Estimation of internal noise using double passes: does it matter how the second pass is delivered?

Human sensory processing is inherently noisy: if a participant is presented with the same set of stimuli multiple times and is asked to perform a task related to some property of the stimulus by pressing one of two buttons, the set of responses generated by the participant will differ on different presentations even though the set of stimuli remained the same. This response variability can be used to estimate the amount of internal noise (i.e. noise that is not present in the stimulus but in the participant's decision making process). The procedure by which the same set of stimuli is presented twice is referred to as double-pass (DP) methodology. This procedure is well-established, but there is no accepted recipe for how the repeated trials may be delivered (e.g. in the same order as they were originally presented, or in a different order); more importantly, it is not known whether the choice of delivery matters to the resulting estimates. Our results show that this factor (as well as feedback) has no measurable impact. We conclude that, for the purpose of estimating internal noise using the DP method, the system can be assumed to have no inter-trial memory.