoacoustic emissions and auditory evoked potentials. Apart from a few still existing gaps, this method inventory covers the whole spectrum of all clinically relevant functional deficits of the auditory system. In its function as receiver of signals, the ear is equipped with outstanding properties that surprise technically interested people, in its function as biological system it fascinates scientists due to its different components and mechanisms, in its role as important element of differentiated communication it is one of the essential characteristics of humans, and as the sense, which is most directly related to the emotional level, it contributes significantly to the well-being of people. Consequently, functional disorders immediately lead to severe disadvantages in many domains of human life. Due to the extraordinary importance of hearing, telecommunication and entertainment electronics using audio reproduction meanwhile cover one of the industry branches with the highest turnover worldwide.In parallel to the high importance of this precise and sensitive signal detector, hearing is also very susceptible to damage by different noxious substances. If we did not know better, the existence of a sensory organ like the human ear would be considered as impossible: the structure of its sensory cells on the one hand are able to react on pressure changes with deflections of atomic dimensions corresponding to an altitude difference of 1.5 µm in the earth’s atmosphere; on the other hand it is sufficiently robust regarding vibrations and differences in height of several 100 or 1000 m. To compensate these requirements, evolution chose embedding this sensory organ in the most solid bone of the skeleton as well as a highly sophisticated mechanism for pressure transmission and a refined supply system. The subsequent level of signal processing involves very complicated and thus efficient procedures in the structures of the ascending hearing pathways and the cerebral cortex. Monitoring, maintenance, and repairing – if necessary – of this complex signal-processing system, is the task of ENT specialists who are the ones disposing of the instruments of functional auditory diagnostics.Audiometry allows identifying and quantifying hearing disorders. Differentiated and quantitative assessment of the hearing capability aims at providing all necessary data which are needed for the choice of the adequate conservative, surgical, technical, or rehabilitative therapy. It seems to be obvious that the clear identification of the nature and severity of the hearing disorder cannot be done with one single functional test. Functional disorders of the hearing system occur in relation to all dimensions of the sound signal – frequency and intensity, time and space. Accordingly, the deficits are not or only partly mirrored in the “hearing test”, i.e. the lowest level of perception of pure tones (hearing threshold). The strength of current audiometry consists of the multitude of methods and their interrelations.Recently, the basic knowledge of audiology could be enormously enlarged, the technology and application spectrum of technical hearing aids made extraordinary advances, and the possibilities of ear surgery grew impressively due to experimental evaluations and theoretical modelling of the middle ear apparatus. Dealing with publicly available knowledge and treatment modalities is no longer a facultative option of the users but an obligation. This fact justifies the high requirements to audiological competence in ENT practice. This present contribution aims to describe the current status of audiological functional diagnostics, however, despite its claim to be as exhaustive as possible, it will be limited to hearing tests applied in practice that are relevant for therapy planning.It may be assumed that the readers of this article dispose of basic knowledge of physical as well as technical acoustics and of the anatomy and physiology of the hearing system. A short description of the most important terms, however, is essential to allow clarity of the explanations.In the field of audiometry, the correct use of the parameters regarding sound signals is essential. The three acoustic dimensions are frequency, intensity, and time. There is only low need for explanation with regard to the frequency, which is measured in Hz (Hertz). For a periodic sound event this parameter defines the number of vibrations per second. Via the sound velocity, it is reciprocally connected with the wave length that has to be taken into account in audiometry only in the context of propagation of sound in limited spaces  – with the consequence of resonances or standing waves – as well as the effect of obstacles .The intensity of an acoustic event describes the energy transported per time unit and area. It is measured in W/m² (Watt per square meter), a unit that is neither descriptive nor occurs in daily life. Between this unit and the amplitude or sound pressure measured in µPa , there is a simple (quadratic) relation. It is due to the large dynamic range of the human ear (the range between the lowest perceptible and the highest tolerable intensity is divided into 12 orders of magnitude) and its functionality  that neither the parameters of intensity nor sound pressure are used but the calculated sound level measured in Decibel (dB) – named after Alexander Graham Bell. Perhaps this is the only physical unit that is exclusively used as tenth (“deci”).In nearly all cases, the sound level requires a reference in addition to the dB measurement. “dB SPL” (sound pressure level) refers to 20 µPa  or “dB HL” (hearing level – not hearing loss) that corresponds to the physiologically normal threshold of the according frequency. Using dB without a reference is only allowed to describe differences (“hearing loss has increased by 10 dB”). A level of “0 dB” does not mean that there is no sound but it refers to the sound intensity given by the reference value, which is based on its definition as logarithmic measure so that an increase by 10 dB is accompanied by a 10-fold sound intensity or 100-fold sound amplitude (pressure or density), leading to approximately the double of the perceived loudness.The time course of the sound signal is always important where (time-related) modulations occur, such as for example in cases of frequency-modulated wobble tones in free-field audiometry or amplitude-modulated test tones of the SISI test. In spoken language, the time modulations of amplitudes and frequency are the actual information carriers corresponding to a syllable frequency of around 4 Hz. This is taken into consideration by the use of modulated speech-simulating noise in speech audiometry .In audiometric examinations, acoustic stimuli are provided via ear phones, bone vibrators, insert phones, or free-field loudspeakers. These technical devices are summarized as (electroacoustic) transducers. Their output signal can be measured in dB. Bone vibrators represent a special case because they do not cause a sound but a force level, which can be translated into a sensitivity level (dB HL) based on predefined technical requirements.The sensory organ for perceiving sound waves is the organ of Corti in the inner ear. The signal reaches it via the air, the external ear, the external auditory meatus, the tympanic membrane, and the middle ear. From the inner ear, the stimulus triggered by the acoustic signal is processed, registered, interpreted, and classified via the neural structures of the hearing pathway . During their course, the neural pathways of the right and left inner ear branch several times to the contralateral side so that information from both ears reach both brain hemispheres. This binaural processing of signals means that the right and the left ear are interrelated so that hearing must be considered as a singular sensory organ equipped with two peripheral “receivers”.The middle ear is responsible for the low-loss transmission of vibrations into the inner ear. The apparatus consisting of tympanic membrane, ossicles, and tympanic cavity works as impedance transducer. Its effect is based on increasing the sound pressure as well as the deflection and thus velocity of the vibrations.The vibrations transmitted by the stapes cause hydromechanic pressure variations in the perilymph of the cochlea including the cochlear partition and spread along the cochlear turns. Due to the location-depending physical properties of the liquid and the membrane, this transducing wave causes a local amplitude maximum in a place that depends on the frequency: coming from the cochlear base, the amplitude of the hydromechanic wave slowly increases until it suddenly collapses. In this way, high frequencies are processed at the base and low frequencies are processed at the apex.The deflection of the cilia triggers active movements in the outer hair cells (OHC) of the organ of Corti located on the basilar membrane, and electric and chemical processes in the inner hair cells (IHC) leading to the discharge of neurotransmitters. The latter ones trigger the generation of action potentials by the corresponding fibers of the hearing nerve that spread afferently along the neural fibers. Functional or organic disorders may occur in nearly all structures of the hearing system , 3], , . In. In7]. IThe simplest method to get information about hearing loss is performing so-called orienting hearing tests . In this way, the ear can be examined without any technical equipment, achieving a relatively low precision, however, a reasonable specificity.Some reliable methods even from the time before introduction of the first valve audiometers for testing of the hearing capacities have survived until now. Those are for example some tuning fork tests. They do not provide quantitative measurements for the severity of hearing loss, but they give a certain orientation regarding its origin and nature. When placed on the skull, the vibrating tuning fork leads to direct stimulation of the inner ear via bone conduction. In the case of unilateral hearing loss, the perception is lateralized in a way that is specific for the pathology (Weber test): In cases of sensory or neural hearing loss, the patient hears the sound of the tuning fork in the healthy (better hearing) ear; in cases of conductive hearing loss, however, the sound is lateralized to the poorly hearing ear. This phenomenon can be explained by an amplification of the osteo-tympanic vibration component caused by the interrupted sound conduction pathway.Another tuning fork test compares the sound perception via bone conduction with the one via air conduction (Rinne test): The tuning fork is first placed on the mastoid. As soon as it is no longer perceived, the examiner holds the fork in front of the entrance of the ear canal. A patient suffering from hearing loss in the inner ear  can now hear the sound in contrast to a patient with conductive hearing loss. In contrast, if the sound of the tuning fork is perceived louder via boneconduction (“behind the ear”) than in front of the ear (air conduction), a middle ear hearing loss of about 20 dB or more is present . The results of Weber and Rinne tests cannot be clearly interpreted in cases of combined hearing loss; furthermore the Weber test is not relevant for bilateral hearing loss. See Table 1 Since the sound pressure level decreases with growing distance from the sound source, understanding of whispering and daily language via the ear directed to the examiner can be assessed depending from the distance between the examiner and the patient. Words of four syllables (preferably numbers between 21 and 99) are whispered or spoken in normal daily pronunciation from various distances. When 3 or more of the whispered words are repeated correctly by the patient from a distance of 6 m or more, a middle or high-grade hearing disorder can most likely be excluded. The volume and the spectrum of the test signal are influenced by changing the distance to the tested ear  and by switching from whispering to normal pronunciation (the sound level of whispering is lower by 20 dB compared to daily language for the same distance and whispering contains significantly higher frequencies). A skillful examiner can roughly estimate the extent of hearing loss and derive information about the affected frequencies.The largest distance for which at least three subsequent numbers are repeated correctly is noted as test result. In cases of relevant differences between the hearing thresholds of both sides in favor of the non-test ear, its auditory canal has to be closed or effectively masked by sound via ear phones . Even if all mentioned rules are respected, the results obtained from speaker distance examination are not more than an orienting starting point for further diagnostics.The attenuation component of a hearing impairment, i.e. the reduced sensitivity for sound signals of low intensity, is documented in a perception threshold for pure tones which is increased compared to normally hearing people. Its measurement is rather difficult because the most significant characteristic of the lowest perceptible level is the high uncertainty with regard to its perception. Thus the information given by the patient is generally limited regarding reliability and accuracy . AnotherPure tone audiometry shows the thresholds between 125 Hz and 8 kHz in octaves and semi-octaves. For examination at higher frequencies, the frequency is increased in steps of sixths octaves up to 16 kHz (DIN EN 60645-1:2015-11). Measurement of the hearing threshold in the high frequencies, which is only possible with few standardized earphones (DIN EN 60645-1:2015-11), is only necessary and useful in the context of particular questions . Those aThe complete pure tone audiometry contains graphs for air conduction and bone conduction. Air and bone vibrators are calibrated in a way that in case of intact physiological sound conduction both graphs are congruent . The bone conduction threshold can only be measured reliably for frequencies above 250 Hz because at lower frequencies the bone conduction stimulus is not only heard but also felt before reaching the perception threshold (about 15 dB HL at 125 Hz). At frequencies between 250 and 1000 Hz, the threshold for tactile sensation is reached at hearing levels of around 40 dB HL at 250 Hz, 60 dB HL at 500 HZ, and 70 dB HL at 1000 Hz , , , 20], , , 22], , , 24], , , 26] ev ev26] evThe conductive hearing loss that is apparent in the difference between air and bone conduction threshold (air-bone gap) never amounts to more than 50–60 dB because this corresponds to the amplification of the middle ear system and every sufficiently intensive air sound also causes mechanical vibration.Stimulation of the ear via bone conduction is not side-specific because it causes vibration of the whole skull, nearly independent from the location of the transducer. If the bone vibrator is placed on the mastoid, the interaural attenuation amounts to max. 10 dB. Even when stimulating via air conduction, part of the vibration energy is transformed into bone vibration and thus stimulates not only the test ear but also the non-test contralateral ear. Regarding the closed supra-aural earphones mainly used in audiometry, the interaural attenuation amounts to about 50 dB, which can be improved to 80–90 dB with in-ear phones . PerceptAccording to its significance as a measure for reduced hearing perception, the audiometric hearing loss is a key criterion for the prescription of hearing aids. Based on §22 of the guidelines of the German Federal Joint Committee regarding the prescription of medical aids , the preIn some areas, the hearing loss in percent plays an important role. It reduces the two-dimensional diversity of the audiometric hearing loss measured for many frequencies in dB to one single number given in percent which simplifies the situation for several purposes (even if the detailed information is lost). If the hearing loss at 1, 2, 3, and 4 kHz is known, the audiometry results included in the four frequency table , 34] pr pr34] prThe assessment of the hearing capacities in children is associated with several problems, like missing cooperation and the difficult evaluation of the reaction to acoustic stimuli, that do not occur in adults.th week of life at the earliest, conscious reactions occur. Qualified and reliable data about the hearing threshold can only be expected in school children ..th week Hearing tests in children require particular preconditions. Since younger children cannot be placed in an acoustic booth, a soundproof and acoustically isolated room is needed with an area of at least 12 m². The space should be free from excessive optical stimuli (possibly containing neither pictures nor toys) so that the children are not distracted from their actual task.For free-field audiometry, the so-called Mainzer Kindertisch (children’s table) is necessary at which the child is placed (perhaps on its mother’s or father’s lap). On the table, loudspeakers are installed emitting wobble tones and noises. For distraction and rewarding, pictures are displayed (mostly on screens that are controlled via the audiometer) and other stimuli such as a moving train or lights at the loudspeakers. For this kind of audiometry, appropriate playing material is necessary .If the child sits on the mother’s or father’s lap during the test, careful attention must be paid to not influence the child by conscious  or unconscious contributions of the helper (turning to the source of the sound). The child should be awake and attentive (no examination late in the afternoon or after a long school day). Another precondition is a sensitive and patient examiner experienced in pediatric audiometry. The tests have to be performed without time pressure in a friendly and relaxed atmosphere. It is important to be open with the child and to appropriately explain the planned examinations.Especially with restless or multiply handicapped children, it might be difficult to differentiate between incidental reactions and hearing reaction. Even experienced examiners seek advice of a colleague in order to discuss the child’s reactions. A good examiner also admits when he does not see clear hearing reactions and describes the reactions as “not evaluable”. Further examinations might then be necessary for assessing the hearing threshold. The child with hearing impairment does not benefit at all if its hearing is erroneously stated as too good by “favorable” assessment.The subjective hearing tests are at least as important for the determination of the hearing threshold as the objective measurements. In the case of contradictory findings, one should rather rely on the results of the subjective tests.In the context of audiometry, acoustic stimuli such as paper crackles, Orff instruments, rattles and whispering are offered and the child's reactions are observed. However, only an uncertain threshold definition is possible, since the stimuli are only imprecisely defined with regard to frequency range and sound level. Possible sources of error are vibrations, air draught or a simultaneous optical stimulus (e.g. rattles in front of the eye or the shadow of the examiner). Hearing impaired children can compensate for their handicap surprisingly well by using other sensory modalities.th week, reflex reactions are observed for acoustic stimuli. The reactions are, for example, the Moro reflex (embracing reaction), the auropalpebral reflex (fast closing and opening of the eyes and contraction of the eyebrows), respiratory deceleration, pauses in nuckling or a fright reflex (e.g. crying). The acoustic stimuli can be offered via loudspeakers or via bone vibrators . T. Tth weeth to 12th week of life, not only unconditioned reflexes but specific reactions can be observed in the presence of childlike stimuli in the free-field. Signs of a hearing reaction are, for example, the change of breathing, sucking, mimics, or gesture. The reactions vary from child to child. Since both ears are always exposed in the free-field situation, a separate assessment of the ears is only possible to a very limited extent.From the 6At the age of 6 months to 2 years, the reactions are clearer. Then the child can turn the head to the sound source or point to the loudspeaker . HeadphoIn conditioning audiometry, children from the age of 2 years onwards are offered a visual stimulus at the same time as a supra-threshold acoustic stimulus. In this way, the child should learn that both stimuli appear simultaneously (conditioning). In the subsequent hearing test, the visual stimulus is then activated later than the sound as a kind of reward. The level of the tone stimulus is then successively lowered in order to determine the hearing threshold.For children from the age of 3 years, it is possible to train a game-like action that has to be performed when acoustic stimuli are perceived. For example, the child is asked to put a building brick into a box when it hears a sound.From the age of 4 years, the examination can be performed separately for each ear by using headphones. If the child is able to make clear statements, it is also possible to test bone conduction by play audiometry in order to identify conductive hearing loss.Determination of the hearing threshold with headphones and masking can be reliably performed from the age of 5 or 6 years. Then a child may be asked to press a manual switch when perceiving a sound stimulus, similar to audiometry in adults.The hearing threshold of a regularly hearing child depends from its development and not necessarily from the age. In cases of retardation, normal hearing reactions may correspond to much younger children. All age spans given here should refer to the developmental age. According to our experience, the following values should apply to normal hearing . See TabProbably the most important deficit of pure tone audiometry in neonates, infants and toddlers is that the threshold obtained in the test is higher or even significantly higher than the actual hearing threshold. This is all the more true the younger the child is . If we keep in mind that the perception of strong stimuli is not, or only slightly different, from that of normal hearing (recruitment), the difference between normal and impaired hearing is sometimes completely eliminated. If a newborn responds to an 80 dB stimulus, it can be normally hearing according to the above-mentioned table, but it is also possible that it is moderately to severely hearing impaired.The discrepancy between the observed response threshold and the actual hearing threshold is reduced when the child's response is enhanced by attractive visual stimuli (illuminated and animated toys) , 46], , . In thisRegarding the conversion of the sound intensity to an auditory perception, the hearing threshold is nothing more than the lower limit of the dynamic range. The upper limit of this area is the uncomfortable level (UCL) or loudness discomfort level (LDL) which should be part of the audiometric examination especially when provision of sound amplifying hearing aids is planned. Between the upper and the lower limit of the dynamic area, the loudness perception continuously increases according to the loudness growth function. As direct description of a possible dynamic compression, this function is suitable to differentiate a pathological recruitment. This is achieved with particular certainty in the binaural comparison of patients who are only hearing impaired in one ear. Less direct are the test paradigms of traditional “supra-threshold tests” that do not identify the recruitment itself but recruitment equivalents such as the ability to distinguish between the different levels of the hearing threshold in noise. Because of the increasing significance of objective audiometry and of imaging procedures, most supra-threshold tests became less important in the clinical practice over the last years. However, no other test could substitute the original test procedures for assessing the recruitment.The simplest option to audiologically assess individual changes of the perceptible dynamic area – which may occur due to recruitment, tinnitus, or hyperacusis – is to measure the discomfort level. In order to measure this supra-threshold parameter that in normally hearing people amounts to about 90 dB HL, different acoustic signals are offered separately via headphones – depending on the diagnostic question. In the clinical routine, mostly sinus tones of the frequencies from 0.5 kHz to 4 kHz are used. Their level – starting in the slightly supra-threshold range  – is incBefore starting a discussion about the term of loudness perception, this term has to be exactly defined. Psychoacoustics provide different concepts in order to solve this question that is not trivial at all , 59]. T. T59]. TIn this procedure, the patient scales his subjective loudness perception by categorizing the provided stimuli in verbal descriptions reaching from “not heard” to “extremely loud”. On a numeric scale, those values can be further categorized (0–50 units). Center frequency and level of the narrow-band pulses possibly cover the whole field of 250 Hz to 8 kHz; the stimuli are offered in a randomized way in the free-field or via headphones. For each tested frequency, the examiner receives a characteristic level-loudness curve of which the slope shows the recruitment. From the summary of those psychometric functions, isophones may be constructed and noted as individual hearing field in the audiogram.The point of intersection of the single level-loudness functions with the x-axis is correlated to the hearing threshold (0 KU), the level described as “extremely loud” corresponds to the discomfort threshold (50 KU). If a pathological loudness growth function is found, the characteristic line is very steep, i.e. the horizontal distance between the individual curve and the normal value decreases with increasing level . This hoThe recruitment can be diagnosed in a simple and reliable way when a patient suffers only from unilateral hearing impairment, i.e. the other ear is normally or nearly normally hearing. The Fowler test or ABLB test  provides an interaural comparison of the loudness . The patFor the diagnosis of recruitment, also the SISI test is used (short increment sensitivity index) . The tarTo perform the SISI test, a test frequency is chosen at which the hearing loss amounts to at least 40 dB. For lower hearing impairment, the application of the test is not suitable because only a substantial functional loss of the outer hair cells leads to pathological loudness growth. The continuous tone is adjusted at 20 dB above the threshold. In regular intervals of 5 seconds, the level is automatically increased for 0.2 seconds. For conditioning of the patient, 5 dB increments are offered, then the actual test starts with 1 dB increments. If the patient perceives at least 70% of those increments, it is considered as indication for recruitment and thus a cochlea-related hearing loss. Negative test results (less than 15%) speak against inner ear damage and indicate a neural origin of the hearing loss (e.g. depletion of hearing nerve fibers). Recognition rates between 20 and 65% should be interpreted carefully since they could be due to insufficient cooperation of the patient or inappropriate test parameters (frequency and intensity of the stimulus) , 30], , . BecauseThe ability to perceive intensity changes can also be determined by the Lüscher test which is different from SISI test regarding its performance but the statements and results are similar . In thisNoise audiometry according to Langenbeck is another method by which a recruitment equivalent can be identified. In this test, the hearing threshold of a sinus tone is determined for several frequencies masked by narrowband noise . The perThe level of the masking broadband or narrowband noise is adjusted at a defined value between 45 and 75 dB according to the audiogram. Lower levels are not useful from a physiological point of view , higher levels may lead to hearing fatigue and thus to invalid results. Third octave band noise is first mixed with an inaudible sinus tone of low frequency. The test tone level is gradually increased and the perception threshold indicated by the patient is registered. After increasing the sound frequency , the next masked threshold is determined. When the frequencies approach to the area affected by the hearing loss, it does not have an effect on the location of the masked threshold in cases of pathological loudness growth. This convergence of the masked threshold into the threshold in quiet is the characteristic parameter of a sensory hearing loss. In cases of neural hearing impairment, however, the masked threshold deviates from the threshold in quiet, i.e. the masked threshold is increased in the frequency range affected by the hearing loss. This phenomenon can be expected and is plausible when the retrocochlear disorder is due to a significant depletion of the hearing nerve fibers so that the capacity to transmit information is already exhausted with processing pure tones or noise close to the hearing threshold. The practical significance of the “noise audiometry according to Langenbeck” is generally considered as being low. Together with Lüscher test and Békésy audiometry , that wiIf the inner hair cells do not function properly in a clearly delineated area of the organ of Corti, the perception for the corresponding frequencies is selectively reduced within the so-called “dead region”. Steep notches in the audiogram indicate dead regions but they are not reliable since the characteristic of a dead region is that the perception of the test tone of the selectively “poor” frequency is falsified by cross hearing in the neighboring regions .It is the objective of the TEN test according to Moore  to identFor patients affected by tinnitus, the application of classical subjective and objective procedures is most important – regardless if the tinnitus occurs as accompanying phenomenon of a disease or as main and isolated symptom. As a standard procedure, its frequency and loudness are evaluated in addition to audiometry. For frequency evaluation, the patient receives a comparable sound at 10 dB in the affected ear , the frequency is modified – starting with the frequency of highest hearing loss – until it is most similar to the tinnitus frequency , 52]. I. I52]. IAfter determining the tinnitus frequency, the individual loudness of the tinnitus is assessed with pulsed sounds or with narrowband noise in small dB intervals. Independent from the subjective loudness perception, the tinnitus level is mostly not higher than 5–10 dB SL , 84]..84].The assessment of tinnitus masking, i.e. the combination of noise and level that makes the tinnitus “disappear” by masking  as well According to Prof. Friedrich Bezold (1842–1908) , the lanThe complexity of speech and its processing shows another difficulty. In contrast to pure tone audiometry, the result of the examination is influenced by other factors besides hearing ability, attention, and concentration. Those factors are memory span, working memory, mother tongue, vocabulary, and association abilities of the patient. Because of the multitude of the contributing factors, it is not possible to establish a universal speech discrimination test assessing all aspects of speech understanding. Thus, speech audiometry comprises many tests that vary according to their field of application and their significance. The common parameter of all speech tests is that they check the ability of the patient to perceive linguistic speech stimuli. If the speech perception depends on the sound level, a psychometric discrimination function (performance-intensity function) may be defined that reflects the test results and allows comparison of different test procedures .The selection of the test material used in speech audiometry depends on the objective of the examination. Perception limited to only rudimentary performance can only be assessed if the test stimulus contains enough redundancy as for example in case of semantically reasonable sentences or numbers. The other extreme represent nearly redundancy-free monosyllabic test words. When the speech material is defined, the difficulty can still be influenced by offering response alternatives (closed test). In order to repeatedly perform the same test in the same patient without expecting falsification of the results due to learning effects, the material has to be classified in equivalent test lists. Some tests, however, require that one or two test lists are presented to the patient prior to the actual examination so that he might appropriately adjust to the examination (exclusion of training effects), which increases the accuracy of the test results , 88]. I. I88]. IA group or list of test items stored on mostly digital recording media is presented via headphones or loudspeakers, optionally with simultaneous, predefined noise. The patient is invited to repeat the item (word or sentence) or to select the correct response out of a list of alternatives and the examiner counts the correct answers. The test result then consists of a percentage of correctly repeated test words depending on the absolute or relative speech level (related to the noise level). The correlation between stimulus level (or level difference) and the percentage of correct answers (speech recognition index) is called discrimination function. Its main properties may be described by two parameters with sufficient exactness: the level  for which the probability of a correct answer amounts to 50% , and the slope of the discrimination function at this point.1). Since the correct perception of low vocal frequencies is already sufficient for the recognition of numbers, this hearing loss correlates well with the pure tone threshold at low frequencies. For orientation, the hearing threshold at 500 Hz is considered. A pure high frequency hearing loss, however, has only a low impact on the discrimination curve for numbers.In German speaking countries, the Freiburg speech intelligibility test introduced by Hahlbrock in 1953 , 90], ,  is stillCompared to numbers, the monosyllables curve is shifted in direction of higher levels and its course is flatter in case of hearing loss. Both aspects are due to missing redundancy and to the fact that for correct recognition of the test words not only loud vowels but also soft consonants are important. Hearing disorders do not only influence the location but also the shape of the discrimination curve. So it is not useful to characterize this curve only by its shift. Especially in the case of severe high frequency hearing loss, the curve is very flat because of the difficult recognition of high consonants. Often, no 100% understanding of monosyllables is achieved until the level of discomfort is reached, i.e. a discrimination loss is found. In rare cases, speech discrimination decreases at higher levels after having achieved a maximal value (“R curve” or roll-off). The discrimination loss and the speech intelligibility reached at a level of 65 dB SPL are the most important measurement parameters of the monosyllabic test.The role of the Freiburg test in hearing aid provision is defined in the corresponding guideline . Thus th1 value evaluated according to the already described speech recognition threshold and the “overall speech comprehension” calculated from the sum of the monosyllabic recognition at 60, 80, and 100 dB SPL , , 102], , 104]..104].The accuracy of measurement and thus the sensitivity are only low .The test of speech recognition in noise is not supported , 107]..107].The test procedure cannot be automated because the patient’s reply has to be evaluated by the examiner.The patient’s answer is only evaluated as correct or wrong, phoneme confusions are not evaluated.The missing announcement stimulus leads to an inappropriately high ratio of false answers (“attention test”).The missing announcement and the short duration of the stimulus may lead to problems in case of hearing aids with automatic gain control.Because of these disadvantages, further speech intelligibility tests have been developed and introduced in practice. However, despite the quantity of those tests, none of them meets all the mentioned criteria nor the standard of 8253-5 , one tesPossible alternatives to the Freiburg test might be the rhyme test according to von Wallenberg and Kollmeier (WaKo)  in combiWaKo: introductory sentence announcing the stimulus item, closed response inventory, automatic procedure and evaluation of phoneme confusions, percentage of speech recognition and speech perception threshold with and without noise.OLSA and GÖSA: adaptive determination of SRT with and without noise.The most important parameter of those newer tests is not the percentage of correct answers (depending on the stimulus level) but the speech recognition threshold. The SRT is defined as sound level for which 50% of the test items have been repeated correctly. Adaptive procedures are applied for the determination of SRT : the preCompared to the traditional Freiburg test, the focus of modern speech audiometry is no longer directed to the speech intelligibility in % but to the parameter SRT measured in dB. Together with the test-specific slope of the discrimination function which is measured in “% per dB” (i.e. “what is the percentage of improvement of the speech intelligibility if the speech level is increased by 1 dB?”) different but comparable parameter describing the effect of a therapeutic intervention is obtained. Due to the well-known nature of logarithmic relationships it must be kept in mind that the measure of “dB” without any further specification is only suitable for differences (for example the threshold with and without hearing aid). Dealing with relative (related to the level of the noise) or absolute values without noise (SRT in a quiet environment), the speech level is measured in “dB SNR”  or in “dB SPL” (sound pressure level). The transition from the traditional to the new tests does not cause any problem with regard to the measures. It is further facilitated by an overview where all tests are presented in a comparative way based on the example of indication and follow-up of hearing aid supply .In the following, the three most common modern procedures of speech audiometry will be described. Apart from these tests also the HSM sentence test , which In the monosyllables rhyme test WaKo according to von Wallenberg and Kollmeier (1989) , the acoThe presentation of the stimulus items of one list is performed at a constant level, the percentage of the speech intelligibility results from the number of correct answers after correction regarding the guess probability. In order to determine the maximal speech understanding or its complement (discrimination loss) and the necessary speech level of dB-opt, the measurement series are performed at different levels.The WaKo test offers the possibility to evaluate phoneme confusions based on falsely understood or not correctly identified speech sounds. Thus mistakes of the patients with regard to acoustic and articulatory characteristics of speech can be identified and specified. Another characteristic of the rhyme test is the automatic setting which does not require the continuous presence and intervention of the examiner.The discrimination function of the WaKo test reveals a slope of 6% per dB in its inflection point (in quiet and noisy environment). If needed, the disturbing noise is a stationary noise simulating speech according to CCITT . It overFor a long time, the Marburg sentence test that had reached the status of a standard  was the The GÖSA consists of 20 test lists with 10 sentences of daily life each, as for example “Is it time to go home?”. Those sentences have 3–7 words each. For measurements in noise, a speech simulating noise was generated by statistically overlaying words of the monosyllabic rhyme test , 124] r r124] reEven if the test was developed carefully, especially with the aim that the test situation should resemble a real hearing environment as far as possible, some disadvantages could not be avoided. The repeated use of test lists in the same patient represents a real problem because of the high informational content of the test sentences . FurtherRecent investigations show that despite some disadvantages, similar speech intelligibility thresholds may be achieved with the GÖSA compared to the Freiburg test with numbers . Even thSince earlier approaches did not lead to the desired result, Wagener et al. , 109], , 109],  developeThe open Oldenburg sentence test (OLSA) resulting from this project contains – similar to the “Hagerman test” – syntactically correct sentences which are semantically not predictable. The sentences are composed of a name, a verb, a number, an adjective, and an object (e.g. “Doris draws nine wet chairs”) . Each ofBeside the high accuracy for determining the SRT in noise, which amounts to 0.5 dB for hearing impaired people , one of Even if the “modern” sentence tests may represent different hearing situations – as the presence of noise and different spatial arrangements of the sources of speech and noise – and thus quantify speech understanding, further methodic options are desirable for the sake of practical applicability . See TabIn pre-school children, the speech audiometric tests used for adults can be applied only to a limited extent. Referring to the Freiburg test, this is particularly true for monosyllables, whereas the numbers may be part of the limited vocabulary of (hearing impaired) children . RegardiThe pediatric Mainz speech test consists of 3 parts that are adapted to different ages and developmental stages . All 3 pA general problem in speech audiometry is that the patient has to repeat the test word so that the examiner knows if the word was correctly understood. This may lead to the phenomenon that possible dysfunctions of the speech-production system are included in the result of the hearing test . This prThe Mainz and Göttingen children tests are not suitable for testing speech understanding in noise. Especially for this purpose, the Oldenburg pediatric sentence test (OLKISA) was developed from the Oldenburg sentence test (OLSA) by modifying the test material , 136]. . 136]. IIn pediatric patients, speech audiometry is mainly applied for prescription and fitting of hearing aids and and later follow-up, because the supply of technical devices in hearing impaired children aims primarily to support speaking and development. Hyper- and hypostimulation may impede the success of the supply or lead to damage of the ear. By means of the functional gain or with objective methods, the success can be validated only to a limited extent, but since speech understanding depends on the speech level, they can be seen in the speech audiogram. The aim of hearing aids is to achieve a normalized speech discrimination curve or at least a normal level of 50% speech understanding. See Table 16 Many tasks of the hearing system such as the detection of signals  under acoustically difficult conditions  or the acoustic localization can only be fulfilled by hearing with both ears. Binaural hearing is more than the sum of its parts because the signals coming from both ears are not processed independently but connected to each other in the centers of auditory processing in the brain stem . WithoutTwo other effects of binaural hearing are based on the processing of interaural intensity and time differences: the acoustic localization of sound sources  and the reconstruction of noisy signals (squelch effect). The acoustic signal originating from a source located outside the median plane reaches the auditory canal of one ear earlier and with a higher intensity than the other ear. The evaluation of weighted delayed coincidences in specialized neuron groups of the brain stem is based on these differences  .Binaural hearing is crucial for perception and recognition of signals in noise. The binaural threshold for the recognition of a test item in noise is lower than the monaural threshold, the difference between both is called BILD . Depending on the spatial source location of signal and noise, the threshold difference amounts to about 10 dB in normally hearing persons.In the context of hearing prosthesis, BILD is a measure for the effect of adding the second ear. The highest value of the parameter is expected in the configuration of S0N90  when the 90° direction corresponds to the side with the better hearing ear. For measuring BILD, a speech intelligibility threshold is assessed in the poorer ear first without and then with hearing aid, and then the difference is calculated from both thresholds . The dirThe improvement of signal recognition described by BILD is closely related to the ability of speech understanding in noise (cocktail party effect) which requires a functioning binaural system. The function of the binaural system may be affected seriously by even minor unilateral hearing disorders. The examination of the uni- or bilateral discrimination thresholds is thus suitable for quantitative description of the ability to follow conversations in noise or buzz. It has been seen that BILD is reduced in hearing impaired patients and also in normally hearing elderly test persons.The ability of spatial hearing and locating sound sources is a predominant consequence of binaural perception and processing of acoustic signals . FurtherInteraural time differences are only useful for the localization of sound sources when the duration of the signal is sufficiently short. This precondition is not fulfilled in permanent sounds or in case of echoes. In these cases, the hearing impression of both ears merges to one hearing event. Nonetheless, the sources of permanent stimuli or a short signal that is accompanied by an echo can be localized. This is due to the fact that the location of such a hearing event is mainly determined by the change of the sound pressure that reaches the ear first (“law of the first wavefront” or precedence effect). Of course, this important mechanism may fail in closed rooms where reflections and standing waves are present.In order to test directional hearing, the test person is asked to identify the direction of a sound source which is located in the horizontal plane. Beyond this scheme, there is neither a clear standard nor a generally accepted convention for testing directional hearing. The described test setups vary with regard to the number of loudspeakers and their spatial arrangement, the nature of stimuli and noise as well as the assessment of the test persons’ answers. The results are graphically displayed either in polar diagrams – to show the directions – or as xy graph – with the advantage that the equality of sound and hearing direction are immediately seen. Among others, the numeric results are the confusion matrix, hit rate, and accuracy , 144], , 144], fThe most important practical application of directional hearing tests is to prove the benefit of binaural hearing and especially of the second hearing aid. Because of the great variety of test setups, there are no standardized reference values. The directive for technical aids requires in an unspecific way that the provision of hearing aids for the poorer ear should lead to an improved directional hearing. It is justified to assume that the assessment of not only better but significantly better directional hearing can be performed more reliably in specialized institutions than in private ENT practices. See Table 17 Conspicuities or deficits in the sound processing on higher levels of the hearing system, especially the localization of sound sources or speech understanding in noise going along with the absence of detectable organic defects and a normal non-verbal intelligence are classified as auditory processing disorders . APDs are observed as isolated parameter or in combination with other deficits (attention-deficit/hyperactivity syndrome (ADHS), dyslexia, speech development disorder, or lack of concentration). The suspicion of APD often appears in school children in the first school grades. In accordance with to the definition, the following basic auditory functionsLocalization and lateralization of acoustic eventsAuditory differentiationTemporal aspects of hearingTemporal integration: differentiation of temporal structures, recognition of time sequences, forward maskingAbility of hearing and understanding of competing (speech) signals including dichotic hearing and understandingAbility of hearing and understanding of signals of limited qualityhave to be differentiated from the following higher discrimination performances :Phonologic consciousness including auditory analysis and synthesisAuditory attentivenessAuditory memory including long-term, short-term and working memorySpeech intelligibility, speech understanding, and interpretation of the content.Since it is currently not possible to identify disorders in the field of neuronal processing of the hearing pathways in a reliable and specific manner, it cannot be completely excluded that also primary cognitive deficits have to be taken into consideration for the definition of (C)APD . AccordiIn contrast to subjective audiometry, which is based on psycho-acoustic methods, all procedures measuring physiological reactions that accompany the hearing process and are relevant for hearing itself are called objective audiometry. Compared to subjective procedures, the registered signals are much less subject to the influence, the attention, and the active cooperation of the test person. Among the reactions on acoustic stimuli, the physical properties of the tympanic membrane (impedance audiometry), the oto-acoustic emissions (OAE), and the electric processes occurring in hearing nerve, hearing pathways, and cortex  can be evaluated. Since all signals used for objective audiometry are overlaid by interferences, the accuracy is generally limited. For assessment of the hearing threshold, their application is mainly interesting in patients who are not able or not willing to cooperate. If the patient’s cooperation is sufficient, there is no more reliable, more accurate, and more rapid method than asking the patient about his subjective hearing. However, the objective procedures provide differential diagnostic statements that cannot be gained by subjective audiometry. With regard to identification of hearing disorders and the localization of their origin, objective audiometry cannot replace but rather complete subjective audiometry.The basis of impedance audiometry is the acoustic resistance which is excerted by the tympanic membrane against the incoming sound wave. The measurement of this impedance as a function of the atmospheric pressure and the frequency of the tone (tympanometry) allows a detailed description of the physical properties of tympanic membrane, middle ear, and ossicles. The measurement of the impedance during acoustic stimulation with tone pulses further allows the observation of physiological reactions (stapedius reflex or acoustic reflex).At the interface between two media of different sound impedances, the sound waves are in general partially reflected. The measurement of the impedance is based on the close relation between reflection and impedance difference. Physically, the impedance of the middle ear depends on the mass , on the friction (tympanum and inner ear), and the elasticity  of the anatomic structures involved in the vibration as well as the sound frequency. Most of the mentioned parameters are characteristic for the middle ear. At usual test frequencies, the most important and diagnostically most relevant contribution to impedance is the elasticity.The relation between impedance and sound frequency is most relevant for the selection of the probe tone. In the majority of practical cases, a probe tone frequency of 226 Hz is applied. This is due to the fact that higher frequencies may lead to standing waves and the measurement result is thus influenced by the geometry of the auditory meatus. With higher probe tone frequencies (e.g. 678 or 1000 Hz), however, more information is obtained about the physical processes in the middle ear, possible pathological changes, and the effects of surgical intervention.In the context of tympanometry, it is not the impedance itself but its reciprocal (the admittance) which is measured. Since the impedance describes the resistance of the middle ear, the admittance corresponds to the compliance of the middle ear apparatus to transmit the sound to the inner ear. A high compliance corresponds to a low impedance to sound waves and thus to a high mobility of the tympanic membrane. The most favorable vibration properties of the tympanic membrane are seen when the external pressure is equal to the pressure in the middle ear, which is generally the case for normal atmospheric pressure. Hence a regular tympanogram measured at 226 Hz has its compliance maximum at normal pressure (p=0) with a normal range of ±150 daPa (type A according to Jerger).This compliance maximum is the most important feature of a 226 Hz tympanogram. It is quantitatively described by its position, its height, and a form parameter. The height of the summit varies enormously in different individuals. If the maximum compliance is significantly above the normal range (tympanogram type AD “deep” according to Jerger), a scarred slack tympanic membrane, an interruption of the ossicles, or a defect of the incus are probable. A very flat compliance summit  indicates a scarred rigid tympanic membrane, otitis media, or beginning otosclerosis. The shift of the maximum to positive or negative values (type C) reveals positive or negative pressure in the tympanum. Overpressure may occur in case of tube dysfunction, negative pressure is observed in cases of oxygen-consuming inflammatory middle ear diseases, for example beginning otitis media without effusion. Variations of the middle ear pressure in a range of ±100 daPa have no diagnostic relevance . If a viTympanograms that are measured with higher probe tone frequencies – usually 678 and 1000 Hz – might have more than one summit, symmetrically arranged around the middle axis  in absence of pathological processes . The reaThe second field of application of impedance audiometry is the detection of the stapedius reflex. It is recorded via the registration of an increased impedance during acoustic stimulation of one ear but the reflex can also be elicited by tactile or electric stimulation. Impedance changes occur when strong acoustic stimuli cause the stapedius muscle inserting at the stapes  to contract. This leads to a stiffening of the ossicular chain and thus to an increased impedance of the eardrum. Muscle contraction – and impedance change – follows stimulation after a short delay (latency of about 10 ms); it lasts for the duration of the stimulus and generally it decreases after about 10 s.The reflex-like contraction of the stapedius muscle occurring in cases of loud sounds impedes vibrations of the stapes and thus protects the inner ear from too high sound intensities. The stapedius reflex is an acoustico-facial reflex, this means that the middle ear, inner ear, and hearing nerve belong to the triggering (afferent) branch; the efferent part is the motor facial nerve innervating the middle ear muscles. Afferent and efferent branch of the reflex arc are connected with each other in the nuclei of the hearing and facial nerves of the olivary complexes. Since the efferent branch of the middle ear muscles innervates both ears, monaural sound leads to bilateral impedance changes. The stapedius reflex can be triggered by ipsilateral and contralateral stimulation. In most practical cases, the question must be clarified if the reflex can be triggered in one ear, i.e. mainly the stimulated ear. However, there might also be questions that focus on the ear with the probe.In order to register the ipsilateral stapedius reflex, a reflex triggering sound with a frequency selected by the examiner  and intensity (level between 70 and 110 dB HL) is issued to the probe ear for a limited time (1 s) in addition to the probe tone. For measurement of the contralateral stapedius reflex, a headphone is placed on the stimulated ear; on the probe side the impedance probe is placed in the auditory canal. Measurement of the reflex is always performed with the pressure with largest compliance (maximum of the tympanogram). Starting at about 70 dB HL, the reflex threshold is found by increasing the stimulus level. The reflex threshold is defined as the lowest stimulus level at which an increased impedance can be registered that is typical for the reflex. In normally hearing people it amounts to 70–90 dB HL, in hearing impaired people it might be higher. A low percentage of normally hearing people does not have this reflex.Generally, the stapedius reflex is only triggered by stimuli that are characterized by high subjective loudness. The reflex threshold does not correlate with the level of the stimulus (dB HL) but rather with a level related to the individual hearing threshold of the examined ear (dB SL). In cases of middle ear hearing impairment, the reflex threshold is higher by the amount of the hearing loss. If the hearing loss is more than 30 dB, the reflex cannot be triggered because in this case a stimulation level of at least 110 dB HL (≥70 dB above the threshold) would be required. Therefore, the reflex cannot be triggered in an ear affected by middle ear hearing loss – and (because of other reasons) it cannot be registered in most of the cases. In case of inner ear hearing loss, the reflex threshold is constant up to a hearing loss of 50 dB and increases linearly with larger hearing loss. This means that in many sensory hearing impairments, the reflex threshold is closer to the hearing threshold than in normally hearing persons manifesting the narrow dynamics of the ear with hair cell damage (“Metz recruitment” if the difference of stapedius reflex and hearing threshold is ≤50 dB). Inner ear hearing impairment is only seen on the stimulus side but not on the probe side.The influence of neural hearing loss on the stapedius reflex depends on the question whether the disorder is located peripherally of the reflex connection in the hearing nerve or more centrally in the brainstem. In the first case, the reflex threshold is clearly increased (with negative Metz recruitment: the difference between reflex threshold and hearing threshold is >50 dB) or a pathological reflex decay is observed or the reflex is completely missing; in the second case, the stapedius reflex is not impaired. In the stimulated ear as well as in the probe ear, conspicuous findings may be detected. Even in cases of supraclavicular paresis of the facial nerve as well as damages of the facial nerve that are located behind the branching of the stapedius nerve, the stapedius nerve can be generally registered; peripheral paresis of the facial nerve that usually does not influence the hearing threshold, however, causes failure in the probe ear. See Table 19 Sound waves that emerge from the inner ear and are transmitted via the ossicles and the eardrum into the external meatus, are called otoacoustic emissions (OAE). Spontaneous emissions (SOAE) which are present without acoustic stimulation are distinguished from evoked emissions (EOAE) which occur during or after acoustic stimulation. OAEs originate from non-linear and active processes of the cochlear sound pre-processing that manifest already in the micro-mechanics of the basilar membrane and are responsible for the high sensitivity, the large dynamic range, and the capacity of the ear to distinguish frequencies . The souEvoked OAEs (EOAE) are classified into post-stimulatory (delayed) transient evoked otoacoustic emissions (TEOAE) and per-stimulatory emissions. The latter ones are further differentiated if the frequency of the emissions corresponds to the stimulus  or if the frequency of stimulus and response are different . TEOAEs can be reliably measured, they are well established in audiology. In contrast, the registration of SFOAE is difficult so that among the per-stimulatory OAE exclusively the DPOAE are used for diagnostic purposes , 168]..168].TEOAE and DPOAE reflect two aspects of the same active and non-linear cochlear amplifier measured in different ways. The different measurement techniques have an impact on the practical application and the information because, with comparable stimulus levels, DPOAE can be measured with a higher sensitivity than TEOAE, i.e. also in the context of severer hearing impairment .For the measurement of TEOAEs, the acoustic signal is registered immediately after a transient and repeated stimulation with click stimuli in the auditory canal. By means of shielding as well as with analogue and digital signal processing , the physiological OAE signal is separated from ubiquitous disturbances.The result of TEOAE measurement is displayed as graph that reflects the average time-dependent course of the post-stimulatory sound pressure in the auditory meatus. The transformation of these graphs in the frequency ranges provides the spectra of TEOAE and residual noise. Furthermore, a correlation coefficient (reproducibility) is calculated and the variance of the residual noise is estimated. If the reproducibility is higher than 60%, TEOAE are considered as being proven , 171], , 171], . This crThe most difficult part of the examination is successfully performed and the most important part of the information contained in TEOAE is used with the reliable and clear differentiation between signals of cochlear origin and noise interference. With regard to basic clinical use, OAE behave like a binary variable or a dichotomous system with only the two states: “present” and “not present”. An ear where delayed emissions can be measured, has a nearly normal hearing threshold at least in part of the audiogram. The incidence of measurable TEOAE gradually decreases with increasing inner ear hearing loss from 100% down to 0%. To a small extent, the details of this transition depend on the intensity of the stimulus; for a level of L=80 dB peSPL, the 50% incidence corresponds approximately to the hearing loss of 30 dB HL , 175], , 175], . Hereby The aforementioned correlations between hearing threshold and TEOAE refer to the special case of merely sensory (endocochlear) hearing disorders. Of course, also conductive hearing loss has an effect on the measurement and the amplitude of TEOAE. The impaired sound transmission of the middle ear apparatus leads to a damping of stimulus and emission. If the middle ear component is strong enough (20 dB or more) and if all frequencies are affected, no TEOAE can be measured. In contrast, a merely retrocochlear hearing loss has no influence on the TEOAE. It is characteristic for some neural hearing disorders to find the constellation of poor hearing threshold with nearly normal emissions , 178], , 178], .Measurement of TEOAEs does not allow for quantitative and frequency-specific determination of the hearing threshold. The spectrum of each delayed emission has a fine structure of irregular and individually different peaks and notches, but they do not correspond to hearing loss in the tone audiogram , 181]. . 181]. AWhen a broadband stimulus (click) is used, the spectrum of the TEOAE contains all stimulus frequencies for which the cochlea has a nearly undisturbed function. A hearing loss that exceeds the limit of 30 dB leads to disappearing of the delayed emissions. The complete absence of a physiological “echo” means that the hearing loss exceeds this value at all frequencies. On the other hand, the presence of reproducible emissions allows the conclusion that at least part of the hair cells have a nearly normal function and the “minimal hearing loss”  is less than 30 dB. The validity of these statements is limited to the frequency range between 1 and 4 kHz, hearing losses outside this region cannot be assessed with TEOAE. The dichotomous nature in combination with the sensibility limit of 30 dB hearing loss qualifies TEOAE as ideal procedure for the early detection of congenital hearing disorders in the context of newborn hearing screening , 184], , 184], , 186], , 186], , 188], , 188], , 190], , 190], , 192], , 192], , 194], , 194], , 196], , 196], . The meaBesides dichotomy, the TEOAE are a source of differentiated and also diagnostically valuable information if their amplitude and its behavior is considered after repeated measurements or after changing the examination conditions. An application of this kind is the contralateral suppression of TEOAE that is transferred by the efferent innervation of the OHC via the medial olivo-cochlear bundle , 202], , 202], , 204], , 204], . This suThe comparison between two TEOAE measurements that were carried out under the same conditions at different times contains the potential of objectifying changes of the hair cell function. It could be revealed that a change of the (noise corrected) emission amplitude is significant when the difference of the amplitudes is 4 dB or more , 210]. . 210]. MThe non-linearity of cochlear signal processing leads to the fact that the inner ear cannot process two close frequencies independently. If the inner ear is stimulated with a mixture of two pure tones, the physiological processing results in secondary tones with frequencies that are not contained in the stimulus. Those distortions can be measured as DPOAE (distortion product otoacoustic emissions) in the auditory meatus .The distortion products are evoked by a stimulus that is composed of two supra-threshold sinus tones of nearly equal intensity with the frequencies f1 and f2=1.2xf1 (e.g. f1=4.0 kHz and f2=4.8 kHz). During the DPOAE measurement, the amplitude belonging to the frequency 2f1-f2 of the distortion product is extracted from the spectrum of the microphone signals, which is increasingly freed from background noise in the course of the averaging process, and displayed at the end of the measurement series for several stimulus frequencies together with the amplitude of the respective background noise of a narrow frequency band (DP-gram). For reconstruction of the stable physiological signal from the stochastic noise, the general rules are applied according to which the quality of the result, described by the signal to noise ratio (SNR), doubles only after a fourfold increase of the measurement time. It is due to the narrowband registration that DPOAE measurement achieves extremely good SNR values . This is the reason why in the context of advanced hair cell damage, the vitality signs of a small residual population of OHC can still be identified in contrast to TEOAE . Regarding the correlation between DPOAE and the extent of sensory hearing loss, the rules are qualitatively very similar to those for the TEOAE:The DPOAE evoked by the frequencies f1 and f2=1.2xf1 occur with an incidence of nearly 100% in normally hearing ears .The emission amplitude decreases with increasing hearing loss.If the hearing loss at the frequency f2 exceeds 50 dB, no DPOAE can be identified in the statistical average .Incidence and amplitude of DPOAE are not influenced by a pure retrocochlear hearing impairment.Conductive hearing losses first cause a reduction of the DPOAE of lower frequencies, in cases of severer hearing loss, the DPOAE disappear completely.These statements are valid for all stimulus tone pairs for which the frequency of f2 is between 1 and 4 kHz. For lower frequencies, the incidence of measurable emissions is clearly below 100% even in normally hearing ears; for higher frequencies, the DPOAE measurement is often falsified because of technically induced distortions. Due to their properties , DPOAE turned out to be appropriate for newborn hearing screening. The application in this context has been reported several times , 216], , 216], . In exisBeyond dichotomous statements, DPOAE achieve quantitative results that are expressed for example in approaches to frequency-specific objective determination of hearing thresholds. One of the approaches described in the literature , 219], , 219],  focuses Comparable to TEOAE, also DPOAE were investigated regarding the contralateral suppression of the emission amplitude triggered by efferences of the hearing pathway, , 224], , 224], , 226], , 226], . In specAs a direct image of non-linear sound processing in the inner ear, DPOAE are directly related to the functionality of the OHC and thus generally suitable to objectively observe damage or recovery of the hair cells and ideally even more sensitively than tone audiometry. Their advantage in comparison to TEOAE, which are limited to non-linear signal components because of the special stimulus paradigm, is the assessment of the complete undistorted physiological signal. It has been suggested to apply DPOAE for follow-up and possibly early detection of beginning noise-induced or ototoxic damage , 229], , 229], , 231], , 231], , 233], , 233], . In occuAuditory evoked potentials (AEP) are electric voltages of physiological origin that can be triggered by acoustic stimuli and measured by means of electrodes. The sum of all procedures for the examination of hearing characteristics on the basis of AEP is called electric response audiometry (ERA) . Those aThe difficulty of measuring AEP is that the signal to be detected (the AEP) has a very small amplitude and is strongly contaminated with interfering noise (spontaneous EEG). The amplitude of the interferences – especially when muscular potentials and external electromagnetic signals are present additionally to the EEG – may be significantly above the amplitude of the target signal (depending on the frequency). The measurement of AEP requires first a substantial avoidance of interferences (electric shielding), the relaxed and comfortable positioning of the patient, a linear EEG amplification with high common-mode rejection, filtering of the EEG signal, rejection of artefacts, and effective improvement of the signal to noise ratio by signal averaging. The optimization of these procedures leads to a higher quality and reliability of the results . The onlA major part of electric reactions of the hearing system can only be registered as delayed and transient response at the beginning of a time-limited stimulus. The averaging of many stimulus-related signal epochs (sweeps) results in a time-dependent curve that contains the EEG noise reduced in amplitude  in addition to the AEP. The diagnostic statements regarding hearing are based on the evaluation of these curves measured with stimuli of different quality (e.g. frequency or time course) and intensity and the parameters resulting from a subsequent curve analysis .For the generation of measurable evoked potentials, many nerve action potentials have to be triggered with a high degree of synchronization. This can be achieved only with stimuli with rapid inherent changes of some of their properties. Most frequently, this property is the intensity or the sound pressure of the stimulus. The most drastic changes are accomplished by turning the stimulus on and off. The usual transient stimuli are the broadband click and the frequency-selective tone pulse. Since high frequency selectivity and short duration of stimulus exclude each other, responses that require a high degree of synchronization provide only very limited frequency-specific information. On the other hand, the frequency-specific stimulation yields only very rough information about the latency of the potentials.The transient AEP are composed of many single voltage peaks which originate from different parts of the ascending hearing pathway and may be classified in 3 groups according to their latency. Early auditory evoked potentials (EAEP) describe the components in the time range of 1–10 ms, followed by middle auditory evoked potentials (MAEP) with latencies up to 50 ms, and slow AEP (SAEP) with latencies up to 500 ms. The associated methods are BERA (brainstem electric response audiometry) for early, MLRA (middle latency response audiometry) for middle, and CERA  for the slow AEP. This notation roughly mirrors the anatomical site of the generators or sources of the responses. The classification is not standardized, but it may be considered as certain that the “wave” J1 is generated in the hearing nerve, EAEP J3 and J5 in the brainstem, MAEP in the thalamus and the primary auditory cortex, and SAEP in the auditory cortex.Generally, the normal values for latencies, latency differences, and amplitudes of the responses which are essential for the identification of abnormalities are device-specific because of their dependence from the details of stimulation and signal processing. Thus the values taken from tables are not universally valid . AccordiAt the time of its development, the transtympanic electrocochleography (ECochG) played a major role among the objective methods for hearing measurements , 247]. . 247]. TThe result of ECochG is composed of cochlear microphonics (CM), the compound action potential (CAP), and the summation potential (SP). These components can best be described when stimulation is performed with frequency-selective tone pulses. The CM is an oscillation following the frequency, phase, and duration of the stimulus; it reflects the receptor potential of the sensory cells. The CAP corresponds to the sum of action potentials of all stimulated hearing nerve fibers and is displayed as negative deflection of a latency depending on the stimulus level of about 2–7 ms. The SP appears as a vertex-positive DC voltage component, the duration of which is the same as the stimulus pulse; it reflects the voltage difference between scala media and scala tympani. Since the presynaptic CM is locked to the phase of the stimulus whereas the postsynaptic CAP does not follow the phase, both components may be isolated by the separate recording of the responses following condensation and rarefaction stimuli and the subsequent calculation of sum and difference curves.The determination of the threshold based on the CAP is much more accurate than that obtained from BERA and is frequency-specific in the range from 500 to 4000 Hz. Empirical data show that the “true”  hearing threshold is only a few dB lower than the stimulus response threshold of the CAP . RegardiIn the context of differential diagnosis, ECochG may further contribute to the detection of endolymphatic hydrops in the diagnosis of Menière’s disease. The component SP reflects the voltage differences between scala media and scala tympani, its polarity and amplitude are determined by the movement of the basilar membrane, especially with regard to non-linearity and asymmetry. Therefore, an increased SP can be expected when the basilar membrane is displaced from its balanced position due to disturbed water balance , 251], , 251], . HoweverWith the BERA, all early auditory evoked potentials (EAEP) from hearing nerve and brain stem are examined. The “brainstem audiometry” analyzes the timeframe from of 1 to about 12 ms following the stimulus. EAEPs can only be measured with sufficiently high amplitudes if the stimulus generates a high degree of neural synchronization, as it is ideally the case with a click stimulus. The click is not suitable for the frequency-specific determination of the hearing threshold, however, there is the alternative of stimulating with pulses or chirps (see below). The early potentials are very stable with respect to vigilance variations and pharmacological influences so that their measurement is also possible during sleep or under anesthesia. Regularly, they are present at birth, however, during the first months of life they are observed in a modification that differs from the adult pattern regarding morphology and latency times due to the immature hearing pathway. The EAEPs consist of several components of peaks or “waves”, called J1 to J5 or waves I to V, which are generated in different places of the ascending hearing pathway from the hearing nerve up to the brainstem.The complete wave pattern can only be observed if high supra-threshold stimuli are applied. The amplitudes of the responses increase with growing stimulus intensity, whereas their latency times decrease. These relations are displayed in diagrams (e.g. “latency-intensity-diagram) which facilitates the recognition of abnormalities . The mosThe “objective” quantity deduced from the recordings corresponding to the behavioral hearing threshold is the response threshold. This objective threshold is defined as the lowest stimulation level at which a reproducible physiological response can be recognized visually from the curves or in case of sufficient quality, extracted from the input-output function of wave V. Since this wave can usually be detected down to the subjective hearing threshold (with deviations amounting to 15 dB or less) with click-evoked EAEP, the hearing threshold in the high frequency range (about 2–4 kHz) can be estimated reliably and with acceptable accuracy.Different hearing disorders lead to characteristic changes of the EAEP which in most cases allow differential diagnostic statements based on click-BERA and they are the basis for objective estimation of the hearing threshold. In the case of conductive hearing loss, the effective stimulus level is reduced by the difference between the threshold for bone and air conduction. This level reduction leads to longer latencies and lower amplitudes of the EAEP. The response threshold is elevated and all level-latency and level-amplitude curves are horizontally shifted by the amount of the sound conduction component . The intAnother pathological factor that affects the morphology of brainstem potentials is the recruitment. In the supra-threshold range, the amplitudes of the EAEP of patients suffering from inner ear diseases behave similarly as the steep subjective loudness growth. Close to threshold, the potentials are delayed, in the supra-threshold region, the latencies are nearly regular. Inbetween, a steep amplitude growth can be observed. The latencies of the potentials may be essentially prolonged near threshold, with increasing stimulus level they approach the normal values . EspeciaFor high frequency cochlear hearing losses, the response threshold is closely related to the hearing threshold in the frequency range between 2 and 4 kHz , 260], , 260], , 262]. . 262]. IDue to the acoustic properties of the click stimulus on the one hand and the biomechanics of the cochlear on the other hand, a particular low frequency hearing loss does not influence the click-evoked EAEP and so it cannot be explicitly detected by means of click-BERA.The lack of frequency specificity of the click-evoked EAEP limits a wide application despite their otherwise favorable properties. This was the motivation for intensive research efforts regarding frequency specific audiometry by means of early potentials. One of the numerous approaches is based on stimulation with short tone bursts and simultaneous masking with notched-filtered broadband noise (notched-noise-BERA). The responses obtained with this procedure can generally be measured for frequencies between 500 Hz and 4 kHz – especially for the test frequencies of 2 and 4 kHz – nearly down to the hearing threshold , 265], , 265], . AccordiIn the diagnostic use of the FAEP, the general incompatibility of temporal (click) and spectral sharpness (tone pulse) is associated with fundamental difficulties: Apparently, the neural response is either well-synchronized and thus easily measurable, or it is frequency-specific and temporally dispersed. A useful synthesis of these two extremes seems to be possible with the chirp. For the design of this short-term stimulus, a wave form composed from a frequency continuum of defined bandwidth. Phases, amplitudes, and envelope of the single components are selected on the basis of either experimental , 268], , 268], , 270], , 270],  or of moIn order to obtain differential diagnostic statements, EAEP are measured with click BERA. Latencies and amplitudes are determined for all stimulus levels. By comparing the latency-intensity-diagrams with the normal reference curves, the calculation of latency differences, especially the cochlea-mesencephalic latency difference t5–t1, and the evaluation of side differences, conductive, sensory, and neural lesions can be distinguished. Conductive hearing impairment is characterized by prolongation of the latencies of all waves because lower stimulus levels are associated with longer latencies. Due to the constant attenuation of all stimuli, the latency and amplitude functions are shifted along the level axis. In case of inner ear hearing loss – depending on the frequency range affected by the disorder – latency prolongations occur only for stimuli close to the threshold while often normal latencies are observed at high stimulus levels. The effect of a neural hearing disorder is a prolongation of the neural processing time which is independent from the stimulus level; the latency intensity function is therefore shifted along the latency axis, the amplitude-intensity function is typically flat, i.e. the amplitude does not grow with increasing stimulus level.For a long period, especially as long as MRI scans with sufficient image quality were not yet available, the registration of EAEP was part of the standard audiological inventory, with the expection of additional specific information about retrocochlear disorders. The hit rate is very high for advanced tumors , whereasThe diagnostic criteria for vestibular schwannoma are the latency of the wave V, the prolongation of the interpeak latency t5–t1 and the corresponding interaural differences. Pathophysiologically, the latency prolongations are supposed to originate from the tumor-related impact on the hearing nerve fibers and the loss of neural synchronization . The criUnder the supposition that the high-frequent hearing nerve fibers which are crucial for the stimulus response to unmasked clicks, are not affected by small tumors, the pathological latency changes of the low-frequency “stacked ABR” as well as the associated amplitude reduction of the total response may serve as tumor indicator. With this procedure, the sensitivity may be increased to 95% and the specificity to 88% , 300]. . 300]. TAnother possibility to improve the effectivity of BERA in the diagnosis of small vestibular schwannomas was suggested recently. If the registration of EAEPs is extended down to 40 dB HL in patients with low-grade hearing loss, the consideration of the combination of “pathological absolute latency of the wave V” and “pathological interaural difference of the wave V” can improve the detection of tumors larger than 5 mm .EAEP play a major role in the context of newborn hearing screening . In compth year of life , , 308], .In the latency range of the classic SAEP, the observation of the component P50 in the time course of CI rehabilitation of single individuals led to scientific findings of high practical relevance , 311], , 311], , 313]. . 313]. BWhile the measurement of the transient potentials dealt with up to now requires a pause between the acoustic stimuli, the so-called auditory steady state responses (ASSR) allow the examination of the hearing system in its steady state. The ASSR were first observed by Galambos et al. (1981) . The acoAmong several alternatives of ASSR, the responses on amplitude-modulated stimuli, which were first called “amplitude modulation following responses” (AMFR) by Kuwada et al. (1986) , are belThe impact of vigilance and maturation on the amplitude of the ASSR is generally stronger for high than for low modulation frequencies , 320], , 320], , 322], , 322], , 324]. . 324]. TThe power of the current functional audiological diagnostics is based on the multitude of methods and their interrelation. If several tests are available to answer one diagnostic question, the results obtained for a target parameter will in general, but not always be congruent. In cases of contradictory results, the redundancy of the test inventory assures the possibility of discovering and eliminating inconsistencies. Another valuable characteristic of audiometry is the availability of numerous methods for objectifying findings. This option is missing in many other areas of medicine and would be very welcome there, too. In the field of audiometry it is always essential wherever there is no sufficient ability or readiness for cooperation of the patient which is urgently required for hearing tests. Beside pediatric audiology, also the ENT-specific reporting of expert opinion regarding hearing disorders is based on objective procedures. In those areas, as well as in occupational medicine  and in tDespite the fact that the general situation may be regarded as definitely positive, there are still some gaps in the method inventory. For example, the recruitment, which cannot be ascertained subjectively in a reliable manner, cannot be objectified up to now. Moreover, a test for the identification of the vulnerable inner ear has not been found yet. Finally, the question of the electrical stimulability of the auditory nerve, which is fundamental before the decision to CI provision, can only be assessed by subjective methods and then only unreliably.From the authors’ point of view, those are some of the future focuses of audiological functional diagnostics. Furthermore, procedures to determine the frequency selectivity  will gain in importance. It is known that the ability to distinguish frequencies is reduced in cases of noise-induced and other inner ear damage . PossiblThe already mentioned pathological loudness growth merits deeper consideration. The opinion that the supra-threshold audiometry has been replaced by impedance measurement, BERA, OAE, and imaging procedures, has been repeatedly expressed and is meanwhile generally accepted. However, the mentioned alternatives are not able to discover a pathologically reduced dynamic range, which is crucial for the provision of hearing aids, despite their doubtlessly useful differential diagnostic power. The elimination of the SISI test with the argument that a negative SISI test is not always an indicator for nerve-induced hearing loss  only conSince several years, and still today, speech audiometry is intensively developed. Convincing studies , 121] i i121] inIn objective audiometry, it becomes obvious that the consideration of the accuracy of results expressed in the residual noise will be better supported by appropriate equipment based on the standards (DIN EN 60645-6  and DIN Another field of audiometry that has not yet been fully explored, is the application of objective hearing tests in the context of cochlear implantation , 226], , 226], , 338], , 338],  and the The authors declare that they have no competing interests.