FREQUENTLY ASKED QUESTIONS
What is the TBAC-4?
The TBAC-4 is the most recent version of a battery of auditory tests that has been under development since the early 1980s. It includes six tests of auditory spectral-temporal discrimination using single tones or groups of tones, and two tests using speech sounds.
The tone-based tests are:
1) Single-tone frequency discrimination.
2) Single-tone intensity discrimination.
3) Single-tone duration discrimination.
4) Pulse-train discrimination (rhythm).
5) Embedded tone detection (discrimination of word-length tonal sequences).
6) Temporal-order discrimination for tones.
The speech tests are:
7) Temporal-order discrimination for syllables.
8) Syllable recognition.
What properties make the TBAC-4 useful as a research tool, and also for instruction in courses on auditory science, sensory psychology, psychoacoustics, linguistics and music?
1) The tests have demonstrated reliability.
2) This selection of eight subtests provides scores expressed in percentile ranks relative to a population of young adults with normal hearing, and also estimates of thresholds in Hz, milliseconds or dB, as appropriate. An estimate of the General Auditory Ability, GA, is also provided, as reported in Kidd et al. (2007).
3) The tests employ a trial structure that is designed to minimize the effects of response biases and overall cognitive load, in order to achieve as pure measures of auditory abilities as possible.
4) The goal of (3) is at least partially achieved, as demonstrated by the absence of significant correlations between performance on this test and estimates of general intelligence (Kidd et al. 2007).
What is the pricing system for the TBAC-4, and how was it established?
The TBAC-4 pricing system is based on a payment-per-test approach. The cost of the test battery itself has been kept quite low, so that interested users can gain experience with it at a modest cost. Charges for administration of the test battery are assessed in the form of Scoring Units (SU) with one SU ($4) required for each scoring of a completed test battery. (Eight SU's are bundled with the basic TBAC.)The developers of the test decided to use this system in order to accomplish two things. The first, of course, is to provide sufficient revenue for continuing support of the test battery, assist users with questions about its use, and help develop other assessment measures requested by users. The second is to require uploading of (anonymous) test-battery data, to be used in creating an international auditory-abilities database. The cost of the research that was required for the development of the TBAC-4 is very unlikely to be recovered through sales of this battery or of SUs. Knowledgeable users will appreciate the considerable savings in research budgets that can be achieved through use of this battery rather than developing local versions of it. In one sense, however, the developers of the TBAC hope that some investigators do develop alternative batteries, as the science would benefit from comparisons of performance on multiple auditory assessment systems.
How is the TBAC-4 scored? What measures of performance does it provide?
The TBAC-4 is scored by automatically uploading the test file after the tests have been completed. Test performance is assessed in relation to the scores achieved by a population of 338 young adults with normal hearing (as measured by pure-tone audiometry). The performance measures provided for each subtest are the following:
1) Percent correct.
2) The listener's percentile ranking, in a population of young adults.
3) An estimate of the listener's threshold for each test, in dB, milliseconds, or Hz, as appropriate to the test.
4) A graphical display of the percentile ranks for all tests, for this listener.
In addition, the percentile rank of Auditory (GA) is provided, based on weightings assigned to eight subtests as described in Kidd et al. (2007). Those authors found that this general auditiory ability (GA) accounts for as much of the performance on the test battery as do the four discrete auditory abilities.
What is the value of an auditory test battery for listeners with clinically defined normal hearing (normal pure-tone audiograms)?
"Normal hearing" has generally been defined to mean a normal ability to detect pure tones (although a broad range in that ability is generally accepted as "normal"). Listeners with normal pure-tone thresholds can have widely different spectral or temporal acuity. While some authors have proposed that individual differences in acuity, particularly temporal, might influence language learning or reading, this remains a very controversial hypothesis (Watson and Kidd, 2008). Most studies of this matter have compared a single measure of auditory acuity, rather than a battery of acuity tests, to one or more measures of language skill. Use of batteries like the TBAC might help to clarify the associations between auditory processing skills and language development.
What prompted the development of the TBAC test battery?
In the 1970s auditory research began to turn from studies of such simple stimuli as single tones, noise bursts, and clicks to much more complex sounds, including spectral and temporal patterns comprised of multiple tones (Watson and Kidd, 1997). It had previously been established that for young adults with clinically defined normal hearing, the range of masked thresholds for single tones presented in a noise background was rarely more than 2-3 dB, and the ranges for the discrimination of single tones on the basis of changes in frequency, intensity or duration were similarly quite small. Thus it was somewhat surprising to learn that the range of thresholds for tones presented within complex auditory patterns was as great as 20-30 dB (Green, Profile Analysis, 1988), and the range for the detection of changes in spectral or temporal properties of complex sounds was similarly large (Watson and Kelly, 1981). Some listeners seemed much more able than others to focus their attention on spectral or temporal details of complex sounds. This prompted a return to studies of individual differences in performance on various auditory tests (Johnson, Watson and Jensen, 1987), which had been largely neglected during the last quarter of the 20th century. The TBAC test battery was developed with the goal of establishing norms for auditory abilities beyond that of the sensitivity to pure tones. To help understand this goal, consider that vision might be tested by determining how bright a red, blue or green spot of light must be for a person to barely detect its presence. It does not seem surprising that this analog to determining the intensity required for a pure tone to be detected is NOT the standard method of testing the functioning of the visual system. Instead a person's vision is tested by asking how large letters must be on a screen before they can be correctly identified, or whether they can distinguish a short line segment from a longer one. These latter are acuity measures, and auditory acuity is a property that varies among people considered to have clinically normal hearing, just as visual acuity (and sensitivity) vary among some persons with clinically defined normal vision. When the distributions of auditory sensitivity in the population were first documented in the late 19th and early 20th century, persons who could not detect sine waves until they were raised 15-20 dB above the levels required by most young adults were defined as having abnormal sensitivity, or hearing loss. Later, the amount of sensitivity loss that was considered clinically significant, at many different frequencies across the audible spectrum, was decided by national and international committees [International Standards Organization (ISO), Standard 389]. No such definitions of abnormal auditory acuity have been established, since there have been neither generally accepted tests of acuity nor the large-scale databases needed to determine the range of performance for most young adult listeners without known auditory pathology.
What specific goals are addressed by the TBAC?
The TBAC-4 provides solutions to two problems. First, the subtests in that battery provide a principled basis for estimating Auditory G, the general auditory processing ability. Second, by making these tests available in a form that can be conveniently given to listeners under similar conditions and with identical instructions, it is hoped that a large national, or international, database can be established. On the basis of that database it should be possible to establish meaningful limits of normal auditory acuity comparable to ISO standards for pure-tone sensitivity.
It should be stressed that the neglect of auditory acuity in favor of sensitivity as the primary dimension of normal or disordered functioning is neither an intellectual oversight nor a situation in grave need of correction in order to solve outstanding clinical problems, in the opinion of the authors of the TBAC. From early on it was clear that persons with impaired sensitivity (elevated detection thresholds) suffered serious problems, primarily evident in their difficulty in understanding speech. And, the greater the sensitivity loss, the greater the problem with speech understanding. Some spectral and temporal acuity problems may also be associated with hearing loss. There have been, however, only very rare reports of deficits in spectral or temporal acuity causing functional hearing problems, in the absence of loss of sensitivity. Most such reports were associated with frank neurological problems, generally with head trauma, cancer, or stroke. Clinicians and auditory scientists have been aware that differences in acuity exist, but also that they have not been shown to have anything like the great clinical significance of differences in sensitivity. Thus definitions of normal auditory acuity have been neglected in part because there has been little evidence that establishing such standards would contribute to listeners' well being. No standardized tests of acuity exist partly because there has been no demand for them.
What is the practical importance of individual differences in auditory acuity?
Certain developments in the past 35 years have increased interest in auditory acuity among persons with normal sensitivity. The bulk of these have involved correlations observed between performance on certain identification or discrimination tasks and a variety of clinical conditions, including delayed language development, reading deficits, and general academic difficulties (e.g. Tallal et al., 1983). One problem with these findings has been that poor performance by children on complex tasks, whether auditory or cognitive, can have many explanations other than a frank disorder of the auditory system. A great deal of controversy has been associated with the syndrome termed Central Auditory Processing Disorder (CAPD) (see Cacace and McFarland, 2008). Determining the number and nature of specific auditory abilities among healthy young adults seemed, to the developers of the TBAC, to be the first order of business. After that is achieved, it would be possible to investigate various ways in which those measures may or may not be associated with disorders, for example those of speech perception, language development and reading. Some of that sort of work has been undertaken; however, most studies thus far conducted have examined correlations between performance on some single auditory task and measures of language development or reading, rather than working with any form of estimated auditory ability measures, such as those that may be obtained from a battery such as the TBAC (Kidd et al., 2007).
The National Auditory Capabilities Database (NACD)
The preceding discussion mentioned the lack of any national or international standards for auditory abilities other than for the detection of pure tones (sensitivity). One reason to make the TBAC available in a convenient form is that if it is widely used it will allow the establishment of performance standards for additional auditory abilities. To facilitate the creation of such a database, CDT, Inc., has designed the TBAC scoring procedures so that the data from each application of the test battery are uploaded for inclusion in the National Auditory Capabilities Database (NACD). To make the NACD maximally useful, a modest amount of demographic information is requested, although tests may be scored without providing that information. Specifically, the requested information includes age, sex, known hearing problems if any, native language, and years of formal musical training. It is important to emphasize that it is the TBAC user's responsibility to identify individual listeners with a coded number rather than the listener's name. Names will be immediately deleted from any data files that arrive at CDT, Inc., and will be replaced by locally generated numerical codes. No record of actual names will be retained by CDT, Inc.
Purchasers of the TBAC will receive regular updates showing the breakdown of performance on each of the subtests and on the derived measures of ability for the various subgroups that will be established through use of the requested demographic data. These will include at least age ranges, sex, musical training, reported hearing problems, and native languages.
No claims of clinical significance of listeners' performance on the TBAC-4 subtests, or of the auditory ability measures derived from those performance measures, are made by CDT, Inc. It is only claimed that they are reliable measures of performance, and that the derived GA the only such theoretically based estimate of General Auditory Capabilities currently available (Kidd et al., 2007). These measures may be found to be useful research tools for projects comparing the auditory abilities of various populations; however, it must be stressed that none of the versions of the TBAC have been used with persons younger than about 17. It is strongly suspected that if children are tested with the TBAC, they will do less well than adults on all of the subtests, and probably the differences will be greater on the subtests with more complex stimuli (Subtests 4-8).
The developers of the TBAC-4 are extremely interested in learning about the outcomes of research projects, or about academic courses, in which this test battery is utilized. We would be happy to discuss such projects or pedagogical uses of the battery, in the event that our experience with this instrument might be of value.
References to published work that has utilized the TBAC or that was relevant to its development.
Watson, C. S. and Kidd, G. R. (2008) Associations Between Auditory Abilities, Reading, and other Language Skills in Children and Adults, in Cacace, A. and McFarland, D. (Eds.) Controversies in Central Auditory Processing Disorders, Plural Publishing, San Diego, CA
Kidd, G. R., Watson, C. S. and Gygi, B. (2007) Individual differences in auditory abilities. J. Acoust. Soc. Am. 122 , 418-435.
Watson, C. S. (2004) Temporal acuity and the identification of temporal order: related but distinct auditory abilities. Seminars in Hearing 25, 219-227.
Watson, C.S. and Kidd, G.R. (1997) "The perception of complex waveforms," in M.J. Crocker (Ed.) Handbook of Acoustics, Wiley, New York, 1521-1543.
Green, D. M. (1988) Profile Analysis: Auditory Intensity Discrimination. Oxford University Press, New York.
Johnson, D. M., Watson, C. S. and Jensen, J.K. (1987) Individual differences in auditory capabilities. I. J. Acoust. Soc. Am., 81, 427-38.
Tallal, P., Galaburda, A. M., Llinas, R. R. and Euler, C. v. (Eds.) (1983), Temporal Information Processing in the Nervous System: Special Reference to Dyslexia and Dysphasia. Annals of the New York Academy of Sciences, Vol. 682, 418-420, NYAS, New York.
Watson, C.S. and Kelly, W.J. (1981). The role of stimulus uncertainty in the discrimination of auditory patterns. In D.J. Getty and J.H. Howard (Eds.), Auditory and Visual Pattern Recognition, Bolt, Beranke and Newman, Cambridge, MA.