Forward masking: Adaptation or integration?

The aim of this study was to attempt to distinguish between neural adaptati on and persistence (or temporal integration) as possible explanations of fo rward masking. Thresholds were measured fur a sinusoidal signal as a functi on of signal duration for conditions where the delay between the masker off set and the signal offset (the offset-offset interval) was fixed. The maske r was a 200-ms broadband noise, presented at a spectrum level of 40 dB (re: 20 mu Pa), and the signal was a 4-kHz sinusoid, gated with 2-ms ramps. The offset-offset interval was fixed at various durations between 4 and 102 ms and signal thresholds were measured for a range of signal durations at eac h interval. A substantial decrease in thresholds was observed with increasi ng duration for signal durations up to about 20 ms. At short offset-offset intervals, the amount of temporal integration exceeded that normally found in quiet. The results were simulated using models of temporal integration ( the temporal-window model) and adaptation. For both models, the inclusion o f 3 peripheral nonlinearity, similar to that observed physiologically in st udies of the basilar membrane, was essential in producing a good fit to the data. Both models were about equally successful in accounting for the pres ent data. However, the temporal-window model provided a somewhat better acc ount of similar data from a simultaneous-masking experiment, using the same parameters. This suggests that the linear, time-invariant properties of th e temporal-window approach are appropriate for modeling forward masking. Ov erall the results confirm that forward masking can be described in terms of peripheral nonlinearity followed by linear temporal integration at higher levels in the auditory system. However, the difference in predictions betwe en the adaptation and integration models is relatively small, meaning that influence of adaptation cannot be ruled out. (C) 2001 Acoustical Society of America.