Experiment 4 results, with one choice giving a mini marshmallow followed 4 s later by a Cheerio (A2 → B2), and the other giving a Cheerio followed 4 s later by a mini marshmallow (B2 → A2). The y axis plots the mean percentage of trials that each monkey selected (A2 → B2) from the first significant session to the third significant session. Error bars are standard errors of measurement, the dashed line at 50% is random performance, and asterisks represent each monkey’s chi-squared (χ2) p-value across the sessions: *p < .05, **p < .01, ***p < .001.