Auditory Fusion Test-Revised

Abstract

There has been recent interest in temporal processing disorders following the ASHA Task Force on Central Auditory Processing (ASHA, 1996) and more recently, the American Academy of Audiology Consensus Conferecne on the Diagnosis of Auditory Processing Disorders in School-Aged Children (JAAA, 2000).

Additionally, interest in remediation through FastForward™ and Earobics™, and requests for information about the Auditory Fusion Test-Revised (AFT-R) (McCroskey and Keith, 1996) led to this article on the assessment of auditory temporal processing as one aspect of Auditory Processing Disorders (APDs), also known as Central Auditory Processing Disorders (CAPDs).

This discussion will include basic information on the AFT-R, it's administration, and implications of test findings for remediation.

Introduction to temporal processing disorders

The 1996 report on Central Auditory Processing: Current Status of Research and Implications for Clinical Practice (ASHA, 1996) published definitions of major issues relative to central auditory processing. In that consensus statement "Central Auditory Processes" included the auditory system mechanisms and processes responsible for the following behavioral phenomena:

Sound localization and lateralization
Auditory discrimination
Auditory pattern recognition
Temporal aspects of audition*, including:
- temporal resolution
- temporal masking
- temporal integration
- Temporal ordering
Auditory performance decrements with competing acoustic signals
Auditory performance decrements with degraded acoustic signals

* (Emphasis added here)

According to the ASHA statement, these mechanisms and processes are presumed to apply to verbal and nonverbal signals, and to affect many areas of function, including speech and language. They have neurophysiological as well as behavioral correlates. Further, "Central Auditory Processing Disorder" (CAPD) was defined as an observed deficiency in one or more of the behaviors listed above. The diagnosis of a CAPD is accomplished using a variety of indices, including behavioral auditory measures including; tests of temporal processes - ordering, discrimination, resolution (e.g., gap detection), and integration.

Several authors have discussed temporal processing as it relates to the perception of speech and specifically speech discrimination. A brief summary of their findings is that auditory analysis of the temporal aspects of auditory signals is important to the understanding of speech and language. Disorders in the discrimination of temporal (timing) or spectral cues of speech can lead to a breakdown in phonemic discrimination, and consequent disorders in receptive and expressive language and reading.

The general time frame of temporal processing required for discrimination of phonemes appears to be in the range of 20 to 125 msec. For example, the distinction between the durations of the voice onset time (VOT) of consonants such as /p/ versus /b/ is approximately 20 msecs (Eimas, 1975), but the duration of the silent interval itself may vary across a range from 65 msec to 125 msecs. Of course, the exact duration of any speech element is related to the overall rate of speaking.

Phillips and Farmer (1990) explored the processing disorder that underlies the speech discrimination deficit in the syndrome of acquired word deafness from pathology to the primary auditory cortex. They concluded, the perceptual dimension disturbed in word deafness is temporal (timing). Their position was that the disorder is limited to processing of sounds with temporal content in milliseconds or smaller time frames. They presented neurophysiological evidence that the primary auditory cortex has a special role in the representation of auditory events in that small time frame. Their position was similar to Musiek and his colleagues, in that abnormalities in the Duration Patterns Test have a cortical basis (Musiek, Baran, and Pinheiro, 1990).

Tallal and her associates (Tallal, Miller and Fitch, 1993; Merzenich et al., 1996, Tallal et al., 1996) contended that dysfunction of higher level speech processing, necessary for normal language and reading development, may result from difficulties in the processing of basic sensory information. Specifically, they emphasized the role that temporal processing plays in relation to identification of brief phonetic elements presented in speech contexts (Tallal, 1996). Tallal stated rather than deriving from a primarily linguistic or cognitive impairment, the phonological and language difficulties of language-learning impaired children may result from a basic deficit in processing rapidly changing sensory inputs. She proposed that temporal deficits disrupt the normal development of an efficient phonological system, and that these phonological processing deficits result in subsequent failure to speak and read normally (Tallal et al., 1993).

Wright et al. (1997) reported that children with specific language impairment have severe auditory perceptual deficits for brief sounds, but not long tones, in specific sound contexts. According to Thompson and Abel (1992) the ability to process basic acoustic parameters such as frequency and duration may predict speech intelligibility. They stated that deficits in the ability to hear small differences in the timing aspects of ongoing speech contributed to speech discrimination errors, even though hearing thresholds may be normal.

In summary, the data reviewed (above) indicates that sensory analysis of the temporal aspects of auditory signals is important to understanding speech and language. Disorders in the discrimination of temporal (timing) or spectral cues of speech can lead to a breakdown in phonemic discrimination and consequent disorders in receptive and expressive language and reading.

Methods of assessing temporal processing disorders

Many techniques for assessing temporal aspects of acoustic signals are available, including:

Various Tests of Temporal Processing:

• Brief tone audiometry


• Interaural time discrimination


• Psychoacoustic Pattern Discrimination


• Simultaneous Binaural Median Plane Localization


• Acoustic reflex latency tests


• Masking Level Differences


• ABR stimulus rate effects


• Serial Temporal Assessment Report


• Auditory Fusion Test-Revised


• Duration Patterns Test

The tests (above) include assessment of thresholds for brief tones, testing for temporal ordering and sequencing of tonal or click stimuli, and discrimination of time compressed speech. All of the tests (above) find that disturbances in the temporal aspects of audition are occasionally related to cortical lesions. These findings are summarized in several references (Pinheiro and Musiek, 1985; Olsen, 1991; Baran and Musiek, 1991, Thompson and Abel, 1992, Katz, 1994).

In this article, only the Auditory Fusion Test-Revised will be reviewed.

Auditory Fusion Test-Revised

The Auditory Fusion Test-Revised (AFT-R) is designed to measure temporal resolution. The method of evaluating temporal resolution in the AFT-R is through determination of the Auditory Fusion Threshold (AFT^hreshold). The auditory fusion threshold is measured in milliseconds (msec) and is obtained by having a listener attend to a series of pure tones presented in pairs.

The silent time interval (the interpulse interval, IPI) between each pair of tones increases and decreases in duration. As the silent interval changes, the listener reports whether the stimulus pairs are heard as one or two tones.

The interval at which the tone pairs are perceived as two (when the IPI is increasing) is averaged with the interval at which the tone pairs are perceived as one (when the IPI is decreasing) and that average is called the auditory fusion threshold (AFT^hreshold). The auditory fusion threshold is measured in milliseconds (msec). This stimulus protocol is sometimes called "gap detection."

The AFT-R can be used to identify temporal processing disorders that may account for language learning problems. The AFT-R is viewed as a test of temporal integrity at the level of the cortex. Even though it is a cortical measure, the test has a low linguistic and cognitive load, e.g., the listener must simply respond by indicating whether one or two tone pulses were heard. As with the duration patterns test, the AFT-R is unaffected by peripheral hearing loss.

Background research on the Auditory Fusion Test-Revised was conducted in the 1980's by McCroskey and his colleagues at Wichita State University. At that time the procedure was known as the Wichita Auditory Fusion Test (WAFT). McCroskey and Kidder (1980) investigated the temporal integrity of the auditory system using an auditory fusion threshold technique. One hundred-thirty-five children aged seven to nine years were studied. They were grouped in equal numbers of children who were normally achieving, reading disordered, and learning disabled. The children were administered the original version of the Wichita Auditory Fusion Test (WAFT). Auditory Fusion Thresholds (AFT^hresholds) were computed by averaging the ascending-descending fusion points for two tone bursts at five frequencies and three intensities. There was a significant difference in the AFT^hresholds between the children who were considered normal and the other two groups. Interestingly, there was no significant difference in AFT^hresholds between children who were reading disordered and those who were learning disabled. This and many other studies by McCroskey underlined the importance of temporal processing regarding language and learning problems, and the need to identify temporal processing disorders.

Isaacs, et. al., (1982) studied children from 9 to 18 years. Isaacs separated subjects into two groups. The first group had language/learning disabilities and the second group was composaed of normally achieving children. Subjects in the two groups were matched for mental age and adolescent development. Auditory Fusion Thresholds were significantly different between groups, with language/learning disabled children having larger AFT^hresholds than control subjects.

Overview of AFT-R subtests

Following publication of the ASHA Task Force on Central Auditory Processing (ASHA, 1996) with emphasis on testing of temporal processing, McCroskey and Keith revised the WAFT in the following manner.

The original test was recorded on audio tapes that had lost their precision and quality. Therefore the original test was re-recorded onto CD. The test stimuli were precisely recorded using digital recording techniques as originally described in the WAFT test manual. The resulting test is therefore a high quality, low signal-to-noise recording with precise test stimuli. We did not repeat all of the normative data studies that McCroskey published with the WAFT. Because there was no change in the acoustic stimuli, the original normative test results apply to the new recording. Small sample validity studies of the AFT-R confirmed that the original norms appear unchanged by the new CD format. The test is described as follows:

Subtest 1, Practice and preliminary screening. The screening subtest begins with a brief 500 Hz calibration tone and is followed by eighteen 500 Hz tone pairs that ascend from a 0 msec to a 300 msec interpulse interval (IPI).

Subtest 2, Standard Test. Subtest 2 contains interpulse intervals that range from 0 through 40 msec. The specific order encompasses ascending and descending interpulse intervals; for example, the test sequence at a given frequency begins with 0 msec IPI and proceeds to a maximum of 40 msec IPI, which is repeated, and then the intervals decrease to 0 msec.

Subtest 2 begins and ends with the 500 Hz stimulus pairs. Repetition of the 500 Hz stimuli serves at least two purposes. If the initial instruction and the practice afforded by the Screening Test have not stabilized the responses of the listener, the first administration of the 500 Hz stimuli can serve as additional practice. In that case results from the first administration of the 500 Hz stimuli would be disregarded and only the data from the second administration would be used in computing the auditory fusion threshold. The repetition also serves as a measure of whether the listener has changed strategies during the course of the test and serves as a measure of reliability.

Subtest 3, Expanded test. This subtest is included for individuals who did not detect the IPI until a 60 msec or greater interval occurred on the Screening AFT-R (subtest 1). This version of the test begins at the point where the regular test ends, at 40 msec. The test includes only three frequencies but retains 18 stimuli per frequency. The IPI ascends from 40 msec to 300 msec and then descends to 30 msec. Individuals who require this test to establish an AFT^hreshold have (by definition) demonstrated abnormally poor temporal processing abilities. The test simply identifies whether there are frequency differences that could also contribute to auditory reception, speech, language, or reading disorders.

General Factors in Interpretation

Age. Normative data are available in the test manual on subjects 3 years of age to the eighth decade of life. Similarities in results emerge at both ends of the age spectrum. In general, as age increases from three through nine years of age there is a systematic decrease in auditory fusion thresholds; that is, the AFT^hreshold decreases with increasing age. Table 1 shows the age, normal mean, standard deviation, and suggested cut-off score between normal and abnormal performance. These data are the means of AFT^hresholds across the frequency range of 500 through 4000 Hz. The table shows that there is a decrease in auditory fusion threshold with increasing age and a reduction in the variability around the mean as individuals get older, until subjects reach 50 years.


 

• Cut-off scores are based on two standard deviations above the normal mean. They can be adjusted according to examiner preferences, and the willingness to make errors in false positive, or false negative identification of temporal processing deficits.

Case Presentations:

Case one.
This child was a nine year old fourth grade student referred primarily for having problems in "listening." He was rated by adults as being "a poor auditory learner." In addition he had problems in reading, spelling, and expressive language. His birth history was normal. He had normal hearing and no history of ear infections. He was speech and language delayed, and had received speech and language therapy in school since first grade.

Results of central auditory and language testing were as follows:



Results of this examination indicate this child has significant auditory and language processing problems that complicate learning. He faces daily challenges in the classroom.

Recommendations include:

• Comprehensive psychoeducational evaluation


• Comprehensive reading evaluation


• Speech and language therapy


• Structured classroom


• Recommendations for classroom management including preferential seating, providing visual clues, a classroom "buddy" who can help when directions are misunderstood, written homework assignments


• Enrollment in a Fast ForWord^TM program


• Classroom tests administered one on one, given orally when possible

Case two.
This child was a 7 year 11 month old girl with a delay in language development and concerns about reading skills. She was a healthy child with normal hearing and no history of ear infections.

Results of central auditory and language testing were as follows:



These test results indicate problems in areas of auditory perception and language.

Recommendations included:

• Multisensory approach to reading, such as the Orton-Gillingham method


• Referral to a speech language pathologist for evaluation and therapy.


• Preferential seating


• Asking teachers to slow their rate of instruction when providing directions and check for understanding


• Break lengthy directions into simple steps


• Teachers and parents should pause between statements to provide time for processing, speak clearly and be face to face so that she can see facial movements


• Identify some learning computer games to assist in learning basic auditory and reading skills Check for understanding


• Provide a listening buddy.

Comments
Both children presented above have multiple auditory, speech, and language problems that require comprehensive remediation. Central auditory and language test results indicate problems in many areas. While these children demonstrate significant temporal processing disorders, that finding did not exist in isolation. The identification of a temporal processing disorder provides insight into possible related causes for their auditory and language problems, and indicates direction for management and remediation.

The recommendations included a slower rate of speech presented to these children, use of smaller language units, frequent repetition, deliberate pauses that provide time for auditory comprehension and checking for understanding. The provision of visual clues should also help auditory comprehension. Perceptual training and computer assisted remediation may be helpful.

While we have a great deal to learn about optimal management of children with temporal processing disorders, the recent focus on this problem provides impetus for research and clinical innovation.

One criticism of the Auditory Fusion Test-Revised offered by some examiners is the time it takes to administer the test. In the original audio tape version of the WAFT it was necessary to proceed linearly through the test, due to the limits of tape related technology. A suggestion for abbreviating the AFT-R is to screen children by measuring only the ascending gap detection at each octave frequency between 500 and 4000. Because it is so easy to advance tracks using CD technology, it is possible to advance through the practice and four frequencies very quickly.

If the ascending gap detection threshold is 10 to 15 msec at all frequencies the child is assumed to have normal temporal processing abilities. If the ascending gap detection threshold exceeds 15 msec it would be necessary to proceed through the test in the way described in the manual.

It should be understood that the test was not normed in this fashion, and so the examiner is simply extending the 'screening' test which was designed for training and practice. We are in the process of gathering data to support the validity of this test approach and we welcome any other studies regarding validity of this modification. This modification is offered here based on the author's clinical experience which indicates that the modification works efficiently and reliably and effectively reduces test time without sacrificing accuracy.

As a final comment, there are as of yet, no published data on the prevalence of temporal processing disorders as a subset of Central Auditory Processing Disorders. Clinical experience, (a factor that we always fall back on when there are no data available) suggests there exists a small percentage of children with CAPD who have this problem, and who would benefit from treatment. The AFT-R provides a relatively efficient method of identifying children who have temporal processing disorders, so their special needs can be met.

Summary

In summary, recent awareness in temporal processing disorders including interest in remediation through FastForward™ and Earobics™ led to the development of the Auditory Fusion Test-Revised (AFT-R) (McCroskey and Keith, 1996). The test provides an efficient instrument for the identification of temporal processing disorders in children and a basis for classroom management of affected children. The AFT-R also provides an objective method for both the recommendation of, and outcome measurements for computer assisted remediation programs such as FastForward™ or Earobics™.

References

AAA, (2000): Report of the Consensus Conference on the Diagnosis of Auditory Processing Disorders in School-Aged Children . JAAA, Vol. 11, No. 9, October, 2000, pgs 467-474.

ASHA, (1996) Central Auditory Processing: Current Status or Research and Implications for Clinical Practice Technical report prepared by the ASHA Task Force on Central auditory Processing Consensus Development

Baran JA and Musiek FE, (1991) Behavioral Assessment of the central auditory nervous system. Chapter 11 in Hearing Assessment, 2nd Ed. Rintlemann, WF (Ed.) Pro-Ed, Austin.

Beasley DS, Maki JE, and Orchik DJ, (1976) Children's perception of time compressed speech on two measures of speech discrimination. Journal of Speech and Hearing Disorders, 41, 216-225.

Eimas PD, Developmental studies of speech perception. (1975) In L.B. Cohen, and P. Salaptek (Eds.), Infant Perception: from Sensation to Cognition. New York: Academic Press, Vol. 2, 193-231.

Hall JW and Mueller HG. (1997). Audiologists' Desk Reference 1(11):507. Singular Publishing Group, Inc., San Diego.

Helzer JR, Champlin CA, Gillam RB (1996). Auditory temporal resolution in specifically language-impaired age-matched children. Perception and Motor Skills, 83(3 Pt 2):1171-81

Hurley RM, Museik FM. (1997). Effectiveness of Three Central Auditory Processing (CAP) Tests in Identifying Cerebral Lesions. Journal of the American Academy of Audiology, (JAAA) 8:257-262.

Isaacs LE, Horn DG, Keith RW, and McGrath M, (1982) Auditory Fusion in Learning-Disabled and Normal Adolescent Children. Presented at the annual ASHA convention, Toronto.

Katz, J (1994) Handbook of Clinical Audiology - Fourth Edition. Williams and Wilkins, Baltimore.

McCroskey RL, (1981) Auditory Timing in Speech-Language Pathology. Paper presented to Louisiana Speech-Language-Hearing Association. New Orleans.

McCroskey RL and Kidder HC, (1980) Auditory fusion among learning disabled, reading disabled and normal children. Journal of Learning Disabilities, 13, 69-76.

McCroskey RL and Pavlovic D, Allen M. and Nelson P., (1981) Auditory fusion procedures assess reverberation in a theater, Sound and Vibration, 15 (6), 24-26.

McCroskey RL and Thompson NW, (1973) Comprehension of rate-controlled sentences of varying linguistic complexity by children with reading disorders. Paper presented to national convention of American Speech and Hearing Association. Detroit, Michigan. Summarized in McCroskey RS, Auditory timing: Its role in speech-language pathology. Speech and Language: Advances in Basic Research and Practice, Vol 10, 1984 by Academic Press.

Musiek FE, Baran JA, Pinheiro ML. (1990). Duration pattern recognition in normal subjects and patients with cerebral and cochlear lesions. Audiology 29:304-313.

Olsen WO, (1991) Special Auditory Tests: A Historical Perspective. Chapter 2 in Diagnostic Audiology, Jacobson JT and Northern JL, Eds. Pro-Ed, Austin.

Phillips DP (1995) Central Auditory Processing: A view from auditory neuroscience. American Journal of Otology, 16, 338-352,.

Phillips DP, Farmer ME. (1990). Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex. Behavioral Brain Research, 15;40:85-94.

Pickett JM, (1980) The sounds of speech communication: a primer for acoustic tic phonetics and speech perception. Baltimore:University Park Press.

Pinheiro ML and Musiek FE, (1985) Sequencing and temporal ordering in the auditory system. Chapter 13 in Assessment of Central Auditory Dysfunction; Foundations and Clinical Correlates. Pinheiro ML and Musiek FE (Eds.) Williams and Wilkins, Baltimore.

Pisoni DB, (1977) Identification and discrimination of the relative onset time of two component tones: implications for voicing perception in stops. Journal of Acoustical Society of America, 61, 1352-1361

Reed MA (1989). Speech perception and the discrimination of brief auditory cues in reading disabled children. Journal of Child Experimental Psychology, 48(2):270-92.

Schulte-Korne G, Deimel W, Bartling J, Remschmidt H (1998). Role of auditory temporal processing for reading and spelling disability. Perception and Motor Skills, 86(3 Pt 2):1043-7

Tallal P, Miller SL, Bedi G, Byma G, et al., (1996) Language Comprehension in Language-Learning Impaired Children Improved with Acoustically Modified Speech. Science, 271, 81-84.

Tallal P, Miller S, and Fitch RH, (1993) Neurobiological Basis of Speech: A case for the preeminence of temporal processing. Annals of the New York Academy of Sciences, 682, 27-46.

Thompson ME, and Abel SM, (1992) Indices of Hearing in Patients with Central Auditory Pathology. Scandanavian Audiology, 21 (suppl 35): 3-15.

Warren RM, and Warren RP, (1970) Auditory illusions and confusions. Scientific American, 223, 30-36.

Watson BU (1992). Auditory temporal acuity in normally achieving and learning-disabled college students. Journal of Speech and Hearing Research, 35(1):148-56

Wright BA, Lombardino LJ, King WM, Puranik CS, Leonard CM, Merzenich MM (1997). Deficits in auditory temporal and spectral resolution in language-impaired children. Nature 8;387(6629) 176-8

Acknowledgements:

Parts of this article were published in Educational Audiology Review, Volume 16, No. 1, February 1999. Those parts are reprinted here with permission (April, 2001).

Dr. Keith thanks Maxine Young, M.S. for providing the two case studies included in this article.

This article originally appeared on www.audiologyjournal.com. Audiology Online (www.audiologyonline.com) has acquired the Audiology Journal. This paper has been re-edited and updated and appears here as a courtesy to our readers for educational and informational purposes. We are grateful to the author and to Audiology Journal for allowing us (Audiology Online) to re-publish this updated version here. ---Douglas L. Beck Au.D. Editor-In-Chief, Audiology Online.