ATA-FUNDED RESEARCH The Effect of Tinnitus on Gap Detection By Rebecca Haas, Au.D., Jacek Smurzynski, Ph.D., and Marc Fagelson, Ph.D. Temporal Processing and Tinnitus


There is compelling evidence that temporal processing plays a impor- tant role in speech perception. It is also clear that patients with tinnitus experience difficulty understanding degraded speech. Measurement of


gap detection threshold (GDT) is a task often used to evaluate temporal processing. A sound sequence con- sisting of a leading marker, a silent gap, and a trailing marker is presented, and the GDT is the shortest silent gap between the two markers that a listener can detect. Several recent studies reported application of the acoustic startle reflex to measure gap detection in rats. The results indicated that rats exhibiting noise- induced tinnitus had deficiency in detecting silent gaps when compared to the controls and suggested that tinnitus may affect temporal processing. Human data on temporal processing in patients with tinnitus are scarce. The purpose of the study was to provide a quantitative assessment of temporal processing in tinnitus patients by measuring their GDTs. It was hypothesized that neural activity in tinnitus patients might prolong GDTs when compared to those in non-tinnitus subjects.


Testing of Tinnitus Patients and Controls


Nine tinnitus patients recruited for the study reported unilateral or bilateral constant tinnitus of greater than three-month duration. Their hearing thresholds were within normal limits at least up to one kilohertz (kHz) and any hearing impairment was not worse than moderately severe at four kHz. Only five patients completed the entire research protocol. The control group included 11 normal-hearing subjects with no complaints of tinnitus.


The first experiment used the gaps-in-noise (GIN) test developed for assessment of temporal resolution in a clinical population. The test requires detection of gaps ranging from two to 20 milliseconds (ms) embedded in six-second bursts of noise. It provides the approximate threshold of gap detection. The results of several studies indicated that patients with central lesions demonstrated a statistically significant increase of their threshold when compared to the controls. Feasability of the GIN test as a screening tool of temporal resolution in tinnitus patients was evaluated. The second experiment used an adaptive procedure to measure GDT for bursts of broadband


10 Tinnitus Today | Summer 2012


Figure 1. Pure-tone thresholds of the study subjects. Black open circles corre- spond to the median values of 11 non- tinnitus ears selected for the gap detection threshold (GDT)


testing using the adaptive procedure. Individual thresholds of four tinnitus patients who completed all GIN and adaptive GDT procedures are depicted by color symbols. Gray symbols represent two tinnitus patients who only completed GIN tests at 50 dB SL and some GDT testing. All hearing thresholds for tinnitus patients depicted here were measured in their right ears.


noise. Markers with 40- and 250-ms durations were used with gaps placed at the stimulus midpoint, and the gap duration was adapted systematically to deter- mine the threshold value. Both experiments were performed for the stimuli presented 50 and 30 decibels (dB) above the threshold determined individually for each subject, i.e., at 50 and 30 dB SL (sensation level). Each subject needed up to eight hours split into three or four sessions to complete the entire protocol.


Subjects Presentation level


50 dB SL Tinnitus Non-tinnitus 30 dB SL Tinnitus Non-tinnitus


10.0 8.0


5-12 6-15


7 22


Table 1. The summary of the gaps-in-noise (GIN) test results. Median and range values in milliseconds (ms) were calculated based on the approximate threshold (A.th.) values.


Hearing Sensitivity and Tinnitus


Most cases of tinnitus are associated with peripheral hearing loss. However, some tinnitus patients do not show any hearing loss in their audiogram. Tinnitus patients who participated in our study included both normal-hearing and hearing-impaired individuals as illustrated in Figure 1.


8.0 5.5


5-12 3-8


13 22


Median A. th. (ms)


A.th. range Number of (ms)


ears tested


Continued on Page 30


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32