The measurement of tinnitus in humans relies on subjective measures such as self-report, visual analog scales and questionnaires. Gap detection impairments have been tested in animals in an attempt to objectify the presence of tinnitus. The main purpose of this study was to investigate the gap startle paradigm in human participants with high-frequency tinnitus. Fifteen adults with bilateral high-frequency tinnitus but normal hearing at standard frequencies and seventeen matched controls without tinnitus were tested. The psychoacoustic characteristics of the tinnitus spectrum (pitch and loudness) were assessed using novel participant-directed custom-made methods. The startle task consisted of startle-alone, prepulse inhibition and gap-in-noise condition at low- and high-background noise frequencies. All measurements were retested after several months. Data indicate normal prepulse inhibition but higher reactivity to the startle sounds in the tinnitus group in comparison with controls. Most importantly, the tinnitus group displayed a consistent deficit in gap processing at both low- and high-background noise frequencies. All effects were identified consistently and were reproducible at retest. We propose that the higher reactivity to startle might reflect hyperacusis and that the gap deficit might be an index of abnormal cortical auditory processing in tinnitus.
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