The decision process in forward-masked intensity discrimination: Evidence from molecular analyses

Abstract

In a two-interval forced-choice intensity discrimination task presenting a fixed increment, the level of the forward masker in interval 1 and interval 2 was sampled independently from the same normal distribution on each trial. Mean and standard deviation of the distribution were varied. Correlational analyses of the trial-by-trial data revealed different decision strategies depending on the relation between mean masker level and standard level. If the two levels were identical, listeners tended to select the interval containing the higher-level masker, behaving like an energy detector at the output of a temporal window of integration. For mean masker level higher than the standard level, most listeners showed a negative correlation between the masker level in a given interval and the probability of selecting this interval, indicating a strategy of comparing the masker loudness and the target loudness in each of the two observation intervals, and voting for the interval where the loudness difference was smaller. Implications for models of forward-masked intensity discrimination and differences from decision strategies reported for forward-masked detection tasks [Jesteadt et al., (2005). "Effect of variability in level on forward masking and on increment detection," J. Acoust. Soc. Am. 118, 325-337] are discussed.