Forward Masking: Temporal Integration or Adaptation?

When a short signal tone is presented after a noise or tone masker, the threshold for detecting the signal is raised the smaller the gap duration between the masker and the signal is. This phenomenon is termed forward masking and refers to the fact that a masker affects the signal threshold when both are presented in a non-simultaneous, consecutive manner. With increasing temporal separation, signal threshold usually drops to performance in silence when the gap is in the region of hundreds of milliseconds. As a possible explanation for forward masking, mainly two different mechanisms have been discussed in the literature: (i) continuation or persistence of neural activity (e.g., Plomp 1964; Oxenham and Moore 1994), referring to temporal integration of neural activity at presumably higher stages than the auditory nerve; (ii) neural adaptation (e.g., Duifhuis 1973; Nelson and Swain 1996), assuming adaptation at various levels of the auditory pathway (including high levels). A third possible source for interaction of masker and signal is linked to the ringing of the auditory filters but is generally assumed to be negligible for signal frequencies of 1 kHz or higher (e.g., Vogten 1978). It is still unclear whether temporal integration or adaptation can better account for forward masking in various stimulus configurations (Oxenham 2001), nor have both mechanisms been compared directly in a common modeling framework to investigate their relation.