What are the factors for gap detection (related to parameters of procedures, stimuli, etc.)?
Assessment for identification of temporal processing disorders was a recommendation of the ASHA consensus conference on APD and the report of the Consensus Conference on the Diagnosis of Auditory-Processing disorders in School-Aged Children (Jerger and Musiek, 2000). A test of temporal processing was designed by McCroskey in the early 1980's that evolved into the Random Gap Detection Test (Keith, 2000). At the moment that is the only clinical test of temporal processing that is available. That is, other tests with ''time'' in their titles are tests of pattern recognition (e.g. the Duration Patterns Test) or degraded speech (e.g. the Time Compressed Speech Test.) Gap detection testing can be done several ways, but the premise is to introduce two stimuli (tones, clicks, broad band noise) of some duration with a variable gap between them. The subject is to identify when the temporal gap when the two stimuli are heard as one sound or two. The threshold at which the gap is sufficiently wide to be heard as two sounds is the ''gap detection threshold.'' Research on speech perception indicates that persons should be able to hear transitions of formant frequencies of speech in the 0 to 20 millisecond range, so that the assumption is that gap detection thresholds greater than 20 milliseconds are abnormal and a temporal processing disorder may be present. The greater the gap detection threshold, e.g. up to 300 msec, the greater the probability that a person will have difficulty with speech discrimination. That kind of abnormality would represent a bottom-up auditory processing disorder. No one knows the prevalence of such problems in school aged children, but while it may be low the identification of these problems is important in order to provide appropriate recommendations for management.
The Random Gap Detection Test recording consists of a 1000 Hz calibration tone, a practice subtest for tonal stimuli and four subtests consisting of the frequencies 500, 1000, 2000, and 4000 Hz of seven-msec duration. A final subtest includes a practice test for click stimuli of 230 uSec duration followed by a subtest of clicks presented in random order. Tone and click pairs are presented with inter-stimulus intervals of 0 to 40 msec with the following specific intervals: 0, 2, 5, 10, 15, 20, 25, 30, and 40 milliseconds. The inter-stimulus intervals are recorded with gaps randomly assigned using a table of random numbers. The stimulus pairs are recorded with 4.5-second intervals to allow subjects time to respond.
Fan-Gang Zeng, Ph.D. at College Park, has a unique website where you can measure your own gap detection threshold to broad band noise. Check it out at: http://www.bsos.umd.edu/hesp/zeng/gapdetection/
I hope this is helpful.
Robert W. Keith, professor of Audiology at the University of Cincinnati, College of Medicine. Background includes publications in the area of auditory processing and APD, and author of several tests of auditory processing.
Robert W. Keith, Ph.D.
Board Certified in Audiology
Professor and Director
Division of Audiology
University of Cincinnati Medical Center
P.O. Box 670528
Cincinnati, Ohio 45267-0528