Shifting the criterion is not the difficult part of trial-by-trial criterion shifts in recognition memory.

In recognition memory, participants often fail to shift their response criterion within a test even when they see cues signaling whether they should expect weak or strong memory (e.g., Stretch & Wixted Journal of Experimental Psychology: Learning, Memory, and Cognition, 24, 1397-1410, 1998b). We contrasted two possible accounts for this failure to shift. The first assumes that shifting the criterion requires effortful processing, so participants are unwilling to make shifts even when they expect different levels of strength. The second assumes that participants are unwilling to decide which strength category is indicated by the cue for each trial, so their expectations for memory strength do not change across trials. Targets appeared in different test formats ("cues") depending on whether they were studied once (weak) or five times (strong), and lures were evenly divided between the two formats. Some participants had two response keys for "old" and "new" (2-key), and others had to use different keys to respond "old" for the two strength cues (3-key). The goal of the 3-key condition was to force participants to decide which strength cue was presented on each trial. The 3-key participants had a lower false alarm rate for lures shown with the strong than with the weak cue, but the 2-key participants showed no evidence of a criterion shift. Response times were unaffected by trial-by-trial criterion shifts. We conclude that participants willingly shift their response criterion on the basis of changes in expected strength, but they are unwilling to decide which strength to expect unless they are compelled to do this by other aspects of the task.