The inter-stimulus interval critical value in backward masking testing

Abstract

Backward masking (BM) has been studied both as a psychoacoustic phenomenon and as a potential diagnostic indicator of auditory processing difficulty. In BM assessment, the subject responds to a brief tonal signal followed by an inter-stimulus interval (ISI) of silence and then by a noise masker. In all previous studies, an adaptive auditory threshold is obtained at each ISI. This study used unique instrumentation that allowed the adaptive ISI to maintain threshold. Twelve subjects were utilized. All had normal hearing with an age range of 18–30 years. The critical ISI was varied with an adaptive procedure in 2 ms steps. The critical ISI value was obtained for stimulus intensity levels above the tonal threshold found in a longer ISI condition. This procedure allowed less fatigue and provided an easier task for the subject compared to the tonal intensity tracking task.