Uncertainty about amplitude eliminates negative masking in a pure-tone amplitude discrimination experiment.

The role of uncertainty and its reduction in producing the "negative masking" of amplitude increments that is often observed in pure-tone amplitude discrimination experiments using circathreshold pedestals was investigated. It was found that negative masking is eliminated by uncertainty induced by roving the pedestal level across trials. On the basis of this finding, as well as those from a previous study, it is argued that, consistent with a longstanding theory of negative masking based on the notion of "intrinsic uncertainty," negative masking requires near-optimal stimulus conditions, under which uncertainty about increment parameters is more or less absent.