USING VARIABILITY IN MASKER LEVEL TO STUDY THE DECISION PROCESS IN FORWARD-MASKED INTENSITY DISCRIMINATION
The decision process in a forward-masked intensity discrimination task was studied by introducing within-trial variability in masker level. In a 2IFC paradigm, the level of the masker presented in interval 1 and interval 2, respectively, was sampled independently from a normal distribution in each trial. Mean and standard deviation of the distribution were varied. Standard level was constant; the level increment was fixed in each block. Correlational analyses revealed different response strategies depending on masker level. With mean masker level equal to standard level, listeners tended to select the interval with the higher masker level, behaving like an energy detector. For mean masker level larger than standard level, three of the four listeners showed a negative correlation between the masker level in a given interval and the probability of responding that the increment had been presented in this very interval. This indicates a strategy of forming a contrast between masker loudness and target tone loudness and voting for the interval in which their difference was smaller. The weight assigned to masker level was larger for the intermediate mean masker level and increased with masker variability.