(A) Performance of rats across three consecutive training sessions on the odor span task in the no-sand and sand masking conditions before probe testing. (B) The four stages of the expanded probe experiment, with the maximum number of stimuli possible visualized in each stage. The target locations are highlighted for each stage, while other, incorrect stimuli are represented by gray shaded circles. Locations left white would have no stimulus at that location for that given trial. Locations of stimuli were randomized for each trial. Stage 1 consisted of a standard pairing of a session-novel odor with food reward. Starting with an empty table, six incremental trials were run at this stage with the addition of a novel odor paired with food reward on each trial. Six odors were on the table at the end of this stage, and all odors were removed by the experimenter at the end of this stage. Stage 2 consisted of a session-novel odor without food reward. Starting with an empty table, six incremental trials were run at this stage with the addition of a novel odor without food reward on each trial. If rats flipped a correct lid, they were quickly rewarded with food provided by the experimenter. Six odors were on the table at the end of this stage, and they were used by the experimenter for stage 3. Stage 3 used a previously presented odor paired with a food reward. Using the same previously presented odors from stage 2, one odor at a time was baited for six nonincremental trials. Six odors were on the table at the end of this stage, and they were used by the experimenter for stage 4. Stage 4 used a cross condition in which a previously presented odor paired with a food reward and a session-novel odor without a food reward were both presented. Six incremental trials were run in this stage, with 12 odors on the table at the end of the session.
